Fix opengraph meta for wiki pages (#4427)

Fixes https://codeberg.org/forgejo/forgejo/issues/4417 by adding a conditional branch to the `head_opengraph` template to match wiki pages. I tried to be consistent with the other types:

- `og:title` is the wiki page title
- `og:url` is built via `{{AppUrl}}{{.Link}}` like it is done for commit and file views. This has the caveat of doubling the slash (see test below). Should we `{{trimSuffix "/" AppUrl}}` to remove this, if sprig is available?
- `og:description` is the repository description to match GH behaviour. Also, the first sentences of the page might not be descriptive enough. Should we prefix the repo description with the repo name?
- `og:type` and `og:image` are common

Added a `TestOpenGraphProperties` integration test using existing fixtures. Coverage is not 100% but can be improved later.

## Output on a test repo

```html
<meta property="og:title" content="Project architecture">
<meta property="og:url" content="http://localhost:3000//xvello/wiki-test/wiki/Project-architecture">
<meta property="og:description" content="description for a test project">
<meta property="og:type" content="object">
<meta property="og:image" content="http://localhost:3000/avatars/3dd4d1e4eef065d1b4ad4bdb081ab6e7">
```

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/4427
Co-authored-by: Xavier Vello <xavier.vello@gmail.com>
Co-committed-by: Xavier Vello <xavier.vello@gmail.com>

release-notes/9.0.0/fix/4427.md

@@ -0,0 +1 @@
+Fixed social media previews for links to wiki pages.

templates/base/head_opengraph.tmpl

@@ -24,6 +24,12 @@
 				<meta property="og:description" content="{{StringUtils.EllipsisString $commitMessageBody 300}}">
 			{{- end -}}
 		{{end}}
+	{{else if .Pages}}
+		<meta property="og:title" content="{{.Title}}">
+		<meta property="og:url" content="{{AppUrl}}{{.Link}}">
+		{{if .Repository.Description}}
+			<meta property="og:description" content="{{StringUtils.EllipsisString .Repository.Description 300}}">
+		{{end}}
 	{{else}}
 		<meta property="og:title" content="{{.Repository.Name}}">
 		<meta property="og:url" content="{{.Repository.HTMLURL}}">

tests/integration/opengraph_test.go

@@ -0,0 +1,150 @@
+// Copyright 2024 The Forgejo Authors c/o Codeberg e.V.. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"net/http"
+	"testing"
+
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/tests"
+
+	"github.com/PuerkitoBio/goquery"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestOpenGraphProperties(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+	siteName := "Forgejo: Beyond coding. We Forge."
+
+	cases := []struct {
+		name     string
+		url      string
+		expected map[string]string
+	}{
+		{
+			name: "website root",
+			url:  "/",
+			expected: map[string]string{
+				"og:title":       siteName,
+				"og:url":         setting.AppURL,
+				"og:description": "Forgejo is a self-hosted lightweight software forge. Easy to install and low maintenance, it just does the job.",
+				"og:type":        "website",
+				"og:image":       "/assets/img/logo.png",
+				"og:site_name":   siteName,
+			},
+		},
+		{
+			name: "profile page without description",
+			url:  "/user30",
+			expected: map[string]string{
+				"og:title":     "User Thirty",
+				"og:url":       setting.AppURL + "user30",
+				"og:type":      "profile",
+				"og:image":     "https://secure.gravatar.com/avatar/eae1f44b34ff27284cb0792c7601c89c?d=identicon",
+				"og:site_name": siteName,
+			},
+		},
+		{
+			name: "profile page with description",
+			url:  "/the_34-user.with.all.allowedchars",
+			expected: map[string]string{
+				"og:title":       "the_1-user.with.all.allowedChars",
+				"og:url":         setting.AppURL + "the_34-user.with.all.allowedChars",
+				"og:description": "some [commonmark](https://commonmark.org/)!",
+				"og:type":        "profile",
+				"og:image":       setting.AppURL + "avatars/avatar34",
+				"og:site_name":   siteName,
+			},
+		},
+		{
+			name: "issue",
+			url:  "/user2/repo1/issues/1",
+			expected: map[string]string{
+				"og:title":       "issue1",
+				"og:url":         setting.AppURL + "user2/repo1/issues/1",
+				"og:description": "content for the first issue",
+				"og:type":        "object",
+				"og:image":       "https://secure.gravatar.com/avatar/ab53a2911ddf9b4817ac01ddcd3d975f?d=identicon",
+				"og:site_name":   siteName,
+			},
+		},
+		{
+			name: "pull request",
+			url:  "/user2/repo1/pulls/2",
+			expected: map[string]string{
+				"og:title":       "issue2",
+				"og:url":         setting.AppURL + "user2/repo1/pulls/2",
+				"og:description": "content for the second issue",
+				"og:type":        "object",
+				"og:image":       "https://secure.gravatar.com/avatar/ab53a2911ddf9b4817ac01ddcd3d975f?d=identicon",
+				"og:site_name":   siteName,
+			},
+		},
+		{
+			name: "file in repo",
+			url:  "/user27/repo49/src/branch/master/test/test.txt",
+			expected: map[string]string{
+				"og:title":     "repo49/test/test.txt at master",
+				"og:url":       setting.AppURL + "/user27/repo49/src/branch/master/test/test.txt",
+				"og:type":      "object",
+				"og:image":     "https://secure.gravatar.com/avatar/7095710e927665f1bdd1ced94152f232?d=identicon",
+				"og:site_name": siteName,
+			},
+		},
+		{
+			name: "wiki page for repo without description",
+			url:  "/user2/repo1/wiki/Page-With-Spaced-Name",
+			expected: map[string]string{
+				"og:title":     "Page With Spaced Name",
+				"og:url":       setting.AppURL + "/user2/repo1/wiki/Page-With-Spaced-Name",
+				"og:type":      "object",
+				"og:image":     "https://secure.gravatar.com/avatar/ab53a2911ddf9b4817ac01ddcd3d975f?d=identicon",
+				"og:site_name": siteName,
+			},
+		},
+		{
+			name: "index page for repo without description",
+			url:  "/user2/repo1",
+			expected: map[string]string{
+				"og:title":     "repo1",
+				"og:url":       setting.AppURL + "user2/repo1",
+				"og:type":      "object",
+				"og:image":     "https://secure.gravatar.com/avatar/ab53a2911ddf9b4817ac01ddcd3d975f?d=identicon",
+				"og:site_name": siteName,
+			},
+		},
+		{
+			name: "index page for repo with description",
+			url:  "/user27/repo49",
+			expected: map[string]string{
+				"og:title":       "repo49",
+				"og:url":         setting.AppURL + "user27/repo49",
+				"og:description": "A wonderful repository with more than just a README.md",
+				"og:type":        "object",
+				"og:image":       "https://secure.gravatar.com/avatar/7095710e927665f1bdd1ced94152f232?d=identicon",
+				"og:site_name":   siteName,
+			},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			req := NewRequest(t, "GET", tc.url)
+			resp := MakeRequest(t, req, http.StatusOK)
+			doc := NewHTMLParser(t, resp.Body)
+
+			foundProps := make(map[string]string)
+			doc.Find("head meta[property^=\"og:\"]").Each(func(_ int, selection *goquery.Selection) {
+				prop, foundProp := selection.Attr("property")
+				assert.True(t, foundProp)
+				content, foundContent := selection.Attr("content")
+				assert.True(t, foundContent, "opengraph meta tag without a content property")
+				foundProps[prop] = content
+			})
+
+			assert.EqualValues(t, tc.expected, foundProps, "mismatching opengraph properties")
+		})
+	}
+}