Write size info to separate file per bundle

`bundle-sizes.json` contains the combined size information for every
build. This makes it easier to store and process, but it prevents us
from parallelizing the build script, because each process would need to
write to the same file.

So I've updated the Rollup script to output individual files per build.
A downstream CI job consolidates them into a single file.

I have not parallelized the Rollup script yet. I'll do that next.

.circleci/config.yml

@@ -125,15 +125,6 @@ jobs:
       - run: ./scripts/circleci/add_build_info_json.sh
       - run: ./scripts/circleci/update_package_versions.sh
       - run: ./scripts/circleci/build.sh
-      - run: cp ./scripts/rollup/results.json ./build/bundle-sizes.json
-      - run: ./scripts/circleci/upload_build.sh
-      - run: ./scripts/circleci/pack_and_store_artifact.sh
-      - store_artifacts:
-          path: ./node_modules.tgz
-      - store_artifacts:
-          path: ./build.tgz
-      - store_artifacts:
-          path: ./build/bundle-sizes.json
       - store_artifacts:
           path: ./scripts/error-codes/codes.json
       - persist_to_workspace:
@@ -142,18 +133,26 @@ jobs:
             - facebook-www
             - node_modules
             - react-native
-            - bundle-sizes.json
+            - sizes/*.json
 
-  sizebot:
-    build:
+  process_artifacts:
     docker: *docker
     environment: *environment
     steps:
       - checkout
       - attach_workspace: *attach_workspace
       - *restore_yarn_cache
       - *run_yarn
+      - run: node ./scripts/rollup/consolidateBundleSizes.js
       - run: node ./scripts/tasks/danger
+      - run: ./scripts/circleci/upload_build.sh
+      - run: ./scripts/circleci/pack_and_store_artifact.sh
+      - store_artifacts:
+          path: ./node_modules.tgz
+      - store_artifacts:
+          path: ./build.tgz
+      - store_artifacts:
+          path: ./build/bundle-sizes.json
 
   test_build:
     docker: *docker
@@ -204,12 +203,12 @@ workflows:
       - build:
           requires:
             - setup
-      - sizebot:
+      - process_artifacts:
           requires:
             - build
       - test_build:
           requires:
-            - build
+            - process_artifacts
       - test_build_prod:
           requires:
-            - build
+            - process_artifacts

.gitignore

@@ -1,7 +1,6 @@
 .DS_STORE
 node_modules
 scripts/flow/*/.flowconfig
-scripts/rollup/results.json
 *~
 *.pyc
 .grunt

scripts/circleci/upload_build.sh

@@ -10,7 +10,7 @@ if [ -z "$CI_PULL_REQUEST" ] && [ -n "$BUILD_SERVER_ENDPOINT" ]; then
     -F "react-dom.production.min=@build/dist/react-dom.production.min.js" \
     -F "react-dom-server.browser.development=@build/dist/react-dom-server.browser.development.js" \
     -F "react-dom-server.browser.production.min=@build/dist/react-dom-server.browser.production.min.js" \
-    -F "results.json=@build/../scripts/rollup/results.json" \
+    -F "results.json=@build/../build/bundle-sizes.json" \
     -F "commit=$CIRCLE_SHA1" \
     -F "date=$(git log --format='%ct' -1)" \
     -F "pull_request=false" \

scripts/rollup/consolidateBundleSizes.js

@@ -0,0 +1,25 @@
+'use strict';
+
+// Script that combines bundle size information for each build into a single
+// JSON file for easier storage and processing.
+
+const fs = require('fs');
+const path = require('path');
+
+const BUILD_DIR = path.join(__dirname, '../../build');
+
+const filenames = fs.readdirSync(path.join(BUILD_DIR, 'sizes'));
+
+let bundleSizes = [];
+for (let i = 0; i < filenames.length; i++) {
+  const filename = filenames[i];
+  if (filename.endsWith('.size.json')) {
+    const json = fs.readFileSync(path.join(BUILD_DIR, 'sizes', filename));
+    bundleSizes.push(JSON.parse(json));
+  }
+}
+
+const outputFilename = path.join(BUILD_DIR, 'bundle-sizes.json');
+const outputContents = JSON.stringify({bundleSizes}, null, 2);
+
+fs.writeFileSync(outputFilename, outputContents);

scripts/rollup/stats.js

@@ -5,21 +5,35 @@ const filesize = require('filesize');
 const chalk = require('chalk');
 const join = require('path').join;
 const fs = require('fs');
-const prevBuildResults = fs.existsSync(__dirname + '/results.json')
-  ? require('./results.json')
+const mkdirp = require('mkdirp');
+
+const BUNDLE_SIZES_FILE_NAME = join(__dirname, '../../build/bundle-sizes.json');
+const prevBuildResults = fs.existsSync(BUNDLE_SIZES_FILE_NAME)
+  ? require(BUNDLE_SIZES_FILE_NAME)
   : {bundleSizes: []};
 
 const currentBuildResults = {
   // Mutated inside build.js during a build run.
-  // We make a copy so that partial rebuilds don't erase other stats.
-  bundleSizes: [...prevBuildResults.bundleSizes],
+  bundleSizes: [],
 };
 
 function saveResults() {
+  // Write all the bundle sizes to a single JSON file.
   fs.writeFileSync(
-    join('scripts', 'rollup', 'results.json'),
+    BUNDLE_SIZES_FILE_NAME,
     JSON.stringify(currentBuildResults, null, 2)
   );
+
+  // Also write each bundle size to a separate file. That way multiple build
+  // processes can run in parallel and generate separate size artifacts.
+  // A downstream job can combine them into a single JSON file.
+  mkdirp.sync('build/sizes');
+  currentBuildResults.bundleSizes.forEach(results => {
+    fs.writeFileSync(
+      join('build', 'sizes', `${results.filename}.size.json`),
+      JSON.stringify(results, null, 2)
+    );
+  });
 }
 
 function fractionalChange(prev, current) {