provision: Do not require that no other yarn precedes us in $PATH.

`check_version` in `install-yarn` had the rather careful check that
the yarn it installed into `/usr/bin/yarn` was the yarn which was
first in the user's `$PATH`.  This caused problems when the user had a
pre-existing `/usr/local/bin/yarn`; however, those problems are
limited to the `install-yarn` script itself, since the nearly all
calls to yarn from Zulip's code already hardcode the `/srv/zulip-yarn`
location, and do not depend on what is in `$PATH`.

Remove the checks in `install-yarn` that depend on the local `$PATH`,
and stop installing our `yarn` into it.  We also adjust the two
callsites which did not specify the full path to `yarn`, so use
`/srv/zulip-yarn`.

Fixes: #23993

Co-authored-by: Alex Vandiver <alexmv@zulip.com>

scripts/lib/install-yarn

@@ -8,9 +8,7 @@ tarball="yarn-$version.tgz"
 check_version() {
     # Reading the version of Yarn from its package.json is much faster
     # than running yarn --version.
-    link="$(command -v yarn)" \
-        && [ "$link" -ef /srv/zulip-yarn/bin/yarn ] \
-        && current_version="$(jq -r '.version' /srv/zulip-yarn/package.json)" \
+    current_version="$(jq -r '.version' /srv/zulip-yarn/package.json)" \
         && [ "$current_version" = "$version" ]
 }
 
@@ -23,6 +21,5 @@ if ! check_version; then
     rm -rf /srv/zulip-yarn
     mkdir /srv/zulip-yarn
     tar -xzf "$tarball" --no-same-owner --strip-components=1 -C /srv/zulip-yarn
-    ln -nsf /srv/zulip-yarn/bin/yarn /usr/bin/yarn
     check_version
 fi

tools/ci/production-build

@@ -44,8 +44,10 @@ cp -a \
     /tmp/production-build
 
 # Check that webpack bundles use only ES2019 syntax.
+# Use the yarn binary installed by tools/provision.
+YARN="/srv/zulip-yarn/bin/yarn"
 tar -C /tmp -xzf /tmp/production-build/zulip-server-test.tar.gz zulip-server-test/prod-static/serve/webpack-bundles
 (
     GLOBIGNORE=/tmp/zulip-server-test/prod-static/serve/webpack-bundles/katex-cli.js
-    yarn run es-check es2019 /tmp/zulip-server-test/prod-static/serve/webpack-bundles/*.js
+    $YARN run es-check es2019 /tmp/zulip-server-test/prod-static/serve/webpack-bundles/*.js
 )

tools/setup/optimize-svg

@@ -42,6 +42,7 @@ if [ "$#" -gt 0 ]; then
 fi
 
 ZULIP_PATH="$(readlink -f "$(dirname "$0")"/../..)"
+YARN="/srv/zulip-yarn/bin/yarn"
 
 if [ -n "$CHECK_UNOPTIMIZED" ]; then
     if [ "$(node_modules/.bin/svgo -f static/images/integrations/logos | grep -o '\.[0-9]% = ' | wc -l)" -ge 1 ]; then
@@ -52,6 +53,6 @@ if [ -n "$CHECK_UNOPTIMIZED" ]; then
         echo "SUCCESS: SVG files in static/images/integrations/logos are all optimized!"
     fi
 else
-    yarn run svgo -q -f static/images/integrations/logos
+    $YARN run svgo -q -f static/images/integrations/logos
     "$ZULIP_PATH"/tools/setup/generate_integration_bots_avatars.py
 fi