fix(ivy): i18n - support lazy-load template string helpers (#33097)

There are numerous approaches to downlevelling backticked
template strings to ES5.
This commit handles yet another one that Babel applies.

PR Close #33097

packages/localize/src/tools/src/translate/source_files/source_file_utils.ts

@@ -79,21 +79,29 @@ export function unwrapMessagePartsFromLocalizeCall(call: NodePath<t.CallExpressi
     }
   }
 
-  // Check for `__makeTemplateObject(cooked, raw)` call
+  // Check for `__makeTemplateObject(cooked, raw)` or `__templateObject()` calls.
   if (cooked.isCallExpression()) {
-    const arg2 = cooked.get('arguments')[1];
-    if (!arg2.isExpression()) {
-      throw new BabelParseError(
-          arg2.node,
-          'Unexpected `raw` argument to the "makeTemplateObject()" function (expected an expression).');
+    let call = cooked;
+    if (call.get('arguments').length === 0) {
+      // No arguments so perhaps it is a `__templateObject()` call.
+      // Unwrap this to get the `_taggedTemplateLiteral(cooked, raw)` call.
+      call = unwrapLazyLoadHelperCall(call);
     }
-    raw = arg2;
-    cooked = cooked.get('arguments')[0];
+
+    cooked = call.get('arguments')[0];
     if (!cooked.isExpression()) {
       throw new BabelParseError(
           cooked.node,
           'Unexpected `cooked` argument to the "makeTemplateObject()" function (expected an expression).');
     }
+    const arg2 = call.get('arguments')[1];
+    if (arg2 && !arg2.isExpression()) {
+      throw new BabelParseError(
+          arg2.node,
+          'Unexpected `raw` argument to the "makeTemplateObject()" function (expected an expression).');
+    }
+    // If there is no second argument then assume that raw and cooked are the same
+    raw = arg2 !== undefined ? arg2 : cooked;
   }
 
   const cookedStrings = unwrapStringLiteralArray(cooked.node);
@@ -153,6 +161,93 @@ export function unwrapStringLiteralArray(array: t.Expression): string[] {
   return array.elements.map((str: t.StringLiteral) => str.value);
 }
 
+/**
+ * This expression is believed to be a call to a "lazy-load" template object helper function.
+ * This is expected to be of the form:
+ *
+ * ```ts
+ *  function _templateObject() {
+ *    var e = _taggedTemplateLiteral(['cooked string', 'raw string']);
+ *    return _templateObject = function() { return e }, e
+ *  }
+ * ```
+ *
+ * We unwrap this to return the call to `_taggedTemplateLiteral()`.
+ *
+ * @param call the call expression to unwrap
+ * @returns the  call expression
+ */
+export function unwrapLazyLoadHelperCall(call: NodePath<t.CallExpression>):
+    NodePath<t.CallExpression> {
+  const callee = call.get('callee');
+  if (!callee.isIdentifier()) {
+    throw new BabelParseError(
+        callee.node,
+        'Unexpected lazy-load helper call (expected a call of the form `_templateObject()`).');
+  }
+  const lazyLoadBinding = call.scope.getBinding(callee.node.name);
+  if (!lazyLoadBinding) {
+    throw new BabelParseError(callee.node, 'Missing declaration for lazy-load helper function');
+  }
+  const lazyLoadFn = lazyLoadBinding.path;
+  if (!lazyLoadFn.isFunctionDeclaration()) {
+    throw new BabelParseError(
+        lazyLoadFn.node, 'Unexpected expression (expected a function declaration');
+  }
+  const returnedNode = getReturnedExpression(lazyLoadFn);
+
+  if (returnedNode.isCallExpression()) {
+    return returnedNode;
+  }
+
+  if (returnedNode.isIdentifier()) {
+    const identifierName = returnedNode.node.name;
+    const declaration = returnedNode.scope.getBinding(identifierName);
+    if (declaration === undefined) {
+      throw new BabelParseError(
+          returnedNode.node, 'Missing declaration for return value from helper.');
+    }
+    if (!declaration.path.isVariableDeclarator()) {
+      throw new BabelParseError(
+          declaration.path.node,
+          'Unexpected helper return value declaration (expected a variable declaration).');
+    }
+    const initializer = declaration.path.get('init');
+    if (!initializer.isCallExpression()) {
+      throw new BabelParseError(
+          declaration.path.node,
+          'Unexpected return value from helper (expected a call expression).');
+    }
+
+    // Remove the lazy load helper if this is the only reference to it.
+    if (lazyLoadBinding.references === 1) {
+      lazyLoadFn.remove();
+    }
+
+    return initializer;
+  }
+  return call;
+}
+
+function getReturnedExpression(fn: NodePath<t.FunctionDeclaration>): NodePath<t.Expression> {
+  const bodyStatements = fn.get('body').get('body');
+  for (const statement of bodyStatements) {
+    if (statement.isReturnStatement()) {
+      const argument = statement.get('argument');
+      if (argument.isSequenceExpression()) {
+        const expressions = argument.get('expressions');
+        return Array.isArray(expressions) ? expressions[expressions.length - 1] : expressions;
+      } else if (argument.isExpression()) {
+        return argument;
+      } else {
+        throw new BabelParseError(
+            statement.node, 'Invalid return argument in helper function (expected an expression).');
+      }
+    }
+  }
+  throw new BabelParseError(fn.node, 'Missing return statement in helper function.');
+}
+
 /**
 * Is the given `node` an array of literal strings?
 *

packages/localize/src/tools/test/translate/source_files/es5_translate_plugin_spec.ts

@@ -103,6 +103,33 @@ describe('makeEs5Plugin', () => {
       expect(output.code).toEqual('"try" + (40 + 2) + "me";');
     });
 
+    it('should handle lazy-load helper calls', () => {
+      const diagnostics = new Diagnostics();
+      const input = `
+      function _templateObject2() {
+        var e = _taggedTemplateLiteral([':escaped-colons:Welcome to the i18n app.'], ['\\\\\\:escaped-colons:Welcome to the i18n app.']);
+        return _templateObject2 = function() { return e }, e
+      }
+      function _templateObject() {
+        var e = _taggedTemplateLiteral([' Hello ', ':INTERPOLATION:! ']);
+        return _templateObject = function() { return e }, e
+      }
+      function _taggedTemplateLiteral(e, t) {
+        return t || (t = e.slice(0)),
+               Object.freeze(Object.defineProperties(e, {raw: {value: Object.freeze(t)}}))
+      }
+      const message = $localize(_templateObject2());
+      function foo() {
+        console.log($localize(_templateObject(), '\ufffd0\ufffd'));
+      }
+      `;
+      const output = transformSync(input, {plugins: [makeEs5TranslatePlugin(diagnostics, {})]}) !;
+      expect(output.code).toContain('const message = ":escaped-colons:Welcome to the i18n app."');
+      expect(output.code).toContain('console.log(" Hello " + \'\ufffd0\ufffd\' + "! ");');
+      expect(output.code).not.toContain('templateObject');
+      expect(output.code).not.toContain('templateObject2');
+    });
+
     it('should add diagnostic error with code-frame information if the arguments to `$localize` are missing',
        () => {
          const diagnostics = new Diagnostics();

packages/localize/src/tools/test/translate/source_files/source_file_utils_spec.ts

@@ -9,7 +9,7 @@ import {ɵmakeTemplateObject} from '@angular/localize';
 import {NodePath, transformSync} from '@babel/core';
 import generate from '@babel/generator';
 import template from '@babel/template';
-import {Expression, Identifier, TaggedTemplateExpression, ExpressionStatement, FunctionDeclaration, CallExpression, isParenthesizedExpression, numericLiteral, binaryExpression, NumericLiteral, traverse} from '@babel/types';
+import {Expression, Identifier, TaggedTemplateExpression, ExpressionStatement, FunctionDeclaration, CallExpression, isParenthesizedExpression, numericLiteral, binaryExpression, NumericLiteral} from '@babel/types';
 import {isGlobalIdentifier, isNamedIdentifier, isStringLiteralArray, isArrayOfExpressions, unwrapStringLiteralArray, unwrapMessagePartsFromLocalizeCall, wrapInParensIfNecessary, buildLocalizeReplacement, unwrapSubstitutionsFromLocalizeCall, unwrapMessagePartsFromTemplateLiteral} from '../../../src/translate/source_files/source_file_utils';
 
 describe('utils', () => {
@@ -71,18 +71,45 @@ describe('utils', () => {
 
   describe('unwrapMessagePartsFromLocalizeCall', () => {
     it('should return an array of string literals from a direct call to a tag function', () => {
-      const call = getFirstCallExpression(`$localize(['a', 'b\\t', 'c'], 1, 2)`);
-      const parts = unwrapMessagePartsFromLocalizeCall(call);
+      const localizeCall = getLocalizeCall(`$localize(['a', 'b\\t', 'c'], 1, 2)`);
+      const parts = unwrapMessagePartsFromLocalizeCall(localizeCall);
       expect(parts).toEqual(['a', 'b\t', 'c']);
     });
 
     it('should return an array of string literals from a downleveled tagged template', () => {
-      let call = getFirstCallExpression(
+      let localizeCall = getLocalizeCall(
           `$localize(__makeTemplateObject(['a', 'b\\t', 'c'], ['a', 'b\\\\t', 'c']), 1, 2)`);
-      const parts = unwrapMessagePartsFromLocalizeCall(call);
+      const parts = unwrapMessagePartsFromLocalizeCall(localizeCall);
       expect(parts).toEqual(['a', 'b\t', 'c']);
       expect(parts.raw).toEqual(['a', 'b\\t', 'c']);
     });
+
+    it('should return an array of string literals from a lazy load template helper', () => {
+      let localizeCall = getLocalizeCall(`
+        function _templateObject() {
+          var e = _taggedTemplateLiteral(['a', 'b', 'c'], ['a', 'b', 'c']);
+          return _templateObject = function() { return e }, e
+        }
+        $localize(_templateObject(), 1, 2)`);
+      const parts = unwrapMessagePartsFromLocalizeCall(localizeCall);
+      expect(parts).toEqual(['a', 'b', 'c']);
+      expect(parts.raw).toEqual(['a', 'b', 'c']);
+    });
+
+    it('should remove a lazy load template helper', () => {
+      let localizeCall = getLocalizeCall(`
+        function _templateObject() {
+          var e = _taggedTemplateLiteral(['a', 'b', 'c'], ['a', 'b', 'c']);
+          return _templateObject = function() { return e }, e
+        }
+        $localize(_templateObject(), 1, 2)`);
+      const localizeStatement = localizeCall.parentPath as NodePath<ExpressionStatement>;
+      const statements = localizeStatement.container as object[];
+      expect(statements.length).toEqual(2);
+      unwrapMessagePartsFromLocalizeCall(localizeCall);
+      expect(statements.length).toEqual(1);
+      expect(statements[0]).toBe(localizeStatement.node);
+    });
   });
 
   describe('unwrapSubstitutionsFromLocalizeCall', () => {
@@ -180,20 +207,15 @@ function collectExpressionsPlugin() {
   return {expressions, plugin: {visitor}};
 }
 
-function getFirstCallExpression(code: string): NodePath<CallExpression> {
-  let callPath: NodePath<CallExpression>|undefined = undefined;
-  transformSync(code, {
-    plugins: [{
-      visitor: {
-        CallExpression(path) {
-          callPath = path;
-          path.stop();
-        }
-      }
-    }]
+function getLocalizeCall(code: string): NodePath<CallExpression> {
+  let callPaths: NodePath<CallExpression>[] = [];
+  transformSync(code, {plugins: [{visitor: {CallExpression(path) { callPaths.push(path); }}}]});
+  const localizeCall = callPaths.find(p => {
+    const callee = p.get('callee');
+    return (callee.isIdentifier() && callee.node.name === '$localize');
   });
-  if (callPath === undefined) {
-    throw new Error('CallExpression not found in code:' + code);
+  if (!localizeCall) {
+    throw new Error(`$localize cannot be found in ${code}`);
   }
-  return callPath;
+  return localizeCall;
 }