internal/source: support gitlab module paths

gitlab.com serves source information just like github. Add it to the list
of known patterns.

Change-Id: I0b102d2c56c03a4ec8904f089f09ef6793db9c7f
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/562177
Reviewed-by: Julie Qiu <julieqiu@google.com>

internal/source/source.go

@@ -214,6 +214,12 @@ var patterns = []struct {
 	// git.openstack.org has been rebranded.
 	// chiselapp.com has no Go packages in godoc.org.
 
+	// Patterns that are not (yet) part of the go command.
+	{
+		regexp.MustCompile(`^(?P<repo>gitlab\.com/[a-z0-9A-Z_.\-]+/[a-z0-9A-Z_.\-]+)`),
+		githubURLTemplates,
+	},
+
 	// Patterns that match the general go command pattern, where they must have
 	// a ".git" repo suffix in an import path. If matching a repo URL from a meta tag,
 	// there is no ".git".

internal/source/source_test.go

@@ -138,6 +138,15 @@ func TestModuleInfo(t *testing.T) {
 			"https://cue.googlesource.com/cue/+/v0.0.9/cuego/doc.go",
 			"https://cue.googlesource.com/cue/+/v0.0.9/cuego/doc.go#1",
 		},
+		{
+			"gitlab",
+			"gitlab.com/akita/akita", "v1.4.1", "event.go",
+
+			"https://gitlab.com/akita/akita",
+			"https://gitlab.com/akita/akita/tree/v1.4.1",
+			"https://gitlab.com/akita/akita/blob/v1.4.1/event.go",
+			"https://gitlab.com/akita/akita/blob/v1.4.1/event.go#L1",
+		},
 	} {
 		t.Run(test.desc, func(t *testing.T) {
 			check := func(msg, got, want string) {