Add check for submission URL being a Git repository

With the current submission system, it's common for people to provide the tag/release URL rather than the repository
URL. I think it likely the same sort of thing will occur with the new system. Previously, a very naive check was done
for the path component of the URL to have two levels. It turns out that the Gitlab repository URLs have more levels than
that. The superior approach is to use `git ls-remote` to verify that the URL is a Git repository.

manager/main.go

@@ -227,11 +227,7 @@ func populateSubmission(submissionURL string, listPath *paths.Path) (submissionT
 	}
 
 	// Resolve redirects and normalize.
-	normalizedURLObject, err := normalizeURL(httpResponse.Request.URL)
-	if err != nil {
-		submission.Error = err.Error()
-		return submission, ""
-	}
+	normalizedURLObject := normalizeURL(httpResponse.Request.URL)
 
 	submission.NormalizedURL = normalizedURLObject.String()
 
@@ -241,6 +237,17 @@ func populateSubmission(submissionURL string, listPath *paths.Path) (submissionT
 		return submission, ""
 	}
 
+	// Check if URL is a Git repository
+	err = exec.Command("git", "ls-remote", normalizedURLObject.String()).Run()
+	if err != nil {
+		if _, ok := err.(*exec.ExitError); ok {
+			submission.Error = "Submission URL is not a Git clone URL (e.g., https://github.com/arduino-libraries/Servo)."
+			return submission, ""
+		}
+
+		panic(err)
+	}
+
 	// Check if the URL is already in the index.
 	listLines, err := listPath.ReadFileAsLines()
 	occurrences := 0
@@ -249,11 +256,8 @@ func populateSubmission(submissionURL string, listPath *paths.Path) (submissionT
 		if err != nil {
 			panic(err) // All list items have already passed parsing so something is broken if this happens.
 		}
-		normalizedListURLObject, err := normalizeURL(listURLObject)
-		if err != nil {
-			panic(fmt.Errorf("When processing list item %s: %s", listURL, err)) // All list items have already been through normalization without error so something is broken if this happens.
-		}
 
+		normalizedListURLObject := normalizeURL(listURLObject)
 		if normalizedListURLObject.String() == normalizedURLObject.String() {
 			occurrences++
 			if occurrences > 1 {
@@ -350,21 +354,17 @@ func populateSubmission(submissionURL string, listPath *paths.Path) (submissionT
 }
 
 // normalizeURL converts the URL into the standardized format used in the index.
-func normalizeURL(rawURL *url.URL) (url.URL, error) {
+func normalizeURL(rawURL *url.URL) url.URL {
 	normalizedPath := strings.TrimRight(rawURL.Path, "/")
 	if !strings.HasSuffix(normalizedPath, ".git") {
 		normalizedPath += ".git"
 	}
-	if len(strings.Split(normalizedPath, "/")) != 3 {
-		return url.URL{}, fmt.Errorf("Submission URL must point to the root of the repository")
-	}
 
 	return url.URL{
-			Scheme: "https",
-			Host:   rawURL.Host,
-			Path:   normalizedPath,
-		},
-		nil
+		Scheme: "https",
+		Host:   rawURL.Host,
+		Path:   normalizedPath,
+	}
 }
 
 func uRLIsUnder(childURL url.URL, parentCandidates []string) bool {

manager/main_test.go

@@ -13,7 +13,6 @@
 package main
 
 import (
-	"fmt"
 	"net/url"
 	"testing"
 
@@ -154,14 +153,11 @@ func Test_normalizeURL(t *testing.T) {
 		testName              string
 		rawURL                string
 		expectedNormalizedURL string
-		expectedError         string
 	}{
-		{"Trailing slash", "https://github.com/foo/bar/", "https://github.com/foo/bar.git", ""},
-		{".git suffix", "https://github.com/foo/bar.git", "https://github.com/foo/bar.git", ""},
-		{"Too few path elements", "https://github.com/foo", "", "Submission URL must point to the root of the repository"},
-		{"Too many path elements", "https://github.com/foo/bar/baz", "", "Submission URL must point to the root of the repository"},
-		{"http://", "http://github.com/foo/bar", "https://github.com/foo/bar.git", ""},
-		{"git://", "git://github.com/foo/bar", "https://github.com/foo/bar.git", ""},
+		{"Trailing slash", "https://github.com/foo/bar/", "https://github.com/foo/bar.git"},
+		{".git suffix", "https://github.com/foo/bar.git", "https://github.com/foo/bar.git"},
+		{"http://", "http://github.com/foo/bar", "https://github.com/foo/bar.git"},
+		{"git://", "git://github.com/foo/bar", "https://github.com/foo/bar.git"},
 	}
 
 	for _, testTable := range testTables {
@@ -170,13 +166,7 @@ func Test_normalizeURL(t *testing.T) {
 		expectedNormalizedURL, err := url.Parse(testTable.expectedNormalizedURL)
 		require.Nil(t, err)
 
-		normalizedURL, err := normalizeURL(rawURL)
-		assert.Equal(t, *expectedNormalizedURL, normalizedURL, testTable.testName)
-		if testTable.expectedError == "" {
-			assert.Nil(t, err, testTable.testName)
-		} else {
-			assert.Equal(t, fmt.Errorf(testTable.expectedError), err, testTable.testName)
-		}
+		assert.Equal(t, *expectedNormalizedURL, normalizeURL(rawURL), testTable.testName)
 	}
 }