Fix native Closure Compiler to work. (#995)

* Fix native Closure Compiler to work. Reverts my earlier PR #803 which was a great mistake, as it caused Emscripten to silently fall back to Java version of the Closure Compiler. After this PR, Closure Compiler will work on user platforms that do not have Java installed. Also forcibly remove Java version of Closure Compiler on systems where installing the native version succeeds, in order to save on code size.

* Add note to bug

* Improve google-closure-compiler-java uninstall.

* Read Closure version from Emscripten repository

* Skip native google-closure-compiler install when it is not present in the emscripten branch in package.json

* Print error

Author: juj

emsdk.py

@@ -1402,6 +1402,8 @@ def emscripten_npm_install(tool, directory):
   env = os.environ.copy()
   env["PATH"] = node_path + os.pathsep + env["PATH"]
   print('Running post-install step: npm ci ...')
+  # Do a --no-optional install to avoid bloating disk size:
+  # https://github.com/emscripten-core/emscripten/issues/12406
   try:
     subprocess.check_output(
         [npm, 'ci', '--production', '--no-optional'],
@@ -1411,6 +1413,66 @@ def emscripten_npm_install(tool, directory):
     errlog('Error running %s:\n%s' % (e.cmd, e.output))
     return False
 
+  # Manually install the appropriate native Closure Compiler package
+  # This is currently needed because npm ci would install the packages
+  # for Closure for all platforms, adding 180MB to the download size
+  # There are two problems here:
+  #   1. npm ci does not consider the platform of optional dependencies
+  #      https://github.com/npm/cli/issues/558
+  #   2. A bug with the native compiler has bloated the packages from
+  #      30MB to almost 300MB
+  #      https://github.com/google/closure-compiler-npm/issues/186
+  # If either of these bugs are fixed then we can remove this exception
+  # See also https://github.com/google/closure-compiler/issues/3925
+  closure_compiler_native = ''
+  if LINUX and ARCH in ('x86', 'x86_64'):
+    closure_compiler_native = 'google-closure-compiler-linux'
+  if MACOS and ARCH in ('x86', 'x86_64'):
+    closure_compiler_native = 'google-closure-compiler-osx'
+  if WINDOWS and ARCH == 'x86_64':
+    closure_compiler_native = 'google-closure-compiler-windows'
+
+  if closure_compiler_native:
+    # Check which version of native Closure Compiler we want to install via npm.
+    # (npm install command has this requirement that we must explicitly tell the pinned version)
+    try:
+      closure_version = json.load(open(os.path.join(directory, 'package.json')))['dependencies']['google-closure-compiler']
+    except KeyError as e:
+      # The target version of Emscripten does not (did not) have a package.json that would contain google-closure-compiler. (fastcomp)
+      # Skip manual native google-closure-compiler installation there.
+      print(str(e))
+      print('Emscripten version does not have a npm package.json with google-closure-compiler dependency, skipping native google-closure-compiler install step')
+      return True
+
+    closure_compiler_native += '@' + closure_version
+    print('Running post-install step: npm install', closure_compiler_native)
+    try:
+      subprocess.check_output(
+        [npm, 'install', '--production', '--no-optional', closure_compiler_native],
+        cwd=directory, stderr=subprocess.STDOUT, env=env,
+        universal_newlines=True)
+
+      # Installation of native Closure compiler was successful, so remove import of Java Closure Compiler module to avoid
+      # a Java dependency.
+      compiler_filename = os.path.join(directory, 'node_modules', 'google-closure-compiler', 'lib', 'node', 'closure-compiler.js')
+      if os.path.isfile(compiler_filename):
+        old_js = open(compiler_filename, 'r').read()
+        new_js = old_js.replace("require('google-closure-compiler-java')", "''/*require('google-closure-compiler-java') XXX Removed by Emsdk*/")
+        if old_js == new_js:
+          raise Exception('Failed to patch google-closure-compiler-java dependency away!')
+        open(compiler_filename, 'w').write(new_js)
+
+        # Now that we succeeded to install the native version and patch away the Java dependency, delete the Java version
+        # since that takes up ~12.5MB of installation space that is no longer needed.
+        # This process is currently a little bit hacky, see https://github.com/google/closure-compiler/issues/3926
+        remove_tree(os.path.join(directory, 'node_modules', 'google-closure-compiler-java'))
+        print('Removed google-closure-compiler-java dependency.')
+      else:
+        errlog('Failed to patch away google-closure-compiler Java dependency. ' + compiler_filename + ' does not exist.')
+    except subprocess.CalledProcessError as e:
+      errlog('Error running %s:\n%s' % (e.cmd, e.output))
+      return False
+
   print('Done running: npm ci')
   return True