Fix Parser.Range returning wrong offset for error highlights

The subsliceOffset method incorrectly computed offset as
len(p.data) - len(b), which only works when b is a suffix (tail) of
p.data. However, error highlights (ParserError.Highlight) are arbitrary
subslices from the middle of the input (e.g., b[0:1] from parseSimpleKey),
so their len has no relationship to their position.

This was a regression introduced in commit 3aaf147 (Remove unsafe package
usage) which replaced danger.SubsliceOffset (pointer arithmetic) with the
incorrect len-based approach.

Fix by using reflect.ValueOf().Pointer() to compute the actual byte
offset between slice data pointers, matching the approach already used
in errors.go:subsliceOffset.

Fixes #1047

Co-authored-by: Thomas Pelletier <thomas@pelletier.dev>
This commit is contained in:
Cursor Agent
2026-04-12 12:40:14 +00:00
parent f36a3ece9e
commit d528d3c6b4
3 changed files with 199 additions and 3 deletions
+94
View File
@@ -286,6 +286,100 @@ 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
+12 -3
View File
@@ -3,6 +3,7 @@ package unstable
import (
"bytes"
"fmt"
"reflect"
"unicode"
"github.com/pelletier/go-toml/v2/internal/characters"
@@ -83,10 +84,18 @@ func (p *Parser) rangeOfToken(token, rest []byte) Range {
}
// subsliceOffset returns the byte offset of subslice b within p.data.
// b must be a suffix (tail) of p.data.
// b must share the same backing array as 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)
if len(b) == 0 {
return 0
}
dataPtr := reflect.ValueOf(p.data).Pointer()
subPtr := reflect.ValueOf(b).Pointer()
offset := int(subPtr - dataPtr)
if offset < 0 || offset > len(p.data) {
panic("subslice is not within parser data")
}
return offset
}
// Raw returns the slice corresponding to the bytes in the given range.
+93
View File
@@ -1,6 +1,7 @@
package unstable
import (
"errors"
"fmt"
"strconv"
"strings"
@@ -673,6 +674,98 @@ key3 = "value3"
assert.Equal(t, []string{"key1", "key2", "key3"}, keys)
}
func TestRangeOffsetAfterComment(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)
}
r := p.Range(perr.Highlight)
shape := p.Shape(r)
if r.Offset != 10 {
t.Errorf("Range offset: got %d, want 10", r.Offset)
}
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)
}
r := p.Range(perr.Highlight)
shape := p.Shape(r)
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"