Issue #153 - Fix: The DiffViewer should not fail if the coverage data for a changeset is PENDING

Normally, from the SummaryViewer you should not be able to get to the DiffViewer since
there's no link to navigate to it.

However, people clicking on links from GitHub issues can reach the DiffViewer, thus,
failing because there `coverage` object contains a summary property rather than
being undefined.

This change shows an error message to the user letting them know that they should
try again later.

There's also some linting fixes in this change.

src/components/diffviewer.js

@@ -5,6 +5,7 @@ import { orderBy } from 'lodash';
 import { csetWithCcovData } from '../utils/data';
 import hash from '../utils/hash';
 import * as FetchAPI from '../utils/fetch_data';
+import { PENDING } from '../settings';
 
 const parse = require('parse-diff');
 
@@ -31,7 +32,13 @@ export default class DiffViewerContainer extends Component {
 
   async fetchSetCoverageData(changeset) {
     try {
-      this.setState({ csetMeta: await csetWithCcovData({ node: changeset }) });
+      const csetMeta = await csetWithCcovData({ node: changeset });
+      if (csetMeta.summary === PENDING) {
+        this.setState({
+          appError: 'The coverage data is still pending. Try again later.',
+        });
+      }
+      this.setState({ csetMeta });
     } catch (error) {
       console.error(error);
       this.setState({
@@ -85,15 +92,20 @@ const sortByPercent = (parsedDiff, coverage) => {
 };
 
 
-const DiffViewer = ({ appError, coverage, parsedDiff, summary }) => (
+const DiffViewer = ({
+  appError, coverage, parsedDiff, summary,
+}) => (
   <div className="codecoverage-diffviewer">
-    <div className="return-home"><Link to="/">Return to main page</Link></div>
+    <div className="return-home">
-    {(coverage) &&
+      <Link to="/" href="/">Return to main page</Link>
+    </div>
+    <span className="error_message">{appError}</span>
+    {(coverage && summary !== PENDING) && (
+      <div>
         <CoverageMeta
           coverage={coverage}
           summary={summary}
-      />}
+        />,
-    <span className="error_message">{appError}</span>
         {sortByPercent(parsedDiff, coverage).map((diffBlock) => {
           // We only push down the subset of code coverage data
           // applicable to a file
@@ -105,11 +117,12 @@ const DiffViewer = ({ appError, coverage, parsedDiff, summary }) => (
             key={path}
             path={path}
           />);
-    })}
+        })},
-    {(parsedDiff.length > 0) &&
+        <CoverageFooter
-      <DiffFooter
           coverage={coverage}
-      />}
+        />
+      </div>
+    )}
   </div>
 );
 
@@ -132,7 +145,7 @@ const CoverageMeta = ({ coverage, summary }) => (
   </div>
 );
 
-const DiffFooter = ({ coverage }) => (
+const CoverageFooter = ({ coverage }) => (
   <div className="meta-footer">
     <a href={coverage.gh} target="_blank">GitHub</a>
     <a href={coverage.codecov} target="_blank">Codecov</a>
@@ -141,11 +154,19 @@ const DiffFooter = ({ coverage }) => (
 );
 
 /* A DiffLine contains all diff changes for a specific file */
-const DiffFile = ({ buildRev, diffBlock, fileCoverageDiffs, path }) => (
+const DiffFile = ({
+  buildRev, diffBlock, fileCoverageDiffs, path,
+}) => (
   <div className="diff-file">
     <div className="file-summary">
       <div className="file-path">
-        <Link class="diff-viewer-link" to={`/file?revision=${buildRev}&path=${path}`}>{path}</Link>
+        <Link
+          class="diff-viewer-link"
+          to={`/file?revision=${buildRev}&path=${path}`}
+          href={`/file?revision=${buildRev}&path=${path}`}
+        >
+          {path}
+        </Link>
       </div>
     </div>
     {diffBlock.chunks.map(block => (