Provide compiled JSON to TypeScript compiler. (#4404)

Fixes #4101

Previously, we would just provide the raw JSON to the TypeScript
compiler worker, but TypeScript does not transform JSON.  This caused
a problem when emitting a bundle, that the JSON would just be "inlined"
into the output, instead of being transformed into a module.

This fixes this problem by providing the compiled JSON to the TypeScript
compiler, so TypeScript just sees JSON as a "normal" TypeScript module.

1 files changed, 4 insertions, 1 deletions

diff --git a/cli/js/compiler/sourcefile.ts b/cli/js/compiler/sourcefile.ts
index 159ccda85..e400acbf5 100644
--- a/cli/js/compiler/sourcefile.ts
+++ b/cli/js/compiler/sourcefile.ts
@@ -35,7 +35,10 @@ function getExtension(fileName: string, mediaType: MediaType): ts.Extension {
     case MediaType.TSX:
       return ts.Extension.Tsx;
     case MediaType.Json:
-      return ts.Extension.Json;
+      // we internally compile JSON, so what gets provided to the TypeScript
+      // compiler is an ES module, but in order to get TypeScript to handle it
+      // properly we have to pretend it is TS.
+      return ts.Extension.Ts;
     case MediaType.Wasm:
       // Custom marker for Wasm type.
       return ts.Extension.Js;