84 lines
3.6 KiB
TypeScript
84 lines
3.6 KiB
TypeScript
/**
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* @license
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* Copyright Google Inc. All Rights Reserved.
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*
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* Use of this source code is governed by an MIT-style license that can be
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* found in the LICENSE file at https://angular.io/license
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*/
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import * as html from './ast';
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import {ParseTreeResult} from './parser';
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import {NGSP_UNICODE} from './tags';
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export const PRESERVE_WS_ATTR_NAME = 'ngPreserveWhitespaces';
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const SKIP_WS_TRIM_TAGS = new Set(['pre', 'template', 'textarea', 'script', 'style']);
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function hasPreserveWhitespacesAttr(attrs: html.Attribute[]): boolean {
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return attrs.some((attr: html.Attribute) => attr.name === PRESERVE_WS_ATTR_NAME);
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}
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/**
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* This visitor can walk HTML parse tree and remove / trim text nodes using the following rules:
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* - consider spaces, tabs and new lines as whitespace characters;
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* - drop text nodes consisting of whitespace characters only;
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* - for all other text nodes replace consecutive whitespace characters with one space;
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* - convert &ngsp; pseudo-entity to a single space;
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*
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* The idea of using &ngsp; as a placeholder for non-removable space was originally introduced in
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* Angular Dart, see:
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* https://github.com/dart-lang/angular/blob/0bb611387d29d65b5af7f9d2515ab571fd3fbee4/_tests/test/compiler/preserve_whitespace_test.dart#L25-L32
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* In Angular Dart &ngsp; is converted to the 0xE500 PUA (Private Use Areas) unicode character
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* and later on replaced by a space. We are re-implementing the same idea here.
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*
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* Removal and trimming of whitespaces have positive performance impact (less code to generate
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* while compiling templates, faster view creation). At the same time it can be "destructive"
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* in some cases (whitespaces can influence layout). Becouse of the potential of breaking layout
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* this visitor is not activated by default in Angular 5 and people need to explicitly opt-in for
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* whitespace removal. The default option for whitespace removal will be revisited in Angular 6
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* and might be changed to "on" by default.
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*/
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class WhitespaceVisitor implements html.Visitor {
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visitElement(element: html.Element, context: any): any {
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if (SKIP_WS_TRIM_TAGS.has(element.name) || hasPreserveWhitespacesAttr(element.attrs)) {
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// don't descent into elements where we need to preserve whitespaces
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// but still visit all attributes to eliminate one used as a market to preserve WS
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return new html.Element(
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element.name, html.visitAll(this, element.attrs), element.children, element.sourceSpan,
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element.startSourceSpan, element.endSourceSpan);
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}
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return new html.Element(
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element.name, element.attrs, html.visitAll(this, element.children), element.sourceSpan,
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element.startSourceSpan, element.endSourceSpan);
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}
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visitAttribute(attribute: html.Attribute, context: any): any {
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return attribute.name !== PRESERVE_WS_ATTR_NAME ? attribute : null;
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}
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visitText(text: html.Text, context: any): any {
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const isBlank = text.value.trim().length === 0;
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if (!isBlank) {
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// lexer is replacing the &ngsp; pseudo-entity with NGSP_UNICODE
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return new html.Text(
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text.value.replace(NGSP_UNICODE, ' ').replace(/\s\s+/g, ' '), text.sourceSpan);
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}
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return null;
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}
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visitComment(comment: html.Comment, context: any): any { return comment; }
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visitExpansion(expansion: html.Expansion, context: any): any { return expansion; }
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visitExpansionCase(expansionCase: html.ExpansionCase, context: any): any { return expansionCase; }
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}
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export function removeWhitespaces(htmlAstWithErrors: ParseTreeResult): ParseTreeResult {
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return new ParseTreeResult(
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html.visitAll(new WhitespaceVisitor(), htmlAstWithErrors.rootNodes),
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htmlAstWithErrors.errors);
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}
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