Improve support for clang information flags like -print-target-triple

emcc.py

@@ -86,6 +86,19 @@
     '--threadprofiler', '--use-preload-plugins',
 }
 
+PASSTHROUGH_FLAGS = {
+  '-print-resource-dir',
+  '--print-resource-dir',
+  '-dumpmachine',
+  '-print-target-triple',
+  '--print-target-triple',
+}
+
+PASSTHROUGH_PREFIXES = {
+  '-print-prog-name',
+  '--print-prog-name',
+}
+
 
 @unique
 class Mode(Enum):
@@ -263,10 +276,9 @@ def main(args):
     print(utils.EMSCRIPTEN_VERSION)
     return 0
 
-  if '-dumpmachine' in args or '-print-target-triple' in args or '--print-target-triple' in args:
-    print(shared.get_llvm_target())
-    return 0
-
+  # Sadly we cannot rely on PASSTHROUGH_FLAGS for -print-search-dirs or -print-libgcc-file-name
+  # because there is no way to tell clang today about our custom library paths.
+  # TODO: Teach clang about emscripten's library layout so we can remove this code.
   if '-print-search-dirs' in args or '--print-search-dirs' in args:
     print(f'programs: ={config.LLVM_ROOT}')
     resource_dir = get_clang_resource_dir(args)
@@ -307,8 +319,10 @@ def main(args):
   if 'EMCC_REPRODUCE' in os.environ:
     options.reproduce = os.environ['EMCC_REPRODUCE']
 
-  if '-print-resource-dir' in args or any(a.startswith('--print-prog-name') for a in args):
-    shared.exec_process([clang, *compile.get_cflags(tuple(args)), *args])
+  if any(a in PASSTHROUGH_FLAGS for a in args) or any(a.startswith(p) for p in PASSTHROUGH_PREFIXES for a in args):
+    # For several -print-xxx-name flags we just defer to clang rather than
+    # trying to re-implement the logic.
+    shared.exec_process([clang, *compile.get_cflags(tuple(args)), *newargs])
     assert False, 'exec_process should not return'
 
   if '--cflags' in args:

test/test_other.py

@@ -756,7 +756,7 @@ def test_print_resource_dir(self):
 
   @crossplatform
   def test_print_prog_name(self):
-    output = self.run_process([EMCC, '--print-prog-name=clang'], stdout=PIPE).stdout
+    output = self.run_process([EMCC, '-sASSERTIONS', '--print-prog-name=clang'], stdout=PIPE).stdout
     expected = CLANG_CC
     if WINDOWS:
       expected = os.path.normpath(utils.unsuffixed(CLANG_CC))