Deno.bundle supports targets < ES2017. (#6328)

This commit provides a "system_loader_es5.js" bundle loader which will be added
to the bundle when the target is < ES2017, which is the minimum target syntax
required for "system_loader.js".

Supports #5913 (via Deno.bundle()) with a couple caveats:

* Allowing "deno bundle" to take a different target is not supported, as we
specifically ignore "target" when passed in a TypeScript config file. This is
because deno bundle is really intended to generate bundles that work in Deno.
It is an unintentional side effect that some bundles are loadable in browsers.

* While a target of "es3" will be accepted, the module loader will still only be
compatible with ES5 or later. Realistically no one should be expecting bundles
generated by Deno to be used on IE8 and prior, and there is just too much
"baggage" to support that at this point.

1 files changed, 27 insertions, 7 deletions

diff --git a/cli/js/compiler.ts b/cli/js/compiler.ts
index abe145da2..46dbfcaf9 100644
--- a/cli/js/compiler.ts
+++ b/cli/js/compiler.ts
@@ -307,6 +307,10 @@ class Host implements ts.CompilerHost {
     }
   }
 
+  get options(): ts.CompilerOptions {
+    return this.#options;
+  }
+
   configure(
     cwd: string,
     path: string,
@@ -528,6 +532,7 @@ const _TS_SNAPSHOT_PROGRAM = ts.createProgram({
 
 // This function is called only during snapshotting process
 const SYSTEM_LOADER = getAsset("system_loader.js");
+const SYSTEM_LOADER_ES5 = getAsset("system_loader_es5.js");
 
 function buildLocalSourceFileCache(
   sourceFileMap: Record<string, SourceFileMapEntry>
@@ -683,7 +688,12 @@ function createBundleWriteFile(state: WriteFileState): WriteFileCallback {
     assert(state.bundle);
     // we only support single root names for bundles
     assert(state.rootNames.length === 1);
-    state.bundleOutput = buildBundle(state.rootNames[0], data, sourceFiles);
+    state.bundleOutput = buildBundle(
+      state.rootNames[0],
+      data,
+      sourceFiles,
+      state.host.options.target ?? ts.ScriptTarget.ESNext
+    );
   };
 }
 
@@ -949,7 +959,8 @@ function normalizeUrl(rootName: string): string {
 function buildBundle(
   rootName: string,
   data: string,
-  sourceFiles: readonly ts.SourceFile[]
+  sourceFiles: readonly ts.SourceFile[],
+  target: ts.ScriptTarget
 ): string {
   // when outputting to AMD and a single outfile, TypeScript makes up the module
   // specifiers which are used to define the modules, and doesn't expose them
@@ -967,8 +978,8 @@ function buildBundle(
   let instantiate: string;
   if (rootExports && rootExports.length) {
     instantiate = hasTla
-      ? `const __exp = await __instantiateAsync("${rootName}");\n`
-      : `const __exp = __instantiate("${rootName}");\n`;
+      ? `const __exp = await __instantiate("${rootName}", true);\n`
+      : `const __exp = __instantiate("${rootName}", false);\n`;
     for (const rootExport of rootExports) {
       if (rootExport === "default") {
         instantiate += `export default __exp["${rootExport}"];\n`;
@@ -978,10 +989,19 @@ function buildBundle(
     }
   } else {
     instantiate = hasTla
-      ? `await __instantiateAsync("${rootName}");\n`
-      : `__instantiate("${rootName}");\n`;
+      ? `await __instantiate("${rootName}", true);\n`
+      : `__instantiate("${rootName}", false);\n`;
   }
-  return `${SYSTEM_LOADER}\n${data}\n${instantiate}`;
+  const es5Bundle =
+    target === ts.ScriptTarget.ES3 ||
+    target === ts.ScriptTarget.ES5 ||
+    target === ts.ScriptTarget.ES2015 ||
+    target === ts.ScriptTarget.ES2016
+      ? true
+      : false;
+  return `${
+    es5Bundle ? SYSTEM_LOADER_ES5 : SYSTEM_LOADER
+  }\n${data}\n${instantiate}`;
 }
 
 function setRootExports(program: ts.Program, rootModule: string): void {