Disable merge button if dependencies are still open

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/341916

app/assets/javascripts/vue_merge_request_widget/components/states/ready_to_merge.vue

@@ -295,13 +295,6 @@ export default {
 
       return enableSquashBeforeMerge;
     },
-    shouldShowMergeControls() {
-      if (this.glFeatures.restructuredMrWidget) {
-        return this.restructuredWidgetShowMergeButtons;
-      }
-
-      return this.isMergeAllowed || this.isAutoMergeAvailable;
-    },
     shouldShowSquashEdit() {
       return this.squashBeforeMerge && this.shouldShowSquashBeforeMerge;
     },

app/assets/javascripts/vue_merge_request_widget/mixins/ready_to_merge.js

@@ -22,6 +22,13 @@ export default {
           this.mr.preventMerge,
       );
     },
+    shouldShowMergeControls() {
+      if (this.glFeatures.restructuredMrWidget) {
+        return this.restructuredWidgetShowMergeButtons;
+      }
+
+      return this.isMergeAllowed || this.isAutoMergeAvailable;
+    },
     mergeDisabledText() {
       if (this.pipeline?.status === PIPELINE_SKIPPED_STATUS) {
         return MERGE_DISABLED_SKIPPED_PIPELINE_TEXT;

ee/app/assets/javascripts/vue_merge_request_widget/mixins/ready_to_merge.js

@@ -31,6 +31,17 @@ export default {
           this.mr.preventMerge,
       );
     },
+    shouldShowMergeControls() {
+      if (this.glFeatures.restructuredMrWidget) {
+        return this.restructuredWidgetShowMergeButtons;
+      }
+
+      if (this.mr.blockingMergeRequests?.total_count > 0) {
+        return false;
+      }
+
+      return this.isMergeAllowed || this.isAutoMergeAvailable;
+    },
     mergeDisabledText() {
       if (this.isApprovalNeeded) {
         return MERGE_DISABLED_TEXT_UNAPPROVED;

ee/spec/frontend/vue_mr_widget/components/states/mr_widget_ready_to_merge_spec.js

@@ -373,6 +373,28 @@ describe('ReadyToMerge', () => {
         expect(button.exists()).toBe(true);
         expect(button.attributes('disabled')).toBe('true');
       });
+
+      it.each`
+        disabled     | disabledText | totalCount
+        ${'true'}    | ${'disable'} | ${1}
+        ${undefined} | ${'enable'}  | ${0}
+      `(
+        'should $disabledText merge button blockingMergeRequests.total_count is $totalCount',
+        ({ disabled, totalCount }) => {
+          factory({
+            isMergeAllowed: true,
+            availableAutoMergeStrategies: [],
+            blockingMergeRequests: {
+              total_count: totalCount,
+            },
+          });
+
+          const button = findMergeButton();
+
+          expect(button.exists()).toBe(true);
+          expect(button.attributes('disabled')).toBe(disabled);
+        },
+      );
     });
   });