From a4b66fe1e5acaf148069933720499652f21a7bce Mon Sep 17 00:00:00 2001
From: JoostK <joost.koehoorn@gmail.com>
Date: Wed, 21 Sep 2022 19:56:37 +0200
Subject: [PATCH] perf(compiler-cli): cache source file for reporting
 type-checking diagnostics (#47508)

When reporting type-checking diagnostics in external templates we create a
`ts.SourceFile` of the template text, as this is needed to report Angular
template diagnostics using TypeScript's diagnostics infrastructure. Each
reported diagnostic would create its own `ts.SourceFile`, resulting in
repeatedly parsing of the template text and potentially high memory usage
if the template is large and there are many diagnostics reported. This commit
caches the parsed template in the template mapping, such that all reported
diagnostics get to reuse the same `ts.SourceFile`.

Closes #47470

PR Close #47508
---
 .../typecheck/diagnostics/src/diagnostic.ts   | 23 +++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/packages/compiler-cli/src/ngtsc/typecheck/diagnostics/src/diagnostic.ts b/packages/compiler-cli/src/ngtsc/typecheck/diagnostics/src/diagnostic.ts
index dbaaf842a528c..da778fdd91fe8 100644
--- a/packages/compiler-cli/src/ngtsc/typecheck/diagnostics/src/diagnostic.ts
+++ b/packages/compiler-cli/src/ngtsc/typecheck/diagnostics/src/diagnostic.ts
@@ -9,7 +9,7 @@
 import {ParseSourceSpan} from '@angular/compiler';
 import ts from 'typescript';
 
-import {ExternalTemplateSourceMapping, TemplateDiagnostic, TemplateId, TemplateSourceMapping} from '../../api';
+import {ExternalTemplateSourceMapping, IndirectTemplateSourceMapping, TemplateDiagnostic, TemplateId, TemplateSourceMapping} from '../../api';
 
 /**
  * Constructs a `ts.Diagnostic` for a given `ParseSourceSpan` within a template.
@@ -66,9 +66,7 @@ export function makeTemplateDiagnostic(
         (mapping as ExternalTemplateSourceMapping).templateUrl;
     // TODO(alxhub): investigate creating a fake `ts.SourceFile` here instead of invoking the TS
     // parser against the template (HTML is just really syntactically invalid TypeScript code ;).
-    // Also investigate caching the file to avoid running the parser multiple times.
-    const sf = ts.createSourceFile(
-        fileName, mapping.template, ts.ScriptTarget.Latest, false, ts.ScriptKind.JSX);
+    const sf = getParsedTemplateSourceFile(fileName, mapping);
 
     let relatedInformation: ts.DiagnosticRelatedInformation[] = [];
     if (relatedMessages !== undefined) {
@@ -113,6 +111,23 @@ export function makeTemplateDiagnostic(
   }
 }
 
+const TemplateSourceFile = Symbol('TemplateSourceFile');
+
+type TemplateSourceMappingWithSourceFile =
+    (ExternalTemplateSourceMapping|IndirectTemplateSourceMapping)&{
+  [TemplateSourceFile]?: ts.SourceFile;
+};
+
+function getParsedTemplateSourceFile(
+    fileName: string, mapping: TemplateSourceMappingWithSourceFile): ts.SourceFile {
+  if (mapping[TemplateSourceFile] === undefined) {
+    mapping[TemplateSourceFile] = ts.createSourceFile(
+        fileName, mapping.template, ts.ScriptTarget.Latest, false, ts.ScriptKind.JSX);
+  }
+
+  return mapping[TemplateSourceFile];
+}
+
 export function isTemplateDiagnostic(diagnostic: ts.Diagnostic): diagnostic is TemplateDiagnostic {
   return diagnostic.hasOwnProperty('componentFile') &&
       ts.isSourceFile((diagnostic as any).componentFile);