Cleaner handling of clusure compiler errors (#7313)

Previously you would see an emscripten internal backtrace
if closure compiler failed.

Sadly we have a lot of existing warnings so we don't display
the process stderr unless we the subprcess returns non-zero.

I guess we should try to address the closure warnings, at least
the ones in emscripten proper.

Author: sbc100

tests/test_other.py

@@ -8594,16 +8594,17 @@ def test_IGNORE_CLOSURE_COMPILER_ERRORS(self):
       }
     ''')
 
-    def test(extra=[]):
-      run_process([PYTHON, EMCC, path_from_root('tests', 'hello_world.c'), '-O2', '--closure', '1', '--pre-js', 'pre.js'] + extra)
+    def test(check, extra=[]):
+      cmd = [PYTHON, EMCC, path_from_root('tests', 'hello_world.c'), '-O2', '--closure', '1', '--pre-js', 'pre.js'] + extra
+      proc = run_process(cmd, check=check, stderr=PIPE)
+      if not check:
+        self.assertNotEqual(proc.returncode, 0)
+      return proc
 
-    failed = False
-    try:
-      test()
-    except:
-      failed = True
-    assert failed
-    test(['-s', 'IGNORE_CLOSURE_COMPILER_ERRORS=1'])
+    proc = test(check=False)
+    self.assertContained('ERROR - Variable dupe declared more than once', proc.stderr)
+    proc = test(check=True, extra=['-s', 'IGNORE_CLOSURE_COMPILER_ERRORS=1'])
+    self.assertEqual(proc.stderr, '')
 
   def test_toolchain_profiler(self):
     environ = os.environ.copy()

tools/shared.py

@@ -2445,14 +2445,15 @@ def closure_compiler(filename, pretty=True):
 
       # Something like this (adjust memory as needed):
       #   java -Xmx1024m -jar CLOSURE_COMPILER --compilation_level ADVANCED_OPTIMIZATIONS --variable_map_output_file src.cpp.o.js.vars --js src.cpp.o.js --js_output_file src.cpp.o.cc.js
+      outfile = filename + '.cc.js'
       args = [JAVA,
               '-Xmx' + (os.environ.get('JAVA_HEAP_SIZE') or '1024m'), # if you need a larger Java heap, use this environment variable
               '-jar', CLOSURE_COMPILER,
               '--compilation_level', 'ADVANCED_OPTIMIZATIONS',
               '--language_in', 'ECMASCRIPT5',
               '--externs', CLOSURE_EXTERNS,
               # '--variable_map_output_file', filename + '.vars',
-              '--js', filename, '--js_output_file', filename + '.cc.js']
+              '--js', filename, '--js_output_file', outfile]
       for extern in NODE_EXTERNS:
         args.append('--externs')
         args.append(extern)
@@ -2466,11 +2467,12 @@ def closure_compiler(filename, pretty=True):
       if os.environ.get('EMCC_CLOSURE_ARGS'):
         args += shlex.split(os.environ.get('EMCC_CLOSURE_ARGS'))
       logging.debug('closure compiler: ' + ' '.join(args))
-      process = run_process(args, stdout=PIPE, stderr=STDOUT, check=False)
-      if process.returncode != 0 or not os.path.exists(filename + '.cc.js'):
-        raise Exception('closure compiler error: ' + process.stdout + ' (rc: %d)' % process.returncode)
+      proc = run_process(args, stderr=PIPE, check=False)
+      if proc.returncode != 0:
+        sys.stderr.write(proc.stderr)
+        exit_with_error('closure compiler failed (rc: %d)', proc.returncode)
 
-      return filename + '.cc.js'
+      return outfile
 
   # minify the final wasm+JS combination. this is done after all the JS
   # and wasm optimizations; here we do the very final optimizations on them