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perf(ngcc): shortcircuit tokenizing in ESM dependency host #37639

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perf(ngcc): shortcircuit tokenizing in ESM dependency host #37639

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7 changes: 7 additions & 0 deletions packages/compiler-cli/ngcc/src/dependencies/esm_dependency_host.ts
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Expand Up @@ -47,10 +47,14 @@ export class EsmDependencyHost extends DependencyHostBase {
const templateStack: ts.SyntaxKind[] = [];
let lastToken: ts.SyntaxKind = ts.SyntaxKind.Unknown;
let currentToken: ts.SyntaxKind = ts.SyntaxKind.Unknown;
const stopAtIndex = findLastPossibleImportOrReexport(fileContents);

this.scanner.setText(fileContents);

while ((currentToken = this.scanner.scan()) !== ts.SyntaxKind.EndOfFileToken) {
if (this.scanner.getTokenPos() > stopAtIndex) {
break;
}
switch (currentToken) {
case ts.SyntaxKind.TemplateHead:
// TemplateHead indicates the beginning of a backticked string
Expand Down Expand Up @@ -266,6 +270,9 @@ export function hasImportOrReexportStatements(source: string): boolean {
return /(?:import|export)[\s\S]+?(["'])(?:\\\1|.)+?\1/.test(source);
}

function findLastPossibleImportOrReexport(source: string): number {
return Math.max(source.lastIndexOf('import'), source.lastIndexOf(' from '));
}

/**
* Check whether the given statement is an import with a string literal module specifier.
Expand Down