refactor(compiler): move handling of translations to the ConstantPool (#22942)

PR Close #22942

packages/compiler/src/constant_pool.ts

@@ -11,8 +11,16 @@ import {OutputContext, error} from './util';
 
 const CONSTANT_PREFIX = '_c';
 
+// Closure variables holding messages must be named `MSG_[A-Z0-9]+`
+const TRANSLATION_PREFIX = 'MSG_';
+
 export const enum DefinitionKind {Injector, Directive, Component, Pipe}
 
+/**
+ * Closure uses `goog.getMsg(message)` to lookup translations
+ */
+const GOOG_GET_MSG = 'goog.getMsg';
+
 /**
  * Context to use when producing a key.
  *
@@ -68,6 +76,7 @@ class FixupExpression extends o.Expression {
  */
 export class ConstantPool {
   statements: o.Statement[] = [];
+  private translations = new Map<string, o.Expression>();
   private literals = new Map<string, FixupExpression>();
   private literalFactories = new Map<string, o.Expression>();
   private injectorDefinitions = new Map<any, FixupExpression>();
@@ -103,6 +112,40 @@ export class ConstantPool {
     return fixup;
   }
 
+  // Generates closure specific code for translation.
+  //
+  // ```
+  // /**
+  //  * @desc description?
+  //  * @meaning meaning?
+  //  */
+  // const MSG_XYZ = goog.getMsg('message');
+  // ```
+  getTranslation(message: string, meta: {description?: string, meaning?: string}): o.Expression {
+    // The identity of an i18n message depends on the message and its meaning
+    const key = meta.meaning ? `${message}\u0000\u0000${meta.meaning}` : message;
+
+    const exp = this.translations.get(key);
+
+    if (exp) {
+      return exp;
+    }
+
+    const docStmt = i18nMetaToDocStmt(meta);
+    if (docStmt) {
+      this.statements.push(docStmt);
+    }
+
+    // Call closure to get the translation
+    const variable = o.variable(this.freshTranslationName());
+    const fnCall = o.variable(GOOG_GET_MSG).callFn([o.literal(message)]);
+    const msgStmt = variable.set(fnCall).toDeclStmt(o.INFERRED_TYPE, [o.StmtModifier.Final]);
+    this.statements.push(msgStmt);
+
+    this.translations.set(key, variable);
+    return variable;
+  }
+
   getDefinition(type: any, kind: DefinitionKind, ctx: OutputContext, forceShared: boolean = false):
       o.Expression {
     const definitions = this.definitionsOf(kind);
@@ -213,26 +256,37 @@ export class ConstantPool {
 
   private freshName(): string { return this.uniqueName(CONSTANT_PREFIX); }
 
+  private freshTranslationName(): string {
+    return this.uniqueName(TRANSLATION_PREFIX).toUpperCase();
+  }
+
   private keyOf(expression: o.Expression) {
     return expression.visitExpression(new KeyVisitor(), KEY_CONTEXT);
   }
 }
 
+/**
+ * Visitor used to determine if 2 expressions are equivalent and can be shared in the
+ * `ConstantPool`.
+ *
+ * When the id (string) generated by the visitor is equal, expressions are considered equivalent.
+ */
 class KeyVisitor implements o.ExpressionVisitor {
   visitLiteralExpr(ast: o.LiteralExpr): string {
     return `${typeof ast.value === 'string' ? '"' + ast.value + '"' : ast.value}`;
   }
+
   visitLiteralArrayExpr(ast: o.LiteralArrayExpr, context: object): string {
     return `[${ast.entries.map(entry => entry.visitExpression(this, context)).join(',')}]`;
   }
 
   visitLiteralMapExpr(ast: o.LiteralMapExpr, context: object): string {
-    const mapKey =
-        (entry: o.LiteralMapEntry) => {
-          const quote = entry.quoted ? '"' : '';
-          return `${quote}${entry.key}${quote}`;
-        } const mapEntry = (entry: o.LiteralMapEntry) =>
-            `${mapKey(entry)}:${entry.value.visitExpression(this, context)}`;
+    const mapKey = (entry: o.LiteralMapEntry) => {
+      const quote = entry.quoted ? '"' : '';
+      return `${quote}${entry.key}${quote}`;
+    };
+    const mapEntry = (entry: o.LiteralMapEntry) =>
+        `${mapKey(entry)}:${entry.value.visitExpression(this, context)}`;
     return `{${ast.entries.map(mapEntry).join(',')}`;
   }
 
@@ -241,13 +295,7 @@ class KeyVisitor implements o.ExpressionVisitor {
                                   `EX:${ast.value.runtime.name}`;
   }
 
-  visitReadVarExpr(ast: o.ReadVarExpr): string {
-    if (!ast.name) {
-      invalid(ast);
-    }
-    return ast.name as string;
-  }
-
+  visitReadVarExpr = invalid;
   visitWriteVarExpr = invalid;
   visitWriteKeyExpr = invalid;
   visitWritePropExpr = invalid;
@@ -273,3 +321,20 @@ function invalid<T>(arg: o.Expression | o.Statement): never {
 function isVariable(e: o.Expression): e is o.ReadVarExpr {
   return e instanceof o.ReadVarExpr;
 }
+
+// Converts i18n meta informations for a message (description, meaning) to a JsDoc statement
+// formatted as expected by the Closure compiler.
+function i18nMetaToDocStmt(meta: {description?: string, id?: string, meaning?: string}):
+    o.JSDocCommentStmt|null {
+  const tags: o.JSDocTag[] = [];
+
+  if (meta.description) {
+    tags.push({tagName: o.JSDocTagName.Desc, text: meta.description});
+  }
+
+  if (meta.meaning) {
+    tags.push({tagName: o.JSDocTagName.Meaning, text: meta.meaning});
+  }
+
+  return tags.length == 0 ? null : new o.JSDocCommentStmt(tags);
+}