Refactor internal closure_compiler method. NFC (#15761)

This refactoring is to allow for closure to be run
in traspile-only mode in a followup PR.

Author: sbc100

tools/building.py

@@ -707,16 +707,8 @@ def isascii(s):
     return True
 
 
-@ToolchainProfiler.profile_block('closure_compiler')
-def closure_compiler(filename, pretty, advanced=True, extra_closure_args=None):
+def get_closure_compiler_and_env(user_args):
   env = shared.env_with_node_in_path()
-  user_args = []
-  env_args = os.environ.get('EMCC_CLOSURE_ARGS')
-  if env_args:
-    user_args += shlex.split(env_args)
-  if extra_closure_args:
-    user_args += extra_closure_args
-
   closure_cmd = get_closure_compiler()
 
   native_closure_compiler_works = check_closure_compiler(closure_cmd, user_args, env, allowed_to_fail=True)
@@ -737,6 +729,20 @@ def add_to_path(dirname):
       java_home = os.path.dirname(java_bin)
       env.setdefault('JAVA_HOME', java_home)
 
+  return closure_cmd, env
+
+
+@ToolchainProfiler.profile_block('closure_compiler')
+def closure_compiler(filename, pretty, advanced=True, extra_closure_args=None):
+  user_args = []
+  env_args = os.environ.get('EMCC_CLOSURE_ARGS')
+  if env_args:
+    user_args += shlex.split(env_args)
+  if extra_closure_args:
+    user_args += extra_closure_args
+
+  closure_cmd, env = get_closure_compiler_and_env(user_args)
+
   # Closure externs file contains known symbols to be extern to the minification, Closure
   # should not minify these symbol names.
   CLOSURE_EXTERNS = [path_from_root('src/closure-externs/closure-externs.js')]
@@ -792,10 +798,23 @@ def add_to_path(dirname):
   # Tell closure never to inject the 'use strict' directive.
   args += ['--emit_use_strict=false']
 
+  if settings.IGNORE_CLOSURE_COMPILER_ERRORS:
+    args.append('--jscomp_off=*')
+  # Specify input file relative to the temp directory to avoid specifying non-7-bit-ASCII path names.
+  for e in CLOSURE_EXTERNS:
+    args += ['--externs', e]
+  args += user_args
+
+  cmd = closure_cmd + args
+  return run_closure_cmd(cmd, filename, env, pretty=pretty)
+
+
+def run_closure_cmd(cmd, filename, env, pretty):
+  cmd += ['--js', filename]
+
   # Closure compiler is unable to deal with path names that are not 7-bit ASCII:
   # https://github.com/google/closure-compiler/issues/3784
   tempfiles = configuration.get_temp_files()
-  outfile = tempfiles.get('.cc.js').name  # Safe 7-bit filename
 
   def move_to_safe_7bit_ascii_filename(filename):
     if isascii(filename):
@@ -804,23 +823,17 @@ def move_to_safe_7bit_ascii_filename(filename):
     shutil.copyfile(filename, safe_filename)
     return os.path.relpath(safe_filename, tempfiles.tmpdir)
 
-  for e in CLOSURE_EXTERNS:
-    args += ['--externs', move_to_safe_7bit_ascii_filename(e)]
+  for i in range(len(cmd)):
+    if cmd[i] == '--externs' or cmd[i] == '--js':
+      cmd[i + 1] = move_to_safe_7bit_ascii_filename(cmd[i + 1])
 
-  for i in range(len(user_args)):
-    if user_args[i] == '--externs':
-      user_args[i + 1] = move_to_safe_7bit_ascii_filename(user_args[i + 1])
+  outfile = tempfiles.get('.cc.js').name  # Safe 7-bit filename
 
   # Specify output file relative to the temp directory to avoid specifying non-7-bit-ASCII path names.
-  args += ['--js_output_file', os.path.relpath(outfile, tempfiles.tmpdir)]
-
-  if settings.IGNORE_CLOSURE_COMPILER_ERRORS:
-    args.append('--jscomp_off=*')
+  cmd += ['--js_output_file', os.path.relpath(outfile, tempfiles.tmpdir)]
   if pretty:
-    args += ['--formatting', 'PRETTY_PRINT']
-  # Specify input file relative to the temp directory to avoid specifying non-7-bit-ASCII path names.
-  args += ['--js', move_to_safe_7bit_ascii_filename(filename)]
-  cmd = closure_cmd + args + user_args
+    cmd += ['--formatting', 'PRETTY_PRINT']
+
   logger.debug(f'closure compiler: {shared.shlex_join(cmd)}')
 
   # Closure compiler does not work if any of the input files contain characters outside the