Allow CAPABILITY_UNSAFE_POINTER in baseline

Go 1.26 changes how capslock traces through stdlib internals
(reflect, encoding/json), causing it to report UNSAFE_POINTER for
any package that uses reflection. This is a transitive artifact —
go-toml does not import "unsafe" directly. Include it in the
baseline so the check passes on both Go 1.24 and 1.26, and remove
it from FORBIDDEN_CAPS.

https://claude.ai/code/session_01HwDXpKevFLhE5EfrR6JrBn

.github/workflows/capabilities.yml

@@ -0,0 +1,25 @@
+name: capabilities
+on:
+  push:
+    branches:
+      - v2
+  pull_request:
+    branches:
+      - v2
+
+jobs:
+  check:
+    name: check capabilities
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+      - name: Setup go
+        uses: actions/setup-go@v6
+        with:
+          go-version: "1.26"
+      - name: Install capslock
+        run: go install github.com/google/capslock/cmd/capslock@latest
+      - name: Check for new capabilities
+        run: ./caps.sh check

AGENTS.md

@@ -53,6 +53,14 @@ go-toml is a TOML library for Go. The goal is to provide an easy-to-use and effi
 - Commit messages must explain **why** the change is needed
 - Keep messages clear and informative even if details are in the PR description
 
+### Capabilities
+
+go-toml tracks system-level capabilities using [capslock](https://github.com/google/capslock). The baseline is in `capability_baseline.txt` and CI enforces that it does not grow.
+
+- **Do not introduce new capabilities.** PRs that increase the capability set (e.g., adding network access, subprocess execution, syscalls) are unlikely to be accepted.
+- If a change causes the capabilities check to fail, do not update the baseline to make it pass. Instead, rethink the approach to avoid requiring new capabilities.
+- To check locally: `./caps.sh check` (requires `capslock` installed via `go install github.com/google/capslock/cmd/capslock@latest`)
+
 ## Pull Request Checklist
 
 Before submitting:
@@ -61,4 +69,5 @@ Before submitting:
 2. No backward-incompatible changes (unless discussed)
 3. Relevant documentation added/updated
 4. No performance regression (verify with benchmarks)
-5. Title is clear and understandable for changelog
+5. Capabilities are not increasing (`./caps.sh check`)
+6. Title is clear and understandable for changelog

CONTRIBUTING.md

@@ -180,6 +180,25 @@ description. Pull requests that lower performance will receive more scrutiny.
 
 [benchstat]: https://pkg.go.dev/golang.org/x/perf/cmd/benchstat
 
+### Capabilities
+
+We use [capslock](https://github.com/google/capslock) to track what
+system-level capabilities (file access, network, syscalls, etc.) each package
+requires. The current baseline is in `capability_baseline.txt`. CI will fail if
+a change introduces a new capability.
+
+**Pull requests that increase the set of capabilities are unlikely to be
+accepted.** go-toml is a parsing library and should not need network access,
+subprocess execution, or other capabilities beyond what it already uses.
+
+If you believe a new capability is genuinely needed, discuss it in an issue
+first. To update the baseline after approval:
+
+```bash
+go install github.com/google/capslock/cmd/capslock@latest
+./caps.sh generate
+```
+
 ### Style
 
 Try to look around and follow the same format and structure as the rest of the

README.md

@@ -235,17 +235,17 @@ the AST level. See https://pkg.go.dev/github.com/pelletier/go-toml/v2/unstable.
 Execution time speedup compared to other Go TOML libraries:
 
 <table>
-    <thead>
-        <tr><th>Benchmark</th><th>go-toml v1</th><th>BurntSushi/toml</th></tr>
-    </thead>
-    <tbody>
-        <tr><td>Marshal/HugoFrontMatter-2</td><td>2.1x</td><td>2.0x</td></tr>
-        <tr><td>Marshal/ReferenceFile/map-2</td><td>2.0x</td><td>2.0x</td></tr>
-        <tr><td>Marshal/ReferenceFile/struct-2</td><td>2.3x</td><td>2.5x</td></tr>
-        <tr><td>Unmarshal/HugoFrontMatter-2</td><td>3.3x</td><td>2.8x</td></tr>
-        <tr><td>Unmarshal/ReferenceFile/map-2</td><td>2.9x</td><td>3.0x</td></tr>
-        <tr><td>Unmarshal/ReferenceFile/struct-2</td><td>4.8x</td><td>5.0x</td></tr>
-     </tbody>
+	<thead>
+		<tr><th>Benchmark</th><th>go-toml v1</th><th>BurntSushi/toml</th></tr>
+	</thead>
+	<tbody>
+		<tr><td>Marshal/HugoFrontMatter-2</td><td>1.9x</td><td>2.2x</td></tr>
+		<tr><td>Marshal/ReferenceFile/map-2</td><td>1.7x</td><td>2.1x</td></tr>
+		<tr><td>Marshal/ReferenceFile/struct-2</td><td>2.2x</td><td>3.0x</td></tr>
+		<tr><td>Unmarshal/HugoFrontMatter-2</td><td>2.9x</td><td>2.7x</td></tr>
+		<tr><td>Unmarshal/ReferenceFile/map-2</td><td>2.6x</td><td>2.7x</td></tr>
+		<tr><td>Unmarshal/ReferenceFile/struct-2</td><td>4.6x</td><td>5.1x</td></tr>
+	 </tbody>
 </table>
 <details><summary>See more</summary>
 <p>The table above has the results of the most common use-cases. The table below
@@ -253,22 +253,22 @@ contains the results of all benchmarks, including unrealistic ones. It is
 provided for completeness.</p>
 
 <table>
-    <thead>
-        <tr><th>Benchmark</th><th>go-toml v1</th><th>BurntSushi/toml</th></tr>
-    </thead>
-    <tbody>
-        <tr><td>Marshal/SimpleDocument/map-2</td><td>2.0x</td><td>2.9x</td></tr>
-        <tr><td>Marshal/SimpleDocument/struct-2</td><td>2.5x</td><td>3.6x</td></tr>
-        <tr><td>Unmarshal/SimpleDocument/map-2</td><td>4.2x</td><td>3.4x</td></tr>
-        <tr><td>Unmarshal/SimpleDocument/struct-2</td><td>5.9x</td><td>4.4x</td></tr>
-        <tr><td>UnmarshalDataset/example-2</td><td>3.2x</td><td>2.9x</td></tr>
-        <tr><td>UnmarshalDataset/code-2</td><td>2.4x</td><td>2.8x</td></tr>
-        <tr><td>UnmarshalDataset/twitter-2</td><td>2.7x</td><td>2.5x</td></tr>
-        <tr><td>UnmarshalDataset/citm_catalog-2</td><td>2.3x</td><td>2.3x</td></tr>
-        <tr><td>UnmarshalDataset/canada-2</td><td>1.9x</td><td>1.5x</td></tr>
-        <tr><td>UnmarshalDataset/config-2</td><td>5.4x</td><td>3.0x</td></tr>
-        <tr><td>geomean</td><td>2.9x</td><td>2.8x</td></tr>
-     </tbody>
+	<thead>
+		<tr><th>Benchmark</th><th>go-toml v1</th><th>BurntSushi/toml</th></tr>
+	</thead>
+	<tbody>
+		<tr><td>Marshal/SimpleDocument/map-2</td><td>1.8x</td><td>2.7x</td></tr>
+		<tr><td>Marshal/SimpleDocument/struct-2</td><td>2.7x</td><td>3.8x</td></tr>
+		<tr><td>Unmarshal/SimpleDocument/map-2</td><td>3.8x</td><td>3.0x</td></tr>
+		<tr><td>Unmarshal/SimpleDocument/struct-2</td><td>5.6x</td><td>4.1x</td></tr>
+		<tr><td>UnmarshalDataset/example-2</td><td>3.0x</td><td>3.2x</td></tr>
+		<tr><td>UnmarshalDataset/code-2</td><td>2.3x</td><td>2.9x</td></tr>
+		<tr><td>UnmarshalDataset/twitter-2</td><td>2.6x</td><td>2.7x</td></tr>
+		<tr><td>UnmarshalDataset/citm_catalog-2</td><td>2.2x</td><td>2.3x</td></tr>
+		<tr><td>UnmarshalDataset/canada-2</td><td>1.8x</td><td>1.5x</td></tr>
+		<tr><td>UnmarshalDataset/config-2</td><td>4.1x</td><td>2.9x</td></tr>
+		<tr><td>geomean</td><td>2.7x</td><td>2.8x</td></tr>
+	 </tbody>
 </table>
 <p>This table can be generated with <code>./ci.sh benchmark -a -html</code>.</p>
 </details>

capability_baseline.txt

@@ -0,0 +1 @@
+github.com/pelletier/go-toml/v2: CAPABILITY_REFLECT, CAPABILITY_UNANALYZED, CAPABILITY_UNSAFE_POINTER

caps.sh

@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+#
+# Generates or checks the capability baseline for go-toml.
+#
+# Usage:
+#   ./caps.sh generate   # regenerate capability_baseline.txt
+#   ./caps.sh check      # check that capabilities haven't grown
+#
+# Requires: go, capslock (go install github.com/google/capslock/cmd/capslock@latest)
+
+set -euo pipefail
+
+BASELINE="capability_baseline.txt"
+CAPSLOCK="${CAPSLOCK:-capslock}"
+
+# Capabilities that must never appear in any package.
+FORBIDDEN_CAPS=(
+    CAPABILITY_NETWORK
+    CAPABILITY_CGO
+    CAPABILITY_EXEC
+)
+
+capslock_to_baseline() {
+    "$CAPSLOCK" -packages=. -output=package -granularity=package \
+        | jq -r 'to_entries | sort_by(.key) | .[] | .key + ": " + (.value | sort | join(", "))'
+}
+
+generate() {
+    capslock_to_baseline > "$BASELINE"
+    echo "Wrote $BASELINE"
+}
+
+check() {
+    if [ ! -f "$BASELINE" ]; then
+        echo "ERROR: $BASELINE not found. Run '$0 generate' first."
+        exit 1
+    fi
+
+    current=$(mktemp)
+    trap 'rm -f "$current"' EXIT
+
+    capslock_to_baseline > "$current"
+
+    failed=0
+
+    # Check for forbidden capabilities in current output.
+    for cap in "${FORBIDDEN_CAPS[@]}"; do
+        if grep -q "$cap" "$current"; then
+            echo "FORBIDDEN capability found: $cap"
+            grep "$cap" "$current"
+            failed=1
+        fi
+    done
+
+    # Extract all unique capability names from baseline and current.
+    baseline_caps=$(grep -oE 'CAPABILITY_[A-Z_]+' "$BASELINE" | sort -u)
+    current_caps=$(grep -oE 'CAPABILITY_[A-Z_]+' "$current" | sort -u)
+
+    # Check for new capability names not in the baseline.
+    new_caps=$(comm -13 <(echo "$baseline_caps") <(echo "$current_caps"))
+    if [ -n "$new_caps" ]; then
+        echo "NEW capabilities detected (not in baseline):"
+        echo "$new_caps"
+        failed=1
+    fi
+
+    # Check for new per-package capabilities (a package gained a capability it didn't have before).
+    while IFS=': ' read -r pkg caps; do
+        baseline_pkg_caps=$(grep "^${pkg}:" "$BASELINE" 2>/dev/null | sed 's/^[^:]*: //' || true)
+        if [ -z "$baseline_pkg_caps" ]; then
+            echo "NEW package with capabilities: $pkg: $caps"
+            failed=1
+            continue
+        fi
+        # Check each capability in current for this package
+        for cap in $(echo "$caps" | tr ', ' '\n' | grep -v '^$'); do
+            if ! echo "$baseline_pkg_caps" | grep -q "$cap"; then
+                echo "NEW capability for $pkg: $cap"
+                failed=1
+            fi
+        done
+    done < "$current"
+
+    if [ "$failed" -eq 1 ]; then
+        echo ""
+        echo "FAILED: capabilities have grown."
+        echo "If this is intentional, run '$0 generate' and commit the updated $BASELINE."
+        exit 1
+    fi
+
+    echo "OK: no new capabilities detected."
+}
+
+case "${1:-}" in
+    generate) generate ;;
+    check)    check ;;
+    *)
+        echo "Usage: $0 {generate|check}"
+        exit 1
+        ;;
+esac

ci.sh

@@ -147,7 +147,7 @@ bench() {
     pushd "$dir"
 
     if [ "${replace}" != "" ]; then
-        find ./benchmark/ -iname '*.go' -exec sed -i -E "s|github.com/pelletier/go-toml/v2\"|${replace}\"|g" {} \;
+        find ./benchmark/ -iname '*.go' -exec sed -i -E "s|github.com/pelletier/go-toml/v2|${replace}|g" {} \;
         go get "${replace}"
     fi
 
@@ -195,11 +195,6 @@ for line in reversed(lines[2:]):
         "%.1fx" % (float(line[3])/v2),  # v1
         "%.1fx" % (float(line[7])/v2),  # bs
     ])
-
-if not results:
-    print("No benchmark results to display.", file=sys.stderr)
-    sys.exit(1)
-
 # move geomean to the end
 results.append(results[0])
 del results[0]

decode.go

@@ -9,60 +9,64 @@ import (
 	"github.com/pelletier/go-toml/v2/unstable"
 )
 
-func parseInteger(b []byte, base int) (int64, error) {
+func parseInteger(b []byte) (int64, error) {
 	if len(b) > 2 && b[0] == '0' {
 		switch b[1] {
 		case 'x':
-			return parseIntHex(b, base)
+			return parseIntHex(b)
 		case 'b':
-			return parseIntBin(b, base)
+			return parseIntBin(b)
 		case 'o':
-			return parseIntOct(b, base)
+			return parseIntOct(b)
 		default:
 			panic(fmt.Errorf("invalid base '%c', should have been checked by scanIntOrFloat", b[1]))
 		}
 	}
 
-	return parseIntDec(b, base)
+	return parseIntDec(b)
 }
 
-func parseLocalDate(b []byte, base int) (LocalDate, error) {
+func parseLocalDate(b []byte) (LocalDate, error) {
+	// full-date      = date-fullyear "-" date-month "-" date-mday
+	// date-fullyear  = 4DIGIT
+	// date-month     = 2DIGIT  ; 01-12
+	// date-mday      = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on month/year
 	var date LocalDate
 
 	if len(b) != 10 || b[4] != '-' || b[7] != '-' {
-		return date, unstable.NewParserError(b, base, "dates are expected to have the format YYYY-MM-DD")
+		return date, unstable.NewParserError(b, "dates are expected to have the format YYYY-MM-DD")
 	}
 
 	var err error
 
-	date.Year, err = parseDecimalDigits(b[0:4], base)
+	date.Year, err = parseDecimalDigits(b[0:4])
 	if err != nil {
 		return LocalDate{}, err
 	}
 
-	date.Month, err = parseDecimalDigits(b[5:7], base+5)
+	date.Month, err = parseDecimalDigits(b[5:7])
 	if err != nil {
 		return LocalDate{}, err
 	}
 
-	date.Day, err = parseDecimalDigits(b[8:10], base+8)
+	date.Day, err = parseDecimalDigits(b[8:10])
 	if err != nil {
 		return LocalDate{}, err
 	}
 
 	if !isValidDate(date.Year, date.Month, date.Day) {
-		return LocalDate{}, unstable.NewParserError(b, base, "impossible date")
+		return LocalDate{}, unstable.NewParserError(b, "impossible date")
 	}
 
 	return date, nil
 }
 
-func parseDecimalDigits(b []byte, base int) (int, error) {
+func parseDecimalDigits(b []byte) (int, error) {
 	v := 0
 
 	for i, c := range b {
 		if c < '0' || c > '9' {
-			return 0, unstable.NewParserError(b[i:i+1], base+i, "expected digit (0-9)")
+			return 0, unstable.NewParserError(b[i:i+1], "expected digit (0-9)")
 		}
 		v *= 10
 		v += int(c - '0')
@@ -71,18 +75,21 @@ func parseDecimalDigits(b []byte, base int) (int, error) {
 	return v, nil
 }
 
-func parseDateTime(b []byte, base int) (time.Time, error) {
-	origLen := len(b)
-	dt, b, err := parseLocalDateTime(b, base)
+func parseDateTime(b []byte) (time.Time, error) {
+	// offset-date-time = full-date time-delim full-time
+	// full-time      = partial-time time-offset
+	// time-offset    = "Z" / time-numoffset
+	// time-numoffset = ( "+" / "-" ) time-hour ":" time-minute
+
+	dt, b, err := parseLocalDateTime(b)
 	if err != nil {
 		return time.Time{}, err
 	}
 
-	tzBase := base + origLen - len(b)
-
 	var zone *time.Location
 
 	if len(b) == 0 {
+		// parser should have checked that when assigning the date time node
 		panic("date time should have a timezone")
 	}
 
@@ -92,7 +99,7 @@ func parseDateTime(b []byte, base int) (time.Time, error) {
 	} else {
 		const dateTimeByteLen = 6
 		if len(b) != dateTimeByteLen {
-			return time.Time{}, unstable.NewParserError(b, tzBase, "invalid date-time timezone")
+			return time.Time{}, unstable.NewParserError(b, "invalid date-time timezone")
 		}
 		var direction int
 		switch b[0] {
@@ -101,27 +108,27 @@ func parseDateTime(b []byte, base int) (time.Time, error) {
 		case '+':
 			direction = +1
 		default:
-			return time.Time{}, unstable.NewParserError(b[:1], tzBase, "invalid timezone offset character")
+			return time.Time{}, unstable.NewParserError(b[:1], "invalid timezone offset character")
 		}
 
 		if b[3] != ':' {
-			return time.Time{}, unstable.NewParserError(b[3:4], tzBase+3, "expected a : separator")
+			return time.Time{}, unstable.NewParserError(b[3:4], "expected a : separator")
 		}
 
-		hours, err := parseDecimalDigits(b[1:3], tzBase+1)
+		hours, err := parseDecimalDigits(b[1:3])
 		if err != nil {
 			return time.Time{}, err
 		}
 		if hours > 23 {
-			return time.Time{}, unstable.NewParserError(b[:1], tzBase, "invalid timezone offset hours")
+			return time.Time{}, unstable.NewParserError(b[:1], "invalid timezone offset hours")
 		}
 
-		minutes, err := parseDecimalDigits(b[4:6], tzBase+4)
+		minutes, err := parseDecimalDigits(b[4:6])
 		if err != nil {
 			return time.Time{}, err
 		}
 		if minutes > 59 {
-			return time.Time{}, unstable.NewParserError(b[:1], tzBase, "invalid timezone offset minutes")
+			return time.Time{}, unstable.NewParserError(b[:1], "invalid timezone offset minutes")
 		}
 
 		seconds := direction * (hours*3600 + minutes*60)
@@ -134,7 +141,7 @@ func parseDateTime(b []byte, base int) (time.Time, error) {
 	}
 
 	if len(b) > 0 {
-		return time.Time{}, unstable.NewParserError(b, tzBase, "extra bytes at the end of the timezone")
+		return time.Time{}, unstable.NewParserError(b, "extra bytes at the end of the timezone")
 	}
 
 	t := time.Date(
@@ -150,15 +157,15 @@ func parseDateTime(b []byte, base int) (time.Time, error) {
 	return t, nil
 }
 
-func parseLocalDateTime(b []byte, base int) (LocalDateTime, []byte, error) {
+func parseLocalDateTime(b []byte) (LocalDateTime, []byte, error) {
 	var dt LocalDateTime
 
 	const localDateTimeByteMinLen = 11
 	if len(b) < localDateTimeByteMinLen {
-		return dt, nil, unstable.NewParserError(b, base, "local datetimes are expected to have the format YYYY-MM-DDTHH:MM:SS[.NNNNNNNNN]")
+		return dt, nil, unstable.NewParserError(b, "local datetimes are expected to have the format YYYY-MM-DDTHH:MM:SS[.NNNNNNNNN]")
 	}
 
-	date, err := parseLocalDate(b[:10], base)
+	date, err := parseLocalDate(b[:10])
 	if err != nil {
 		return dt, nil, err
 	}
@@ -166,10 +173,10 @@ func parseLocalDateTime(b []byte, base int) (LocalDateTime, []byte, error) {
 
 	sep := b[10]
 	if sep != 'T' && sep != ' ' && sep != 't' {
-		return dt, nil, unstable.NewParserError(b[10:11], base+10, "datetime separator is expected to be T or a space")
+		return dt, nil, unstable.NewParserError(b[10:11], "datetime separator is expected to be T or a space")
 	}
 
-	t, rest, err := parseLocalTime(b[11:], base+11)
+	t, rest, err := parseLocalTime(b[11:])
 	if err != nil {
 		return dt, nil, err
 	}
@@ -181,53 +188,53 @@ func parseLocalDateTime(b []byte, base int) (LocalDateTime, []byte, error) {
 // parseLocalTime is a bit different because it also returns the remaining
 // []byte that is didn't need. This is to allow parseDateTime to parse those
 // remaining bytes as a timezone.
-func parseLocalTime(b []byte, base int) (LocalTime, []byte, error) {
+func parseLocalTime(b []byte) (LocalTime, []byte, error) {
 	var (
 		nspow = [10]int{0, 1e8, 1e7, 1e6, 1e5, 1e4, 1e3, 1e2, 1e1, 1e0}
 		t     LocalTime
 	)
 
+	// check if b matches to have expected format HH:MM:SS[.NNNNNN]
 	const localTimeByteLen = 8
 	if len(b) < localTimeByteLen {
-		return t, nil, unstable.NewParserError(b, base, "times are expected to have the format HH:MM:SS[.NNNNNN]")
+		return t, nil, unstable.NewParserError(b, "times are expected to have the format HH:MM:SS[.NNNNNN]")
 	}
 
 	var err error
 
-	t.Hour, err = parseDecimalDigits(b[0:2], base)
+	t.Hour, err = parseDecimalDigits(b[0:2])
 	if err != nil {
 		return t, nil, err
 	}
 
 	if t.Hour > 23 {
-		return t, nil, unstable.NewParserError(b[0:2], base, "hour cannot be greater 23")
+		return t, nil, unstable.NewParserError(b[0:2], "hour cannot be greater 23")
 	}
 	if b[2] != ':' {
-		return t, nil, unstable.NewParserError(b[2:3], base+2, "expecting colon between hours and minutes")
+		return t, nil, unstable.NewParserError(b[2:3], "expecting colon between hours and minutes")
 	}
 
-	t.Minute, err = parseDecimalDigits(b[3:5], base+3)
+	t.Minute, err = parseDecimalDigits(b[3:5])
 	if err != nil {
 		return t, nil, err
 	}
 	if t.Minute > 59 {
-		return t, nil, unstable.NewParserError(b[3:5], base+3, "minutes cannot be greater 59")
+		return t, nil, unstable.NewParserError(b[3:5], "minutes cannot be greater 59")
 	}
 	if b[5] != ':' {
-		return t, nil, unstable.NewParserError(b[5:6], base+5, "expecting colon between minutes and seconds")
+		return t, nil, unstable.NewParserError(b[5:6], "expecting colon between minutes and seconds")
 	}
 
-	t.Second, err = parseDecimalDigits(b[6:8], base+6)
+	t.Second, err = parseDecimalDigits(b[6:8])
 	if err != nil {
 		return t, nil, err
 	}
 
 	if t.Second > 59 {
-		return t, nil, unstable.NewParserError(b[6:8], base+6, "seconds cannot be greater than 59")
+		return t, nil, unstable.NewParserError(b[6:8], "seconds cannot be greater than 59")
 	}
 
 	b = b[8:]
-	base += 8
 
 	if len(b) >= 1 && b[0] == '.' {
 		frac := 0
@@ -237,7 +244,7 @@ func parseLocalTime(b []byte, base int) (LocalTime, []byte, error) {
 		for i, c := range b[1:] {
 			if !isDigit(c) {
 				if i == 0 {
-					return t, nil, unstable.NewParserError(b[0:1], base, "need at least one digit after fraction point")
+					return t, nil, unstable.NewParserError(b[0:1], "need at least one digit after fraction point")
 				}
 				break
 			}
@@ -245,6 +252,13 @@ func parseLocalTime(b []byte, base int) (LocalTime, []byte, error) {
 
 			const maxFracPrecision = 9
 			if i >= maxFracPrecision {
+				// go-toml allows decoding fractional seconds
+				// beyond the supported precision of 9
+				// digits. It truncates the fractional component
+				// to the supported precision and ignores the
+				// remaining digits.
+				//
+				// https://github.com/pelletier/go-toml/discussions/707
 				continue
 			}
 
@@ -254,7 +268,7 @@ func parseLocalTime(b []byte, base int) (LocalTime, []byte, error) {
 		}
 
 		if precision == 0 {
-			return t, nil, unstable.NewParserError(b[:1], base, "nanoseconds need at least one digit")
+			return t, nil, unstable.NewParserError(b[:1], "nanoseconds need at least one digit")
 		}
 
 		t.Nanosecond = frac * nspow[precision]
@@ -265,35 +279,35 @@ func parseLocalTime(b []byte, base int) (LocalTime, []byte, error) {
 	return t, b, nil
 }
 
-func parseFloat(b []byte, base int) (float64, error) {
+func parseFloat(b []byte) (float64, error) {
 	if len(b) == 4 && (b[0] == '+' || b[0] == '-') && b[1] == 'n' && b[2] == 'a' && b[3] == 'n' {
 		return math.NaN(), nil
 	}
 
-	cleaned, err := checkAndRemoveUnderscoresFloats(b, base)
+	cleaned, err := checkAndRemoveUnderscoresFloats(b)
 	if err != nil {
 		return 0, err
 	}
 
 	if cleaned[0] == '.' {
-		return 0, unstable.NewParserError(b, base, "float cannot start with a dot")
+		return 0, unstable.NewParserError(b, "float cannot start with a dot")
 	}
 
 	if cleaned[len(cleaned)-1] == '.' {
-		return 0, unstable.NewParserError(b, base, "float cannot end with a dot")
+		return 0, unstable.NewParserError(b, "float cannot end with a dot")
 	}
 
 	dotAlreadySeen := false
 	for i, c := range cleaned {
 		if c == '.' {
 			if dotAlreadySeen {
-				return 0, unstable.NewParserError(b[i:i+1], base+i, "float can have at most one decimal point")
+				return 0, unstable.NewParserError(b[i:i+1], "float can have at most one decimal point")
 			}
 			if !isDigit(cleaned[i-1]) {
-				return 0, unstable.NewParserError(b[i-1:i+1], base+i-1, "float decimal point must be preceded by a digit")
+				return 0, unstable.NewParserError(b[i-1:i+1], "float decimal point must be preceded by a digit")
 			}
 			if !isDigit(cleaned[i+1]) {
-				return 0, unstable.NewParserError(b[i:i+2], base+i, "float decimal point must be followed by a digit")
+				return 0, unstable.NewParserError(b[i:i+2], "float decimal point must be followed by a digit")
 			}
 			dotAlreadySeen = true
 		}
@@ -304,54 +318,54 @@ func parseFloat(b []byte, base int) (float64, error) {
 		start = 1
 	}
 	if cleaned[start] == '0' && len(cleaned) > start+1 && isDigit(cleaned[start+1]) {
-		return 0, unstable.NewParserError(b, base, "float integer part cannot have leading zeroes")
+		return 0, unstable.NewParserError(b, "float integer part cannot have leading zeroes")
 	}
 
 	f, err := strconv.ParseFloat(string(cleaned), 64)
 	if err != nil {
-		return 0, unstable.NewParserError(b, base, "unable to parse float: %w", err)
+		return 0, unstable.NewParserError(b, "unable to parse float: %w", err)
 	}
 
 	return f, nil
 }
 
-func parseIntHex(b []byte, base int) (int64, error) {
-	cleaned, err := checkAndRemoveUnderscoresIntegers(b[2:], base+2)
+func parseIntHex(b []byte) (int64, error) {
+	cleaned, err := checkAndRemoveUnderscoresIntegers(b[2:])
 	if err != nil {
 		return 0, err
 	}
 
 	i, err := strconv.ParseInt(string(cleaned), 16, 64)
 	if err != nil {
-		return 0, unstable.NewParserError(b, base, "couldn't parse hexadecimal number: %w", err)
+		return 0, unstable.NewParserError(b, "couldn't parse hexadecimal number: %w", err)
 	}
 
 	return i, nil
 }
 
-func parseIntOct(b []byte, base int) (int64, error) {
-	cleaned, err := checkAndRemoveUnderscoresIntegers(b[2:], base+2)
+func parseIntOct(b []byte) (int64, error) {
+	cleaned, err := checkAndRemoveUnderscoresIntegers(b[2:])
 	if err != nil {
 		return 0, err
 	}
 
 	i, err := strconv.ParseInt(string(cleaned), 8, 64)
 	if err != nil {
-		return 0, unstable.NewParserError(b, base, "couldn't parse octal number: %w", err)
+		return 0, unstable.NewParserError(b, "couldn't parse octal number: %w", err)
 	}
 
 	return i, nil
 }
 
-func parseIntBin(b []byte, base int) (int64, error) {
-	cleaned, err := checkAndRemoveUnderscoresIntegers(b[2:], base+2)
+func parseIntBin(b []byte) (int64, error) {
+	cleaned, err := checkAndRemoveUnderscoresIntegers(b[2:])
 	if err != nil {
 		return 0, err
 	}
 
 	i, err := strconv.ParseInt(string(cleaned), 2, 64)
 	if err != nil {
-		return 0, unstable.NewParserError(b, base, "couldn't parse binary number: %w", err)
+		return 0, unstable.NewParserError(b, "couldn't parse binary number: %w", err)
 	}
 
 	return i, nil
@@ -361,8 +375,8 @@ func isSign(b byte) bool {
 	return b == '+' || b == '-'
 }
 
-func parseIntDec(b []byte, base int) (int64, error) {
-	cleaned, err := checkAndRemoveUnderscoresIntegers(b, base)
+func parseIntDec(b []byte) (int64, error) {
+	cleaned, err := checkAndRemoveUnderscoresIntegers(b)
 	if err != nil {
 		return 0, err
 	}
@@ -374,18 +388,18 @@ func parseIntDec(b []byte, base int) (int64, error) {
 	}
 
 	if len(cleaned) > startIdx+1 && cleaned[startIdx] == '0' {
-		return 0, unstable.NewParserError(b, base, "leading zero not allowed on decimal number")
+		return 0, unstable.NewParserError(b, "leading zero not allowed on decimal number")
 	}
 
 	i, err := strconv.ParseInt(string(cleaned), 10, 64)
 	if err != nil {
-		return 0, unstable.NewParserError(b, base, "couldn't parse decimal number: %w", err)
+		return 0, unstable.NewParserError(b, "couldn't parse decimal number: %w", err)
 	}
 
 	return i, nil
 }
 
-func checkAndRemoveUnderscoresIntegers(b []byte, base int) ([]byte, error) {
+func checkAndRemoveUnderscoresIntegers(b []byte) ([]byte, error) {
 	start := 0
 	if b[start] == '+' || b[start] == '-' {
 		start++
@@ -396,11 +410,11 @@ func checkAndRemoveUnderscoresIntegers(b []byte, base int) ([]byte, error) {
 	}
 
 	if b[start] == '_' {
-		return nil, unstable.NewParserError(b[start:start+1], base+start, "number cannot start with underscore")
+		return nil, unstable.NewParserError(b[start:start+1], "number cannot start with underscore")
 	}
 
 	if b[len(b)-1] == '_' {
-		return nil, unstable.NewParserError(b[len(b)-1:], base+len(b)-1, "number cannot end with underscore")
+		return nil, unstable.NewParserError(b[len(b)-1:], "number cannot end with underscore")
 	}
 
 	// fast path
@@ -422,7 +436,7 @@ func checkAndRemoveUnderscoresIntegers(b []byte, base int) ([]byte, error) {
 		c := b[i]
 		if c == '_' {
 			if !before {
-				return nil, unstable.NewParserError(b[i-1:i+1], base+i-1, "number must have at least one digit between underscores")
+				return nil, unstable.NewParserError(b[i-1:i+1], "number must have at least one digit between underscores")
 			}
 			before = false
 		} else {
@@ -434,13 +448,13 @@ func checkAndRemoveUnderscoresIntegers(b []byte, base int) ([]byte, error) {
 	return cleaned, nil
 }
 
-func checkAndRemoveUnderscoresFloats(b []byte, base int) ([]byte, error) {
+func checkAndRemoveUnderscoresFloats(b []byte) ([]byte, error) {
 	if b[0] == '_' {
-		return nil, unstable.NewParserError(b[0:1], base, "number cannot start with underscore")
+		return nil, unstable.NewParserError(b[0:1], "number cannot start with underscore")
 	}
 
 	if b[len(b)-1] == '_' {
-		return nil, unstable.NewParserError(b[len(b)-1:], base+len(b)-1, "number cannot end with underscore")
+		return nil, unstable.NewParserError(b[len(b)-1:], "number cannot end with underscore")
 	}
 
 	// fast path
@@ -463,26 +477,27 @@ func checkAndRemoveUnderscoresFloats(b []byte, base int) ([]byte, error) {
 		switch c {
 		case '_':
 			if !before {
-				return nil, unstable.NewParserError(b[i-1:i+1], base+i-1, "number must have at least one digit between underscores")
+				return nil, unstable.NewParserError(b[i-1:i+1], "number must have at least one digit between underscores")
 			}
 			if i < len(b)-1 && (b[i+1] == 'e' || b[i+1] == 'E') {
-				return nil, unstable.NewParserError(b[i+1:i+2], base+i+1, "cannot have underscore before exponent")
+				return nil, unstable.NewParserError(b[i+1:i+2], "cannot have underscore before exponent")
 			}
 			before = false
 		case '+', '-':
+			// signed exponents
 			cleaned = append(cleaned, c)
 			before = false
 		case 'e', 'E':
 			if i < len(b)-1 && b[i+1] == '_' {
-				return nil, unstable.NewParserError(b[i+1:i+2], base+i+1, "cannot have underscore after exponent")
+				return nil, unstable.NewParserError(b[i+1:i+2], "cannot have underscore after exponent")
 			}
 			cleaned = append(cleaned, c)
 		case '.':
 			if i < len(b)-1 && b[i+1] == '_' {
-				return nil, unstable.NewParserError(b[i+1:i+2], base+i+1, "cannot have underscore after decimal point")
+				return nil, unstable.NewParserError(b[i+1:i+2], "cannot have underscore after decimal point")
 			}
 			if i > 0 && b[i-1] == '_' {
-				return nil, unstable.NewParserError(b[i-1:i], base+i-1, "cannot have underscore before decimal point")
+				return nil, unstable.NewParserError(b[i-1:i], "cannot have underscore before decimal point")
 			}
 			cleaned = append(cleaned, c)
 		default:

errors.go

@@ -2,6 +2,7 @@ package toml
 
 import (
 	"fmt"
+	"reflect"
 	"strconv"
 	"strings"
 
@@ -99,7 +100,7 @@ func (e *DecodeError) Key() Key {
 //
 //nolint:funlen
 func wrapDecodeError(document []byte, de *unstable.ParserError) *DecodeError {
-	offset := de.Offset
+	offset := subsliceOffset(document, de.Highlight)
 
 	errMessage := de.Error()
 	errLine, errColumn := positionAtEnd(document[:offset])
@@ -261,3 +262,22 @@ func positionAtEnd(b []byte) (row int, column int) {
 
 	return row, column
 }
+
+// subsliceOffset returns the byte offset of subslice within data.
+// subslice must share the same backing array as data.
+func subsliceOffset(data []byte, subslice []byte) int {
+	if len(subslice) == 0 {
+		return 0
+	}
+
+	// Use reflect to get the data pointers of both slices.
+	// This is safe because we're only reading the pointer values for comparison.
+	dataPtr := reflect.ValueOf(data).Pointer()
+	subPtr := reflect.ValueOf(subslice).Pointer()
+
+	offset := int(subPtr - dataPtr)
+	if offset < 0 || offset > len(data) {
+		panic("subslice is not within data")
+	}
+	return offset
+}

errors_test.go

@@ -171,7 +171,6 @@ line 5`,
 
 			err := wrapDecodeError(doc, &unstable.ParserError{
 				Highlight: hl,
-				Offset:    start,
 				Message:   e.msg,
 			})
 
@@ -287,100 +286,6 @@ func TestDecodeError_Position(t *testing.T) {
 	}
 }
 
-func TestDecodeError_PositionAfterComments(t *testing.T) {
-	examples := []struct {
-		name        string
-		doc         string
-		expectedRow int
-		expectedCol int
-		errContains string
-	}{
-		{
-			name:        "invalid key after comment",
-			doc:         "# comment\n= \"value\"",
-			expectedRow: 2,
-			expectedCol: 1,
-			errContains: "invalid character at start of key",
-		},
-		{
-			name:        "invalid key after multiple comments",
-			doc:         "# line 1\n# line 2\n= \"value\"",
-			expectedRow: 3,
-			expectedCol: 1,
-			errContains: "invalid character at start of key",
-		},
-		{
-			name:        "invalid key after valid assignment and comment",
-			doc:         "a = 1\n# comment\n= \"value\"",
-			expectedRow: 3,
-			expectedCol: 1,
-			errContains: "invalid character at start of key",
-		},
-		{
-			name:        "invalid key on first line",
-			doc:         "= \"value\"",
-			expectedRow: 1,
-			expectedCol: 1,
-			errContains: "invalid character at start of key",
-		},
-		{
-			name:        "invalid key with leading whitespace",
-			doc:         "# comment\n  = \"value\"",
-			expectedRow: 2,
-			expectedCol: 3,
-			errContains: "invalid character at start of key",
-		},
-	}
-
-	for _, e := range examples {
-		t.Run(e.name, func(t *testing.T) {
-			var v map[string]interface{}
-			err := Unmarshal([]byte(e.doc), &v)
-			if err == nil {
-				t.Fatal("expected an error")
-			}
-
-			var derr *DecodeError
-			if !errors.As(err, &derr) {
-				t.Fatalf("expected DecodeError, got %T: %v", err, err)
-			}
-
-			row, col := derr.Position()
-			if row != e.expectedRow {
-				t.Errorf("row: got %d, want %d (error: %s)", row, e.expectedRow, derr.String())
-			}
-			if col != e.expectedCol {
-				t.Errorf("col: got %d, want %d (error: %s)", col, e.expectedCol, derr.String())
-			}
-			if !strings.Contains(derr.Error(), e.errContains) {
-				t.Errorf("error %q does not contain %q", derr.Error(), e.errContains)
-			}
-		})
-	}
-}
-
-func TestDecodeError_HumanStringAfterComments(t *testing.T) {
-	doc := "# comment\n= \"value\""
-	var v map[string]interface{}
-	err := Unmarshal([]byte(doc), &v)
-	if err == nil {
-		t.Fatal("expected an error")
-	}
-
-	var derr *DecodeError
-	if !errors.As(err, &derr) {
-		t.Fatalf("expected DecodeError, got %T: %v", err, err)
-	}
-
-	human := derr.String()
-	if !strings.Contains(human, "= \"value\"") {
-		t.Errorf("human-readable error should show the offending line, got:\n%s", human)
-	}
-	if !strings.Contains(human, "2|") {
-		t.Errorf("human-readable error should reference line 2, got:\n%s", human)
-	}
-}
-
 func TestStrictErrorUnwrap(t *testing.T) {
 	fo := bytes.NewBufferString(`
 Missing = 1

internal/characters/utf8.go

@@ -24,57 +24,61 @@ import (
 // 0x9 => tab, ok
 // 0xA - 0x1F => invalid
 // 0x7F => invalid
-func Utf8TomlValidAlreadyEscaped(p []byte) int {
-	consumed := 0
-
+func Utf8TomlValidAlreadyEscaped(p []byte) []byte {
 	// Fast path. Check for and skip 8 bytes of ASCII characters per iteration.
 	for len(p) >= 8 {
+		// Combining two 32 bit loads allows the same code to be used
+		// for 32 and 64 bit platforms.
+		// The compiler can generate a 32bit load for first32 and second32
+		// on many platforms. See test/codegen/memcombine.go.
 		first32 := uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
 		second32 := uint32(p[4]) | uint32(p[5])<<8 | uint32(p[6])<<16 | uint32(p[7])<<24
 		if (first32|second32)&0x80808080 != 0 {
+			// Found a non ASCII byte (>= RuneSelf).
 			break
 		}
 
 		for i, b := range p[:8] {
 			if InvalidASCII(b) {
-				return consumed + i
+				return p[i : i+1]
 			}
 		}
 
 		p = p[8:]
-		consumed += 8
 	}
 	n := len(p)
 	for i := 0; i < n; {
 		pi := p[i]
 		if pi < utf8.RuneSelf {
 			if InvalidASCII(pi) {
-				return consumed + i
+				return p[i : i+1]
 			}
 			i++
 			continue
 		}
 		x := first[pi]
 		if x == xx {
-			return consumed + i
+			// Illegal starter byte.
+			return p[i : i+1]
 		}
 		size := int(x & 7)
 		if i+size > n {
-			return consumed + i
+			// Short or invalid.
+			return p[i:n]
 		}
 		accept := acceptRanges[x>>4]
 		if c := p[i+1]; c < accept.lo || accept.hi < c {
-			return consumed + i
+			return p[i : i+2]
 		} else if size == 2 { //revive:disable:empty-block
 		} else if c := p[i+2]; c < locb || hicb < c {
-			return consumed + i
+			return p[i : i+3]
 		} else if size == 3 { //revive:disable:empty-block
 		} else if c := p[i+3]; c < locb || hicb < c {
-			return consumed + i
+			return p[i : i+4]
 		}
 		i += size
 	}
-	return -1
+	return nil
 }
 
 // Utf8ValidNext returns the size of the next rune if valid, 0 otherwise.

localtime.go

@@ -32,7 +32,7 @@ func (d LocalDate) MarshalText() ([]byte, error) {
 
 // UnmarshalText parses b using RFC 3339 to fill d.
 func (d *LocalDate) UnmarshalText(b []byte) error {
-	res, err := parseLocalDate(b, 0)
+	res, err := parseLocalDate(b)
 	if err != nil {
 		return err
 	}
@@ -75,9 +75,9 @@ func (d LocalTime) MarshalText() ([]byte, error) {
 
 // UnmarshalText parses b using RFC 3339 to fill d.
 func (d *LocalTime) UnmarshalText(b []byte) error {
-	res, left, err := parseLocalTime(b, 0)
+	res, left, err := parseLocalTime(b)
 	if err == nil && len(left) != 0 {
-		err = unstable.NewParserError(left, len(b)-len(left), "extra characters")
+		err = unstable.NewParserError(left, "extra characters")
 	}
 	if err != nil {
 		return err
@@ -109,9 +109,9 @@ func (d LocalDateTime) MarshalText() ([]byte, error) {
 
 // UnmarshalText parses b using RFC 3339 to fill d.
 func (d *LocalDateTime) UnmarshalText(data []byte) error {
-	res, left, err := parseLocalDateTime(data, 0)
+	res, left, err := parseLocalDateTime(data)
 	if err == nil && len(left) != 0 {
-		err = unstable.NewParserError(left, len(data)-len(left), "extra characters")
+		err = unstable.NewParserError(left, "extra characters")
 	}
 	if err != nil {
 		return err

marshaler.go

@@ -704,18 +704,15 @@ func (enc *Encoder) encodeMap(b []byte, ctx encoderCtx, v reflect.Value) ([]byte
 	for iter.Next() {
 		v := iter.Value()
 
-		// Handle nil values: convert nil pointers to zero value,
-		// skip nil interfaces and nil maps.
-		switch v.Kind() {
-		case reflect.Ptr:
-			if v.IsNil() {
+		if isNil(v) {
+			// For nil pointers, convert to zero value of the element type.
+			// This allows round-trip marshaling of maps with nil pointer values.
+			// For nil interfaces and nil maps, skip since we can't derive a type.
+			if v.Kind() == reflect.Ptr {
 				v = reflect.Zero(v.Type().Elem())
-			}
-		case reflect.Interface, reflect.Map:
-			if v.IsNil() {
+			} else {
 				continue
 			}
-		default:
 		}
 
 		k, err := enc.keyToString(iter.Key())
@@ -939,7 +936,7 @@ func (enc *Encoder) encodeTable(b []byte, ctx encoderCtx, t table) ([]byte, erro
 		if shouldOmitEmpty(kv.Options, kv.Value) {
 			continue
 		}
-		if kv.Options.omitzero && shouldOmitZero(kv.Options, kv.Value) {
+		if shouldOmitZero(kv.Options, kv.Value) {
 			continue
 		}
 		hasNonEmptyKV = true
@@ -961,7 +958,7 @@ func (enc *Encoder) encodeTable(b []byte, ctx encoderCtx, t table) ([]byte, erro
 		if shouldOmitEmpty(table.Options, table.Value) {
 			continue
 		}
-		if table.Options.omitzero && shouldOmitZero(table.Options, table.Value) {
+		if shouldOmitZero(table.Options, table.Value) {
 			continue
 		}
 		if first {
@@ -998,7 +995,7 @@ func (enc *Encoder) encodeTableInline(b []byte, ctx encoderCtx, t table) ([]byte
 		if shouldOmitEmpty(kv.Options, kv.Value) {
 			continue
 		}
-		if kv.Options.omitzero && shouldOmitZero(kv.Options, kv.Value) {
+		if shouldOmitZero(kv.Options, kv.Value) {
 			continue
 		}
 

strict.go

@@ -54,12 +54,10 @@ func (s *strict) MissingTable(node *unstable.Node) {
 		return
 	}
 
-	loc, offset := s.keyLocation(node)
 	s.missing = append(s.missing, unstable.ParserError{
-		Highlight: loc,
+		Highlight: s.keyLocation(node),
 		Message:   "missing table",
 		Key:       s.key.Key(),
-		Offset:    offset,
 	})
 }
 
@@ -68,12 +66,10 @@ func (s *strict) MissingField(node *unstable.Node) {
 		return
 	}
 
-	loc, offset := s.keyLocation(node)
 	s.missing = append(s.missing, unstable.ParserError{
-		Highlight: loc,
+		Highlight: s.keyLocation(node),
 		Message:   "missing field",
 		Key:       s.key.Key(),
-		Offset:    offset,
 	})
 }
 
@@ -94,7 +90,7 @@ func (s *strict) Error(doc []byte) error {
 	return err
 }
 
-func (s *strict) keyLocation(node *unstable.Node) ([]byte, int) {
+func (s *strict) keyLocation(node *unstable.Node) []byte {
 	k := node.Key()
 
 	hasOne := k.Next()
@@ -102,6 +98,7 @@ func (s *strict) keyLocation(node *unstable.Node) ([]byte, int) {
 		panic("should not be called with empty key")
 	}
 
+	// Get the range from the first key to the last key.
 	firstRaw := k.Node().Raw
 	lastRaw := firstRaw
 
@@ -109,8 +106,9 @@ func (s *strict) keyLocation(node *unstable.Node) ([]byte, int) {
 		lastRaw = k.Node().Raw
 	}
 
+	// Compute the slice from the document using the ranges.
 	start := firstRaw.Offset
 	end := lastRaw.Offset + lastRaw.Length
 
-	return s.doc[start:end], int(start)
+	return s.doc[start:end]
 }

unmarshaler.go

@@ -625,7 +625,7 @@ func (d *decoder) handleTable(key unstable.Iterator, v reflect.Value) (reflect.V
 				}
 			}
 		}
-		return reflect.Value{}, unstable.NewParserError(key.Node().Data, int(key.Node().Raw.Offset), "cannot store a table in a slice")
+		return reflect.Value{}, unstable.NewParserError(key.Node().Data, "cannot store a table in a slice")
 	}
 	if key.Next() {
 		// Still scoping the key
@@ -748,7 +748,7 @@ func (d *decoder) tryTextUnmarshaler(node *unstable.Node, v reflect.Value) (bool
 	if v.CanAddr() && v.Addr().Type().Implements(textUnmarshalerType) {
 		err := v.Addr().Interface().(encoding.TextUnmarshaler).UnmarshalText(node.Data)
 		if err != nil {
-			return false, unstable.NewParserError(d.p.Raw(node.Raw), int(node.Raw.Offset), "%w", err)
+			return false, unstable.NewParserError(d.p.Raw(node.Raw), "%w", err)
 		}
 
 		return true, nil
@@ -896,7 +896,7 @@ func (d *decoder) unmarshalInlineTable(itable *unstable.Node, v reflect.Value) e
 		}
 		return d.unmarshalInlineTable(itable, elem)
 	default:
-		return unstable.NewParserError(d.p.Raw(itable.Raw), int(itable.Raw.Offset), "cannot store inline table in Go type %s", v.Kind())
+		return unstable.NewParserError(d.p.Raw(itable.Raw), "cannot store inline table in Go type %s", v.Kind())
 	}
 
 	it := itable.Children()
@@ -916,26 +916,26 @@ func (d *decoder) unmarshalInlineTable(itable *unstable.Node, v reflect.Value) e
 }
 
 func (d *decoder) unmarshalDateTime(value *unstable.Node, v reflect.Value) error {
-	dt, err := parseDateTime(value.Data, int(value.Raw.Offset))
+	dt, err := parseDateTime(value.Data)
 	if err != nil {
 		return err
 	}
 
 	if v.Kind() != reflect.Interface && v.Type() != timeType {
-		return unstable.NewParserError(d.p.Raw(value.Raw), int(value.Raw.Offset), "%s", d.typeMismatchString("datetime", v.Type()))
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("datetime", v.Type()))
 	}
 	v.Set(reflect.ValueOf(dt))
 	return nil
 }
 
 func (d *decoder) unmarshalLocalDate(value *unstable.Node, v reflect.Value) error {
-	ld, err := parseLocalDate(value.Data, int(value.Raw.Offset))
+	ld, err := parseLocalDate(value.Data)
 	if err != nil {
 		return err
 	}
 
 	if v.Kind() != reflect.Interface && v.Type() != timeType {
-		return unstable.NewParserError(d.p.Raw(value.Raw), int(value.Raw.Offset), "%s", d.typeMismatchString("local date", v.Type()))
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local date", v.Type()))
 	}
 	if v.Type() == timeType {
 		v.Set(reflect.ValueOf(ld.AsTime(time.Local)))
@@ -946,34 +946,34 @@ func (d *decoder) unmarshalLocalDate(value *unstable.Node, v reflect.Value) erro
 }
 
 func (d *decoder) unmarshalLocalTime(value *unstable.Node, v reflect.Value) error {
-	lt, rest, err := parseLocalTime(value.Data, int(value.Raw.Offset))
+	lt, rest, err := parseLocalTime(value.Data)
 	if err != nil {
 		return err
 	}
 
 	if len(rest) > 0 {
-		return unstable.NewParserError(rest, int(value.Raw.Offset)+len(value.Data)-len(rest), "extra characters at the end of a local time")
+		return unstable.NewParserError(rest, "extra characters at the end of a local time")
 	}
 
 	if v.Kind() != reflect.Interface {
-		return unstable.NewParserError(d.p.Raw(value.Raw), int(value.Raw.Offset), "%s", d.typeMismatchString("local time", v.Type()))
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local time", v.Type()))
 	}
 	v.Set(reflect.ValueOf(lt))
 	return nil
 }
 
 func (d *decoder) unmarshalLocalDateTime(value *unstable.Node, v reflect.Value) error {
-	ldt, rest, err := parseLocalDateTime(value.Data, int(value.Raw.Offset))
+	ldt, rest, err := parseLocalDateTime(value.Data)
 	if err != nil {
 		return err
 	}
 
 	if len(rest) > 0 {
-		return unstable.NewParserError(rest, int(value.Raw.Offset)+len(value.Data)-len(rest), "extra characters at the end of a local date time")
+		return unstable.NewParserError(rest, "extra characters at the end of a local date time")
 	}
 
 	if v.Kind() != reflect.Interface && v.Type() != timeType {
-		return unstable.NewParserError(d.p.Raw(value.Raw), int(value.Raw.Offset), "%s", d.typeMismatchString("local datetime", v.Type()))
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("local datetime", v.Type()))
 	}
 	if v.Type() == timeType {
 		v.Set(reflect.ValueOf(ldt.AsTime(time.Local)))
@@ -992,14 +992,14 @@ func (d *decoder) unmarshalBool(value *unstable.Node, v reflect.Value) error {
 	case reflect.Interface:
 		v.Set(reflect.ValueOf(b))
 	default:
-		return unstable.NewParserError(value.Data, int(value.Raw.Offset), "cannot assign boolean to a %t", b)
+		return unstable.NewParserError(value.Data, "cannot assign boolean to a %t", b)
 	}
 
 	return nil
 }
 
 func (d *decoder) unmarshalFloat(value *unstable.Node, v reflect.Value) error {
-	f, err := parseFloat(value.Data, int(value.Raw.Offset))
+	f, err := parseFloat(value.Data)
 	if err != nil {
 		return err
 	}
@@ -1009,13 +1009,13 @@ func (d *decoder) unmarshalFloat(value *unstable.Node, v reflect.Value) error {
 		v.SetFloat(f)
 	case reflect.Float32:
 		if f > math.MaxFloat32 {
-			return unstable.NewParserError(value.Data, int(value.Raw.Offset), "number %f does not fit in a float32", f)
+			return unstable.NewParserError(value.Data, "number %f does not fit in a float32", f)
 		}
 		v.SetFloat(f)
 	case reflect.Interface:
 		v.Set(reflect.ValueOf(f))
 	default:
-		return unstable.NewParserError(value.Data, int(value.Raw.Offset), "float cannot be assigned to %s", v.Kind())
+		return unstable.NewParserError(value.Data, "float cannot be assigned to %s", v.Kind())
 	}
 
 	return nil
@@ -1048,7 +1048,7 @@ func (d *decoder) unmarshalInteger(value *unstable.Node, v reflect.Value) error
 		return d.unmarshalFloat(value, v)
 	}
 
-	i, err := parseInteger(value.Data, int(value.Raw.Offset))
+	i, err := parseInteger(value.Data)
 	if err != nil {
 		return err
 	}
@@ -1116,7 +1116,7 @@ func (d *decoder) unmarshalInteger(value *unstable.Node, v reflect.Value) error
 	case reflect.Interface:
 		r = reflect.ValueOf(i)
 	default:
-		return unstable.NewParserError(d.p.Raw(value.Raw), int(value.Raw.Offset), "%s", d.typeMismatchString("integer", v.Type()))
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("integer", v.Type()))
 	}
 
 	if !r.Type().AssignableTo(v.Type()) {
@@ -1135,7 +1135,7 @@ func (d *decoder) unmarshalString(value *unstable.Node, v reflect.Value) error {
 	case reflect.Interface:
 		v.Set(reflect.ValueOf(string(value.Data)))
 	default:
-		return unstable.NewParserError(d.p.Raw(value.Raw), int(value.Raw.Offset), "%s", d.typeMismatchString("string", v.Type()))
+		return unstable.NewParserError(d.p.Raw(value.Raw), "%s", d.typeMismatchString("string", v.Type()))
 	}
 
 	return nil

unstable/ast.go

@@ -28,16 +28,12 @@ func (c *Iterator) Next() bool {
 	if c.nodes == nil {
 		return false
 	}
-	nodes := *c.nodes
 	if !c.started {
 		c.started = true
-	} else {
-		idx := c.idx
-		if idx >= 0 && int(idx) < len(nodes) {
-			c.idx = nodes[idx].next
-		}
+	} else if c.idx >= 0 {
+		c.idx = (*c.nodes)[c.idx].next
 	}
-	return c.idx >= 0 && int(c.idx) < len(nodes)
+	return c.idx >= 0 && int(c.idx) < len(*c.nodes)
 }
 
 // IsLast returns true if the current node of the iterator is the last

unstable/benchmark_test.go

@@ -35,7 +35,7 @@ func BenchmarkScanComments(b *testing.B) {
 			b.ResetTimer()
 
 			for i := 0; i < b.N; i++ {
-				_, _, _ = scanComment(input, 0)
+				_, _, _ = scanComment(input)
 			}
 		})
 	}

unstable/parser.go

@@ -16,7 +16,6 @@ type ParserError struct {
 	Highlight []byte
 	Message   string
 	Key       []string // optional
-	Offset    int
 }
 
 // Error is the implementation of the error interface.
@@ -28,10 +27,9 @@ func (e *ParserError) Error() string {
 //
 // Warning: Highlight needs to be a subslice of Parser.data, so only slices
 // returned by Parser.Raw are valid candidates.
-func NewParserError(highlight []byte, offset int, format string, args ...interface{}) error {
+func NewParserError(highlight []byte, format string, args ...interface{}) error {
 	return &ParserError{
 		Highlight: highlight,
-		Offset:    offset,
 		Message:   fmt.Errorf(format, args...).Error(),
 	}
 }
@@ -66,8 +64,14 @@ func (p *Parser) Data() []byte {
 	return p.data
 }
 
-func (p *Parser) offsetOf(b []byte) int {
-	return len(p.data) - len(b)
+// Range returns a range description that corresponds to a given slice of the
+// input. If the argument is not a subslice of the parser input, this function
+// panics.
+func (p *Parser) Range(b []byte) Range {
+	return Range{
+		Offset: uint32(p.subsliceOffset(b)), //nolint:gosec // TOML documents are small
+		Length: uint32(len(b)),              //nolint:gosec // TOML documents are small
+	}
 }
 
 // rangeOfToken computes the Range of a token given the remaining bytes after the token.
@@ -78,6 +82,13 @@ func (p *Parser) rangeOfToken(token, rest []byte) Range {
 	return Range{Offset: uint32(offset), Length: uint32(len(token))} //nolint:gosec // TOML documents are small
 }
 
+// subsliceOffset returns the byte offset of subslice b within p.data.
+// b must be a suffix (tail) of p.data.
+func (p *Parser) subsliceOffset(b []byte) int {
+	// b is a suffix of p.data, so its offset is len(p.data) - len(b)
+	return len(p.data) - len(b)
+}
+
 // Raw returns the slice corresponding to the bytes in the given range.
 func (p *Parser) Raw(raw Range) []byte {
 	return p.data[raw.Offset : raw.Offset+raw.Length]
@@ -187,16 +198,16 @@ func (p *Parser) parseNewline(b []byte) ([]byte, error) {
 	}
 
 	if b[0] == '\r' {
-		_, rest, err := scanWindowsNewline(b, p.offsetOf(b))
+		_, rest, err := scanWindowsNewline(b)
 		return rest, err
 	}
 
-	return nil, NewParserError(b[0:1], p.offsetOf(b), "expected newline but got %#U", b[0])
+	return nil, NewParserError(b[0:1], "expected newline but got %#U", b[0])
 }
 
 func (p *Parser) parseComment(b []byte) (reference, []byte, error) {
 	ref := invalidReference
-	data, rest, err := scanComment(b, p.offsetOf(b))
+	data, rest, err := scanComment(b)
 	if p.KeepComments && err == nil {
 		ref = p.builder.Push(Node{
 			Kind: Comment,
@@ -280,12 +291,12 @@ func (p *Parser) parseArrayTable(b []byte) (reference, []byte, error) {
 	p.builder.AttachChild(ref, k)
 	b = p.parseWhitespace(b)
 
-	b, err = expect(']', b, p.offsetOf(b))
+	b, err = expect(']', b)
 	if err != nil {
 		return ref, nil, err
 	}
 
-	b, err = expect(']', b, p.offsetOf(b))
+	b, err = expect(']', b)
 
 	return ref, b, err
 }
@@ -310,7 +321,7 @@ func (p *Parser) parseStdTable(b []byte) (reference, []byte, error) {
 
 	b = p.parseWhitespace(b)
 
-	b, err = expect(']', b, p.offsetOf(b))
+	b, err = expect(']', b)
 
 	return ref, b, err
 }
@@ -334,10 +345,10 @@ func (p *Parser) parseKeyval(b []byte) (reference, []byte, error) {
 	b = p.parseWhitespace(b)
 
 	if len(b) == 0 {
-		return invalidReference, nil, NewParserError(startB[:len(startB)-len(b)], p.offsetOf(startB), "expected = after a key, but the document ends there")
+		return invalidReference, nil, NewParserError(startB[:len(startB)-len(b)], "expected = after a key, but the document ends there")
 	}
 
-	b, err = expect('=', b, p.offsetOf(b))
+	b, err = expect('=', b)
 	if err != nil {
 		return invalidReference, nil, err
 	}
@@ -352,10 +363,9 @@ func (p *Parser) parseKeyval(b []byte) (reference, []byte, error) {
 	p.builder.Chain(valRef, key)
 	p.builder.AttachChild(ref, valRef)
 
-	// Set Raw to span the entire key-value expression.
-	// Access the node directly in the slice to avoid the write barrier
-	// that NodeAt's nodes-pointer setup would trigger.
-	p.builder.tree.nodes[ref].Raw = p.rangeOfToken(startB[:len(startB)-len(b)], b)
+	// Set Raw to span the entire key-value expression
+	node := p.builder.NodeAt(ref)
+	node.Raw = p.rangeOfToken(startB[:len(startB)-len(b)], b)
 
 	return ref, b, err
 }
@@ -366,7 +376,7 @@ func (p *Parser) parseVal(b []byte) (reference, []byte, error) {
 	ref := invalidReference
 
 	if len(b) == 0 {
-		return ref, nil, NewParserError(b, p.offsetOf(b), "expected value, not eof")
+		return ref, nil, NewParserError(b, "expected value, not eof")
 	}
 
 	var err error
@@ -411,7 +421,7 @@ func (p *Parser) parseVal(b []byte) (reference, []byte, error) {
 		return ref, b, err
 	case 't':
 		if !scanFollowsTrue(b) {
-			return ref, nil, NewParserError(atmost(b, 4), p.offsetOf(b), "expected 'true'")
+			return ref, nil, NewParserError(atmost(b, 4), "expected 'true'")
 		}
 
 		ref = p.builder.Push(Node{
@@ -422,7 +432,7 @@ func (p *Parser) parseVal(b []byte) (reference, []byte, error) {
 		return ref, b[4:], nil
 	case 'f':
 		if !scanFollowsFalse(b) {
-			return ref, nil, NewParserError(atmost(b, 5), p.offsetOf(b), "expected 'false'")
+			return ref, nil, NewParserError(atmost(b, 5), "expected 'false'")
 		}
 
 		ref = p.builder.Push(Node{
@@ -449,7 +459,7 @@ func atmost(b []byte, n int) []byte {
 }
 
 func (p *Parser) parseLiteralString(b []byte) ([]byte, []byte, []byte, error) {
-	v, rest, err := scanLiteralString(b, p.offsetOf(b))
+	v, rest, err := scanLiteralString(b)
 	if err != nil {
 		return nil, nil, nil, err
 	}
@@ -481,7 +491,7 @@ func (p *Parser) parseInlineTable(b []byte) (reference, []byte, error) {
 		b = p.parseWhitespace(b)
 
 		if len(b) == 0 {
-			return parent, nil, NewParserError(previousB[:1], p.offsetOf(previousB), "inline table is incomplete")
+			return parent, nil, NewParserError(previousB[:1], "inline table is incomplete")
 		}
 
 		if b[0] == '}' {
@@ -489,7 +499,7 @@ func (p *Parser) parseInlineTable(b []byte) (reference, []byte, error) {
 		}
 
 		if !first {
-			b, err = expect(',', b, p.offsetOf(b))
+			b, err = expect(',', b)
 			if err != nil {
 				return parent, nil, err
 			}
@@ -513,7 +523,7 @@ func (p *Parser) parseInlineTable(b []byte) (reference, []byte, error) {
 		first = false
 	}
 
-	rest, err := expect('}', b, p.offsetOf(b))
+	rest, err := expect('}', b)
 
 	return parent, rest, err
 }
@@ -562,7 +572,7 @@ func (p *Parser) parseValArray(b []byte) (reference, []byte, error) {
 		}
 
 		if len(b) == 0 {
-			return parent, nil, NewParserError(arrayStart[:1], p.offsetOf(arrayStart), "array is incomplete")
+			return parent, nil, NewParserError(arrayStart[:1], "array is incomplete")
 		}
 
 		if b[0] == ']' {
@@ -571,7 +581,7 @@ func (p *Parser) parseValArray(b []byte) (reference, []byte, error) {
 
 		if b[0] == ',' {
 			if first {
-				return parent, nil, NewParserError(b[0:1], p.offsetOf(b), "array cannot start with comma")
+				return parent, nil, NewParserError(b[0:1], "array cannot start with comma")
 			}
 			b = b[1:]
 
@@ -583,7 +593,7 @@ func (p *Parser) parseValArray(b []byte) (reference, []byte, error) {
 				addChild(cref)
 			}
 		} else if !first {
-			return parent, nil, NewParserError(b[0:1], p.offsetOf(b), "array elements must be separated by commas")
+			return parent, nil, NewParserError(b[0:1], "array elements must be separated by commas")
 		}
 
 		// TOML allows trailing commas in arrays.
@@ -610,7 +620,7 @@ func (p *Parser) parseValArray(b []byte) (reference, []byte, error) {
 		first = false
 	}
 
-	rest, err := expect(']', b, p.offsetOf(b))
+	rest, err := expect(']', b)
 
 	return parent, rest, err
 }
@@ -665,7 +675,7 @@ func (p *Parser) parseOptionalWhitespaceCommentNewline(b []byte) (reference, []b
 }
 
 func (p *Parser) parseMultilineLiteralString(b []byte) ([]byte, []byte, []byte, error) {
-	token, rest, err := scanMultilineLiteralString(b, p.offsetOf(b))
+	token, rest, err := scanMultilineLiteralString(b)
 	if err != nil {
 		return nil, nil, nil, err
 	}
@@ -694,7 +704,7 @@ func (p *Parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 	// mlb-quotes = 1*2quotation-mark
 	// mlb-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
 	// mlb-escaped-nl = escape ws newline *( wschar / newline )
-	token, escaped, rest, err := scanMultilineBasicString(b, p.offsetOf(b))
+	token, escaped, rest, err := scanMultilineBasicString(b)
 	if err != nil {
 		return nil, nil, nil, err
 	}
@@ -711,15 +721,14 @@ func (p *Parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 	// fast path
 	startIdx := i
 	endIdx := len(token) - len(`"""`)
-	tokenBase := p.offsetOf(token)
 
 	if !escaped {
 		str := token[startIdx:endIdx]
-		invalidIdx := characters.Utf8TomlValidAlreadyEscaped(str)
-		if invalidIdx < 0 {
+		highlight := characters.Utf8TomlValidAlreadyEscaped(str)
+		if len(highlight) == 0 {
 			return token, str, rest, nil
 		}
-		return nil, nil, nil, NewParserError(str[invalidIdx:invalidIdx+1], tokenBase+startIdx+invalidIdx, "invalid UTF-8")
+		return nil, nil, nil, NewParserError(highlight, "invalid UTF-8")
 	}
 
 	var builder bytes.Buffer
@@ -784,14 +793,14 @@ func (p *Parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 			case 'e':
 				builder.WriteByte(0x1B)
 			case 'u':
-				x, err := hexToRune(atmost(token[i+1:], 4), tokenBase+i+1, 4)
+				x, err := hexToRune(atmost(token[i+1:], 4), 4)
 				if err != nil {
 					return nil, nil, nil, err
 				}
 				builder.WriteRune(x)
 				i += 4
 			case 'U':
-				x, err := hexToRune(atmost(token[i+1:], 8), tokenBase+i+1, 8)
+				x, err := hexToRune(atmost(token[i+1:], 8), 8)
 				if err != nil {
 					return nil, nil, nil, err
 				}
@@ -799,13 +808,13 @@ func (p *Parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 				builder.WriteRune(x)
 				i += 8
 			default:
-				return nil, nil, nil, NewParserError(token[i:i+1], tokenBase+i, "invalid escaped character %#U", c)
+				return nil, nil, nil, NewParserError(token[i:i+1], "invalid escaped character %#U", c)
 			}
 			i++
 		} else {
 			size := characters.Utf8ValidNext(token[i:])
 			if size == 0 {
-				return nil, nil, nil, NewParserError(token[i:i+1], tokenBase+i, "invalid character %#U", c)
+				return nil, nil, nil, NewParserError(token[i:i+1], "invalid character %#U", c)
 			}
 			builder.Write(token[i : i+size])
 			i += size
@@ -860,9 +869,12 @@ func (p *Parser) parseKey(b []byte) (reference, []byte, error) {
 
 func (p *Parser) parseSimpleKey(b []byte) (raw, key, rest []byte, err error) {
 	if len(b) == 0 {
-		return nil, nil, nil, NewParserError(b, p.offsetOf(b), "expected key but found none")
+		return nil, nil, nil, NewParserError(b, "expected key but found none")
 	}
 
+	// simple-key = quoted-key / unquoted-key
+	// unquoted-key = 1*( ALPHA / DIGIT / %x2D / %x5F ) ; A-Z / a-z / 0-9 / - / _
+	// quoted-key = basic-string / literal-string
 	switch {
 	case b[0] == '\'':
 		return p.parseLiteralString(b)
@@ -872,7 +884,7 @@ func (p *Parser) parseSimpleKey(b []byte) (raw, key, rest []byte, err error) {
 		key, rest = scanUnquotedKey(b)
 		return key, key, rest, nil
 	default:
-		return nil, nil, nil, NewParserError(b[0:1], p.offsetOf(b), "invalid character at start of key: %c", b[0])
+		return nil, nil, nil, NewParserError(b[0:1], "invalid character at start of key: %c", b[0])
 	}
 }
 
@@ -892,7 +904,7 @@ func (p *Parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 	// escape-seq-char =/ %x74         ; t    tab             U+0009
 	// escape-seq-char =/ %x75 4HEXDIG ; uXXXX                U+XXXX
 	// escape-seq-char =/ %x55 8HEXDIG ; UXXXXXXXX            U+XXXXXXXX
-	token, escaped, rest, err := scanBasicString(b, p.offsetOf(b))
+	token, escaped, rest, err := scanBasicString(b)
 	if err != nil {
 		return nil, nil, nil, err
 	}
@@ -903,15 +915,13 @@ func (p *Parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 	// Fast path. If there is no escape sequence, the string should just be
 	// an UTF-8 encoded string, which is the same as Go. In that case,
 	// validate the string and return a direct reference to the buffer.
-	tokenBase := p.offsetOf(token)
-
 	if !escaped {
 		str := token[startIdx:endIdx]
-		invalidIdx := characters.Utf8TomlValidAlreadyEscaped(str)
-		if invalidIdx < 0 {
+		highlight := characters.Utf8TomlValidAlreadyEscaped(str)
+		if len(highlight) == 0 {
 			return token, str, rest, nil
 		}
-		return nil, nil, nil, NewParserError(str[invalidIdx:invalidIdx+1], tokenBase+startIdx+invalidIdx, "invalid UTF-8")
+		return nil, nil, nil, NewParserError(highlight, "invalid UTF-8")
 	}
 
 	i := startIdx
@@ -942,7 +952,7 @@ func (p *Parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 			case 'e':
 				builder.WriteByte(0x1B)
 			case 'u':
-				x, err := hexToRune(token[i+1:len(token)-1], tokenBase+i+1, 4)
+				x, err := hexToRune(token[i+1:len(token)-1], 4)
 				if err != nil {
 					return nil, nil, nil, err
 				}
@@ -950,7 +960,7 @@ func (p *Parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 				builder.WriteRune(x)
 				i += 4
 			case 'U':
-				x, err := hexToRune(token[i+1:len(token)-1], tokenBase+i+1, 8)
+				x, err := hexToRune(token[i+1:len(token)-1], 8)
 				if err != nil {
 					return nil, nil, nil, err
 				}
@@ -958,13 +968,13 @@ func (p *Parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 				builder.WriteRune(x)
 				i += 8
 			default:
-				return nil, nil, nil, NewParserError(token[i:i+1], tokenBase+i, "invalid escaped character %#U", c)
+				return nil, nil, nil, NewParserError(token[i:i+1], "invalid escaped character %#U", c)
 			}
 			i++
 		} else {
 			size := characters.Utf8ValidNext(token[i:])
 			if size == 0 {
-				return nil, nil, nil, NewParserError(token[i:i+1], tokenBase+i, "invalid character %#U", c)
+				return nil, nil, nil, NewParserError(token[i:i+1], "invalid character %#U", c)
 			}
 			builder.Write(token[i : i+size])
 			i += size
@@ -974,9 +984,9 @@ func (p *Parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 	return token, builder.Bytes(), rest, nil
 }
 
-func hexToRune(b []byte, base int, length int) (rune, error) {
+func hexToRune(b []byte, length int) (rune, error) {
 	if len(b) < length {
-		return -1, NewParserError(b, base, "unicode point needs %d character, not %d", length, len(b))
+		return -1, NewParserError(b, "unicode point needs %d character, not %d", length, len(b))
 	}
 	b = b[:length]
 
@@ -991,13 +1001,13 @@ func hexToRune(b []byte, base int, length int) (rune, error) {
 		case 'A' <= c && c <= 'F':
 			d = uint32(c - 'A' + 10)
 		default:
-			return -1, NewParserError(b[i:i+1], base+i, "non-hex character")
+			return -1, NewParserError(b[i:i+1], "non-hex character")
 		}
 		r = r*16 + d
 	}
 
 	if r > unicode.MaxRune || 0xD800 <= r && r < 0xE000 {
-		return -1, NewParserError(b, base, "escape sequence is invalid Unicode code point")
+		return -1, NewParserError(b, "escape sequence is invalid Unicode code point")
 	}
 
 	return rune(r), nil
@@ -1017,7 +1027,7 @@ func (p *Parser) parseIntOrFloatOrDateTime(b []byte) (reference, []byte, error)
 	switch b[0] {
 	case 'i':
 		if !scanFollowsInf(b) {
-			return invalidReference, nil, NewParserError(atmost(b, 3), p.offsetOf(b), "expected 'inf'")
+			return invalidReference, nil, NewParserError(atmost(b, 3), "expected 'inf'")
 		}
 
 		return p.builder.Push(Node{
@@ -1027,7 +1037,7 @@ func (p *Parser) parseIntOrFloatOrDateTime(b []byte) (reference, []byte, error)
 		}), b[3:], nil
 	case 'n':
 		if !scanFollowsNan(b) {
-			return invalidReference, nil, NewParserError(atmost(b, 3), p.offsetOf(b), "expected 'nan'")
+			return invalidReference, nil, NewParserError(atmost(b, 3), "expected 'nan'")
 		}
 
 		return p.builder.Push(Node{
@@ -1186,7 +1196,7 @@ func (p *Parser) scanIntOrFloat(b []byte) (reference, []byte, error) {
 				}), b[i+3:], nil
 			}
 
-			return invalidReference, nil, NewParserError(b[i:i+1], p.offsetOf(b)+i, "unexpected character 'i' while scanning for a number")
+			return invalidReference, nil, NewParserError(b[i:i+1], "unexpected character 'i' while scanning for a number")
 		}
 
 		if c == 'n' {
@@ -1198,14 +1208,14 @@ func (p *Parser) scanIntOrFloat(b []byte) (reference, []byte, error) {
 				}), b[i+3:], nil
 			}
 
-			return invalidReference, nil, NewParserError(b[i:i+1], p.offsetOf(b)+i, "unexpected character 'n' while scanning for a number")
+			return invalidReference, nil, NewParserError(b[i:i+1], "unexpected character 'n' while scanning for a number")
 		}
 
 		break
 	}
 
 	if i == 0 {
-		return invalidReference, b, NewParserError(b, p.offsetOf(b), "incomplete number")
+		return invalidReference, b, NewParserError(b, "incomplete number")
 	}
 
 	kind := Integer
@@ -1242,13 +1252,13 @@ func isValidBinaryRune(r byte) bool {
 	return r == '0' || r == '1' || r == '_'
 }
 
-func expect(x byte, b []byte, base int) ([]byte, error) {
+func expect(x byte, b []byte) ([]byte, error) {
 	if len(b) == 0 {
-		return nil, NewParserError(b, base, "expected character %c but the document ended here", x)
+		return nil, NewParserError(b, "expected character %c but the document ended here", x)
 	}
 
 	if b[0] != x {
-		return nil, NewParserError(b[0:1], base, "expected character %c", x)
+		return nil, NewParserError(b[0:1], "expected character %c", x)
 	}
 
 	return b[1:], nil

unstable/parser_test.go

@@ -1,7 +1,6 @@
 package unstable
 
 import (
-	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -674,96 +673,6 @@ key3 = "value3"
 	assert.Equal(t, []string{"key1", "key2", "key3"}, keys)
 }
 
-func TestErrorOffsetAfterComment(t *testing.T) {
-	input := []byte("# comment\n= \"value\"")
-
-	p := Parser{}
-	p.Reset(input)
-	for p.NextExpression() {
-	}
-	err := p.Error()
-	if err == nil {
-		t.Fatal("expected an error")
-	}
-	var perr *ParserError
-	if !errors.As(err, &perr) {
-		t.Fatalf("expected ParserError, got %T", err)
-	}
-
-	if perr.Offset != 10 {
-		t.Errorf("offset: got %d, want 10", perr.Offset)
-	}
-	shape := p.Shape(Range{Offset: uint32(perr.Offset), Length: uint32(len(perr.Highlight))})
-	if shape.Start.Line != 2 || shape.Start.Column != 1 {
-		t.Errorf("position: got %d:%d, want 2:1", shape.Start.Line, shape.Start.Column)
-	}
-}
-
-func TestErrorHighlightPositions(t *testing.T) {
-	examples := []struct {
-		desc       string
-		input      string
-		wantLine   int
-		wantColumn int
-	}{
-		{
-			desc:       "invalid key start after comment",
-			input:      "# comment\n= \"value\"",
-			wantLine:   2,
-			wantColumn: 1,
-		},
-		{
-			desc:       "invalid key start on first line",
-			input:      "= \"value\"",
-			wantLine:   1,
-			wantColumn: 1,
-		},
-		{
-			desc:       "invalid key after multiple comments",
-			input:      "# comment 1\n# comment 2\n= \"value\"",
-			wantLine:   3,
-			wantColumn: 1,
-		},
-		{
-			desc:       "invalid key after valid key-value",
-			input:      "a = 1\n= \"value\"",
-			wantLine:   2,
-			wantColumn: 1,
-		},
-		{
-			desc:       "invalid key after whitespace on line",
-			input:      "a = 1\n  = \"value\"",
-			wantLine:   2,
-			wantColumn: 3,
-		},
-	}
-
-	for _, e := range examples {
-		t.Run(e.desc, func(t *testing.T) {
-			p := Parser{}
-			p.Reset([]byte(e.input))
-			for p.NextExpression() {
-			}
-			err := p.Error()
-			if err == nil {
-				t.Fatal("expected an error")
-			}
-			var perr *ParserError
-			if !errors.As(err, &perr) {
-				t.Fatalf("expected ParserError, got %T", err)
-			}
-			shape := p.Shape(Range{Offset: uint32(perr.Offset), Length: uint32(len(perr.Highlight))})
-
-			if shape.Start.Line != e.wantLine {
-				t.Errorf("line: got %d, want %d", shape.Start.Line, e.wantLine)
-			}
-			if shape.Start.Column != e.wantColumn {
-				t.Errorf("column: got %d, want %d", shape.Start.Column, e.wantColumn)
-			}
-		})
-	}
-}
-
 func ExampleParser() {
 	doc := `
 	hello = "world"

unstable/scanner.go

@@ -47,31 +47,48 @@ func isUnquotedKeyChar(r byte) bool {
 	return (r >= 'A' && r <= 'Z') || (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '-' || r == '_'
 }
 
-func scanLiteralString(b []byte, base int) ([]byte, []byte, error) {
+func scanLiteralString(b []byte) ([]byte, []byte, error) {
+	// literal-string = apostrophe *literal-char apostrophe
+	// apostrophe = %x27 ; ' apostrophe
+	// literal-char = %x09 / %x20-26 / %x28-7E / non-ascii
 	for i := 1; i < len(b); {
 		switch b[i] {
 		case '\'':
 			return b[:i+1], b[i+1:], nil
 		case '\n', '\r':
-			return nil, nil, NewParserError(b[i:i+1], base+i, "literal strings cannot have new lines")
+			return nil, nil, NewParserError(b[i:i+1], "literal strings cannot have new lines")
 		}
 		size := characters.Utf8ValidNext(b[i:])
 		if size == 0 {
-			return nil, nil, NewParserError(b[i:i+1], base+i, "invalid character")
+			return nil, nil, NewParserError(b[i:i+1], "invalid character")
 		}
 		i += size
 	}
 
-	return nil, nil, NewParserError(b[len(b):], base+len(b), "unterminated literal string")
+	return nil, nil, NewParserError(b[len(b):], "unterminated literal string")
 }
 
-func scanMultilineLiteralString(b []byte, base int) ([]byte, []byte, error) {
+func scanMultilineLiteralString(b []byte) ([]byte, []byte, error) {
+	// ml-literal-string = ml-literal-string-delim [ newline ] ml-literal-body
+	// ml-literal-string-delim
+	// ml-literal-string-delim = 3apostrophe
+	// ml-literal-body = *mll-content *( mll-quotes 1*mll-content ) [ mll-quotes ]
+	//
+	// mll-content = mll-char / newline
+	// mll-char = %x09 / %x20-26 / %x28-7E / non-ascii
+	// mll-quotes = 1*2apostrophe
 	for i := 3; i < len(b); {
 		switch b[i] {
 		case '\'':
 			if scanFollowsMultilineLiteralStringDelimiter(b[i:]) {
 				i += 3
 
+				// At that point we found 3 apostrophe, and i is the
+				// index of the byte after the third one. The scanner
+				// needs to be eager, because there can be an extra 2
+				// apostrophe that can be accepted at the end of the
+				// string.
+
 				if i >= len(b) || b[i] != '\'' {
 					return b[:i], b[i:], nil
 				}
@@ -83,39 +100,39 @@ func scanMultilineLiteralString(b []byte, base int) ([]byte, []byte, error) {
 				i++
 
 				if i < len(b) && b[i] == '\'' {
-					return nil, nil, NewParserError(b[i-3:i+1], base+i-3, "''' not allowed in multiline literal string")
+					return nil, nil, NewParserError(b[i-3:i+1], "''' not allowed in multiline literal string")
 				}
 
 				return b[:i], b[i:], nil
 			}
 		case '\r':
 			if len(b) < i+2 {
-				return nil, nil, NewParserError(b[len(b):], base+len(b), `need a \n after \r`)
+				return nil, nil, NewParserError(b[len(b):], `need a \n after \r`)
 			}
 			if b[i+1] != '\n' {
-				return nil, nil, NewParserError(b[i:i+2], base+i, `need a \n after \r`)
+				return nil, nil, NewParserError(b[i:i+2], `need a \n after \r`)
 			}
-			i += 2
+			i += 2 // skip the \n
 			continue
 		}
 		size := characters.Utf8ValidNext(b[i:])
 		if size == 0 {
-			return nil, nil, NewParserError(b[i:i+1], base+i, "invalid character")
+			return nil, nil, NewParserError(b[i:i+1], "invalid character")
 		}
 		i += size
 	}
 
-	return nil, nil, NewParserError(b[len(b):], base+len(b), `multiline literal string not terminated by '''`)
+	return nil, nil, NewParserError(b[len(b):], `multiline literal string not terminated by '''`)
 }
 
-func scanWindowsNewline(b []byte, base int) ([]byte, []byte, error) {
+func scanWindowsNewline(b []byte) ([]byte, []byte, error) {
 	const lenCRLF = 2
 	if len(b) < lenCRLF {
-		return nil, nil, NewParserError(b, base, "windows new line expected")
+		return nil, nil, NewParserError(b, "windows new line expected")
 	}
 
 	if b[1] != '\n' {
-		return nil, nil, NewParserError(b, base, `windows new line should be \r\n`)
+		return nil, nil, NewParserError(b, `windows new line should be \r\n`)
 	}
 
 	return b[:lenCRLF], b[lenCRLF:], nil
@@ -134,7 +151,13 @@ func scanWhitespace(b []byte) ([]byte, []byte) {
 	return b, b[len(b):]
 }
 
-func scanComment(b []byte, base int) ([]byte, []byte, error) {
+func scanComment(b []byte) ([]byte, []byte, error) {
+	// comment-start-symbol = %x23 ; #
+	// non-ascii = %x80-D7FF / %xE000-10FFFF
+	// non-eol = %x09 / %x20-7F / non-ascii
+	//
+	// comment = comment-start-symbol *non-eol
+
 	for i := 1; i < len(b); {
 		if b[i] == '\n' {
 			return b[:i], b[i:], nil
@@ -143,11 +166,11 @@ func scanComment(b []byte, base int) ([]byte, []byte, error) {
 			if i+1 < len(b) && b[i+1] == '\n' {
 				return b[:i+1], b[i+1:], nil
 			}
-			return nil, nil, NewParserError(b[i:i+1], base+i, "invalid character in comment")
+			return nil, nil, NewParserError(b[i:i+1], "invalid character in comment")
 		}
 		size := characters.Utf8ValidNext(b[i:])
 		if size == 0 {
-			return nil, nil, NewParserError(b[i:i+1], base+i, "invalid character in comment")
+			return nil, nil, NewParserError(b[i:i+1], "invalid character in comment")
 		}
 
 		i += size
@@ -156,7 +179,12 @@ func scanComment(b []byte, base int) ([]byte, []byte, error) {
 	return b, b[len(b):], nil
 }
 
-func scanBasicString(b []byte, base int) ([]byte, bool, []byte, error) {
+func scanBasicString(b []byte) ([]byte, bool, []byte, error) {
+	// basic-string = quotation-mark *basic-char quotation-mark
+	// quotation-mark = %x22            ; "
+	// basic-char = basic-unescaped / escaped
+	// basic-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
+	// escaped = escape escape-seq-char
 	escaped := false
 	i := 1
 
@@ -165,20 +193,31 @@ func scanBasicString(b []byte, base int) ([]byte, bool, []byte, error) {
 		case '"':
 			return b[:i+1], escaped, b[i+1:], nil
 		case '\n', '\r':
-			return nil, escaped, nil, NewParserError(b[i:i+1], base+i, "basic strings cannot have new lines")
+			return nil, escaped, nil, NewParserError(b[i:i+1], "basic strings cannot have new lines")
 		case '\\':
 			if len(b) < i+2 {
-				return nil, escaped, nil, NewParserError(b[i:i+1], base+i, "need a character after \\")
+				return nil, escaped, nil, NewParserError(b[i:i+1], "need a character after \\")
 			}
 			escaped = true
 			i++ // skip the next character
 		}
 	}
 
-	return nil, escaped, nil, NewParserError(b[len(b):], base+len(b), `basic string not terminated by "`)
+	return nil, escaped, nil, NewParserError(b[len(b):], `basic string not terminated by "`)
 }
 
-func scanMultilineBasicString(b []byte, base int) ([]byte, bool, []byte, error) {
+func scanMultilineBasicString(b []byte) ([]byte, bool, []byte, error) {
+	// ml-basic-string = ml-basic-string-delim [ newline ] ml-basic-body
+	// ml-basic-string-delim
+	// ml-basic-string-delim = 3quotation-mark
+	// ml-basic-body = *mlb-content *( mlb-quotes 1*mlb-content ) [ mlb-quotes ]
+	//
+	// mlb-content = mlb-char / newline / mlb-escaped-nl
+	// mlb-char = mlb-unescaped / escaped
+	// mlb-quotes = 1*2quotation-mark
+	// mlb-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
+	// mlb-escaped-nl = escape ws newline *( wschar / newline )
+
 	escaped := false
 	i := 3
 
@@ -188,6 +227,12 @@ func scanMultilineBasicString(b []byte, base int) ([]byte, bool, []byte, error)
 			if scanFollowsMultilineBasicStringDelimiter(b[i:]) {
 				i += 3
 
+				// At that point we found 3 apostrophe, and i is the
+				// index of the byte after the third one. The scanner
+				// needs to be eager, because there can be an extra 2
+				// apostrophe that can be accepted at the end of the
+				// string.
+
 				if i >= len(b) || b[i] != '"' {
 					return b[:i], escaped, b[i:], nil
 				}
@@ -199,27 +244,27 @@ func scanMultilineBasicString(b []byte, base int) ([]byte, bool, []byte, error)
 				i++
 
 				if i < len(b) && b[i] == '"' {
-					return nil, escaped, nil, NewParserError(b[i-3:i+1], base+i-3, `""" not allowed in multiline basic string`)
+					return nil, escaped, nil, NewParserError(b[i-3:i+1], `""" not allowed in multiline basic string`)
 				}
 
 				return b[:i], escaped, b[i:], nil
 			}
 		case '\\':
 			if len(b) < i+2 {
-				return nil, escaped, nil, NewParserError(b[len(b):], base+len(b), "need a character after \\")
+				return nil, escaped, nil, NewParserError(b[len(b):], "need a character after \\")
 			}
 			escaped = true
 			i++ // skip the next character
 		case '\r':
 			if len(b) < i+2 {
-				return nil, escaped, nil, NewParserError(b[len(b):], base+len(b), `need a \n after \r`)
+				return nil, escaped, nil, NewParserError(b[len(b):], `need a \n after \r`)
 			}
 			if b[i+1] != '\n' {
-				return nil, escaped, nil, NewParserError(b[i:i+2], base+i, `need a \n after \r`)
+				return nil, escaped, nil, NewParserError(b[i:i+2], `need a \n after \r`)
 			}
 			i++ // skip the \n
 		}
 	}
 
-	return nil, escaped, nil, NewParserError(b[len(b):], base+len(b), `multiline basic string not terminated by """`)
+	return nil, escaped, nil, NewParserError(b[len(b):], `multiline basic string not terminated by """`)
 }