r3_template_transform.ts

/**
 * @license
 * Copyright Google LLC 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 {ParsedEvent, ParsedProperty, ParsedVariable} from '../expression_parser/ast';
import * as i18n from '../i18n/i18n_ast';
import * as html from '../ml_parser/ast';
import {replaceNgsp} from '../ml_parser/html_whitespaces';
import {isNgTemplate} from '../ml_parser/tags';
import {InterpolatedAttributeToken, InterpolatedTextToken} from '../ml_parser/tokens';
import {ParseError, ParseErrorLevel, ParseSourceSpan} from '../parse_util';
import {isStyleUrlResolvable} from '../style_url_resolver';
import {BindingParser} from '../template_parser/binding_parser';
import {PreparsedElementType, preparseElement} from '../template_parser/template_preparser';

import * as t from './r3_ast';
import {createForLoop, createIfBlock, createSwitchBlock, isConnectedForLoopBlock, isConnectedIfLoopBlock} from './r3_control_flow';
import {createDeferredBlock, isConnectedDeferLoopBlock} from './r3_deferred_blocks';
import {I18N_ICU_VAR_PREFIX, isI18nRootNode} from './view/i18n/util';

const BIND_NAME_REGEXP = /^(?:(bind-)|(let-)|(ref-|#)|(on-)|(bindon-)|(@))(.*)$/;

// Group 1 = "bind-"
const KW_BIND_IDX = 1;
// Group 2 = "let-"
const KW_LET_IDX = 2;
// Group 3 = "ref-/#"
const KW_REF_IDX = 3;
// Group 4 = "on-"
const KW_ON_IDX = 4;
// Group 5 = "bindon-"
const KW_BINDON_IDX = 5;
// Group 6 = "@"
const KW_AT_IDX = 6;
// Group 7 = the identifier after "bind-", "let-", "ref-/#", "on-", "bindon-" or "@"
const IDENT_KW_IDX = 7;

const BINDING_DELIMS = {
  BANANA_BOX: {start: '[(', end: ')]'},
  PROPERTY: {start: '[', end: ']'},
  EVENT: {start: '(', end: ')'},
};

const TEMPLATE_ATTR_PREFIX = '*';

// Result of the html AST to Ivy AST transformation
export interface Render3ParseResult {
  nodes: t.Node[];
  errors: ParseError[];
  styles: string[];
  styleUrls: string[];
  ngContentSelectors: string[];
  // Will be defined if `Render3ParseOptions['collectCommentNodes']` is true
  commentNodes?: t.Comment[];
}

interface Render3ParseOptions {
  collectCommentNodes: boolean;
}

export function htmlAstToRender3Ast(
    htmlNodes: html.Node[], bindingParser: BindingParser,
    options: Render3ParseOptions): Render3ParseResult {
  const transformer = new HtmlAstToIvyAst(bindingParser, options);
  const ivyNodes = html.visitAll(transformer, htmlNodes, htmlNodes);

  // Errors might originate in either the binding parser or the html to ivy transformer
  const allErrors = bindingParser.errors.concat(transformer.errors);

  const result: Render3ParseResult = {
    nodes: ivyNodes,
    errors: allErrors,
    styleUrls: transformer.styleUrls,
    styles: transformer.styles,
    ngContentSelectors: transformer.ngContentSelectors
  };
  if (options.collectCommentNodes) {
    result.commentNodes = transformer.commentNodes;
  }
  return result;
}

class HtmlAstToIvyAst implements html.Visitor {
  errors: ParseError[] = [];
  styles: string[] = [];
  styleUrls: string[] = [];
  ngContentSelectors: string[] = [];
  // This array will be populated if `Render3ParseOptions['collectCommentNodes']` is true
  commentNodes: t.Comment[] = [];
  private inI18nBlock: boolean = false;

  /**
   * Keeps track of the nodes that have been processed already when previous nodes were visited.
   * These are typically blocks connected to other blocks or text nodes between connected blocks.
   */
  private processedNodes = new Set<html.Block|html.Text>();

  constructor(private bindingParser: BindingParser, private options: Render3ParseOptions) {}

  // implements html.Visitor
  visit?(node: html.Node, context: any) {}
  visitCdata(text: html.CDATA, context: any) {}
  visitDocType(docType: html.DocType, context: any) {}

  // HTML visitor
  visitElement(element: html.Element): t.Node|null {
    const isI18nRootElement = isI18nRootNode(element.i18n);
    if (isI18nRootElement) {
      if (this.inI18nBlock) {
        this.reportError(
            'Cannot mark an element as translatable inside of a translatable section. Please remove the nested i18n marker.',
            element.sourceSpan);
      }
      this.inI18nBlock = true;
    }
    const preparsedElement = preparseElement(element);
    if (preparsedElement.type === PreparsedElementType.SCRIPT) {
      return null;
    } else if (preparsedElement.type === PreparsedElementType.STYLE) {
      const contents = textContents(element);
      if (contents !== null) {
        this.styles.push(contents);
      }
      return null;
    } else if (
        preparsedElement.type === PreparsedElementType.STYLESHEET &&
        isStyleUrlResolvable(preparsedElement.hrefAttr)) {
      this.styleUrls.push(preparsedElement.hrefAttr);
      return null;
    }

    // Whether the element is a `<ng-template>`
    const isTemplateElement = isNgTemplate(element.name);

    const parsedProperties: ParsedProperty[] = [];
    const boundEvents: t.BoundEvent[] = [];
    const variables: t.Variable[] = [];
    const references: t.Reference[] = [];
    const attributes: t.TextAttribute[] = [];
    const i18nAttrsMeta: {[key: string]: i18n.I18nMeta} = {};

    const templateParsedProperties: ParsedProperty[] = [];
    const templateVariables: t.Variable[] = [];

    // Whether the element has any *-attribute
    let elementHasInlineTemplate = false;

    for (const attribute of element.attrs) {
      let hasBinding = false;
      const normalizedName = normalizeAttributeName(attribute.name);

      // `*attr` defines template bindings
      let isTemplateBinding = false;

      if (attribute.i18n) {
        i18nAttrsMeta[attribute.name] = attribute.i18n;
      }

      if (normalizedName.startsWith(TEMPLATE_ATTR_PREFIX)) {
        // *-attributes
        if (elementHasInlineTemplate) {
          this.reportError(
              `Can't have multiple template bindings on one element. Use only one attribute prefixed with *`,
              attribute.sourceSpan);
        }
        isTemplateBinding = true;
        elementHasInlineTemplate = true;
        const templateValue = attribute.value;
        const templateKey = normalizedName.substring(TEMPLATE_ATTR_PREFIX.length);

        const parsedVariables: ParsedVariable[] = [];
        const absoluteValueOffset = attribute.valueSpan ?
            attribute.valueSpan.start.offset :
            // If there is no value span the attribute does not have a value, like `attr` in
            //`<div attr></div>`. In this case, point to one character beyond the last character of
            // the attribute name.
            attribute.sourceSpan.start.offset + attribute.name.length;

        this.bindingParser.parseInlineTemplateBinding(
            templateKey, templateValue, attribute.sourceSpan, absoluteValueOffset, [],
            templateParsedProperties, parsedVariables, true /* isIvyAst */);
        templateVariables.push(...parsedVariables.map(
            v => new t.Variable(v.name, v.value, v.sourceSpan, v.keySpan, v.valueSpan)));
      } else {
        // Check for variables, events, property bindings, interpolation
        hasBinding = this.parseAttribute(
            isTemplateElement, attribute, [], parsedProperties, boundEvents, variables, references);
      }

      if (!hasBinding && !isTemplateBinding) {
        // don't include the bindings as attributes as well in the AST
        attributes.push(this.visitAttribute(attribute));
      }
    }

    let children: t.Node[];

    if (preparsedElement.nonBindable) {
      // The `NonBindableVisitor` may need to return an array of nodes for blocks so we need
      // to flatten the array here. Avoid doing this for the `HtmlAstToIvyAst` since `flat` creates
      // a new array.
      children = html.visitAll(NON_BINDABLE_VISITOR, element.children).flat(Infinity);
    } else {
      children = html.visitAll(this, element.children, element.children);
    }

    let parsedElement: t.Content|t.Template|t.Element|undefined;
    if (preparsedElement.type === PreparsedElementType.NG_CONTENT) {
      // `<ng-content>`
      if (element.children &&
          !element.children.every(
              (node: html.Node) => isEmptyTextNode(node) || isCommentNode(node))) {
        this.reportError(`<ng-content> element cannot have content.`, element.sourceSpan);
      }
      const selector = preparsedElement.selectAttr;
      const attrs: t.TextAttribute[] = element.attrs.map(attr => this.visitAttribute(attr));
      parsedElement = new t.Content(selector, attrs, element.sourceSpan, element.i18n);

      this.ngContentSelectors.push(selector);
    } else if (isTemplateElement) {
      // `<ng-template>`
      const attrs = this.extractAttributes(element.name, parsedProperties, i18nAttrsMeta);

      parsedElement = new t.Template(
          element.name, attributes, attrs.bound, boundEvents, [/* no template attributes */],
          children, references, variables, element.sourceSpan, element.startSourceSpan,
          element.endSourceSpan, element.i18n);
    } else {
      const attrs = this.extractAttributes(element.name, parsedProperties, i18nAttrsMeta);
      parsedElement = new t.Element(
          element.name, attributes, attrs.bound, boundEvents, children, references,
          element.sourceSpan, element.startSourceSpan, element.endSourceSpan, element.i18n);
    }

    if (elementHasInlineTemplate) {
      // If this node is an inline-template (e.g. has *ngFor) then we need to create a template
      // node that contains this node.
      // Moreover, if the node is an element, then we need to hoist its attributes to the template
      // node for matching against content projection selectors.
      const attrs = this.extractAttributes('ng-template', templateParsedProperties, i18nAttrsMeta);
      const templateAttrs: (t.TextAttribute|t.BoundAttribute)[] = [];
      attrs.literal.forEach(attr => templateAttrs.push(attr));
      attrs.bound.forEach(attr => templateAttrs.push(attr));
      const hoistedAttrs = parsedElement instanceof t.Element ?
          {
            attributes: parsedElement.attributes,
            inputs: parsedElement.inputs,
            outputs: parsedElement.outputs,
          } :
          {attributes: [], inputs: [], outputs: []};

      // For <ng-template>s with structural directives on them, avoid passing i18n information to
      // the wrapping template to prevent unnecessary i18n instructions from being generated. The
      // necessary i18n meta information will be extracted from child elements.
      const i18n = isTemplateElement && isI18nRootElement ? undefined : element.i18n;
      const name = parsedElement instanceof t.Template ? null : parsedElement.name;

      parsedElement = new t.Template(
          name, hoistedAttrs.attributes, hoistedAttrs.inputs, hoistedAttrs.outputs, templateAttrs,
          [parsedElement], [/* no references */], templateVariables, element.sourceSpan,
          element.startSourceSpan, element.endSourceSpan, i18n);
    }
    if (isI18nRootElement) {
      this.inI18nBlock = false;
    }
    return parsedElement;
  }

  visitAttribute(attribute: html.Attribute): t.TextAttribute {
    return new t.TextAttribute(
        attribute.name, attribute.value, attribute.sourceSpan, attribute.keySpan,
        attribute.valueSpan, attribute.i18n);
  }

  visitText(text: html.Text): t.Node|null {
    return this.processedNodes.has(text) ?
        null :
        this._visitTextWithInterpolation(text.value, text.sourceSpan, text.tokens, text.i18n);
  }

  visitExpansion(expansion: html.Expansion): t.Icu|null {
    if (!expansion.i18n) {
      // do not generate Icu in case it was created
      // outside of i18n block in a template
      return null;
    }
    if (!isI18nRootNode(expansion.i18n)) {
      throw new Error(`Invalid type "${expansion.i18n.constructor}" for "i18n" property of ${
          expansion.sourceSpan.toString()}. Expected a "Message"`);
    }
    const message = expansion.i18n;
    const vars: {[name: string]: t.BoundText} = {};
    const placeholders: {[name: string]: t.Text|t.BoundText} = {};
    // extract VARs from ICUs - we process them separately while
    // assembling resulting message via goog.getMsg function, since
    // we need to pass them to top-level goog.getMsg call
    Object.keys(message.placeholders).forEach(key => {
      const value = message.placeholders[key];
      if (key.startsWith(I18N_ICU_VAR_PREFIX)) {
        // Currently when the `plural` or `select` keywords in an ICU contain trailing spaces (e.g.
        // `{count, select , ...}`), these spaces are also included into the key names in ICU vars
        // (e.g. "VAR_SELECT "). These trailing spaces are not desirable, since they will later be
        // converted into `_` symbols while normalizing placeholder names, which might lead to
        // mismatches at runtime (i.e. placeholder will not be replaced with the correct value).
        const formattedKey = key.trim();

        const ast = this.bindingParser.parseInterpolationExpression(value.text, value.sourceSpan);

        vars[formattedKey] = new t.BoundText(ast, value.sourceSpan);
      } else {
        placeholders[key] = this._visitTextWithInterpolation(value.text, value.sourceSpan, null);
      }
    });
    return new t.Icu(vars, placeholders, expansion.sourceSpan, message);
  }

  visitExpansionCase(expansionCase: html.ExpansionCase): null {
    return null;
  }

  visitComment(comment: html.Comment): null {
    if (this.options.collectCommentNodes) {
      this.commentNodes.push(new t.Comment(comment.value || '', comment.sourceSpan));
    }
    return null;
  }

  visitBlockParameter() {
    return null;
  }

  visitBlock(block: html.Block, context: html.Node[]) {
    const index = Array.isArray(context) ? context.indexOf(block) : -1;

    if (index === -1) {
      throw new Error(
          'Visitor invoked incorrectly. Expecting visitBlock to be invoked siblings array as its context');
    }

    // Connected blocks may have been processed as a part of the previous block.
    if (this.processedNodes.has(block)) {
      return null;
    }

    let result: {node: t.Node|null, errors: ParseError[]}|null = null;

    switch (block.name) {
      case 'defer':
        result = createDeferredBlock(
            block, this.findConnectedBlocks(index, context, isConnectedDeferLoopBlock), this,
            this.bindingParser);
        break;

      case 'switch':
        result = createSwitchBlock(block, this, this.bindingParser);
        break;

      case 'for':
        result = createForLoop(
            block, this.findConnectedBlocks(index, context, isConnectedForLoopBlock), this,
            this.bindingParser);
        break;

      case 'if':
        result = createIfBlock(
            block, this.findConnectedBlocks(index, context, isConnectedIfLoopBlock), this,
            this.bindingParser);
        break;

      default:
        let errorMessage: string;

        if (isConnectedDeferLoopBlock(block.name)) {
          errorMessage = `@${block.name} block can only be used after an @defer block.`;
          this.processedNodes.add(block);
        } else if (isConnectedForLoopBlock(block.name)) {
          errorMessage = `@${block.name} block can only be used after an @for block.`;
          this.processedNodes.add(block);
        } else if (isConnectedIfLoopBlock(block.name)) {
          errorMessage = `@${block.name} block can only be used after an @if or @else if block.`;
          this.processedNodes.add(block);
        } else {
          errorMessage = `Unrecognized block @${block.name}.`;
        }

        result = {
          node: new t.UnknownBlock(block.name, block.sourceSpan, block.sourceSpan),
          errors: [new ParseError(block.sourceSpan, errorMessage)],
        };
        break;
    }

    this.errors.push(...result.errors);
    return result.node;
  }

  private findConnectedBlocks(
      primaryBlockIndex: number, siblings: html.Node[],
      predicate: (blockName: string) => boolean): html.Block[] {
    const relatedBlocks: html.Block[] = [];

    for (let i = primaryBlockIndex + 1; i < siblings.length; i++) {
      const node = siblings[i];

      // Ignore empty text nodes between blocks.
      if (node instanceof html.Text && node.value.trim().length === 0) {
        // Add the text node to the processed nodes since we don't want
        // it to be generated between the connected nodes.
        this.processedNodes.add(node);
        continue;
      }

      // Stop searching as soon as we hit a non-block node or a block that is unrelated.
      if (!(node instanceof html.Block) || !predicate(node.name)) {
        break;
      }

      relatedBlocks.push(node);
      this.processedNodes.add(node);
    }

    return relatedBlocks;
  }

  // convert view engine `ParsedProperty` to a format suitable for IVY
  private extractAttributes(
      elementName: string, properties: ParsedProperty[],
      i18nPropsMeta: {[key: string]: i18n.I18nMeta}):
      {bound: t.BoundAttribute[], literal: t.TextAttribute[]} {
    const bound: t.BoundAttribute[] = [];
    const literal: t.TextAttribute[] = [];

    properties.forEach(prop => {
      const i18n = i18nPropsMeta[prop.name];
      if (prop.isLiteral) {
        literal.push(new t.TextAttribute(
            prop.name, prop.expression.source || '', prop.sourceSpan, prop.keySpan, prop.valueSpan,
            i18n));
      } else {
        // Note that validation is skipped and property mapping is disabled
        // due to the fact that we need to make sure a given prop is not an
        // input of a directive and directive matching happens at runtime.
        const bep = this.bindingParser.createBoundElementProperty(
            elementName, prop, /* skipValidation */ true, /* mapPropertyName */ false);
        bound.push(t.BoundAttribute.fromBoundElementProperty(bep, i18n));
      }
    });

    return {bound, literal};
  }

  private parseAttribute(
      isTemplateElement: boolean, attribute: html.Attribute, matchableAttributes: string[][],
      parsedProperties: ParsedProperty[], boundEvents: t.BoundEvent[], variables: t.Variable[],
      references: t.Reference[]) {
    const name = normalizeAttributeName(attribute.name);
    const value = attribute.value;
    const srcSpan = attribute.sourceSpan;
    const absoluteOffset =
        attribute.valueSpan ? attribute.valueSpan.start.offset : srcSpan.start.offset;

    function createKeySpan(srcSpan: ParseSourceSpan, prefix: string, identifier: string) {
      // We need to adjust the start location for the keySpan to account for the removed 'data-'
      // prefix from `normalizeAttributeName`.
      const normalizationAdjustment = attribute.name.length - name.length;
      const keySpanStart = srcSpan.start.moveBy(prefix.length + normalizationAdjustment);
      const keySpanEnd = keySpanStart.moveBy(identifier.length);
      return new ParseSourceSpan(keySpanStart, keySpanEnd, keySpanStart, identifier);
    }

    const bindParts = name.match(BIND_NAME_REGEXP);

    if (bindParts) {
      if (bindParts[KW_BIND_IDX] != null) {
        const identifier = bindParts[IDENT_KW_IDX];
        const keySpan = createKeySpan(srcSpan, bindParts[KW_BIND_IDX], identifier);
        this.bindingParser.parsePropertyBinding(
            identifier, value, false, srcSpan, absoluteOffset, attribute.valueSpan,
            matchableAttributes, parsedProperties, keySpan);

      } else if (bindParts[KW_LET_IDX]) {
        if (isTemplateElement) {
          const identifier = bindParts[IDENT_KW_IDX];
          const keySpan = createKeySpan(srcSpan, bindParts[KW_LET_IDX], identifier);
          this.parseVariable(identifier, value, srcSpan, keySpan, attribute.valueSpan, variables);
        } else {
          this.reportError(`"let-" is only supported on ng-template elements.`, srcSpan);
        }

      } else if (bindParts[KW_REF_IDX]) {
        const identifier = bindParts[IDENT_KW_IDX];
        const keySpan = createKeySpan(srcSpan, bindParts[KW_REF_IDX], identifier);
        this.parseReference(identifier, value, srcSpan, keySpan, attribute.valueSpan, references);
      } else if (bindParts[KW_ON_IDX]) {
        const events: ParsedEvent[] = [];
        const identifier = bindParts[IDENT_KW_IDX];
        const keySpan = createKeySpan(srcSpan, bindParts[KW_ON_IDX], identifier);
        this.bindingParser.parseEvent(
            identifier, value, /* isAssignmentEvent */ false, srcSpan,
            attribute.valueSpan || srcSpan, matchableAttributes, events, keySpan);
        addEvents(events, boundEvents);
      } else if (bindParts[KW_BINDON_IDX]) {
        const identifier = bindParts[IDENT_KW_IDX];
        const keySpan = createKeySpan(srcSpan, bindParts[KW_BINDON_IDX], identifier);
        this.bindingParser.parsePropertyBinding(
            identifier, value, false, srcSpan, absoluteOffset, attribute.valueSpan,
            matchableAttributes, parsedProperties, keySpan);
        this.parseAssignmentEvent(
            identifier, value, srcSpan, attribute.valueSpan, matchableAttributes, boundEvents,
            keySpan);
      } else if (bindParts[KW_AT_IDX]) {
        const keySpan = createKeySpan(srcSpan, '', name);
        this.bindingParser.parseLiteralAttr(
            name, value, srcSpan, absoluteOffset, attribute.valueSpan, matchableAttributes,
            parsedProperties, keySpan);
      }
      return true;
    }

    // We didn't see a kw-prefixed property binding, but we have not yet checked
    // for the []/()/[()] syntax.
    let delims: {start: string, end: string}|null = null;
    if (name.startsWith(BINDING_DELIMS.BANANA_BOX.start)) {
      delims = BINDING_DELIMS.BANANA_BOX;
    } else if (name.startsWith(BINDING_DELIMS.PROPERTY.start)) {
      delims = BINDING_DELIMS.PROPERTY;
    } else if (name.startsWith(BINDING_DELIMS.EVENT.start)) {
      delims = BINDING_DELIMS.EVENT;
    }
    if (delims !== null &&
        // NOTE: older versions of the parser would match a start/end delimited
        // binding iff the property name was terminated by the ending delimiter
        // and the identifier in the binding was non-empty.
        // TODO(ayazhafiz): update this to handle malformed bindings.
        name.endsWith(delims.end) && name.length > delims.start.length + delims.end.length) {
      const identifier = name.substring(delims.start.length, name.length - delims.end.length);
      const keySpan = createKeySpan(srcSpan, delims.start, identifier);
      if (delims.start === BINDING_DELIMS.BANANA_BOX.start) {
        this.bindingParser.parsePropertyBinding(
            identifier, value, false, srcSpan, absoluteOffset, attribute.valueSpan,
            matchableAttributes, parsedProperties, keySpan);
        this.parseAssignmentEvent(
            identifier, value, srcSpan, attribute.valueSpan, matchableAttributes, boundEvents,
            keySpan);
      } else if (delims.start === BINDING_DELIMS.PROPERTY.start) {
        this.bindingParser.parsePropertyBinding(
            identifier, value, false, srcSpan, absoluteOffset, attribute.valueSpan,
            matchableAttributes, parsedProperties, keySpan);
      } else {
        const events: ParsedEvent[] = [];
        this.bindingParser.parseEvent(
            identifier, value, /* isAssignmentEvent */ false, srcSpan,
            attribute.valueSpan || srcSpan, matchableAttributes, events, keySpan);
        addEvents(events, boundEvents);
      }

      return true;
    }

    // No explicit binding found.
    const keySpan = createKeySpan(srcSpan, '' /* prefix */, name);
    const hasBinding = this.bindingParser.parsePropertyInterpolation(
        name, value, srcSpan, attribute.valueSpan, matchableAttributes, parsedProperties, keySpan,
        attribute.valueTokens ?? null);
    return hasBinding;
  }

  private _visitTextWithInterpolation(
      value: string, sourceSpan: ParseSourceSpan,
      interpolatedTokens: InterpolatedAttributeToken[]|InterpolatedTextToken[]|null,
      i18n?: i18n.I18nMeta): t.Text|t.BoundText {
    const valueNoNgsp = replaceNgsp(value);
    const expr = this.bindingParser.parseInterpolation(valueNoNgsp, sourceSpan, interpolatedTokens);
    return expr ? new t.BoundText(expr, sourceSpan, i18n) : new t.Text(valueNoNgsp, sourceSpan);
  }

  private parseVariable(
      identifier: string, value: string, sourceSpan: ParseSourceSpan, keySpan: ParseSourceSpan,
      valueSpan: ParseSourceSpan|undefined, variables: t.Variable[]) {
    if (identifier.indexOf('-') > -1) {
      this.reportError(`"-" is not allowed in variable names`, sourceSpan);
    } else if (identifier.length === 0) {
      this.reportError(`Variable does not have a name`, sourceSpan);
    }

    variables.push(new t.Variable(identifier, value, sourceSpan, keySpan, valueSpan));
  }

  private parseReference(
      identifier: string, value: string, sourceSpan: ParseSourceSpan, keySpan: ParseSourceSpan,
      valueSpan: ParseSourceSpan|undefined, references: t.Reference[]) {
    if (identifier.indexOf('-') > -1) {
      this.reportError(`"-" is not allowed in reference names`, sourceSpan);
    } else if (identifier.length === 0) {
      this.reportError(`Reference does not have a name`, sourceSpan);
    } else if (references.some(reference => reference.name === identifier)) {
      this.reportError(`Reference "#${identifier}" is defined more than once`, sourceSpan);
    }

    references.push(new t.Reference(identifier, value, sourceSpan, keySpan, valueSpan));
  }

  private parseAssignmentEvent(
      name: string, expression: string, sourceSpan: ParseSourceSpan,
      valueSpan: ParseSourceSpan|undefined, targetMatchableAttrs: string[][],
      boundEvents: t.BoundEvent[], keySpan: ParseSourceSpan) {
    const events: ParsedEvent[] = [];
    this.bindingParser.parseEvent(
        `${name}Change`, `${expression} =$event`, /* isAssignmentEvent */ true, sourceSpan,
        valueSpan || sourceSpan, targetMatchableAttrs, events, keySpan);
    addEvents(events, boundEvents);
  }

  private reportError(
      message: string, sourceSpan: ParseSourceSpan,
      level: ParseErrorLevel = ParseErrorLevel.ERROR) {
    this.errors.push(new ParseError(sourceSpan, message, level));
  }
}

class NonBindableVisitor implements html.Visitor {
  // implements html.Visitor
  visit?(node: html.Node, context: any) {}
  visitCdata(text: html.CDATA, context: any) {}
  visitDocType(docType: html.DocType, context: any) {}

  visitElement(ast: html.Element): t.Element|null {
    const preparsedElement = preparseElement(ast);
    if (preparsedElement.type === PreparsedElementType.SCRIPT ||
        preparsedElement.type === PreparsedElementType.STYLE ||
        preparsedElement.type === PreparsedElementType.STYLESHEET) {
      // Skipping <script> for security reasons
      // Skipping <style> and stylesheets as we already processed them
      // in the StyleCompiler
      return null;
    }

    const children: t.Node[] = html.visitAll(this, ast.children, null);
    return new t.Element(
        ast.name, html.visitAll(this, ast.attrs) as t.TextAttribute[],
        /* inputs */[], /* outputs */[], children, /* references */[], ast.sourceSpan,
        ast.startSourceSpan, ast.endSourceSpan);
  }

  visitComment(comment: html.Comment): any {
    return null;
  }

  visitAttribute(attribute: html.Attribute): t.TextAttribute {
    return new t.TextAttribute(
        attribute.name, attribute.value, attribute.sourceSpan, attribute.keySpan,
        attribute.valueSpan, attribute.i18n);
  }

  visitText(text: html.Text): t.Text {
    return new t.Text(text.value, text.sourceSpan);
  }

  visitExpansion(expansion: html.Expansion): any {
    return null;
  }

  visitExpansionCase(expansionCase: html.ExpansionCase): any {
    return null;
  }

  visitBlock(block: html.Block, context: any) {
    const nodes = [
      // In an ngNonBindable context we treat the opening/closing tags of block as plain text.
      // This is the as if the `tokenizeBlocks` option was disabled.
      new t.Text(block.startSourceSpan.toString(), block.startSourceSpan),
      ...html.visitAll(this, block.children)
    ];

    if (block.endSourceSpan !== null) {
      nodes.push(new t.Text(block.endSourceSpan.toString(), block.endSourceSpan));
    }

    return nodes;
  }

  visitBlockParameter(parameter: html.BlockParameter, context: any) {
    return null;
  }
}

const NON_BINDABLE_VISITOR = new NonBindableVisitor();

function normalizeAttributeName(attrName: string): string {
  return /^data-/i.test(attrName) ? attrName.substring(5) : attrName;
}

function addEvents(events: ParsedEvent[], boundEvents: t.BoundEvent[]) {
  boundEvents.push(...events.map(e => t.BoundEvent.fromParsedEvent(e)));
}

function isEmptyTextNode(node: html.Node): boolean {
  return node instanceof html.Text && node.value.trim().length == 0;
}

function isCommentNode(node: html.Node): boolean {
  return node instanceof html.Comment;
}

function textContents(node: html.Element): string|null {
  if (node.children.length !== 1 || !(node.children[0] instanceof html.Text)) {
    return null;
  } else {
    return (node.children[0] as html.Text).value;
  }
}