fix(shaker): use the last export statement instead of the 1st (#804)

packages/babel/__tests__/evaluators/__snapshots__/shaker.test.ts.snap

@@ -65,6 +65,18 @@ color.green = '#0f0';
 exports.__linariaPreval = [color];"
 `;
 
+exports[`keeps only the last assignment of each exported variable 1`] = `
+"\\"use strict\\";
+
+var bar = function bar() {
+  return 'hello world';
+};
+
+exports.bar = bar;
+var foo = exports.bar();
+exports.__linariaPreval = [foo];"
+`;
+
 exports[`keeps reused exports 1`] = `
 "\\"use strict\\";
 

packages/babel/__tests__/evaluators/shaker.test.ts

@@ -241,3 +241,19 @@ it('keeps reused exports', () => {
 
   expect(shaken).toMatchSnapshot();
 });
+
+it('keeps only the last assignment of each exported variable', () => {
+  const [shaken] = _shake()`
+    const bar = function() {
+      return 'hello world';
+    };
+
+    exports.bar = "bar";
+    exports.bar = bar;
+
+    const foo = exports.bar();
+    exports.__linariaPreval = [foo];
+  `;
+
+  expect(shaken).toMatchSnapshot();
+});

packages/shaker/src/scope.ts

@@ -112,9 +112,10 @@ export default class ScopeManager {
       const name = getExportName(memberExp);
       if (!this.global.has(name)) {
         this.global.set(name, new Set());
-        this.declarations.set(getId(this.global, name), memberExp);
       }
 
+      // There can be a few `export.foo = …` statements, but we need only the last one
+      this.declarations.set(getId(this.global, name), memberExp);
       this.global.get(name)!.add(memberExp);
       return;
     }