🚀 Transform Function Declarations

build-system/babel-plugins/babel-plugin-transform-function-declarations/index.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const BAIL_OUT_CONDITIONS = {
+  // If this isn't a FunctionDeclaration, bail out on modification.
+  isNotFunction: (t, path) => !t.isFunctionDeclaration(path.node),
+
+  // If this FunctionDeclaration is a Generator, bail out on modification.
+  isGenerator: (t, path) => path.node.generator,
+
+  // If this FunctionDeclaration doesn't have a single return statement, bail out on modification
+  isNotSingleReturnStatment: (t, path) => {
+    if (!path.get('body').isBlockStatement()) {
+      return false;
+    }
+    const body = path.get('body.body.0');
+    return !body || !body.isReturnStatement();
+  },
+
+  // Since we don't know if exported members are 'new'd, bail out on modification.
+  isExported: (t, path) =>
+    path.findParent(
+      path =>
+        path.isExportNamedDeclaration() || path.isExportDefaultDeclaration()
+    ),
+
+  // If the function contains usage of `arguments`, bail out on modification.
+  containsArgumentsUsage: (t, path) => {
+    let containsArgumentsUsage = false;
+    path.traverse({
+      Identifier(path) {
+        if (t.isIdentifier(path.node, {name: 'arguments'})) {
+          containsArgumentsUsage = true;
+          path.stop();
+        }
+      },
+    });
+    return containsArgumentsUsage;
+  },
+
+  // If the function contains a ThisExpression, converting from a FunctionDeclaration to a
+  // VariableDeclaration => VariableDeclarator => ArrowFunctionExpression isn't necessarily valid.
+  // Bail out on modification.
+  containsThisExpression: (t, path) => {
+    let containsThis = false;
+    path.traverse({
+      ThisExpression() {
+        containsThis = true;
+        path.stop();
+      },
+    });
+    return containsThis;
+  },
+
+  // If the FunctionDeclaration identifier is newed in the scope of this program, bail out on modification.
+  isNewedInProgramScope: (t, path) => {
+    const {name} = path.get('id').node;
+    let isNewed = false;
+    path
+      .findParent(path => path.isProgram())
+      .traverse({
+        NewExpression(path) {
+          if (t.isIdentifier(path.node.callee, {name})) {
+            isNewed = true;
+            path.stop();
+          }
+        },
+      });
+    return isNewed;
+  },
+};
+
+function createVariableDeclaration(t, path) {
+  const {params, body, async, id} = t.cloneNode(path.node);
+  const arrowFunction = t.arrowFunctionExpression(
+    params,
+    body.body[0].argument,
+    async
+  );
+  const declarations = t.variableDeclarator(
+    t.identifier(id.name),
+    arrowFunction
+  );
+
+  // Making an existing FunctionDeclaration a const VariableDeclaration is safe.
+  // The name was already reserved for the FunctionDeclaration.
+  return t.variableDeclaration('const', [declarations]);
+}
+
+// Attempt to convert simple single ReturnStatement FunctionDeclarations to ArrowFunctionExpressions.
+// See BAIL_OUT_CONDITIONS for reasons why FunctionDeclarations would not be modified.
+module.exports = function({types: t}) {
+  const DEBUG = false;
+  const REPORT = true;
+
+  return {
+    name: 'safe-arrows',
+    pre() {
+      this.bailoutCount = Object.assign({}, BAIL_OUT_CONDITIONS);
+      Object.keys(this.bailoutCount).forEach(
+        key => (this.bailoutCount[key] = [])
+      );
+      this.successCount = [];
+    },
+    visitor: {
+      FunctionDeclaration(path) {
+        const name = (path.get('id') && path.get('id').node.name) || '';
+        for (const [id, method] of Object.entries(BAIL_OUT_CONDITIONS)) {
+          if (method(t, path)) {
+            this.bailoutCount[id].push(name);
+            if (DEBUG) {
+              console /*OK*/
+                .log(
+                  `Bail on ${
+                    name !== '' ? `function ${name}:` : 'item:'
+                  } Reason ${id}.`
+                );
+            }
+            return;
+          }
+        }
+        this.successCount.push(name);
+        if (DEBUG) {
+          console /*OK*/
+            .log(`Success for function ${path.get('id').node.name}.`);
+        }
+        path.replaceWith(createVariableDeclaration(t, path));
+      },
+    },
+    post() {
+      if (REPORT) {
+        console.log(`Success Count: ${this.successCount.length}`);
+        console.log('Bail Out Reason Counts');
+        Object.keys(this.bailoutCount).forEach(name =>
+          console.log(`${name}: ${this.bailoutCount[name].length}`)
+        );
+        console.log('\n');
+      }
+    },
+  };
+};

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/arguments-identifier/input.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+function argumentsUsage() {
+  return arguments[0] + arguments[1];
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/arguments-identifier/options.json

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+{
+  "plugins": ["../../../../../babel-plugin-transform-function-declarations"]
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/arguments-identifier/output.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+function argumentsUsage() {
+  return arguments[0] + arguments[1];
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/async-function/input.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+async function test(a, b) {
+  return a + b;
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/async-function/options.json

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+{
+  "plugins": ["../../../../../babel-plugin-transform-function-declarations"]
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/async-function/output.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const test = async (a, b) => a + b;

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/class-function-declaration-in-public-method/input.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+class Foo {
+  foo() {
+    function testInFooClass() {
+      return '';
+    }
+  }
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/class-function-declaration-in-public-method/options.json

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+{
+  "plugins": ["../../../../../babel-plugin-transform-function-declarations"]
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/class-function-declaration-in-public-method/output.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+class Foo {
+  foo() {
+    const testInFooClass = () => '';
+  }
+
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/existing-arrow-function/input.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const thing = (a, b) => a + b;

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/existing-arrow-function/options.json

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+{
+  "plugins": ["../../../../../babel-plugin-transform-function-declarations"]
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/existing-arrow-function/output.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const thing = (a, b) => a + b;

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/existing-async-arrow-function/input.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const thing = async (a, b) => a + b;

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/existing-async-arrow-function/options.json

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+{
+  "plugins": ["../../../../../babel-plugin-transform-function-declarations"]
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/existing-async-arrow-function/output.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const thing = async (a, b) => a + b;

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/export-default-named-declaration/input.js

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+/**
+ * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+export default function exportedFunctionDefault(a, b) {
+  return a + b;
+}

build-system/babel-plugins/babel-plugin-transform-function-declarations/test/fixtures/transform-assertions/export-default-named-declaration/options.json

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+{
+  "plugins": ["../../../../../babel-plugin-transform-function-declarations"],
+  "sourceType": "module"
+}