test: add regression test for nil token dereference in findKeyPos

Verifies that findKeyPos does not panic when a MappingNode entry has a
key whose GetToken() returns nil. Without the fix at parser.go:469 this
test panics with a nil pointer dereference.

Author: Claude

parser_niltoken_test.go

@@ -0,0 +1,46 @@
+package publiccode
+
+import (
+	"testing"
+
+	"github.com/goccy/go-yaml/ast"
+	"github.com/goccy/go-yaml/token"
+)
+
+// TestFindKeyPosNilToken verifies that findKeyPos does not panic when a
+// MappingNode key has a nil token (GetToken() == nil).
+//
+// Before the fix at parser.go:469, the direct dereference
+//
+//	keyVal := mv.Key.GetToken().Value
+//
+// would panic with a nil pointer dereference in this case.
+func TestFindKeyPosNilToken(t *testing.T) {
+	// First entry: NullNode key with Token == nil → GetToken() returns nil.
+	nilKeyEntry := &ast.MappingValueNode{
+		BaseNode: &ast.BaseNode{},
+		Key:      &ast.NullNode{BaseNode: &ast.BaseNode{}},
+		Value:    &ast.StringNode{BaseNode: &ast.BaseNode{}, Value: "v"},
+	}
+
+	// Second entry: a real StringNode key so the traversal has something to match.
+	realTok := &token.Token{Type: token.StringType, Value: "target"}
+	realKeyEntry := &ast.MappingValueNode{
+		BaseNode: &ast.BaseNode{},
+		Key:      &ast.StringNode{BaseNode: &ast.BaseNode{}, Token: realTok, Value: "target"},
+		Value:    &ast.StringNode{BaseNode: &ast.BaseNode{}, Value: "v2"},
+	}
+
+	node := &ast.MappingNode{
+		BaseNode: &ast.BaseNode{},
+		Values:   []*ast.MappingValueNode{nilKeyEntry, realKeyEntry},
+	}
+
+	// Search for a key that does not exist: exercises the nil-token skip
+	// without entering the "found" branch that would need a real Position.
+	// Must not panic — that is the primary assertion.
+	line, col := findKeyPos(node, []string{"nonexistent"})
+	if line != 0 || col != 0 {
+		t.Errorf("expected (0,0) for missing key, got (%d,%d)", line, col)
+	}
+}