[core] add prettier to CircleCI

A file can be formatted without knowledge about other files.
For this reason we only check the format for files which were
changed compared to master. A broken format that was merged into
master will not be picked up by CI until the file was changed
again. This can be a good thing since this will not trigger CI
errors in unrelated builds and since we are only talking about
code style this a manageable tradeoff especially because formatting
can be very expensive.

Author: eps1lon

.circleci/config.yml

@@ -42,6 +42,21 @@ jobs:
     <<: *defaults
     steps:
       - *restore_repo
+      - run:
+          name: Check if yarn prettier was run
+          command: |
+            # Files changed on this branch
+            CHANGED_FILES=$(git diff --name-only master...)
+            # Files that should have been formatted while working on this branch
+            FORMATTED_FILES=$(yarn --silent prettier:files | grep "$CHANGED_FILES")
+            # if we run prettier unconditionally prettier will exit with non-zero
+            # because no file path was given
+            if [ $FORMATTED_FILES ]; then
+              echo "changes, let's check if they are formatted"
+              yarn prettier:ci "$FORMATTED_FILES"
+            else
+              echo "no changes"
+            fi
       - run:
           name: Lint
           command: yarn lint

package.json

@@ -34,7 +34,10 @@
     "docs:deploy": "git push material-ui-docs master:latest",
     "lint": "eslint . --cache && echo \"eslint: no lint errors\"",
     "lint:fix": "eslint . --cache --fix && echo \"eslint: no lint errors\"",
-    "prettier": "find . -name \"*.js\" -o -name \"*.d.ts\" -o -name \"*.tsx\" | grep -v -f .eslintignore | xargs prettier --write",
+    "prettier": "yarn --silent prettier:files | xargs prettier --write",
+    "prettier:files": "find . -name \"*.js\" -o -name \"*.d.ts\" -o -name \"*.tsx\" | grep -v -f .eslintignore",
+    "prettier:check": "yarn --silent prettier:files | xargs prettier --list-different",
+    "prettier:ci": "prettier --list-different",
     "size": "size-limit",
     "size:why": "size-limit --why packages/material-ui/build/index.js",
     "size:overhead:why": "size-limit --why ./test/size/overhead.js",