internal/frontend: translate relative non-image links in readmes

If a Readme has a relative link that is not an image, convert
it to an absolute link to the file using source info.

Fixes b/140250096.

Change-Id: I9ca629963ca87d7605c0217e49671b33c7dd0f86
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/576296
CI-Result: Cloud Build <devtools-proctor-result-processor@system.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>

3 files changed, 33 insertions, 8 deletions

diff --git a/internal/frontend/overview.go b/internal/frontend/overview.go
index 2a256090..45fc11e5 100644
--- a/internal/frontend/overview.go
+++ b/internal/frontend/overview.go
@@ -77,7 +77,7 @@ func readmeHTML(vi *internal.VersionInfo) template.HTML {
 	b := &bytes.Buffer{}
 	rootNode := parser.Parse(vi.ReadmeContents)
 	rootNode.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
-		if node.Type == blackfriday.Image {
+		if node.Type == blackfriday.Image || node.Type == blackfriday.Link {
 			translateRelativeLink(node, vi)
 		}
 		return renderer.RenderNode(b, node, entering)
@@ -93,14 +93,19 @@ func readmeHTML(vi *internal.VersionInfo) template.HTML {
 // full repository content, in order for the image to render, we need to
 // convert the relative path to an absolute URL to a hosted image.
 func translateRelativeLink(node *blackfriday.Node, vi *internal.VersionInfo) {
-	imageURL, err := url.Parse(string(node.LinkData.Destination))
-	if err != nil || imageURL.IsAbs() {
+	destURL, err := url.Parse(string(node.LinkData.Destination))
+	if err != nil || destURL.IsAbs() {
 		return
 	}
 	// Paths are relative to the README location.
-	imagePath := path.Join(path.Dir(vi.ReadmeFilePath), path.Clean(imageURL.Path))
-	rawURL := vi.SourceInfo.RawURL(imagePath)
-	if rawURL != "" {
-		node.LinkData.Destination = []byte(rawURL)
+	destPath := path.Join(path.Dir(vi.ReadmeFilePath), path.Clean(destURL.Path))
+	var newURL string
+	if node.Type == blackfriday.Image {
+		newURL = vi.SourceInfo.RawURL(destPath)
+	} else {
+		newURL = vi.SourceInfo.FileURL(destPath)
+	}
+	if newURL != "" {
+		node.LinkData.Destination = []byte(newURL)
 	}
 }
diff --git a/internal/frontend/overview_test.go b/internal/frontend/overview_test.go
index a4ee8aff..3a84c921 100644
--- a/internal/frontend/overview_test.go
+++ b/internal/frontend/overview_test.go
@@ -133,7 +133,7 @@ func TestReadmeHTML(t *testing.T) {
 			want: template.HTML("<p><img src=\"https://raw.githubusercontent.com/gohugoio/hugo/v0.56.3/doc/logo.png\" alt=\"Hugo logo\"/></p>\n"),
 		},
 		{
-			name: "URLs relative to README directory",
+			name: "image URLs relative to README directory",
 			vi: &internal.VersionInfo{
 				ReadmeFilePath: "dir/sub/README.md",
 				ReadmeContents: []byte("![alt](img/thing.png)"),
@@ -143,6 +143,17 @@ func TestReadmeHTML(t *testing.T) {
 			},
 			want: template.HTML(`<p><img src="https://raw.githubusercontent.com/some/repo/v1.2.3/dir/sub/img/thing.png" alt="alt"/></p>` + "\n"),
 		},
+		{
+			name: "non-image links relative to README directory",
+			vi: &internal.VersionInfo{
+				ReadmeFilePath: "dir/sub/README.md",
+				ReadmeContents: []byte("[something](doc/thing.md)"),
+				Version:        "v1.2.3",
+				VersionType:    version.TypeRelease,
+				SourceInfo:     source.NewGitHubInfo("https://github.com/some/repo", "", "v1.2.3"),
+			},
+			want: template.HTML(`<p><a href="https://github.com/some/repo/blob/v1.2.3/dir/sub/doc/thing.md" rel="nofollow">something</a></p>` + "\n"),
+		},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
diff --git a/internal/source/source.go b/internal/source/source.go
index fa4dc551..289ffb6d 100644
--- a/internal/source/source.go
+++ b/internal/source/source.go
@@ -63,6 +63,9 @@ func (i *Info) ModuleURL() string {
 
 // DirectoryURL returns a URL for a directory relative to the module's home directory.
 func (i *Info) DirectoryURL(dir string) string {
+	if i == nil {
+		return ""
+	}
 	return strings.TrimSuffix(expand(i.templates.Directory, map[string]string{
 		"repo":   i.repoURL,
 		"commit": i.commit,
@@ -72,6 +75,9 @@ func (i *Info) DirectoryURL(dir string) string {
 
 // FileURL returns a URL for a file whose pathname is relative to the module's home directory.
 func (i *Info) FileURL(pathname string) string {
+	if i == nil {
+		return ""
+	}
 	return expand(i.templates.File, map[string]string{
 		"repo":   i.repoURL,
 		"commit": i.commit,
@@ -81,6 +87,9 @@ func (i *Info) FileURL(pathname string) string {
 
 // LineURL returns a URL referring to a line in a file relative to the module's home directory.
 func (i *Info) LineURL(pathname string, line int) string {
+	if i == nil {
+		return ""
+	}
 	return expand(i.templates.Line, map[string]string{
 		"repo":   i.repoURL,
 		"commit": i.commit,