Fix for antlr#293

Fix bug that prevented loading template groups from a template group dir if the path returned by getResource() ended in a '/' by removing the initial '/' from the parent if the root ends with '/'.

src/org/stringtemplate/v4/STGroupDir.java

@@ -125,12 +125,33 @@ protected CompiledST load(String name) {
 //            return loadTemplateFile("/", name+TEMPLATE_FILE_EXTENSION); // load t.st file
 //      }
 
+        // Avoid creating invalid file URLs when root ends with '/'
+        // and parent starts with '/'
+        if (root.toString().endsWith("/")) {
+            if (parent.startsWith("/")) {
+                // root: 'a/', parent: '/b' -> 'b'
+                parent = parent.substring(1);
+            }
+        }
+        // Avoid creating invalid file URLs when root doesn't end with '/'
+        // and parent doesn't start with '/'
+        else if (!parent.startsWith("/")) {
+            // root: 'a', parent:  'b' -> '/b'
+            parent = "/" + parent;
+        }
+
+        String groupFileString = root+parent+GROUP_FILE_EXTENSION;
+
         URL groupFileURL;
         try { // see if parent of template name is a group file
-            groupFileURL = new URI(root+parent+GROUP_FILE_EXTENSION).normalize().toURL();
+            groupFileURL = new URI(groupFileString).normalize().toURL();
+        }
+        catch (MalformedURLException e) {
+            badURLError(groupFileString, e);
+            return null;
         }
-        catch (MalformedURLException | URISyntaxException e) {
-            errMgr.internalError(null, "bad URL: "+root+parent+GROUP_FILE_EXTENSION, e);
+        catch (URISyntaxException e) {
+            badURLError(groupFileString, e);
             return null;
         }
 
@@ -145,17 +166,21 @@ protected CompiledST load(String name) {
         }
         finally { // clean up
             try {
-                if (is!=null ) is.close();
+                if (is!=null) is.close();
             }
             catch (IOException ioe) {
                 errMgr.internalError(null, "can't close template file stream "+name, ioe);
             }
         }
 
-        loadGroupFile(prefix, root+parent+GROUP_FILE_EXTENSION);
+        loadGroupFile(prefix, groupFileString);
         return rawGetTemplate(name);
     }
 
+    private void badURLError(String fullPath, Exception e) {
+        errMgr.internalError(null, "bad URL: "+fullPath, e);
+    }
+
     /** Load .st as relative file name relative to root by {@code prefix}. */
     public CompiledST loadTemplateFile(String prefix, String unqualifiedFileName) {
         if ( verbose ) System.out.println("loadTemplateFile("+unqualifiedFileName+") in groupdir "+
@@ -164,9 +189,12 @@ public CompiledST loadTemplateFile(String prefix, String unqualifiedFileName) {
         try {
             f = new URI(root+prefix+unqualifiedFileName).normalize().toURL();
         }
-        catch (MalformedURLException | URISyntaxException me) {
-            errMgr.runTimeError(null, null, ErrorType.INVALID_TEMPLATE_NAME,
-                                me, root + unqualifiedFileName);
+        catch (MalformedURLException e) {
+            invalidTemplateError(unqualifiedFileName, e);
+            return null;
+        }
+        catch (URISyntaxException e) {
+            invalidTemplateError(unqualifiedFileName, e);
             return null;
         }
 
@@ -184,6 +212,11 @@ public CompiledST loadTemplateFile(String prefix, String unqualifiedFileName) {
         return loadTemplateFile(prefix, unqualifiedFileName, fs);
     }
 
+    private void invalidTemplateError(String unqualifiedFileName, Exception e) {
+        errMgr.runTimeError(null, null, ErrorType.INVALID_TEMPLATE_NAME,
+        e, root + unqualifiedFileName);
+    }
+
     @Override
     public String getName() { return groupDirName; }
     @Override