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refactor(compiler): align &ngsp; handling with Angular Dart implementation (#18774)

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PR Close #18774
This commit is contained in:
Pawel Kozlowski
2017-08-18 15:00:12 +02:00
committed by Miško Hevery
parent 7f4c964eef
commit 7d72d0eb9b
3 changed files with 35 additions and 13 deletions
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23
packages/compiler/src/ml_parser/html_whitespaces.ts
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@ -18,6 +18,17 @@ function hasPreserveWhitespacesAttr(attrs: html.Attribute[]): boolean {
return attrs.some((attr: html.Attribute) => attr.name === PRESERVE_WS_ATTR_NAME);
}
/**
* Angular Dart introduced &ngsp; as a placeholder for non-removable space, see:
* https://github.com/dart-lang/angular/blob/0bb611387d29d65b5af7f9d2515ab571fd3fbee4/_tests/test/compiler/preserve_whitespace_test.dart#L25-L32
* In Angular Dart &ngsp; is converted to the 0xE500 PUA (Private Use Areas) unicode character
* and later on replaced by a space. We are re-implementing the same idea here.
*/
export function replaceNgsp(value: string): string {
// lexer is replacing the &ngsp; pseudo-entity with NGSP_UNICODE
return value.replace(new RegExp(NGSP_UNICODE, 'g'), ' ');
}
/**
* This visitor can walk HTML parse tree and remove / trim text nodes using the following rules:
* - consider spaces, tabs and new lines as whitespace characters;
@ -25,15 +36,9 @@ function hasPreserveWhitespacesAttr(attrs: html.Attribute[]): boolean {
* - for all other text nodes replace consecutive whitespace characters with one space;
* - convert &ngsp; pseudo-entity to a single space;
*
* The idea of using &ngsp; as a placeholder for non-removable space was originally introduced in
* Angular Dart, see:
* https://github.com/dart-lang/angular/blob/0bb611387d29d65b5af7f9d2515ab571fd3fbee4/_tests/test/compiler/preserve_whitespace_test.dart#L25-L32
* In Angular Dart &ngsp; is converted to the 0xE500 PUA (Private Use Areas) unicode character
* and later on replaced by a space. We are re-implementing the same idea here.
*
* Removal and trimming of whitespaces have positive performance impact (less code to generate
* while compiling templates, faster view creation). At the same time it can be "destructive"
* in some cases (whitespaces can influence layout). Becouse of the potential of breaking layout
* in some cases (whitespaces can influence layout). Because of the potential of breaking layout
* this visitor is not activated by default in Angular 5 and people need to explicitly opt-in for
* whitespace removal. The default option for whitespace removal will be revisited in Angular 6
* and might be changed to "on" by default.
@ -61,9 +66,7 @@ class WhitespaceVisitor implements html.Visitor {
const isBlank = text.value.trim().length === 0;
if (!isBlank) {
// lexer is replacing the &ngsp; pseudo-entity with NGSP_UNICODE
return new html.Text(
text.value.replace(NGSP_UNICODE, ' ').replace(/\s\s+/g, ' '), text.sourceSpan);
return new html.Text(replaceNgsp(text.value).replace(/\s\s+/g, ' '), text.sourceSpan);
}
return null;