Fallback language detection with meta.js extensions

CodeMirror ships meta.js with a map of file extensions.  Fallback to
this table if the server was unable to provide a valid MIME type.

Change-Id: I24930a8f79f8e1e2b919b81c8dab15c9c585d35e

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/SideBySide2.java

@@ -76,6 +76,7 @@ import net.codemirror.lib.CodeMirror.LineHandle;
 import net.codemirror.lib.Configuration;
 import net.codemirror.lib.KeyMap;
 import net.codemirror.lib.Pos;
+import net.codemirror.mode.ModeInfo;
 import net.codemirror.mode.ModeInjector;
 
 import java.util.ArrayList;
@@ -991,11 +992,12 @@ public class SideBySide2 extends Screen {
   }
 
   private String getContentType(DiffInfo.FileMeta meta) {
-    return prefs.syntaxHighlighting()
-          && meta != null
-          && meta.content_type() != null
-        ? ModeInjector.getContentType(meta.content_type())
-        : null;
+    if (prefs.syntaxHighlighting() && meta != null
+        && meta.content_type() != null) {
+     ModeInfo m = ModeInfo.findMode(meta.content_type(), path);
+     return m != null ? m.mime() : null;
+   }
+   return null;
   }
 
   private void injectMode(DiffInfo diffInfo, AsyncCallback<Void> cb) {

gerrit-gwtui/src/main/java/com/google/gerrit/client/editor/EditScreen.java

@@ -39,6 +39,7 @@ import com.google.gwtexpui.globalkey.client.GlobalKey;
 
 import net.codemirror.lib.CodeMirror;
 import net.codemirror.lib.Configuration;
+import net.codemirror.mode.ModeInfo;
 import net.codemirror.mode.ModeInjector;
 
 public class EditScreen extends Screen {
@@ -86,7 +87,8 @@ public class EditScreen extends Screen {
           cmGroup.addFinal(new GerritCallback<String>() {
             @Override
             public void onSuccess(String result) {
-              type = result;
+              ModeInfo mode = ModeInfo.findMode(result, path);
+              type = mode != null ? mode.mime() : null;
               injectMode(result, modeInjectorCb);
             }
           }));
@@ -148,7 +150,7 @@ public class EditScreen extends Screen {
         .set("styleSelectedText", true)
         .set("showTrailingSpace", true)
         .set("keyMap", "default")
-        .set("mode", ModeInjector.getContentType(type));
+        .set("mode", type);
   }
 
   private void initPath() {

gerrit-gwtui/src/main/java/net/codemirror/mode/ModeInfo.java

@@ -30,6 +30,7 @@ import java.util.Map;
 /** Description of a CodeMirror language mode. */
 public class ModeInfo extends JavaScriptObject {
   private static NativeMap<ModeInfo> byMime;
+  private static NativeMap<ModeInfo> byExt;
 
   /** Map of names such as "clike" to URI for code download. */
   private static final Map<String, SafeUri> modeUris = new HashMap<>();
@@ -100,7 +101,7 @@ public class ModeInfo extends JavaScriptObject {
     $wnd.CodeMirror.modeInfo = m
   }-*/;
 
-  /** Lookup mode by primary or alternate MIME types. */
+  /** Look up mode by primary or alternate MIME types. */
   public static ModeInfo findModeByMIME(String mime) {
     return byMime.get(mime);
   }
@@ -109,6 +110,30 @@ public class ModeInfo extends JavaScriptObject {
     return modeUris.get(mode);
   }
 
+  /** Look up mode by MIME type or file extension from a path. */
+  public static ModeInfo findMode(String mime, String path) {
+    ModeInfo m = byMime.get(mime);
+    if (m != null) {
+      return m;
+    }
+
+    int s = path.lastIndexOf('/');
+    int d = path.lastIndexOf('.');
+    if (d == -1 || s > d) {
+      return null; // punt on "foo.src/bar" type paths.
+    }
+
+    if (byExt == null) {
+      byExt = NativeMap.create();
+      for (ModeInfo mode : Natives.asList(all())) {
+        for (String ext : Natives.asList(mode.ext())) {
+          byExt.put(ext, mode);
+        }
+      }
+    }
+    return byExt.get(path.substring(d + 1));
+  }
+
   private static void alias(String serverMime, String toMime) {
     ModeInfo mode = byMime.get(toMime);
     if (mode != null) {
@@ -158,6 +183,9 @@ public class ModeInfo extends JavaScriptObject {
   public final native JsArrayString mimes()
   /*-{ return this.mimes || [this.mime] }-*/;
 
+  private final native JsArrayString ext()
+  /*-{ return this.ext || [] }-*/;
+
   protected ModeInfo() {
   }
 

gerrit-gwtui/src/main/java/net/codemirror/mode/ModeInjector.java

@@ -29,15 +29,6 @@ public class ModeInjector {
     return ModeInfo.getModeScriptUri(mode) != null;
   }
 
-  public static String getContentType(String mode) {
-    if (canLoad(mode)) {
-      return mode;
-    }
-
-    ModeInfo m = ModeInfo.findModeByMIME(mode);
-    return m != null ? m.mime() : mode;
-  }
-
   private static native boolean isModeLoaded(String n)
   /*-{ return $wnd.CodeMirror.modes.hasOwnProperty(n); }-*/;