parser/pageparser: Fix Org Mode summary delimiter assignment

Closes #13152

parser/pageparser/pagelexer_intro.go

@@ -91,14 +91,14 @@ func lexFrontMatterOrgMode(l *pageLexer) stateFunc {
 		#+DESCRIPTION: Just another golang parser for org content!
 	*/
 
-	l.summaryDivider = summaryDividerOrg
-
 	l.backup()
 
 	if !l.hasPrefix(delimOrg) {
 		return lexMainSection
 	}
 
+	l.summaryDivider = summaryDividerOrg
+
 	// Read lines until we no longer see a #+ prefix
 LOOP:
 	for {

parser/pageparser/pagelexer_intro_test.go

@@ -0,0 +1,46 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package pageparser
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func Test_lexIntroSection(t *testing.T) {
+	t.Parallel()
+	c := qt.New(t)
+	for i, tt := range []struct {
+		input                string
+		expectItemType       ItemType
+		expectSummaryDivider []byte
+	}{
+		{"{\"title\": \"JSON\"}\n", TypeFrontMatterJSON, summaryDivider},
+		{"#+TITLE: ORG\n", TypeFrontMatterORG, summaryDividerOrg},
+		{"+++\ntitle = \"TOML\"\n+++\n", TypeFrontMatterTOML, summaryDivider},
+		{"---\ntitle: YAML\n---\n", TypeFrontMatterYAML, summaryDivider},
+		// Issue 13152
+		{"# ATX Header Level 1\n", tText, summaryDivider},
+	} {
+		errMsg := qt.Commentf("[%d] %v", i, tt.input)
+
+		l := newPageLexer([]byte(tt.input), lexIntroSection, Config{})
+		l.run()
+
+		c.Assert(l.items[0].Type, qt.Equals, tt.expectItemType, errMsg)
+		c.Assert(l.summaryDivider, qt.DeepEquals, tt.expectSummaryDivider, errMsg)
+
+	}
+}