Allow default branch to be inferred on compare page (#17908)

* Allow default branch to be inferred

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Add test for inferred default branch

Signed-off-by: jolheiser <john.olheiser@gmail.com>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

integrations/compare_test.go

@@ -27,3 +27,15 @@ func TestCompareTag(t *testing.T) {
 	resp = session.MakeRequest(t, req, http.StatusNotFound)
 	assert.False(t, strings.Contains(resp.Body.String(), "/assets/img/500.png"), "expect 404 page not 500")
 }
+
+// Compare with inferred default branch (master)
+func TestCompareDefault(t *testing.T) {
+	defer prepareTestEnv(t)()
+
+	session := loginUser(t, "user2")
+	req := NewRequest(t, "GET", "/user2/repo1/compare/v1.1")
+	resp := session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc := NewHTMLParser(t, resp.Body)
+	selection := htmlDoc.doc.Find(".choose.branch .filter.dropdown")
+	assert.Lenf(t, selection.Nodes, 2, "The template has changed")
+}

routers/web/repo/compare.go

@@ -186,6 +186,9 @@ func ParseCompareInfo(ctx *context.Context) *CompareInfo {
 	// 1. /{:baseOwner}/{:baseRepoName}/compare/{:baseBranch}...{:headBranch}
 	// 2. /{:baseOwner}/{:baseRepoName}/compare/{:baseBranch}...{:headOwner}:{:headBranch}
 	// 3. /{:baseOwner}/{:baseRepoName}/compare/{:baseBranch}...{:headOwner}/{:headRepoName}:{:headBranch}
+	// 4. /{:baseOwner}/{:baseRepoName}/compare/{:headBranch}
+	// 5. /{:baseOwner}/{:baseRepoName}/compare/{:headOwner}:{:headBranch}
+	// 6. /{:baseOwner}/{:baseRepoName}/compare/{:headOwner}/{:headRepoName}:{:headBranch}
 	//
 	// Here we obtain the infoPath "{:baseBranch}...[{:headOwner}/{:headRepoName}:]{:headBranch}" as ctx.Params("*")
 	// with the :baseRepo in ctx.Repo.
@@ -213,9 +216,12 @@ func ParseCompareInfo(ctx *context.Context) *CompareInfo {
 	infos := strings.SplitN(infoPath, "...", 2)
 
 	if len(infos) != 2 {
-		infos = strings.SplitN(infoPath, "..", 2)
-		ci.DirectComparison = true
-		ctx.Data["PageIsComparePull"] = false
+		infos = []string{baseRepo.DefaultBranch, infoPath}
+		if strings.Contains(infoPath, "..") {
+			infos = strings.SplitN(infoPath, "..", 2)
+			ci.DirectComparison = true
+			ctx.Data["PageIsComparePull"] = false
+		}
 	}
 
 	if len(infos) != 2 {