From ed02a1f192ff91fd58697694c3462bae6af7712b Mon Sep 17 00:00:00 2001
From: Thomas Pelletier <pelletier.thomas@gmail.com>
Date: Fri, 22 Oct 2021 23:25:28 -0400
Subject: [PATCH] seen: check for explicit tables on dotted keys (#639)

The TOML spec is being clarified to say that dotted keys "define" their
intermediate tables. Therefore the seen tracker needs to verify that none of
them reference an explicit table.

Also added a missing seen expression check for key-values parsed as part of a
table section.

See https://github.com/toml-lang/toml/issues/846
---
 internal/tracker/seen.go | 4 +++-
 toml_testgen_test.go     | 2 --
 unmarshaler.go           | 5 +++++
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/internal/tracker/seen.go b/internal/tracker/seen.go
index af70241..8990dae 100644
--- a/internal/tracker/seen.go
+++ b/internal/tracker/seen.go
@@ -106,7 +106,6 @@ func (s *SeenTracker) create(parentIdx int, name []byte, kind keyKind, explicit
 // that have been seen in previous calls, and validates that types are consistent.
 func (s *SeenTracker) CheckExpression(node *ast.Node) error {
 	if s.entries == nil {
-		// s.entries = make([]entry, 0, 8)
 		// Skip ID = 0 to remove the confusion between nodes whose parent has
 		// id 0 and root nodes (parent id is 0 because it's the zero value).
 		s.nextID = 1
@@ -221,6 +220,9 @@ func (s *SeenTracker) checkKeyValue(node *ast.Node) error {
 			if s.entries[idx].kind != tableKind {
 				return fmt.Errorf("toml: expected %s to be a table, not a %s", string(k), s.entries[idx].kind)
 			}
+			if s.entries[idx].explicit {
+				return fmt.Errorf("toml: cannot redefine table %s that has already been explicitly defined", string(k))
+			}
 		} else {
 			idx = s.create(parentIdx, k, tableKind, false)
 		}
diff --git a/toml_testgen_test.go b/toml_testgen_test.go
index 3f3bcf5..61985ff 100644
--- a/toml_testgen_test.go
+++ b/toml_testgen_test.go
@@ -886,13 +886,11 @@ func TestTOMLTest_Invalid_Table_EqualsSign(t *testing.T) {
 }
 
 func TestTOMLTest_Invalid_Table_Injection1(t *testing.T) {
-	t.Skip("FIXME")
 	input := "[a.b.c]\n  z = 9\n[a]\n  b.c.t = \"Using dotted keys to add to [a.b.c] after explicitly defining it above is not allowed\"\n  \n# see https://github.com/toml-lang/toml/issues/846\n"
 	testgenInvalid(t, input)
 }
 
 func TestTOMLTest_Invalid_Table_Injection2(t *testing.T) {
-	t.Skip("FIXME")
 	input := "[a.b.c.d]\n  z = 9\n[a]\n  b.c.d.k.t = \"Using dotted keys to add to [a.b.c.d] after explicitly defining it above is not allowed\"\n  \n# see https://github.com/toml-lang/toml/issues/846\n"
 	testgenInvalid(t, input)
 }
diff --git a/unmarshaler.go b/unmarshaler.go
index dbe7cb0..19efaa4 100644
--- a/unmarshaler.go
+++ b/unmarshaler.go
@@ -516,6 +516,11 @@ func (d *decoder) handleKeyValues(v reflect.Value) (reflect.Value, error) {
 			break
 		}
 
+		err := d.seen.CheckExpression(expr)
+		if err != nil {
+			return reflect.Value{}, err
+		}
+
 		x, err := d.handleKeyValue(expr, v)
 		if err != nil {
 			return reflect.Value{}, err