angular/modules/@angular/compiler/src/i18n/extractor.ts

/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import * as html from '../ml_parser/ast';
import {I18nError} from './parse_util';

const _I18N_ATTR = 'i18n';
const _I18N_ATTR_PREFIX = 'i18n-';

/**
 * Extract translatable message from an html AST as a list of html AST nodes
 */
export function extractAstMessages(
    sourceAst: html.Node[], implicitTags: string[],
    implicitAttrs: {[k: string]: string[]}): ExtractionResult {
  const visitor = new _ExtractVisitor(implicitTags, implicitAttrs);
  return visitor.extract(sourceAst);
}

export class ExtractionResult {
  constructor(public messages: Message[], public errors: I18nError[]) {}
}

class _ExtractVisitor implements html.Visitor {
  // <el i18n>...</el>
  private _inI18nNode = false;
  private _depth: number = 0;

  // <!--i18n-->...<!--/i18n-->
  private _blockMeaningAndDesc: string;
  private _blockChildren: html.Node[];
  private _blockStartDepth: number;
  private _inI18nBlock: boolean;

  // {<icu message>}
  private _inIcu = false;

  private _sectionStartIndex: number;
  private _errors: I18nError[];

  constructor(private _implicitTags: string[], private _implicitAttrs: {[k: string]: string[]}) {}

  extract(nodes: html.Node[]): ExtractionResult {
    const messages: Message[] = [];
    this._inI18nBlock = false;
    this._inI18nNode = false;
    this._depth = 0;
    this._inIcu = false;
    this._sectionStartIndex = void 0;
    this._errors = [];

    nodes.forEach(node => node.visit(this, messages));

    if (this._inI18nBlock) {
      this._reportError(nodes[nodes.length - 1], 'Unclosed block');
    }

    return new ExtractionResult(messages, this._errors);
  }

  visitExpansionCase(icuCase: html.ExpansionCase, messages: Message[]): any {
    html.visitAll(this, icuCase.expression, messages);
  }

  visitExpansion(icu: html.Expansion, messages: Message[]): any {
    this._mayBeAddBlockChildren(icu);

    const wasInIcu = this._inIcu;

    if (!this._inIcu) {
      if (this._inI18nNode || this._inI18nBlock) {
        this._addMessage(messages, [icu]);
      }
      this._inIcu = true;
    }

    html.visitAll(this, icu.cases, messages);

    this._inIcu = wasInIcu;
  }

  visitComment(comment: html.Comment, messages: Message[]): any {
    const isOpening = _isOpeningComment(comment);

    if (isOpening && (this._inI18nBlock || this._inI18nNode)) {
      this._reportError(comment, 'Could not start a block inside a translatable section');
      return;
    }

    const isClosing = _isClosingComment(comment);

    if (isClosing && !this._inI18nBlock) {
      this._reportError(comment, 'Trying to close an unopened block');
      return;
    }

    if (!(this._inI18nNode || this._inIcu)) {
      if (!this._inI18nBlock) {
        if (isOpening) {
          this._inI18nBlock = true;
          this._blockStartDepth = this._depth;
          this._blockChildren = [];
          this._blockMeaningAndDesc = comment.value.replace(/^i18n:?/, '').trim();
          this._startSection(messages);
        }
      } else {
        if (isClosing) {
          if (this._depth == this._blockStartDepth) {
            this._endSection(messages, this._blockChildren);
            this._inI18nBlock = false;
            this._addMessage(messages, this._blockChildren, this._blockMeaningAndDesc);
          } else {
            this._reportError(comment, 'I18N blocks should not cross element boundaries');
            return;
          }
        }
      }
    }
  }

  visitText(text: html.Text, messages: Message[]): any { this._mayBeAddBlockChildren(text); }

  visitElement(el: html.Element, messages: Message[]): any {
    this._mayBeAddBlockChildren(el);
    this._depth++;
    const wasInI18nNode = this._inI18nNode;
    let useSection = false;

    // Extract only top level nodes with the (implicit) "i18n" attribute if not in a block or an ICU
    // message
    const i18nAttr = _getI18nAttr(el);
    const isImplicitI18n =
        this._implicitTags.some((tagName: string): boolean => el.name === tagName);
    if (!(this._inI18nNode || this._inIcu || this._inI18nBlock)) {
      if (i18nAttr) {
        this._inI18nNode = true;
        this._addMessage(messages, el.children, i18nAttr.value);
        useSection = true;
      } else if (isImplicitI18n) {
        this._inI18nNode = true;
        this._addMessage(messages, el.children);
      }
    } else {
      if (i18nAttr || isImplicitI18n) {
        // TODO(vicb): we should probably allow nested implicit element (ie <div>)
        this._reportError(
            el, 'Could not mark an element as translatable inside a translatable section');
      }
    }

    this._extractFromAttributes(el, messages);

    if (useSection) {
      this._startSection(messages);
      html.visitAll(this, el.children, messages);
      this._endSection(messages, el.children);
    } else {
      html.visitAll(this, el.children, messages);
    }

    this._depth--;
    this._inI18nNode = wasInI18nNode;
  }

  visitAttribute(attribute: html.Attribute, messages: Message[]): any {
    throw new Error('unreachable code');
  }

  private _extractFromAttributes(el: html.Element, messages: Message[]): void {
    const explicitAttrNameToValue: {[k: string]: string} = {};
    const implicitAttrNames: string[] = this._implicitAttrs[el.name] || [];

    el.attrs.filter(attr => attr.name.startsWith(_I18N_ATTR_PREFIX))
        .forEach(
            attr => explicitAttrNameToValue[attr.name.slice(_I18N_ATTR_PREFIX.length)] =
                attr.value);

    el.attrs.forEach(attr => {
      if (attr.name in explicitAttrNameToValue) {
        this._addMessage(messages, [attr], explicitAttrNameToValue[attr.name]);
      } else if (implicitAttrNames.some(name => attr.name === name)) {
        this._addMessage(messages, [attr]);
      }
    });
  }

  private _addMessage(messages: Message[], ast: html.Node[], meaningAndDesc?: string): void {
    if (ast.length == 0 ||
        ast.length == 1 && ast[0] instanceof html.Attribute && !(<html.Attribute>ast[0]).value) {
      // Do not create empty messages
      return;
    }
    const [meaning, description] = _splitMeaningAndDesc(meaningAndDesc);
    messages.push(new Message(ast, meaning, description));
  }

  /**
   * Add the node as a child of the block when:
   * - we are in a block,
   * - we are not inside a ICU message (those are handled separately),
   * - the node is a "direct child" of the block
   */
  private _mayBeAddBlockChildren(node: html.Node): void {
    if (this._inI18nBlock && !this._inIcu && this._depth == this._blockStartDepth) {
      this._blockChildren.push(node);
    }
  }

  /**
   * Marks the start of a section, see `_endSection`
   */
  private _startSection(messages: Message[]): void {
    if (this._sectionStartIndex !== void 0) {
      throw new Error('Unexpected section start');
    }

    this._sectionStartIndex = messages.length;
  }

  /**
   * Terminates a section.
   *
   * If a section has only one significant children (comments not significant) then we should not
   * keep the message
   * from this children:
   *
   * `<p i18n="meaning|description">{ICU message}</p>` would produce two messages:
   * - one for the <p> content with meaning and description,
   * - another one for the ICU message.
   *
   * In this case the last message is discarded as it contains less information (the AST is
   * otherwise identical).
   *
   * Note that we should still keep messages extracted from attributes inside the section (ie in the
   * ICU message here)
   */
  private _endSection(messages: Message[], directChildren: html.Node[]): void {
    if (this._sectionStartIndex === void 0) {
      throw new Error('Unexpected section end');
    }

    const startIndex = this._sectionStartIndex;
    const significantChildren: number = directChildren.reduce(
        (count: number, node: html.Node): number => count + (node instanceof html.Comment ? 0 : 1),
        0);

    if (significantChildren == 1) {
      for (let i = messages.length - 1; i >= startIndex; i--) {
        const ast = messages[i].nodes;
        if (!(ast.length == 1 && ast[0] instanceof html.Attribute)) {
          messages.splice(i, 1);
          break;
        }
      }
    }

    this._sectionStartIndex = void 0;
  }

  private _reportError(node: html.Node, msg: string): void {
    this._errors.push(new I18nError(node.sourceSpan, msg));
  }
}

/**
 * A Message contain a fragment (= a subtree) of the source html AST.
 */
export class Message {
  constructor(public nodes: html.Node[], public meaning: string, public description: string) {}
}

function _isOpeningComment(n: html.Node): boolean {
  return n instanceof html.Comment && n.value && n.value.startsWith('i18n');
}

function _isClosingComment(n: html.Node): boolean {
  return n instanceof html.Comment && n.value && n.value === '/i18n';
}

function _getI18nAttr(p: html.Element): html.Attribute {
  return p.attrs.find(attr => attr.name === _I18N_ATTR) || null;
}

function _splitMeaningAndDesc(i18n: string): [string, string] {
  if (!i18n) return ['', ''];
  const pipeIndex = i18n.indexOf('|');
  return pipeIndex == -1 ? ['', i18n] : [i18n.slice(0, pipeIndex), i18n.slice(pipeIndex + 1)];
}