resources/page: Escape hash sign in permalinks

When creating a link to a file with a `#` in the filename, the link gets
truncated. This happens because the filename is eventaully passed to
`url.Parse` which (correctly!) interprets the `#` as fragment separator.

This commit escapes the `#` in the filename before creating the link.

Fixes #4926
Fixes #8232
Fixes #12342

Co-authored-by: Joe Mooring <joe.mooring@veriphor.com>

resources/page/page_paths.go

@@ -268,6 +268,13 @@ func CreateTargetPaths(d TargetPathDescriptor) (tp TargetPaths) {
 		tp.SubResourceBaseTarget = pb.PathDir()
 		tp.SubResourceBaseLink = pb.LinkDir()
 	}
+
+	// paths.{URL,Path}Escape rely on url.Parse which
+	// will consider # a fragment identifier, so it and
+	// and everything after it will be stripped from
+	// `link`, so we need to escape it first.
+	link = strings.ReplaceAll(link, "#", "%23")
+
 	if d.URL != "" {
 		tp.Link = paths.URLEscape(link)
 	} else {

resources/page/path_integration_test.go

@@ -0,0 +1,55 @@
+// 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 page_test
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/hugolib"
+)
+
+// Issue 4926
+// Issue 8232
+// Issue 12342
+func TestHashSignInPermalink(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['section','rss','sitemap','taxonomy']
+[permalinks]
+s1 = '/:section/:slug'
+-- layouts/_default/list.html --
+{{ range site.Pages }}{{ .RelPermalink }}|{{ end }}
+-- layouts/_default/single.html --
+{{ .Title }}
+-- content/s1/p1.md --
+---
+title: p#1
+tags: test#tag#
+---
+-- content/s2/p#2.md --
+---
+title: p#2
+---
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileExists("public/s1/p#1/index.html", true)
+	b.AssertFileExists("public/s2/p#2/index.html", true)
+	b.AssertFileExists("public/tags/test#tag#/index.html", true)
+
+	b.AssertFileContentExact("public/index.html", "/|/s1/p%231/|/s2/p%232/|/tags/test%23tag%23/|")
+}