From 48f0004e918c84c33a6db2717bf7c56b81fa4328 Mon Sep 17 00:00:00 2001
From: Charith Ellawala <charith@cerbos.dev>
Date: Mon, 2 Dec 2024 13:32:42 +0000
Subject: [PATCH] Fix panic when parsing unattached comment

The parser panics when there's a comment without anything to attach it
to. This PR fixes that case.

Signed-off-by: Charith Ellawala <charith@cerbos.dev>
---
 parser/parser.go      | 11 ++++++++++-
 parser/parser_test.go |  8 ++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/parser/parser.go b/parser/parser.go
index 5173393..88ae994 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -152,6 +152,10 @@ func (p *parser) parseDocumentBody(ctx *context) (ast.Node, error) {
 }
 
 func (p *parser) parseToken(ctx *context, tk *Token) (ast.Node, error) {
+	if tk == nil {
+		return nil, nil
+	}
+
 	switch tk.GroupType() {
 	case TokenGroupMapKey, TokenGroupMapKeyValue:
 		return p.parseMap(ctx)
@@ -1063,7 +1067,12 @@ func (p *parser) parseDirective(ctx *context, g *TokenGroup) (*ast.DirectiveNode
 
 func (p *parser) parseComment(ctx *context) (ast.Node, error) {
 	cm := p.parseHeadComment(ctx)
-	node, err := p.parseToken(ctx, ctx.currentToken())
+	nextTok := ctx.currentToken()
+	if nextTok == nil {
+		return cm, nil
+	}
+
+	node, err := p.parseToken(ctx, nextTok)
 	if err != nil {
 		return nil, err
 	}
diff --git a/parser/parser_test.go b/parser/parser_test.go
index 14980b5..8d1db7b 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -1471,6 +1471,14 @@ foo: | # comment
 			yaml: `
 foo: > # comment
   x: 42
+`,
+		},
+		{
+			name: "unattached comment",
+			yaml: `
+# This comment is in its own document
+---
+a: b
 `,
 		},
 	}