Render embedded code preview by permlink in markdown (#30234)

The permlink in markdown will be rendered as a code preview block, like GitHub

Co-authored-by: silverwind <me@silverwind.io>

modules/markup/html_codepreview_test.go

@@ -0,0 +1,34 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package markup_test
+
+import (
+	"context"
+	"html/template"
+	"strings"
+	"testing"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/markup"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderCodePreview(t *testing.T) {
+	markup.Init(&markup.ProcessorHelper{
+		RenderRepoFileCodePreview: func(ctx context.Context, opts markup.RenderCodePreviewOptions) (template.HTML, error) {
+			return "<div>code preview</div>", nil
+		},
+	})
+	test := func(input, expected string) {
+		buffer, err := markup.RenderString(&markup.RenderContext{
+			Ctx:  git.DefaultContext,
+			Type: "markdown",
+		}, input)
+		assert.NoError(t, err)
+		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>`)
+}