Improvements to bundling. (#3965)

Moves to using a minimal System loader for bundles generated by Deno.
TypeScript in 3.8 will be able to output TLA for modules, and the loader
is written to take advantage of that as soon as we update Deno to TS
3.8.

System also allows us to support `import.meta` and provide more ESM
aligned assignment of exports, as well as there is better handling of
circular imports.

The loader is also very terse versus to try to save overhead.

Also, fixed an issue where abstract classes were not being re-exported.

Fixes #2553
Fixes #3559
Fixes #3751
Fixes #3825
Refs #3301

2 files changed, 86 insertions, 1 deletions

diff --git a/deno_typescript/lib.rs b/deno_typescript/lib.rs
index 7977b7cfe..9056fd903 100644
--- a/deno_typescript/lib.rs
+++ b/deno_typescript/lib.rs
@@ -245,7 +245,7 @@ pub fn get_asset(name: &str) -> Option<&'static str> {
     };
   }
   match name {
-    "bundle_loader.js" => Some(include_str!("bundle_loader.js")),
+    "system_loader.js" => Some(include_str!("system_loader.js")),
     "bootstrap.ts" => Some("console.log(\"hello deno\");"),
     "typescript.d.ts" => inc!("typescript.d.ts"),
     "lib.esnext.d.ts" => inc!("lib.esnext.d.ts"),
diff --git a/deno_typescript/system_loader.js b/deno_typescript/system_loader.js
new file mode 100644
index 000000000..c1365f6c8
--- /dev/null
+++ b/deno_typescript/system_loader.js
@@ -0,0 +1,85 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+
+// This is a specialised implementation of a System module loader.
+
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+let System;
+let __inst;
+
+(() => {
+  const mMap = new Map();
+  System = {
+    register(id, deps, f) {
+      mMap.set(id, {
+        id,
+        deps,
+        f,
+        exp: {}
+      });
+    }
+  };
+
+  const gC = (data, main) => {
+    const { id } = data;
+    return {
+      id,
+      import: async id => mMap.get(id)?.exp,
+      meta: { url: id, main }
+    };
+  };
+
+  const gE = data => {
+    const { exp } = data;
+    return (id, value) => {
+      const values = typeof id === "string" ? { [id]: value } : id;
+      for (const [id, value] of Object.entries(values)) {
+        Object.defineProperty(exp, id, {
+          value,
+          writable: true,
+          enumerable: true
+        });
+      }
+    };
+  };
+
+  const iQ = [];
+
+  const enq = ids => {
+    for (const id of ids) {
+      if (!iQ.includes(id)) {
+        const { deps } = mMap.get(id);
+        iQ.push(id);
+        enq(deps);
+      }
+    }
+  };
+
+  const dr = async main => {
+    const rQ = [];
+    let id;
+    while ((id = iQ.pop())) {
+      const m = mMap.get(id);
+      const { f } = m;
+      if (!f) {
+        return;
+      }
+      rQ.push([m.deps, f(gE(m), gC(m, id === main))]);
+      m.f = undefined;
+    }
+    let r;
+    while ((r = rQ.shift())) {
+      const [deps, { execute, setters }] = r;
+      for (let i = 0; i < deps.length; i++) setters[i](mMap.get(deps[i])?.exp);
+      const e = execute();
+      if (e) await e;
+    }
+  };
+
+  __inst = async id => {
+    System = undefined;
+    __inst = undefined;
+    enq([id]);
+    await dr(id);
+    return mMap.get(id)?.exp;
+  };
+})();