Add yarn-plugin-conditions to update Babel 8 dependencies (#12659)

* Add `yarn-plugin-conditions` to update Babel 8 dependencies

https://github.com/nicolo-ribaudo/yarn-plugin-conditions

* Update .gitattributes

.gitattributes

@@ -1 +1,2 @@
 * text eol=lf
+/.yarn/** linguist-vendored

.yarnrc.yml

@@ -7,6 +7,8 @@ nodeLinker: node-modules
 plugins:
   - path: .yarn/plugins/@yarnpkg/plugin-babel-release-tool.cjs
     spec: "https://raw.githubusercontent.com/nicolo-ribaudo/yarn-plugin-babel-release-tool/main/bundles/%40yarnpkg/plugin-babel-release-tool.js"
+  - path: .yarn/plugins/@yarnpkg/plugin-conditions.cjs
+    spec: "https://raw.githubusercontent.com/nicolo-ribaudo/yarn-plugin-conditions/main/bundles/%40yarnpkg/plugin-conditions.js"
 
 releaseTool:
   ignoreChanges:
@@ -16,11 +18,17 @@ releaseTool:
     - "**/test/**"
     - codemods/**
     - "@(!(native-modules|built-ins|plugins|package)).json"
-
   implicitDependencies:
-    "@babel/runtime": ["@babel/helpers"]
-    "@babel/runtime-corejs2": ["@babel/helpers"]
-    "@babel/runtime-corejs3": ["@babel/helpers"]
+    "@babel/runtime":
+      - "@babel/helpers"
+    "@babel/runtime-corejs2":
+      - "@babel/helpers"
+    "@babel/runtime-corejs3":
+      - "@babel/helpers"
+
+conditions:
+  BABEL_8_BREAKING:
+    default: false
 
 unsafeHttpWhitelist:
   - localhost

babel.config.js

@@ -293,6 +293,16 @@ function pluginToggleBabel8Breaking({ types: t }, { breaking }) {
           keepConsequent = !keepConsequent;
         }
 
+        // yarn-plugin-conditions inject bool(process.env.BABEL_8_BREAKING)
+        // tests, to properly cast the env variable to a boolean.
+        if (
+          test.isCallExpression() &&
+          test.get("callee").isIdentifier({ name: "bool" }) &&
+          test.get("arguments").length === 1
+        ) {
+          test = test.get("arguments")[0];
+        }
+
         if (!test.matchesPattern("process.env.BABEL_8_BREAKING")) return;
 
         path.replaceWith(