Rename `wasm2asm` to `wasm2js`, emit ESM by default (#1642)

* Rename the `wasm2asm` tool to `wasm2js`

This commit performs a relatively simple rename of the `wasm2asm` tool to
`wasm2js`. The functionality of the tool doesn't change just yet but it's
intended that we'll start generating an ES module instead of just an `asm.js`
function soon.

* wasm2js: Support `*.wasm` input files

Previously `wasm2js` only supported `*.wast` files but to make it a bit easier
to use in tooling pipelines this commit adds support for reading in a `*.wasm`
file directly. Determining which parser to use depends on the input filename,
where the binary parser is used with `*.wasm` files and the wast parser is used
for all other files.

* wasm2js: Emit ESM imports/exports by default

This commit alters the default behavior of `wasm2js` to emit an ESM by default,
either importing items from the environment or exporting. Items like
initialization of memory are also handled here.

5 files changed, 77 insertions, 40 deletions

diff --git a/scripts/test/node-esm-loader.mjs b/scripts/test/node-esm-loader.mjs
new file mode 100644
index 000000000..73ff47800
--- /dev/null
+++ b/scripts/test/node-esm-loader.mjs
@@ -0,0 +1,32 @@
+// originally lifted from https://nodejs.org/api/esm.html
+
+import path from 'path';
+import process from 'process';
+import Module from 'module';
+
+const builtins = Module.builtinModules;
+
+const baseURL = new URL('file://');
+baseURL.pathname = `${process.cwd()}/`;
+
+export function resolve(specifier, parentModuleURL = baseURL, defaultResolve) {
+  if (builtins.includes(specifier)) {
+    return {
+      url: specifier,
+      format: 'builtin'
+    };
+  }
+  // Resolve the 'spectest' module to our special module which has some builtins
+  if (specifier == 'spectest') {
+    const resolved = new URL('./scripts/test/spectest.js', parentModuleURL);
+    return {
+      url: resolved.href,
+      format: 'esm'
+    };
+  }
+  const resolved = new URL(specifier, parentModuleURL);
+  return {
+    url: resolved.href,
+    format: 'esm'
+  };
+}
diff --git a/scripts/test/shared.py b/scripts/test/shared.py
index 309f3b59a..a7bdda085 100644
--- a/scripts/test/shared.py
+++ b/scripts/test/shared.py
@@ -166,7 +166,7 @@ WASM_OPT = [os.path.join(options.binaryen_bin, 'wasm-opt')]
 WASM_AS = [os.path.join(options.binaryen_bin, 'wasm-as')]
 WASM_DIS = [os.path.join(options.binaryen_bin, 'wasm-dis')]
 ASM2WASM = [os.path.join(options.binaryen_bin, 'asm2wasm')]
-WASM2ASM = [os.path.join(options.binaryen_bin, 'wasm2asm')]
+WASM2JS = [os.path.join(options.binaryen_bin, 'wasm2js')]
 WASM_CTOR_EVAL = [os.path.join(options.binaryen_bin, 'wasm-ctor-eval')]
 WASM_SHELL = [os.path.join(options.binaryen_bin, 'wasm-shell')]
 WASM_MERGE = [os.path.join(options.binaryen_bin, 'wasm-merge')]
diff --git a/scripts/test/spectest.js b/scripts/test/spectest.js
new file mode 100644
index 000000000..0756209b6
--- /dev/null
+++ b/scripts/test/spectest.js
@@ -0,0 +1,3 @@
+export function print(...args) {
+  console.log(...args);
+}
diff --git a/scripts/test/support.py b/scripts/test/support.py
index d04a85c59..5d03419b9 100644
--- a/scripts/test/support.py
+++ b/scripts/test/support.py
@@ -147,7 +147,7 @@ def split_wast(wastFile):
 
 
 def run_command(cmd, expected_status=0, stderr=None,
-                expected_err=None, err_contains=False):
+                expected_err=None, err_contains=False, err_ignore=None):
   if expected_err is not None:
     assert stderr == subprocess.PIPE or stderr is None,\
         "Can't redirect stderr if using expected_err"
@@ -158,11 +158,13 @@ def run_command(cmd, expected_status=0, stderr=None,
   code = proc.returncode
   if expected_status is not None and code != expected_status:
     raise Exception(('run_command failed (%s)' % code, out + str(err or '')))
-  err_correct = expected_err is None or \
-      (expected_err in err if err_contains else expected_err == err)
-  if not err_correct:
-    raise Exception(('run_command unexpected stderr',
-                     "expected '%s', actual '%s'" % (expected_err, err)))
+  if expected_err is not None:
+    if err_ignore is not None:
+      err = "\n".join([line for line in err.split('\n') if err_ignore not in line])
+    err_correct = expected_err in err if err_contains else expected_err == err
+    if not err_correct:
+      raise Exception(('run_command unexpected stderr',
+                       "expected '%s', actual '%s'" % (expected_err, err)))
   return out
 
 
diff --git a/scripts/test/wasm2asm.py b/scripts/test/wasm2js.py
index 41fdaf9b7..9a72895c1 100755
--- a/scripts/test/wasm2asm.py
+++ b/scripts/test/wasm2js.py
@@ -18,7 +18,7 @@ import os
 
 from support import run_command
 from shared import (
-    WASM2ASM, MOZJS, NODEJS, fail_if_not_identical, options, tests,
+    WASM2JS, MOZJS, NODEJS, fail_if_not_identical, options, tests,
     fail_if_not_identical_to_file
 )
 
@@ -27,26 +27,31 @@ spec_dir = os.path.join(options.binaryen_test, 'spec')
 spec_tests = [os.path.join(spec_dir, t)
               for t in sorted(os.listdir(spec_dir))
               if '.fail' not in t]
-wasm2asm_dir = os.path.join(options.binaryen_test, 'wasm2asm')
-extra_wasm2asm_tests = [os.path.join(wasm2asm_dir, t) for t in
-                        sorted(os.listdir(wasm2asm_dir))]
-assert_tests = ['wasm2asm.wast.asserts']
+wasm2js_dir = os.path.join(options.binaryen_test, 'wasm2js')
+extra_wasm2js_tests = [os.path.join(wasm2js_dir, t) for t in
+                       sorted(os.listdir(wasm2js_dir))]
+assert_tests = ['wasm2js.wast.asserts']
+# These tests exercise functionality not supported by wasm2js
+wasm2js_blacklist = ['empty_imported_table.wast']
 
 
-def test_wasm2asm_output():
-  for wasm in tests + spec_tests + extra_wasm2asm_tests:
+def test_wasm2js_output():
+  for wasm in tests + spec_tests + extra_wasm2js_tests:
     if not wasm.endswith('.wast'):
       continue
+    basename = os.path.basename(wasm)
+    if basename in wasm2js_blacklist:
+      continue
 
-    asm = os.path.basename(wasm).replace('.wast', '.2asm.js')
-    expected_file = os.path.join(wasm2asm_dir, asm)
+    asm = basename.replace('.wast', '.2asm.js')
+    expected_file = os.path.join(wasm2js_dir, asm)
 
     if not os.path.exists(expected_file):
       continue
 
     print '..', wasm
 
-    cmd = WASM2ASM + [os.path.join(options.binaryen_test, wasm)]
+    cmd = WASM2JS + [os.path.join(options.binaryen_test, wasm)]
     out = run_command(cmd)
     fail_if_not_identical_to_file(out, expected_file)
 
@@ -54,32 +59,27 @@ def test_wasm2asm_output():
       print 'No JS interpreters. Skipping spec tests.'
       continue
 
-    open('a.2asm.js', 'w').write(out)
+    open('a.2asm.mjs', 'w').write(out)
 
     cmd += ['--allow-asserts']
     out = run_command(cmd)
 
-    open('a.2asm.asserts.js', 'w').write(out)
+    open('a.2asm.asserts.mjs', 'w').write(out)
 
-    # verify asm.js is valid js
+    # verify asm.js is valid js, note that we're using --experimental-modules
+    # to enable ESM syntax and we're also passing a custom loader to handle the
+    # `spectest` module in our tests.
     if NODEJS:
-      out = run_command([NODEJS, 'a.2asm.js'])
+      node = [NODEJS, '--experimental-modules', '--loader', './scripts/test/node-esm-loader.mjs']
+      cmd = node[:]
+      cmd.append('a.2asm.mjs')
+      out = run_command(cmd)
       fail_if_not_identical(out, '')
-      out = run_command([NODEJS, 'a.2asm.asserts.js'], expected_err='')
+      cmd = node[:]
+      cmd.append('a.2asm.asserts.mjs')
+      out = run_command(cmd, expected_err='', err_ignore='The ESM module loader is experimental')
       fail_if_not_identical(out, '')
 
-    if MOZJS:
-      # verify asm.js validates, if this is asm.js code (we emit
-      # almost-asm instead when we need to)
-      if 'use asm' in open('a.2asm.js').read():
-        # check only subset of err because mozjs emits timing info
-        out = run_command([MOZJS, '-w', 'a.2asm.js'],
-                          expected_err='Successfully compiled asm.js code',
-                          err_contains=True)
-        fail_if_not_identical(out, '')
-        out = run_command([MOZJS, 'a.2asm.asserts.js'], expected_err='')
-        fail_if_not_identical(out, '')
-
 
 def test_asserts_output():
   for wasm in assert_tests:
@@ -90,8 +90,8 @@ def test_asserts_output():
     asserts_expected_file = os.path.join(options.binaryen_test, asserts)
     traps_expected_file = os.path.join(options.binaryen_test, traps)
 
-    wasm = os.path.join(wasm2asm_dir, wasm)
-    cmd = WASM2ASM + [wasm, '--allow-asserts']
+    wasm = os.path.join(wasm2js_dir, wasm)
+    cmd = WASM2JS + [wasm, '--allow-asserts']
     out = run_command(cmd)
     fail_if_not_identical_to_file(out, asserts_expected_file)
 
@@ -100,11 +100,11 @@ def test_asserts_output():
     fail_if_not_identical_to_file(out, traps_expected_file)
 
 
-def test_wasm2asm():
-  print '\n[ checking wasm2asm testcases... ]\n'
-  test_wasm2asm_output()
+def test_wasm2js():
+  print '\n[ checking wasm2js testcases... ]\n'
+  test_wasm2js_output()
   test_asserts_output()
 
 
 if __name__ == "__main__":
-  test_wasm2asm()
+  test_wasm2js()