Fix imported memory fallback and add common stdlib imports to loader

lib/loader/index.js

@@ -23,17 +23,24 @@ function getStringImpl(U32, U16, ptr) {
 function preInstantiate(imports) {
   var baseModule = {};
 
-  // add the internal abort function that is called when an assertion fails or an error is thrown
+  function getString(memory, ptr) {
-  if (!imports.env) imports.env = {};
+    if (!memory) return "<yet unknown>";
-  if (!imports.env.abort) imports.env.abort = function abort(mesg, file, line, colm) {
+    var buffer = memory.buffer;
-    var memory = baseModule.memory || imports.env.memory; // prefer exported, otherwise try imported
+    return getStringImpl(new Uint32Array(buffer), new Uint16Array(buffer), ptr);
-    function getString(memory, ptr) {
+  }
-      if (!memory) return "<yet unknown>";
+
-      var buffer = memory.buffer;
+  // add common imports used by stdlib for convenience
-      return getStringImpl(new Uint32Array(buffer), new Uint16Array(buffer), ptr);
+  var env = (imports.env = imports.env || {});
-    }
+  env.abort = env.abort || function abort(mesg, file, line, colm) {
+    var memory = baseModule.memory || env.memory; // prefer exported, otherwise try imported
     throw Error("abort: " + getString(memory, mesg) + " at " + getString(memory, file) + ":" + line + ":" + colm);
   }
+  env.trace = env.trace || function trace(mesg, n) {
+    var memory = baseModule.memory || env.memory;
+    console.log("trace: " + getString(memory, mesg) + (n ? " " : "") + Array.prototype.slice.call(arguments, 2, 2 + n).join(", "));
+  }
+  imports.Math = imports.Math || Math;
+  imports.Date = imports.Date || Date;
 
   return baseModule;
 }
@@ -176,6 +183,10 @@ function postInstantiate(baseModule, instance) {
 
   baseModule.getFunction = getFunction;
 
+  // Pull basic exports to baseModule so code in preInstantiate can use them
+  baseModule.memory = baseModule.memory || memory;
+  baseModule.table = baseModule.table || table;
+
   // Demangle exports and provide the usual utility on the prototype
   return demangle(rawExports, Object.defineProperties(baseModule, {
     I8: { get: function() { checkMem(); return I8; } },

lib/loader/tests/assembly/index.ts

@@ -60,3 +60,7 @@ export const varadd_ptr = varadd;
 export function calladd(fn: (a: i32, b: i32) => i32, a: i32, b: i32): i32 {
   return fn(a, b);
 }
+
+export function dotrace(num: f64): void {
+  trace("The answer is", 1, num);
+}

lib/loader/tests/index.js

@@ -59,3 +59,6 @@ assert.strictEqual(fn(2), 4);
 // should be able to create a new function and call it from WASM
 ptr = module.newFunction(module.varadd);
 assert.strictEqual(module.calladd(ptr, 2, 3), 5);
+
+// should be able to use trace
+module.dotrace(42);