Support loading additional TS lib files (#3863)

Fixes #3726

This PR provides support for referencing other lib files (like lib.dom.d.ts that are not
used by default in Deno.

1 files changed, 13 insertions, 9 deletions

diff --git a/cli/js/compiler_util.ts b/cli/js/compiler_util.ts
index b58d8da43..a28e2d109 100644
--- a/cli/js/compiler_util.ts
+++ b/cli/js/compiler_util.ts
@@ -92,15 +92,19 @@ function cache(
 }
 
 let OP_FETCH_ASSET: number;
+const encoder = new TextEncoder();
+const decoder = new TextDecoder();
 
-/**
- * This op is called only during snapshotting.
- *
- * We really don't want to depend on JSON dispatch
- * during snapshotting, so this op exchanges strings with Rust
- * as raw byte arrays.
- */
+/** Retrieve an asset from Rust. */
 export function getAsset(name: string): string {
+  // this path should only be called for assets that are lazily loaded at
+  // runtime
+  if (dispatch.OP_FETCH_ASSET) {
+    util.log("compiler_util::getAsset", name);
+    return sendSync(dispatch.OP_FETCH_ASSET, { name }).sourceCode;
+  }
+
+  // this path should only be taken during snapshotting
   if (!OP_FETCH_ASSET) {
     const ops = core.ops();
     const opFetchAsset = ops["fetch_asset"];
@@ -108,8 +112,8 @@ export function getAsset(name: string): string {
     OP_FETCH_ASSET = opFetchAsset;
   }
 
-  const encoder = new TextEncoder();
-  const decoder = new TextDecoder();
+  // We really don't want to depend on JSON dispatch during snapshotting, so
+  // this op exchanges strings with Rust as raw byte arrays.
   const sourceCodeBytes = core.dispatch(OP_FETCH_ASSET, encoder.encode(name));
   return decoder.decode(sourceCodeBytes!);
 }