[build] Show diff to prior size

scripts/check_binary_size.js

@@ -4,6 +4,7 @@ const jwt = require('jsonwebtoken');
 const github = require('@octokit/rest')();
 const prettyBytes = require('pretty-bytes');
 const fs = require('fs');
+const {execSync} = require('child_process');
 
 const SIZE_CHECK_APP_ID = 14028;
 const SIZE_CHECK_APP_INSTALLATION_ID = 229425;
@@ -11,6 +12,7 @@ const SIZE_CHECK_APP_INSTALLATION_ID = 229425;
 const file = process.argv[2];
 const label = process.argv[3];
 const {size} = fs.statSync(file);
+const name = `Size - ${label}`;
 
 process.on('unhandledRejection', error => {
     console.log(error);
@@ -27,21 +29,72 @@ const payload = {
 const token = jwt.sign(payload, key, {algorithm: 'RS256'});
 github.authenticate({type: 'app', token});
 
+function getPriorSize() {
+    const pr = process.env['CIRCLE_PULL_REQUEST'];
+    if (!pr) {
+        console.log('No pull request available.');
+        return Promise.resolve(null);
+    }
+
+    const number = +pr.match(/\/(\d+)\/?$/)[1];
+    console.log(`Pull request ${number}.`);
+
+    return github.pullRequests.get({
+        owner: 'mapbox',
+        repo: 'mapbox-gl-native',
+        number
+    }).then(({data}) => {
+        const head = process.env['CIRCLE_SHA1'];
+        const base = data.base.sha;
+        console.log(`Pull request target is ${base}.`);
+
+        const mergeBase = execSync(`git merge-base ${base} ${head}`).toString().trim();
+        console.log(`Merge base is ${mergeBase}.`);
+
+        return github.checks.listForRef({
+            owner: 'mapbox',
+            repo: 'mapbox-gl-native',
+            ref: mergeBase
+        });
+    }).then(({data}) => {
+        const run = data.check_runs.find(run => run.name === name);
+        if (!run) {
+            console.log('No matching check found.');
+            return Promise.resolve(null);
+        }
+        const prior = +run.output.summary.match(/`.*` is (\d+) bytes/)[1];
+        console.log(`Prior size was ${prettyBytes(prior)}.`);
+        return prior;
+    });
+}
+
 github.apps.createInstallationToken({installation_id: SIZE_CHECK_APP_INSTALLATION_ID})
     .then(({data}) => {
         github.authenticate({type: 'token', token: data.token});
-        return github.checks.create({
-            owner: 'mapbox',
-            repo: 'mapbox-gl-native',
-            name: `Size - ${label}`,
-            head_branch: process.env['CIRCLE_BRANCH'],
-            head_sha: process.env['CIRCLE_SHA1'],
-            status: 'completed',
-            conclusion: 'success',
-            completed_at: new Date().toISOString(),
-            output: {
-                title: prettyBytes(size),
-                summary: `\`${file}\` is ${size} bytes (${prettyBytes(size)})`
-            }
-        });
+        getPriorSize().then(prior => {
+            const title = (() => {
+                if (prior) {
+                    const change = size - prior;
+                    const percent = (change / prior) * 100;
+                    return `${change >= 0 ? '+' : ''}${prettyBytes(change)} ${percent.toFixed(3)}% (${prettyBytes(size)})`;
+                } else {
+                    return prettyBytes(size);
+                }
+            })();
+
+            return github.checks.create({
+                owner: 'mapbox',
+                repo: 'mapbox-gl-native',
+                name: `Size - ${label}`,
+                head_branch: process.env['CIRCLE_BRANCH'],
+                head_sha: process.env['CIRCLE_SHA1'],
+                status: 'completed',
+                conclusion: 'success',
+                completed_at: new Date().toISOString(),
+                output: {
+                    title,
+                    summary: `\`${file}\` is ${size} bytes (${prettyBytes(size)})`
+                }
+            });
+        })
     });