Fix resource bundling for overlapping page.md vs page.txt

Fixes #12320

hugolib/content_map_page.go

@@ -489,12 +489,17 @@ func (m *pageMap) forEachResourceInPage(
 
 	rw.Handle = func(resourceKey string, n contentNodeI, match doctree.DimensionFlag) (bool, error) {
 		if isBranch {
-			ownerKey, _ := m.treePages.LongestPrefixAll(resourceKey)
-			if ownerKey != keyPage && path.Dir(ownerKey) != path.Dir(resourceKey) {
+			// A resourceKey always represents a filename with extension.
+			// A page key points to the logical path of a page, which when sourced from the filesystem
+			// may represent a directory (bundles) or a single content file (e.g. p1.md).
+			// So, to avoid any overlapping ambiguity, we start looking from the owning directory.
+			ownerKey, _ := m.treePages.LongestPrefixAll(path.Dir(resourceKey))
+			if ownerKey != keyPage {
 				// Stop walking downwards, someone else owns this resource.
 				rw.SkipPrefix(ownerKey + "/")
 				return false, nil
 			}
+
 		}
 		return handle(resourceKey, n, match)
 	}

hugolib/pagebundler_test.go

@@ -919,3 +919,42 @@ GetMatch: {{ with .Resources.GetMatch "f1.*" }}{{ .Name }}: {{ .Content }}|{{ en
 
 	b.AssertFileContent("public/mybundle/index.html", "GetMatch: f1.en.txt: F1.|")
 }
+
+func TestBundleBranchIssue12320(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['rss','sitemap','taxonomy','term']
+defaultContentLanguage = 'en'
+defaultContentLanguageInSubdir = true
+[languages.en]
+baseURL = "https://en.example.org/"
+contentDir = "content/en"
+[languages.fr]
+baseURL = "https://fr.example.org/"
+contentDir = "content/fr"
+-- content/en/s1/p1.md --
+---
+title: p1
+---
+-- content/en/s1/p1.txt --
+---
+p1.txt
+---
+-- layouts/_default/single.html --
+{{ .Title }}|
+-- layouts/_default/list.html --
+{{ .Title }}|
+`
+
+	b := Test(t, files)
+
+	b.AssertFileExists("public/en/s1/index.html", true)
+	b.AssertFileExists("public/en/s1/p1/index.html", true)
+	b.AssertFileExists("public/en/s1/p1.txt", true)
+
+	b.AssertFileExists("public/fr/s1/index.html", false)
+	b.AssertFileExists("public/fr/s1/p1/index.html", false)
+	b.AssertFileExists("public/fr/s1/p1.txt", false) // failing test
+}