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.

emsdk.py

diff --git a/emsdk.py b/emsdk.py
index 90b4c55..ceb60f2 100644
--- a/emsdk.py
+++ b/emsdk.py
@@ -1411,6 +1411,47 @@
     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 will 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
+  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:
+    closure_compiler_native += '@20220104.0.0'
+    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)
+
+      # Now that we succeeded to install the native version, delete the Java version
+      # since that takes up ~12.5MB of installation space that is no longer needed
+      # as we have a native version of the compiler instead.
+      # 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'))
+
+      # Remove import of Java Closure Compiler module.
+      compiler_filename = os.path.join(directory, 'node_modules', 'google-closure-compiler', 'lib', 'node', 'closure-compiler.js')
+      compiler_js = open(compiler_filename, 'r').read().replace("require('google-closure-compiler-java')", "''/*require('google-closure-compiler-java') XXX Removed by Emsdk*/")
+      open(compiler_filename, 'w').write(compiler_js)
+    except subprocess.CalledProcessError as e:
+      errlog('Error running %s:\n%s' % (e.cmd, e.output))
+      return False
+
   print('Done running: npm ci')
   return True