Fix: return correct type in GetSubModule

- `GetSubModules` already solely stores the URL of the submodule and not
a `*SubModule` entry, so don't try to type assert it to be a struct.
- I am not able to pinpoint when this was regressed but if I had to
guess it might be #4941.
- Added integration test.

modules/git/commit.go

@@ -395,20 +395,20 @@ func parseSubmoduleContent(bs []byte) (*ObjectCache, error) {
 	return submoduleCache, nil
 }
 
-// GetSubModule get the sub module according entryname
-func (c *Commit) GetSubModule(entryname string) (*SubModule, error) {
+// GetSubModule returns the URL to the submodule according entryname
+func (c *Commit) GetSubModule(entryname string) (string, error) {
 	modules, err := c.GetSubModules()
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
 	if modules != nil {
 		module, has := modules.Get(entryname)
 		if has {
-			return module.(*SubModule), nil
+			return module.(string), nil
 		}
 	}
-	return nil, nil
+	return "", nil
 }
 
 // GetBranchName gets the closest branch name (as returned by 'git name-rev --name-only')

modules/git/commit_info.go

@@ -72,17 +72,15 @@ func (tes Entries) GetCommitsInfo(ctx context.Context, commit *Commit, treePath
 
 		// If the entry if a submodule add a submodule file for this
 		if entry.IsSubModule() {
-			subModuleURL := ""
 			var fullPath string
 			if len(treePath) > 0 {
 				fullPath = treePath + "/" + entry.Name()
 			} else {
 				fullPath = entry.Name()
 			}
-			if subModule, err := commit.GetSubModule(fullPath); err != nil {
+			subModuleURL, err := commit.GetSubModule(fullPath)
+			if err != nil {
 				return nil, nil, err
-			} else if subModule != nil {
-				subModuleURL = subModule.URL
 			}
 			subModuleFile := NewSubModuleFile(commitsInfo[i].Commit, subModuleURL, entry.ID.String())
 			commitsInfo[i].SubModuleFile = subModuleFile