fix: use sha instead of ref for PRs when possible. (#1772)

Resolves #1658

lib/platform/github/index.js

@@ -763,6 +763,7 @@ async function getPrList() {
     config.prList = res.body.map(pr => ({
       number: pr.number,
       branchName: pr.head.ref,
+      sha: pr.head.sha,
       title: pr.title,
       state:
         pr.state === 'closed' && pr.merged_at && pr.merged_at.length
@@ -867,6 +868,7 @@ async function getPr(prNo) {
   pr.displayNumber = `Pull Request #${pr.number}`;
   if (pr.state === 'open') {
     pr.branchName = pr.head ? pr.head.ref : undefined;
+    pr.sha = pr.head ? pr.head.sha : undefined;
     if (pr.mergeable === true) {
       pr.canMerge = true;
     }

lib/workers/repository/validate.js

@@ -36,7 +36,7 @@ async function validatePrs(config) {
         'PR has renovate files'
       );
       for (const file of renovateFiles) {
-        const content = await platform.getFile(file, pr.branchName);
+        const content = await platform.getFile(file, pr.sha || pr.branchName);
         let parsed;
         try {
           parsed = JSON.parse(content);

test/platform/github/__snapshots__/index.spec.js.snap

@@ -456,6 +456,7 @@ Object {
   "isUnmergeable": true,
   "mergeable_state": "dirty",
   "number": 1,
+  "sha": undefined,
   "state": "open",
 }
 `;
@@ -473,6 +474,7 @@ Object {
   "isStale": true,
   "mergeable": true,
   "number": 1,
+  "sha": undefined,
   "state": "open",
 }
 `;
@@ -489,6 +491,7 @@ Object {
   "isUnmergeable": true,
   "mergeable_state": "dirty",
   "number": 1,
+  "sha": undefined,
   "state": "open",
 }
 `;
@@ -505,6 +508,7 @@ Object {
   "isUnmergeable": true,
   "mergeable_state": "dirty",
   "number": 1,
+  "sha": undefined,
   "state": "open",
 }
 `;
@@ -520,6 +524,7 @@ Object {
   "isUnmergeable": true,
   "mergeable_state": "dirty",
   "number": 1,
+  "sha": undefined,
   "state": "open",
 }
 `;