Display the merge message in index viewer

Author: pvigier

src/renderer/components/index-viewer.tsx

@@ -48,8 +48,21 @@ export class IndexViewer extends React.PureComponent<IndexViewerProps, IndexView
     this.handleSubmit = this.handleSubmit.bind(this);
   }
 
-  componentDidMount() {
+  async componentDidMount() {
     this.getPatches();
+    if (this.props.repoState === RepoState.Merge) {
+      this.setState({
+        summary: await this.props.repo.getMergeMessage()
+      });
+    }
+  }
+
+  async componentDidUpdate(prevProps: IndexViewerProps) {
+    if (prevProps.repoState !== this.props.repoState) {
+      this.setState({
+        summary: this.props.repoState === RepoState.Merge ? await this.props.repo.getMergeMessage() : ''
+      });
+    } 
   }
 
   handleUnstagedPatchSelect(patch: Git.ConvenientPatch) {

src/renderer/helpers/repo-wrapper.ts

@@ -563,6 +563,18 @@ export class RepoWrapper {
     }
   }
 
+  async getMergeMessage() {
+    return new Promise<string>((resolve, reject) => {
+      fs.readFile(Path.join(this.path, 'MERGE_MSG'), (error, data) => {
+        if (!error) {
+          resolve(data.toString().split('\n')[0]);
+        } else {
+          reject(error);
+        }
+      });
+    });
+  }
+
   async finishMerge(message: string) {
     try {
       const author = this.getSignature();