content adapter: Fix issue with content starting out with a shortcode

Fixes #12544

hugolib/page__content.go

@@ -57,14 +57,14 @@ type pageContentReplacement struct {
 
 func (m *pageMeta) parseFrontMatter(h *HugoSites, pid uint64) (*contentParseInfo, error) {
 	var (
-		sourceKey  string
+		sourceKey            string
-		openSource hugio.OpenReadSeekCloser
+		openSource           hugio.OpenReadSeekCloser
-		hasContent = m.pageConfig.IsFromContentAdapter
+		isFromContentAdapter = m.pageConfig.IsFromContentAdapter
 	)
 
-	if m.f != nil && !hasContent {
+	if m.f != nil && !isFromContentAdapter {
 		sourceKey = filepath.ToSlash(m.f.Filename())
-		if !hasContent {
+		if !isFromContentAdapter {
 			meta := m.f.FileInfo().Meta()
 			openSource = func() (hugio.ReadSeekCloser, error) {
 				r, err := meta.Open()
@@ -74,7 +74,7 @@ func (m *pageMeta) parseFrontMatter(h *HugoSites, pid uint64) (*contentParseInfo
 				return r, nil
 			}
 		}
-	} else if hasContent {
+	} else if isFromContentAdapter {
 		openSource = m.pageConfig.Content.ValueAsOpenReadSeekCloser()
 	}
 
@@ -96,7 +96,9 @@ func (m *pageMeta) parseFrontMatter(h *HugoSites, pid uint64) (*contentParseInfo
 
 	items, err := pageparser.ParseBytes(
 		source,
-		pageparser.Config{},
+		pageparser.Config{
+			NoFrontMatter: isFromContentAdapter,
+		},
 	)
 	if err != nil {
 		return nil, err
@@ -104,7 +106,7 @@ func (m *pageMeta) parseFrontMatter(h *HugoSites, pid uint64) (*contentParseInfo
 
 	pi.itemsStep1 = items
 
-	if hasContent {
+	if isFromContentAdapter {
 		// No front matter.
 		return pi, nil
 	}

hugolib/pagesfromdata/pagesfromgotmpl_integration_test.go

@@ -585,3 +585,28 @@ value: data1
 
 	b.AssertLogNotContains("WARN")
 }
+
+func TestPagesFromGoTmplShortcodeNoPreceddingCharacterIssue12544(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['home','rss','section','sitemap','taxonomy','term']
+-- content/_content.gotmpl --
+{{ $content := dict "mediaType" "text/html" "value" "x{{< sc >}}" }}
+{{ .AddPage (dict "content" $content "path" "a") }}
+
+{{ $content := dict "mediaType" "text/html" "value" "{{< sc >}}" }}
+{{ .AddPage (dict "content" $content "path" "b") }}
+-- layouts/_default/single.html --
+|{{ .Content }}|
+-- layouts/shortcodes/sc.html --
+foo
+{{- /**/ -}}
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/a/index.html", "|xfoo|")
+	b.AssertFileContent("public/b/index.html", "|foo|") // fails
+}

parser/pageparser/pagelexer.go

@@ -62,7 +62,9 @@ func (l *pageLexer) Input() []byte {
 	return l.input
 }
 
-type Config struct{}
+type Config struct {
+	NoFrontMatter bool
+}
 
 // note: the input position here is normally 0 (start), but
 // can be set if position of first shortcode is known

parser/pageparser/pageparser.go

@@ -36,7 +36,11 @@ var _ Result = (*pageLexer)(nil)
 
 // ParseBytes parses the page in b according to the given Config.
 func ParseBytes(b []byte, cfg Config) (Items, error) {
-	l, err := parseBytes(b, cfg, lexIntroSection)
+	startLexer := lexIntroSection
+	if cfg.NoFrontMatter {
+		startLexer = lexMainSection
+	}
+	l, err := parseBytes(b, cfg, startLexer)
 	if err != nil {
 		return nil, err
 	}