Refactor markup render system (#32612)

This PR removes (almost) all path tricks, and introduces "renderhelper"
package.

Now we can clearly see the rendering behaviors for comment/file/wiki,
more details are in "renderhelper" tests.

Fix #31411 , fix #18592, fix #25632 and maybe more problems. (ps: fix
#32608 by the way)

10 files changed, 603 insertions, 0 deletions

diff --git a/models/renderhelper/commit_checker.go b/models/renderhelper/commit_checker.go
new file mode 100644
index 0000000000..4815643e67
--- /dev/null
+++ b/models/renderhelper/commit_checker.go
@@ -0,0 +1,53 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"io"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/gitrepo"
+	"code.gitea.io/gitea/modules/log"
+)
+
+type commitChecker struct {
+	ctx           context.Context
+	commitCache   map[string]bool
+	gitRepoFacade gitrepo.Repository
+
+	gitRepo       *git.Repository
+	gitRepoCloser io.Closer
+}
+
+func newCommitChecker(ctx context.Context, gitRepo gitrepo.Repository) *commitChecker {
+	return &commitChecker{ctx: ctx, commitCache: make(map[string]bool), gitRepoFacade: gitRepo}
+}
+
+func (c *commitChecker) Close() error {
+	if c != nil && c.gitRepoCloser != nil {
+		return c.gitRepoCloser.Close()
+	}
+	return nil
+}
+
+func (c *commitChecker) IsCommitIDExisting(commitID string) bool {
+	exist, inCache := c.commitCache[commitID]
+	if inCache {
+		return exist
+	}
+
+	if c.gitRepo == nil {
+		r, closer, err := gitrepo.RepositoryFromContextOrOpen(c.ctx, c.gitRepoFacade)
+		if err != nil {
+			log.Error("unable to open repository: %s Error: %v", gitrepo.RepoGitURL(c.gitRepoFacade), err)
+			return false
+		}
+		c.gitRepo, c.gitRepoCloser = r, closer
+	}
+
+	exist = c.gitRepo.IsReferenceExist(commitID) // Don't use IsObjectExist since it doesn't support short hashs with gogit edition.
+	c.commitCache[commitID] = exist
+	return exist
+}
diff --git a/models/renderhelper/main_test.go b/models/renderhelper/main_test.go
new file mode 100644
index 0000000000..331450172a
--- /dev/null
+++ b/models/renderhelper/main_test.go
@@ -0,0 +1,27 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/markup"
+)
+
+func TestMain(m *testing.M) {
+	unittest.MainTest(m, &unittest.TestOptions{
+		FixtureFiles: []string{"repository.yml", "user.yml"},
+		SetUp: func() error {
+			markup.RenderBehaviorForTesting.DisableAdditionalAttributes = true
+			markup.Init(&markup.RenderHelperFuncs{
+				IsUsernameMentionable: func(ctx context.Context, username string) bool {
+					return username == "user2"
+				},
+			})
+			return nil
+		},
+	})
+}
diff --git a/models/renderhelper/repo_comment.go b/models/renderhelper/repo_comment.go
new file mode 100644
index 0000000000..6bd5e91ad1
--- /dev/null
+++ b/models/renderhelper/repo_comment.go
@@ -0,0 +1,73 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"fmt"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/util"
+)
+
+type RepoComment struct {
+	ctx  *markup.RenderContext
+	opts RepoCommentOptions
+
+	commitChecker *commitChecker
+	repoLink      string
+}
+
+func (r *RepoComment) CleanUp() {
+	_ = r.commitChecker.Close()
+}
+
+func (r *RepoComment) IsCommitIDExisting(commitID string) bool {
+	return r.commitChecker.IsCommitIDExisting(commitID)
+}
+
+func (r *RepoComment) ResolveLink(link string, likeType markup.LinkType) (finalLink string) {
+	switch likeType {
+	case markup.LinkTypeApp:
+		finalLink = r.ctx.ResolveLinkApp(link)
+	default:
+		finalLink = r.ctx.ResolveLinkRelative(r.repoLink, r.opts.CurrentRefPath, link)
+	}
+	return finalLink
+}
+
+var _ markup.RenderHelper = (*RepoComment)(nil)
+
+type RepoCommentOptions struct {
+	DeprecatedRepoName  string // it is only a patch for the non-standard "markup" api
+	DeprecatedOwnerName string // it is only a patch for the non-standard "markup" api
+	CurrentRefPath      string // eg: "branch/main" or "commit/11223344"
+}
+
+func NewRenderContextRepoComment(ctx context.Context, repo *repo_model.Repository, opts ...RepoCommentOptions) *markup.RenderContext {
+	helper := &RepoComment{
+		repoLink: repo.Link(),
+		opts:     util.OptionalArg(opts),
+	}
+	rctx := markup.NewRenderContext(ctx)
+	helper.ctx = rctx
+	if repo != nil {
+		helper.repoLink = repo.Link()
+		helper.commitChecker = newCommitChecker(ctx, repo)
+		rctx = rctx.WithMetas(repo.ComposeMetas(ctx))
+	} else {
+		// this is almost dead code, only to pass the incorrect tests
+		helper.repoLink = fmt.Sprintf("%s/%s", helper.opts.DeprecatedOwnerName, helper.opts.DeprecatedRepoName)
+		rctx = rctx.WithMetas(map[string]string{
+			"user": helper.opts.DeprecatedOwnerName,
+			"repo": helper.opts.DeprecatedRepoName,
+
+			"markdownLineBreakStyle":       "comment",
+			"markupAllowShortIssuePattern": "true",
+		})
+	}
+	rctx = rctx.WithHelper(helper)
+	return rctx
+}
diff --git a/models/renderhelper/repo_comment_test.go b/models/renderhelper/repo_comment_test.go
new file mode 100644
index 0000000000..01e20b9e02
--- /dev/null
+++ b/models/renderhelper/repo_comment_test.go
@@ -0,0 +1,76 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"testing"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/markup/markdown"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepoComment(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+
+	repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	t.Run("AutoLink", func(t *testing.T) {
+		rctx := NewRenderContextRepoComment(context.Background(), repo1).WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+65f1bf27bc3bf70f64657658635e66094edbcb4d
+#1
+@user2
+`)
+		assert.NoError(t, err)
+		assert.Equal(t,
+			`<p><a href="/user2/repo1/commit/65f1bf27bc3bf70f64657658635e66094edbcb4d" rel="nofollow"><code>65f1bf27bc</code></a><br/>
+<a href="/user2/repo1/issues/1" class="ref-issue" rel="nofollow">#1</a><br/>
+<a href="/user2" rel="nofollow">@user2</a></p>
+`, rendered)
+	})
+
+	t.Run("AbsoluteAndRelative", func(t *testing.T) {
+		rctx := NewRenderContextRepoComment(context.Background(), repo1).WithMarkupType(markdown.MarkupName)
+
+		// It is Gitea's old behavior, the relative path is resolved to the repo path
+		// It is different from GitHub, GitHub resolves relative links to current page's path
+		rendered, err := markup.RenderString(rctx, `
+[/test](/test)
+[./test](./test)
+![/image](/image)
+![./image](./image)
+`)
+		assert.NoError(t, err)
+		assert.Equal(t,
+			`<p><a href="/user2/repo1/test" rel="nofollow">/test</a><br/>
+<a href="/user2/repo1/test" rel="nofollow">./test</a><br/>
+<a href="/user2/repo1/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/image" alt="/image"/></a><br/>
+<a href="/user2/repo1/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/image" alt="./image"/></a></p>
+`, rendered)
+	})
+
+	t.Run("WithCurrentRefPath", func(t *testing.T) {
+		rctx := NewRenderContextRepoComment(context.Background(), repo1, RepoCommentOptions{CurrentRefPath: "/commit/1234"}).
+			WithMarkupType(markdown.MarkupName)
+
+		// the ref path is only used to render commit message: a commit message is rendered at the commit page with its commit ID path
+		rendered, err := markup.RenderString(rctx, `
+[/test](/test)
+[./test](./test)
+![/image](/image)
+![./image](./image)
+`)
+		assert.NoError(t, err)
+		assert.Equal(t, `<p><a href="/user2/repo1/test" rel="nofollow">/test</a><br/>
+<a href="/user2/repo1/commit/1234/test" rel="nofollow">./test</a><br/>
+<a href="/user2/repo1/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/image" alt="/image"/></a><br/>
+<a href="/user2/repo1/commit/1234/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/commit/1234/image" alt="./image"/></a></p>
+`, rendered)
+	})
+}
diff --git a/models/renderhelper/repo_file.go b/models/renderhelper/repo_file.go
new file mode 100644
index 0000000000..794828c617
--- /dev/null
+++ b/models/renderhelper/repo_file.go
@@ -0,0 +1,77 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"fmt"
+	"path"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/util"
+)
+
+type RepoFile struct {
+	ctx  *markup.RenderContext
+	opts RepoFileOptions
+
+	commitChecker *commitChecker
+	repoLink      string
+}
+
+func (r *RepoFile) CleanUp() {
+	_ = r.commitChecker.Close()
+}
+
+func (r *RepoFile) IsCommitIDExisting(commitID string) bool {
+	return r.commitChecker.IsCommitIDExisting(commitID)
+}
+
+func (r *RepoFile) ResolveLink(link string, likeType markup.LinkType) string {
+	finalLink := link
+	switch likeType {
+	case markup.LinkTypeApp:
+		finalLink = r.ctx.ResolveLinkApp(link)
+	case markup.LinkTypeDefault:
+		finalLink = r.ctx.ResolveLinkRelative(path.Join(r.repoLink, "src", r.opts.CurrentRefPath), r.opts.CurrentTreePath, link)
+	case markup.LinkTypeRaw:
+		finalLink = r.ctx.ResolveLinkRelative(path.Join(r.repoLink, "raw", r.opts.CurrentRefPath), r.opts.CurrentTreePath, link)
+	case markup.LinkTypeMedia:
+		finalLink = r.ctx.ResolveLinkRelative(path.Join(r.repoLink, "media", r.opts.CurrentRefPath), r.opts.CurrentTreePath, link)
+	}
+	return finalLink
+}
+
+var _ markup.RenderHelper = (*RepoFile)(nil)
+
+type RepoFileOptions struct {
+	DeprecatedRepoName  string // it is only a patch for the non-standard "markup" api
+	DeprecatedOwnerName string // it is only a patch for the non-standard "markup" api
+
+	CurrentRefPath  string // eg: "branch/main"
+	CurrentTreePath string // eg: "path/to/file" in the repo
+}
+
+func NewRenderContextRepoFile(ctx context.Context, repo *repo_model.Repository, opts ...RepoFileOptions) *markup.RenderContext {
+	helper := &RepoFile{opts: util.OptionalArg(opts)}
+	rctx := markup.NewRenderContext(ctx)
+	helper.ctx = rctx
+	if repo != nil {
+		helper.repoLink = repo.Link()
+		helper.commitChecker = newCommitChecker(ctx, repo)
+		rctx = rctx.WithMetas(repo.ComposeDocumentMetas(ctx))
+	} else {
+		// this is almost dead code, only to pass the incorrect tests
+		helper.repoLink = fmt.Sprintf("%s/%s", helper.opts.DeprecatedOwnerName, helper.opts.DeprecatedRepoName)
+		rctx = rctx.WithMetas(map[string]string{
+			"user": helper.opts.DeprecatedOwnerName,
+			"repo": helper.opts.DeprecatedRepoName,
+
+			"markdownLineBreakStyle": "document",
+		})
+	}
+	rctx = rctx.WithHelper(helper)
+	return rctx
+}
diff --git a/models/renderhelper/repo_file_test.go b/models/renderhelper/repo_file_test.go
new file mode 100644
index 0000000000..40027ec76f
--- /dev/null
+++ b/models/renderhelper/repo_file_test.go
@@ -0,0 +1,83 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"testing"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/markup/markdown"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepoFile(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+	repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	t.Run("AutoLink", func(t *testing.T) {
+		rctx := NewRenderContextRepoFile(context.Background(), repo1).WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+65f1bf27bc3bf70f64657658635e66094edbcb4d
+#1
+@user2
+`)
+		assert.NoError(t, err)
+		assert.Equal(t,
+			`<p><a href="/user2/repo1/commit/65f1bf27bc3bf70f64657658635e66094edbcb4d" rel="nofollow"><code>65f1bf27bc</code></a>
+#1
+<a href="/user2" rel="nofollow">@user2</a></p>
+`, rendered)
+	})
+
+	t.Run("AbsoluteAndRelative", func(t *testing.T) {
+		rctx := NewRenderContextRepoFile(context.Background(), repo1, RepoFileOptions{CurrentRefPath: "branch/main"}).
+			WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+[/test](/test)
+[./test](./test)
+![/image](/image)
+![./image](./image)
+`)
+		assert.NoError(t, err)
+		assert.Equal(t,
+			`<p><a href="/user2/repo1/src/branch/main/test" rel="nofollow">/test</a>
+<a href="/user2/repo1/src/branch/main/test" rel="nofollow">./test</a>
+<a href="/user2/repo1/media/branch/main/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/media/branch/main/image" alt="/image"/></a>
+<a href="/user2/repo1/media/branch/main/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/media/branch/main/image" alt="./image"/></a></p>
+`, rendered)
+	})
+
+	t.Run("WithCurrentRefPath", func(t *testing.T) {
+		rctx := NewRenderContextRepoFile(context.Background(), repo1, RepoFileOptions{CurrentRefPath: "/commit/1234"}).
+			WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+[/test](/test)
+![/image](/image)
+`)
+		assert.NoError(t, err)
+		assert.Equal(t, `<p><a href="/user2/repo1/src/commit/1234/test" rel="nofollow">/test</a>
+<a href="/user2/repo1/media/commit/1234/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/media/commit/1234/image" alt="/image"/></a></p>
+`, rendered)
+	})
+
+	t.Run("WithCurrentRefPathByTag", func(t *testing.T) {
+		rctx := NewRenderContextRepoFile(context.Background(), repo1, RepoFileOptions{
+			CurrentRefPath:  "/commit/1234",
+			CurrentTreePath: "my-dir",
+		}).
+			WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+<img src="LINK">
+<video src="LINK">
+`)
+		assert.NoError(t, err)
+		assert.Equal(t, `<a href="/user2/repo1/media/commit/1234/my-dir/LINK" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/media/commit/1234/my-dir/LINK"/></a>
+<video src="/user2/repo1/media/commit/1234/my-dir/LINK">
+</video>`, rendered)
+	})
+}
diff --git a/models/renderhelper/repo_wiki.go b/models/renderhelper/repo_wiki.go
new file mode 100644
index 0000000000..aa456bf6ce
--- /dev/null
+++ b/models/renderhelper/repo_wiki.go
@@ -0,0 +1,80 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"fmt"
+	"path"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/markup/markdown"
+	"code.gitea.io/gitea/modules/util"
+)
+
+type RepoWiki struct {
+	ctx  *markup.RenderContext
+	opts RepoWikiOptions
+
+	commitChecker *commitChecker
+	repoLink      string
+}
+
+func (r *RepoWiki) CleanUp() {
+	_ = r.commitChecker.Close()
+}
+
+func (r *RepoWiki) IsCommitIDExisting(commitID string) bool {
+	return r.commitChecker.IsCommitIDExisting(commitID)
+}
+
+func (r *RepoWiki) ResolveLink(link string, likeType markup.LinkType) string {
+	finalLink := link
+	switch likeType {
+	case markup.LinkTypeApp:
+		finalLink = r.ctx.ResolveLinkApp(link)
+	case markup.LinkTypeDefault:
+		finalLink = r.ctx.ResolveLinkRelative(path.Join(r.repoLink, "wiki", r.opts.currentRefPath), r.opts.currentTreePath, link)
+	case markup.LinkTypeMedia:
+		finalLink = r.ctx.ResolveLinkRelative(path.Join(r.repoLink, "wiki/raw", r.opts.currentRefPath), r.opts.currentTreePath, link)
+	case markup.LinkTypeRaw: // wiki doesn't use it
+	}
+
+	return finalLink
+}
+
+var _ markup.RenderHelper = (*RepoWiki)(nil)
+
+type RepoWikiOptions struct {
+	DeprecatedRepoName  string // it is only a patch for the non-standard "markup" api
+	DeprecatedOwnerName string // it is only a patch for the non-standard "markup" api
+
+	// these options are not used at the moment because Wiki doesn't support sub-path, nor branch
+	currentRefPath  string // eg: "branch/main"
+	currentTreePath string // eg: "path/to/file" in the repo
+}
+
+func NewRenderContextRepoWiki(ctx context.Context, repo *repo_model.Repository, opts ...RepoWikiOptions) *markup.RenderContext {
+	helper := &RepoWiki{opts: util.OptionalArg(opts)}
+	rctx := markup.NewRenderContext(ctx).WithMarkupType(markdown.MarkupName)
+	if repo != nil {
+		helper.repoLink = repo.Link()
+		helper.commitChecker = newCommitChecker(ctx, repo)
+		rctx = rctx.WithMetas(repo.ComposeWikiMetas(ctx))
+	} else {
+		// this is almost dead code, only to pass the incorrect tests
+		helper.repoLink = fmt.Sprintf("%s/%s", helper.opts.DeprecatedOwnerName, helper.opts.DeprecatedRepoName)
+		rctx = rctx.WithMetas(map[string]string{
+			"user": helper.opts.DeprecatedOwnerName,
+			"repo": helper.opts.DeprecatedRepoName,
+
+			"markdownLineBreakStyle":       "document",
+			"markupAllowShortIssuePattern": "true",
+		})
+	}
+	rctx = rctx.WithHelper(helper)
+	helper.ctx = rctx
+	return rctx
+}
diff --git a/models/renderhelper/repo_wiki_test.go b/models/renderhelper/repo_wiki_test.go
new file mode 100644
index 0000000000..beab2570e7
--- /dev/null
+++ b/models/renderhelper/repo_wiki_test.go
@@ -0,0 +1,65 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"testing"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/markup/markdown"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepoWiki(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+	repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	t.Run("AutoLink", func(t *testing.T) {
+		rctx := NewRenderContextRepoWiki(context.Background(), repo1).WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+65f1bf27bc3bf70f64657658635e66094edbcb4d
+#1
+@user2
+`)
+		assert.NoError(t, err)
+		assert.Equal(t,
+			`<p><a href="/user2/repo1/commit/65f1bf27bc3bf70f64657658635e66094edbcb4d" rel="nofollow"><code>65f1bf27bc</code></a>
+<a href="/user2/repo1/issues/1" class="ref-issue" rel="nofollow">#1</a>
+<a href="/user2" rel="nofollow">@user2</a></p>
+`, rendered)
+	})
+
+	t.Run("AbsoluteAndRelative", func(t *testing.T) {
+		rctx := NewRenderContextRepoWiki(context.Background(), repo1).WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+[/test](/test)
+[./test](./test)
+![/image](/image)
+![./image](./image)
+`)
+		assert.NoError(t, err)
+		assert.Equal(t,
+			`<p><a href="/user2/repo1/wiki/test" rel="nofollow">/test</a>
+<a href="/user2/repo1/wiki/test" rel="nofollow">./test</a>
+<a href="/user2/repo1/wiki/raw/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/wiki/raw/image" alt="/image"/></a>
+<a href="/user2/repo1/wiki/raw/image" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/wiki/raw/image" alt="./image"/></a></p>
+`, rendered)
+	})
+
+	t.Run("PathInTag", func(t *testing.T) {
+		rctx := NewRenderContextRepoWiki(context.Background(), repo1).WithMarkupType(markdown.MarkupName)
+		rendered, err := markup.RenderString(rctx, `
+<img src="LINK">
+<video src="LINK">
+`)
+		assert.NoError(t, err)
+		assert.Equal(t, `<a href="/user2/repo1/wiki/raw/LINK" target="_blank" rel="nofollow noopener"><img src="/user2/repo1/wiki/raw/LINK"/></a>
+<video src="/user2/repo1/wiki/raw/LINK">
+</video>`, rendered)
+	})
+}
diff --git a/models/renderhelper/simple_document.go b/models/renderhelper/simple_document.go
new file mode 100644
index 0000000000..91d888aa87
--- /dev/null
+++ b/models/renderhelper/simple_document.go
@@ -0,0 +1,29 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/modules/markup"
+)
+
+type SimpleDocument struct {
+	*markup.SimpleRenderHelper
+	ctx      *markup.RenderContext
+	baseLink string
+}
+
+func (r *SimpleDocument) ResolveLink(link string, likeType markup.LinkType) string {
+	return r.ctx.ResolveLinkRelative(r.baseLink, "", link)
+}
+
+var _ markup.RenderHelper = (*SimpleDocument)(nil)
+
+func NewRenderContextSimpleDocument(ctx context.Context, baseLink string) *markup.RenderContext {
+	helper := &SimpleDocument{baseLink: baseLink}
+	rctx := markup.NewRenderContext(ctx).WithHelper(helper).WithMetas(markup.ComposeSimpleDocumentMetas())
+	helper.ctx = rctx
+	return rctx
+}
diff --git a/models/renderhelper/simple_document_test.go b/models/renderhelper/simple_document_test.go
new file mode 100644
index 0000000000..c0d5fd7429
--- /dev/null
+++ b/models/renderhelper/simple_document_test.go
@@ -0,0 +1,40 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package renderhelper
+
+import (
+	"context"
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/markup"
+	"code.gitea.io/gitea/modules/markup/markdown"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSimpleDocument(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+	rctx := NewRenderContextSimpleDocument(context.Background(), "/base").WithMarkupType(markdown.MarkupName)
+	rendered, err := markup.RenderString(rctx, `
+65f1bf27bc3bf70f64657658635e66094edbcb4d
+#1
+@user2
+
+[/test](/test)
+[./test](./test)
+![/image](/image)
+![./image](./image)
+`)
+	assert.NoError(t, err)
+	assert.Equal(t,
+		`<p>65f1bf27bc3bf70f64657658635e66094edbcb4d
+#1
+<a href="/base/user2" rel="nofollow">@user2</a></p>
+<p><a href="/base/test" rel="nofollow">/test</a>
+<a href="/base/test" rel="nofollow">./test</a>
+<a href="/base/image" target="_blank" rel="nofollow noopener"><img src="/base/image" alt="/image"/></a>
+<a href="/base/image" target="_blank" rel="nofollow noopener"><img src="/base/image" alt="./image"/></a></p>
+`, rendered)
+}