Add a tree shaking test that involves the use of Flow types

test/e2e/tree-shaking-flow/fixture/.fusionrc.js

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+module.exports = {
+  assumeNoImportSideEffects: true
+};

test/e2e/tree-shaking-flow/fixture/.gitignore

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+!node_modules
+.fusion_babel_cache/

test/e2e/tree-shaking-flow/fixture/src/main.js

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+// @flow
+
+/* Includes type imports from both node_modules and userland but as
+ * standalone type imports and mixed imports:
+ *    import type {AType, BType} from ...
+ *    import {type AType, type BType, C, D} from ...
+ */
+
+// Import only types from dependency
+import type {
+  UnusedDependencyType,
+  UsedDependencyType,
+} from 'fixture-pkg';
+
+// Import mixed types and values from dependency
+import {
+  type UnusedDependencyOtherType,
+  type UsedDependencyOtherType,
+  unusedDependencyValue,
+  usedDependencyValue
+} from 'fixture-pkg';
+
+// Import only types from userland
+import type {
+  UnusedUserlandType,
+  UsedUserlandType
+} from './user-code.js';
+
+// Import mixed types and values from userland
+import {
+  type UnusedUserlandOtherType,
+  type UsedUserlandOtherType,
+  unusedUserlandValue,
+  usedUserlandValue
+} from './user-code.js';
+
+if (__NODE__) {
+  // unused in the browser
+  //  - node modules
+  const unusedDepVal: UnusedDependencyType = { shouldBeUnused: unusedDependencyValue };
+  const unusedDepVal2: UnusedDependencyOtherType = { alsoShouldBeUnused: unusedDependencyValue };
+  //  - userland
+  const unustedUserlandVal: UnusedUserlandType = { shouldBeUnused: unusedUserlandValue };
+  const unustedUserlandVal2: UnusedUserlandOtherType = { alsoShouldBeUnused: unusedUserlandValue };
+
+  console.log(unusedDepVal, unusedDepVal2, unustedUserlandVal, unustedUserlandVal2);
+}
+
+// used in the browser
+//  - node modules
+const usedDepVal: UsedDependencyType = { shouldBeUsed: usedDependencyValue};
+const usedDepVal2: UsedDependencyOtherType = { alsoShouldBeUsed: usedDependencyValue};;
+//  - userland
+const usedUserlandVal: UsedUserlandType = { shouldBeUsed: usedUserlandValue};
+const usedUserlandVal2: UsedUserlandOtherType = { alsoShouldBeUsed: usedUserlandValue};;
+
+console.log(usedDepVal, usedDepVal2, usedUserlandVal, usedUserlandVal2);
+
+export default () => {};

test/e2e/tree-shaking-flow/fixture/src/unused2.js

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+// @flow
+export type UnusedUserlandType = {| shouldBeUnused: string |};
+export type UnusedUserlandOtherType = {| alsoShouldBeUnused: string |};
+
+export const unusedUserlandValue = '__FIXTURE_USERLAND_UNUSED__';

test/e2e/tree-shaking-flow/fixture/src/used2.js

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+// @flow
+export type UsedUserlandType = {| shouldBeUsed: string |};
+export type UsedUserlandOtherType = {| alsoShouldBeUsed: string |};
+
+export const usedUserlandValue = '__FIXTURE_USERLAND_USED__';

test/e2e/tree-shaking-flow/fixture/src/user-code.js

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+// @flow
+export * from './used2.js';
+export * from './unused2.js';

test/e2e/tree-shaking-flow/test.js

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+// @flow
+/* eslint-env node */
+
+const t = require('assert');
+const path = require('path');
+const fs = require('fs');
+const {promisify} = require('util');
+
+const readdir = promisify(fs.readdir);
+
+const dir = path.resolve(__dirname, './fixture');
+
+const {cmd} = require('../utils.js');
+
+test('`fusion build` strips unused types in dev and correctly tree shakes remaining imports w/ assumeNoImportSideEffects: true', async () => {
+  await cmd(`build --dir=${dir}`);
+
+  const distFolder = path.resolve(dir, '.fusion/dist/development/client');
+  const clientFiles = await readdir(distFolder);
+
+  clientFiles
+    .filter(file => path.extname(file) === '.js')
+    .map(file => path.join(distFolder, file))
+    .forEach(file => {
+      const unusedChecks = [
+        // userland
+        'UnusedUserlandType',
+        'UnusedUserlandOtherType',
+        '__FIXTURE_USERLAND_UNUSED__',
+        // node modules
+        'UnusedDependencyType',
+        'UnusedDependencyOtherType',
+        '__FIXTURE_DEPENDENCY_UNUSED__',
+      ];
+
+      unusedChecks.forEach(name => {
+        t.ok(
+          !fs.readFileSync(file, 'utf-8').includes(name),
+          `should not include unused export in browser: ${name}`
+        );
+      });
+    });
+}, 100000);