Assert empty JS heap/stack in tests

Turns out there was a bug when passing a vector of `JsValue` instances back to
JS all objects were leaked rather than correctly removed from the global slab.

crates/cli-support/src/js/mod.rs

@@ -633,6 +633,15 @@ impl<'a> Context<'a> {
         self.global(&format!("
             let stack = [];
         "));
+        if self.config.debug {
+            self.export("assertStackEmpty", "
+                function() {
+                    if (stack.length === 0)
+                        return;
+                    throw new Error('stack is not currently empty');
+                }
+            ");
+        }
     }
 
     fn expose_global_slab(&mut self) {
@@ -640,6 +649,17 @@ impl<'a> Context<'a> {
             return;
         }
         self.global(&format!("let slab = [];"));
+        if self.config.debug {
+            self.export("assertSlabEmpty", "
+                function() {
+                    for (let i = 0; i < slab.length; i++) {
+                        if (typeof(slab[i]) === 'number')
+                            continue;
+                        throw new Error('slab is not currently empty');
+                    }
+                }
+            ");
+        }
     }
 
     fn expose_global_slab_next(&mut self) {
@@ -882,14 +902,14 @@ impl<'a> Context<'a> {
             return;
         }
         self.expose_get_array_u32_from_wasm();
-        self.expose_get_object();
+        self.expose_take_object();
         self.global(&format!("
             function getArrayJsValueFromWasm(ptr, len) {{
                 const mem = getUint32Memory();
                 const slice = mem.slice(ptr / 4, ptr / 4 + len);
                 const result = [];
                 for (let i = 0; i < slice.length; i++) {{
-                    result.push(getObject(slice[i]))
+                    result.push(takeObject(slice[i]))
                 }}
                 return result;
             }}

tests/all/imports.rs

@@ -283,6 +283,7 @@ fn free_imports() {
 #[test]
 fn import_a_field() {
     project()
+        .debug(false)
         .file("src/lib.rs", r#"
             #![feature(proc_macro, wasm_custom_section, wasm_import_module)]
 

tests/all/main.rs

@@ -48,11 +48,18 @@ fn project() -> Project {
 
             ("run.js".to_string(), r#"
                 import * as process from "process";
+                let wasm = import('./out');
 
                 const test = import("./test");
 
-                test.then(test => {
+                Promise.all([test, wasm]).then(results => {
+                  let [test, wasm] = results;
                   test.test();
+
+                  if (wasm.assertStackEmpty)
+                    wasm.assertStackEmpty();
+                  if (wasm.assertSlabEmpty)
+                    wasm.assertSlabEmpty();
                 }).catch(error => {
                   console.error(error);
                   process.exit(1);

tests/all/simple.rs

@@ -216,7 +216,7 @@ fn no_std() {
 
             use wasm_bindgen::prelude::*;
 
-            #[wasm_bindgen]
+            #[wasm_bindgen(module = "./foo")]
             extern {
                 fn test(a: &str);
 
@@ -238,6 +238,12 @@ fn no_std() {
                 wasm.foo(1);
             }
         "#)
+        .file("foo.js", r#"
+            export class Js {
+                init() {
+                }
+            }
+        "#)
         .test();
 }