fix(shaker): shaker doesn't treat exports as variable references (fixes #1008)

.changeset/empty-papayas-attack.md

@@ -0,0 +1,6 @@
+---
+'@linaria/shaker': patch
+'@linaria/utils': patch
+---
+
+In some cases, the shaker mistakenly removed assignment expressions. Fixes #1008.

packages/shaker/package.json

@@ -58,6 +58,7 @@
     "build:declarations": "tsc --emitDeclarationOnly --outDir types",
     "build:esm": "babel src --out-dir esm --extensions '.js,.jsx,.ts,.tsx' --source-maps --delete-dir-on-start",
     "build:lib": "cross-env NODE_ENV=legacy babel src --out-dir lib --extensions '.js,.jsx,.ts,.tsx' --source-maps --delete-dir-on-start",
+    "test": "jest --config ./jest.config.js --rootDir src",
     "typecheck": "tsc --noEmit --composite false",
     "watch": "npm run build --watch"
   },

packages/shaker/src/plugins/__tests__/__snapshots__/shaker-plugin.test.ts.snap

@@ -1,5 +1,12 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`shaker should keep assigment even if export is marked for removing 1`] = `
+"let _a;
+
+exports.a = _a = {};
+exports.b = _a;"
+`;
+
 exports[`shaker should keep referenced exports 1`] = `
 "var _foo;
 
@@ -46,4 +53,11 @@ export { a };"
 
 exports[`shaker should remove unused export 1`] = `"export const a = 1;"`;
 
+exports[`shaker should respect implicit references 1`] = `
+"let _a;
+
+exports.a = _a = {};
+exports.b = _a;"
+`;
+
 exports[`shaker should throw out unused referenced exports 1`] = `"exports.defaultValue = 20;"`;

packages/shaker/src/plugins/__tests__/shaker-plugin.test.ts

@@ -139,4 +139,26 @@ describe('shaker', () => {
     expect(code).toMatchSnapshot();
     expect(metadata.imports.size).toBe(0);
   });
+
+  it('should respect implicit references', () => {
+    const { code, metadata } = keep(['a'])`
+      let _a;
+      exports.a = _a = {};
+      exports.b = _a;
+    `;
+
+    expect(code).toMatchSnapshot();
+    expect(metadata.imports.size).toBe(0);
+  });
+
+  it('should keep assigment even if export is marked for removing', () => {
+    const { code, metadata } = keep(['b'])`
+      let _a;
+      exports.a = _a = {};
+      exports.b = _a;
+    `;
+
+    expect(code).toMatchSnapshot();
+    expect(metadata.imports.size).toBe(0);
+  });
 });

packages/shaker/src/plugins/shaker-plugin.ts

@@ -57,6 +57,13 @@ function getBindingForExport(exportPath: NodePath): Binding | undefined {
     }
   }
 
+  if (exportPath.isAssignmentExpression()) {
+    const left = exportPath.get('left');
+    if (left.isIdentifier()) {
+      return exportPath.scope.getBinding(left.node.name);
+    }
+  }
+
   return undefined;
 }
 
@@ -157,6 +164,17 @@ export default function shakerPlugin(
         collected.exports
       );
 
+      collected.exports.forEach(({ local }) => {
+        if (local.isAssignmentExpression()) {
+          const left = local.get('left');
+          if (left.isIdentifier()) {
+            // For some reason babel does not mark id in AssignmentExpression as a reference
+            // So we need to do it manually
+            reference(left, left, true);
+          }
+        }
+      });
+
       if (
         onlyExports.length === 1 &&
         onlyExports[0] === '__linariaPreval' &&

packages/utils/src/scopeHelpers.ts

@@ -19,14 +19,15 @@ function getBinding(path: NodePath<Identifier | JSXIdentifier>) {
 
 export function reference(
   path: NodePath<Identifier | JSXIdentifier>,
-  referencePath?: NodePath
+  referencePath: NodePath = path,
+  force = false
 ): void {
-  if (!path.isReferencedIdentifier()) return;
+  if (!force && !path.isReferencedIdentifier()) return;
 
   const binding = getBinding(path);
   if (!binding) return;
 
-  if (binding.referencePaths.includes(referencePath ?? path)) {
+  if (binding.referencePaths.includes(referencePath)) {
     return;
   }
 
@@ -55,8 +56,6 @@ function isReferenced(binding: Binding) {
 export function dereference(
   path: NodePath<Identifier | JSXIdentifier>
 ): Binding | null {
-  if (!path.isReferencedIdentifier()) return null;
-
   const binding = getBinding(path);
   if (!binding) return null;