Cache unchanged templates during IDE editing via TemplateContext

packages/ember-tsc/src/transform/index.ts

@@ -1,4 +1,5 @@
 export type { Directive, default as TransformedModule } from './template/transformed-module.js';
 export type { Diagnostic } from './diagnostics/index.js';
+export type { TemplateContext } from './template/map-template-contents.js';
 
 export { rewriteModule } from './template/rewrite-module.js';

packages/ember-tsc/src/transform/template/inlining/tagged-strings.ts

@@ -9,6 +9,7 @@ import { GlintEnvironment } from '../../../config/index.js';
 import { assert, TSLib } from '../../util.js';
 import { templateToTypescript } from '../template-to-typescript.js';
 import { Directive, Range, SourceFile, TransformError } from '../transformed-module.js';
+import type { TemplateContext } from '../map-template-contents.js';
 import { CorrelatedSpansResult, isEmbeddedInClass, PartialCorrelatedSpan } from './index.js';
 
 export function calculateTaggedTemplateSpans(
@@ -17,6 +18,7 @@ export function calculateTaggedTemplateSpans(
   meta: GlintEmitMetadata | undefined,
   script: SourceFile,
   environment: GlintEnvironment,
+  templateContext?: TemplateContext,
 ): CorrelatedSpansResult {
   let directives: Array<Directive> = [];
   let errors: Array<TransformError> = [];
@@ -69,6 +71,7 @@ export function calculateTaggedTemplateSpans(
       specialForms,
       backingValue: isEmbeddedInClass(ts, node) ? 'this' : undefined,
       useJsDoc: environment.isUntypedScript(script.filename),
+      templateContext,
     });
 
     for (let { message, location } of transformedTemplate.errors) {

packages/ember-tsc/src/transform/template/map-template-contents.ts

@@ -136,8 +136,20 @@ export type EmbeddingSyntax = {
   suffix: string;
 };
 
+/**
+ * Per-template persistent context. Held by the caller (e.g. VirtualGtsCode)
+ * across repeated calls so that unchanged templates can skip expensive work.
+ * One slot per template position — no unbounded growth.
+ */
+export type TemplateContext = {
+  template?: string;
+  ast?: AST.Template;
+  result?: RewriteResult;
+};
+
 export type MapTemplateContentsOptions = {
   embeddingSyntax: EmbeddingSyntax;
+  templateContext?: TemplateContext;
 };
 
 /**
@@ -149,14 +161,22 @@ export type MapTemplateContentsOptions = {
  */
 export function mapTemplateContents(
   template: string,
-  { embeddingSyntax }: MapTemplateContentsOptions,
+  { embeddingSyntax, templateContext }: MapTemplateContentsOptions,
   callback: (ast: AST.Template | null, mapper: Mapper) => void,
 ): RewriteResult {
   let ast: AST.Template | null = null;
   let errors: Array<{ message: string; location: Range | undefined }> = [];
   let lineOffsets = calculateLineOffsets(template, embeddingSyntax.prefix.length);
   try {
-    ast = preprocess(template);
+    if (templateContext && templateContext.template === template && templateContext.ast) {
+      ast = templateContext.ast;
+    } else {
+      ast = preprocess(template);
+      if (templateContext) {
+        templateContext.template = template;
+        templateContext.ast = ast;
+      }
+    }
   } catch (error) {
     let message = getErrorMessage(error);
     let location: Range | undefined;

packages/ember-tsc/src/transform/template/rewrite-module.ts

@@ -6,6 +6,7 @@ import { assert, TSLib } from '../util.js';
 
 import { CorrelatedSpansResult, PartialCorrelatedSpan } from './inlining/index.js';
 import { calculateTaggedTemplateSpans } from './inlining/tagged-strings.js';
+import type { TemplateContext } from './map-template-contents.js';
 import TransformedModule, {
   CorrelatedSpan,
   Directive,
@@ -34,12 +35,14 @@ export function rewriteModule(
   { script }: RewriteInput,
   environment: GlintEnvironment,
   clientId?: string,
+  templateContexts?: TemplateContext[],
 ): TransformedModule | null {
   let { errors, directives, partialSpans } = calculateCorrelatedSpans(
     ts,
     script,
     environment,
     clientId,
+    templateContexts,
   );
 
   if (!partialSpans.length && !errors.length) {
@@ -64,6 +67,7 @@ function calculateCorrelatedSpans(
   script: SourceFile,
   environment: GlintEnvironment,
   clientId?: string,
+  templateContexts?: TemplateContext[],
 ): CorrelatedSpansResult {
   let directives: Array<Directive> = [];
   let errors: Array<TransformError> = [];
@@ -108,6 +112,11 @@ function calculateCorrelatedSpans(
     return { errors, directives, partialSpans };
   }
 
+  // Index into templateContexts by traversal order. If templates are reordered
+  // in an edit, the string check in mapTemplateContents will miss — cache goes
+  // cold for one cycle, then re-populates correctly.
+  let templateIndex = 0;
+
   ts.transform(ast, [
     (context) =>
       function visit<T extends ts.Node>(node: T): T {
@@ -119,7 +128,19 @@ function calculateCorrelatedSpans(
         // https://discord.com/channels/480462759797063690/717767358743183412/1259061848632721480
         if (ts.isTaggedTemplateExpression(node)) {
           let meta = emitMetadata.get(node);
-          let result = calculateTaggedTemplateSpans(ts, node, meta, script, environment);
+          let templateContext: TemplateContext | undefined;
+          if (templateContexts) {
+            templateContext = templateContexts[templateIndex] ??= {};
+          }
+          templateIndex++;
+          let result = calculateTaggedTemplateSpans(
+            ts,
+            node,
+            meta,
+            script,
+            environment,
+            templateContext,
+          );
 
           directives.push(...result.directives);
           errors.push(...result.errors);
@@ -133,6 +154,10 @@ function calculateCorrelatedSpans(
       },
   ]);
 
+  if (templateContexts) {
+    templateContexts.length = templateIndex;
+  }
+
   return { errors, directives, partialSpans };
 }