Support quote selected comments to reply (#32431)

Many existing tests were quite hacky, these could be improved later.

<details>

![image](https://github.com/user-attachments/assets/93aebb4f-9de5-4cb8-910b-50c64cbcd25a)

</details>

6 files changed, 32 insertions, 16 deletions

diff --git a/modules/markup/html.go b/modules/markup/html.go
index a9c3dc9ba2..e2eefefc4b 100644
--- a/modules/markup/html.go
+++ b/modules/markup/html.go
@@ -442,7 +442,10 @@ func createLink(href, content, class string) *html.Node {
 	a := &html.Node{
 		Type: html.ElementNode,
 		Data: atom.A.String(),
-		Attr: []html.Attribute{{Key: "href", Val: href}},
+		Attr: []html.Attribute{
+			{Key: "href", Val: href},
+			{Key: "data-markdown-generated-content"},
+		},
 	}
 
 	if class != "" {
diff --git a/modules/markup/html_codepreview_test.go b/modules/markup/html_codepreview_test.go
index d33630d040..a90de278f5 100644
--- a/modules/markup/html_codepreview_test.go
+++ b/modules/markup/html_codepreview_test.go
@@ -30,5 +30,5 @@ func TestRenderCodePreview(t *testing.T) {
 		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
 	}
 	test("http://localhost:3000/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20", "<p><div>code preview</div></p>")
-	test("http://other/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20", `<p><a href="http://other/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20" rel="nofollow">http://other/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20</a></p>`)
+	test("http://other/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20", `<p><a href="http://other/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20" data-markdown-generated-content="" rel="nofollow">http://other/owner/repo/src/commit/0123456789/foo/bar.md#L10-L20</a></p>`)
 }
diff --git a/modules/markup/html_internal_test.go b/modules/markup/html_internal_test.go
index 74089cffdd..8f516751b0 100644
--- a/modules/markup/html_internal_test.go
+++ b/modules/markup/html_internal_test.go
@@ -33,11 +33,9 @@ func numericIssueLink(baseURL, class string, index int, marker string) string {
 
 // link an HTML link
 func link(href, class, contents string) string {
-	if class != "" {
-		class = " class=\"" + class + "\""
-	}
-
-	return fmt.Sprintf("<a href=\"%s\"%s>%s</a>", href, class, contents)
+	extra := ` data-markdown-generated-content=""`
+	extra += util.Iif(class != "", ` class="`+class+`"`, "")
+	return fmt.Sprintf(`<a href="%s"%s>%s</a>`, href, extra, contents)
 }
 
 var numericMetas = map[string]string{
@@ -353,7 +351,9 @@ func TestRender_FullIssueURLs(t *testing.T) {
 			Metas: localMetas,
 		}, []processor{fullIssuePatternProcessor}, strings.NewReader(input), &result)
 		assert.NoError(t, err)
-		assert.Equal(t, expected, result.String())
+		actual := result.String()
+		actual = strings.ReplaceAll(actual, ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, expected, actual)
 	}
 	test("Here is a link https://git.osgeo.org/gogs/postgis/postgis/pulls/6",
 		"Here is a link https://git.osgeo.org/gogs/postgis/postgis/pulls/6")
diff --git a/modules/markup/html_test.go b/modules/markup/html_test.go
index 32858dbd6b..82aded4407 100644
--- a/modules/markup/html_test.go
+++ b/modules/markup/html_test.go
@@ -116,7 +116,9 @@ func TestRender_CrossReferences(t *testing.T) {
 			Metas: localMetas,
 		}, input)
 		assert.NoError(t, err)
-		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
+		actual := strings.TrimSpace(buffer)
+		actual = strings.ReplaceAll(actual, ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, strings.TrimSpace(expected), actual)
 	}
 
 	test(
@@ -156,7 +158,9 @@ func TestRender_links(t *testing.T) {
 			},
 		}, input)
 		assert.NoError(t, err)
-		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
+		actual := strings.TrimSpace(buffer)
+		actual = strings.ReplaceAll(actual, ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, strings.TrimSpace(expected), actual)
 	}
 
 	oldCustomURLSchemes := setting.Markdown.CustomURLSchemes
@@ -267,7 +271,9 @@ func TestRender_email(t *testing.T) {
 			},
 		}, input)
 		assert.NoError(t, err)
-		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(res))
+		actual := strings.TrimSpace(res)
+		actual = strings.ReplaceAll(actual, ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, strings.TrimSpace(expected), actual)
 	}
 	// Text that should be turned into email link
 
@@ -616,7 +622,9 @@ func TestPostProcess_RenderDocument(t *testing.T) {
 			Metas: localMetas,
 		}, strings.NewReader(input), &res)
 		assert.NoError(t, err)
-		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(res.String()))
+		actual := strings.TrimSpace(res.String())
+		actual = strings.ReplaceAll(actual, ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, strings.TrimSpace(expected), actual)
 	}
 
 	// Issue index shouldn't be post processing in a document.
diff --git a/modules/markup/markdown/markdown_test.go b/modules/markup/markdown/markdown_test.go
index cfb821ab19..ad38e7a088 100644
--- a/modules/markup/markdown/markdown_test.go
+++ b/modules/markup/markdown/markdown_test.go
@@ -311,7 +311,8 @@ func TestTotal_RenderWiki(t *testing.T) {
 			IsWiki: true,
 		}, sameCases[i])
 		assert.NoError(t, err)
-		assert.Equal(t, template.HTML(answers[i]), line)
+		actual := strings.ReplaceAll(string(line), ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, answers[i], actual)
 	}
 
 	testCases := []string{
@@ -336,7 +337,8 @@ func TestTotal_RenderWiki(t *testing.T) {
 			IsWiki: true,
 		}, testCases[i])
 		assert.NoError(t, err)
-		assert.Equal(t, template.HTML(testCases[i+1]), line)
+		actual := strings.ReplaceAll(string(line), ` data-markdown-generated-content=""`, "")
+		assert.EqualValues(t, testCases[i+1], actual)
 	}
 }
 
@@ -356,7 +358,8 @@ func TestTotal_RenderString(t *testing.T) {
 			Metas: localMetas,
 		}, sameCases[i])
 		assert.NoError(t, err)
-		assert.Equal(t, template.HTML(answers[i]), line)
+		actual := strings.ReplaceAll(string(line), ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, answers[i], actual)
 	}
 
 	testCases := []string{}
@@ -996,7 +999,8 @@ space</p>
 	for i, c := range cases {
 		result, err := markdown.RenderString(&markup.RenderContext{Ctx: context.Background(), Links: c.Links, IsWiki: c.IsWiki}, input)
 		assert.NoError(t, err, "Unexpected error in testcase: %v", i)
-		assert.Equal(t, c.Expected, string(result), "Unexpected result in testcase %v", i)
+		actual := strings.ReplaceAll(string(result), ` data-markdown-generated-content=""`, "")
+		assert.Equal(t, c.Expected, actual, "Unexpected result in testcase %v", i)
 	}
 }
 
diff --git a/modules/markup/sanitizer_default.go b/modules/markup/sanitizer_default.go
index 669dc24eae..476ae5e26f 100644
--- a/modules/markup/sanitizer_default.go
+++ b/modules/markup/sanitizer_default.go
@@ -107,6 +107,7 @@ func (st *Sanitizer) createDefaultPolicy() *bluemonday.Policy {
 		"start", "summary", "tabindex", "target",
 		"title", "type", "usemap", "valign", "value",
 		"vspace", "width", "itemprop",
+		"data-markdown-generated-content",
 	}
 
 	generalSafeElements := []string{