New composer: fix tab-complete in commands

src/components/views/rooms/BasicMessageComposer.js

@@ -265,7 +265,7 @@ export default class BasicMessageEditor extends React.Component {
             handled = true;
         // autocomplete or enter to send below shouldn't have any modifier keys pressed.
         } else if (!(event.metaKey || event.altKey || event.shiftKey)) {
-            if (model.autoComplete) {
+            if (model.autoComplete && model.autoComplete.hasCompletions()) {
                 const autoComplete = model.autoComplete;
                 switch (event.key) {
                     case "ArrowUp":
@@ -306,7 +306,11 @@ export default class BasicMessageEditor extends React.Component {
             const position = model.positionForOffset(caret.offset, caret.atNodeEnd);
             const range = model.startRange(position);
             range.expandBackwardsWhile((index, offset, part) => {
-                return part.text[offset] !== " " && (part.type === "plain" || part.type === "pill-candidate");
+                return part.text[offset] !== " " && (
+                    part.type === "plain" ||
+                    part.type === "pill-candidate" ||
+                    part.type === "command"
+                );
             });
             const {partCreator} = model;
             // await for auto-complete to be open

src/editor/autocomplete.js

@@ -41,6 +41,11 @@ export default class AutocompleteWrapperModel {
         return this._getAutocompleterComponent().hasSelection();
     }
 
+    hasCompletions() {
+        const ac = this._getAutocompleterComponent();
+        return ac && ac.countCompletions() > 0;
+    }
+
     onEnter() {
         this._updateCallback({close: true});
     }

src/editor/parts.js

@@ -465,10 +465,6 @@ export class CommandPartCreator extends PartCreator {
 }
 
 class CommandPart extends PillCandidatePart {
-    acceptsInsertion(chr, i) {
-        return PlainPart.prototype.acceptsInsertion.call(this, chr, i);
-    }
-
     get type() {
         return "command";
     }