ci: Vendor yarn into our repo (#28839)

This avoids a dynamic dependency on fetching a package from the internet in our CI.
We have observed that this is not 100% reliable.

PR Close #28839

.circleci/config.yml

@@ -28,14 +28,15 @@ var_2: &browsers_docker_image circleci/node:10.12-browsers
 # See https://circleci.com/docs/2.0/caching/#restoring-cache for how prefixes work in CircleCI.
 var_3: &cache_key v2-angular-node-10.12-{{ checksum "yarn.lock" }}-{{ checksum "WORKSPACE" }}-{{ checksum "packages/bazel/package.bzl" }}
 
-# Initializes the CI environment by setting up common environment variables and
-# downloading Yarn. Yarn is used by most jobs and therefore is part of this anchor.
+# Initializes the CI environment by setting up common environment variables.
 var_4: &init_environment
   run:
-    name: Initializing environment (setting up variables, downloading Yarn)
+    name: Initializing environment (setting up variables, removing Yarn)
+    # Remove the yarn installed in the docker container; we want our own version
     command: |
+      sudo rm /usr/local/bin/yarn
       source ./.circleci/env.sh
-      curl -o- -L https://yarnpkg.com/install.sh | PROFILE=$BASH_ENV bash -s -- --version "$CI_YARN_VERSION"
+      echo "Yarn version: $(yarn --version)"
 
 var_5: &setup_bazel_remote_execution
   run:
@@ -97,7 +98,9 @@ jobs:
       - run: 'yarn bazel:lint ||
               (echo -e "\n.bzl files have lint errors. Please run ''yarn bazel:lint-fix''"; exit 1)'
 
-      - run: ./node_modules/.bin/gulp lint
+      # Use `yarn gulp ...` (instead of `node_modules/.bin/gulp ...`) to ensure that yarn
+      # (which is an exported bash function) will be available to processes spawned by gulp.
+      - run: yarn gulp lint
 
   test:
     <<: *job_defaults

.circleci/env.sh

@@ -32,7 +32,6 @@ setPublicVar CI_COMMIT_RANGE "`[[ ${CIRCLE_PR_NUMBER:-false} != false ]] && echo
 setPublicVar CI_PULL_REQUEST "${CIRCLE_PR_NUMBER:-false}";
 setPublicVar CI_REPO_NAME "$CIRCLE_PROJECT_REPONAME";
 setPublicVar CI_REPO_OWNER "$CIRCLE_PROJECT_USERNAME";
-setPublicVar CI_YARN_VERSION "1.13.0";
 
 
 ####################################################################################################
@@ -63,5 +62,12 @@ setPublicVar SAUCE_TUNNEL_IDENTIFIER "angular-${CIRCLE_BUILD_NUM}-${CIRCLE_NODE_
 setPublicVar SAUCE_READY_FILE_TIMEOUT 120
 
 
+####################################################################################################
+# Define our own yarn command for CircleCI.
+####################################################################################################
+echo "function yarn () { /usr/bin/env node $projectDir/third_party/github.com/yarnpkg/yarn/releases/yarn-1.13.0.js \"\$@\"; }" >> $BASH_ENV;
+echo "export -f yarn;" >> $BASH_ENV;
+
+
 # Source `$BASH_ENV` to make the variables available immediately.
 source $BASH_ENV;

third_party/github.com/yarnpkg/yarn/releases/BUILD.bazel

@@ -0,0 +1,2 @@
+# Fetched from https://github.com/yarnpkg/yarn/releases/download/v1.13.0/yarn-1.13.0.js
+licenses(["notice"])

third_party/github.com/yarnpkg/yarn/releases/LICENSE

@@ -0,0 +1,26 @@
+BSD 2-Clause License
+
+For Yarn software
+
+Copyright (c) 2016-present, Yarn Contributors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+ * Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+ * Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.