support template processing customization

packages/core/src/config/environment.ts

@@ -94,11 +94,15 @@ export class GlintEnvironment {
    * they support.
    */
   public getStandaloneTemplateConfig():
-    | Pick<GlintTemplateConfig, 'typesModule' | 'specialForms'>
+    | Pick<
+        GlintTemplateConfig,
+        'typesModule' | 'specialForms' | 'preprocess' | 'postprocessAst' | 'mapTemplateContent'
+      >
     | undefined {
     if (this.standaloneTemplateConfig) {
-      let { typesModule, specialForms } = this.standaloneTemplateConfig;
-      return { typesModule, specialForms };
+      let { typesModule, specialForms, preprocess, postprocessAst, mapTemplateContent } =
+        this.standaloneTemplateConfig;
+      return { typesModule, specialForms, preprocess, postprocessAst, mapTemplateContent };
     }
   }
 
@@ -189,7 +193,6 @@ function loadMergedEnvironmentConfig(
     }
 
     let config = envFunction(envUserConfig ?? {}) as GlintEnvironmentConfig;
-
     if (config.template) {
       if (template) {
         throw new SilentError(

packages/core/src/config/types.cts

@@ -1,4 +1,5 @@
 import type * as ts from 'typescript';
+import { AST } from '@glimmer/syntax';
 
 // This file is explicitly `.cts` so that environment packages written
 // in CJS can import its types from `@glint/core/config-types`.
@@ -96,6 +97,12 @@ export type PathCandidateWithDeferral = {
 };
 
 export type GlintTemplateConfig = {
+  preprocess?: (
+    templateInfo: { contents: string; filename: string },
+    args: { globals?: string[]; preamble?: string[] }
+  ) => { globals: string[]; preamble: string[]; template: string };
+  postprocessAst?: (ast: AST.Template) => AST.Template;
+  mapTemplateContent?: Record<string, any>;
   typesModule: string;
   specialForms?: { [global: string]: GlintSpecialForm };
   getPossibleTemplatePaths(scriptPath: string): Array<PathCandidate>;

packages/core/src/transform/template/inlining/companion-file.ts

@@ -31,11 +31,15 @@ export function calculateCompanionTemplateSpans(
     return { errors, directives, partialSpans };
   }
 
-  let { typesModule, specialForms } = templateConfig;
+  let { typesModule, specialForms, preprocess, postprocessAst, mapTemplateContent } =
+    templateConfig;
   let useJsDoc = environment.isUntypedScript(script.filename);
   let targetNode = findCompanionTemplateTarget(ts, ast);
   if (targetNode && ts.isClassLike(targetNode)) {
-    let rewriteResult = templateToTypescript(template.contents, {
+    let rewriteResult = templateToTypescript(template, {
+      preprocess,
+      postprocessAst,
+      mapTemplateContent,
       typesModule,
       specialForms,
       useJsDoc,
@@ -56,7 +60,10 @@ export function calculateCompanionTemplateSpans(
         : `({} as unknown as typeof import('./${moduleName}').default)`;
     }
 
-    let rewriteResult = templateToTypescript(template.contents, {
+    let rewriteResult = templateToTypescript(template, {
+      preprocess,
+      postprocessAst,
+      mapTemplateContent,
       typesModule,
       backingValue,
       specialForms,

packages/core/src/transform/template/map-template-contents.ts

@@ -118,6 +118,7 @@ export type EmbeddingSyntax = {
 
 export type MapTemplateContentsOptions = {
   embeddingSyntax: EmbeddingSyntax;
+  postprocessAst?: (ast: AST.Template) => AST.Template;
 };
 
 /**
@@ -128,14 +129,15 @@ export type MapTemplateContentsOptions = {
  */
 export function mapTemplateContents(
   template: string,
-  { embeddingSyntax }: MapTemplateContentsOptions,
+  { embeddingSyntax, postprocessAst }: 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);
+    ast = postprocessAst?.(ast) || ast;
   } catch (error) {
     let message = getErrorMessage(error);
     let location: Range | undefined;