[emcmake] Insert toolchain/emulator arg after user args (emscripten-core#15265)

ngzhian · web-flow · commit 5e6c74153b85 · 2021-10-11T09:58:45.000-07:00
This allows user specified command line arg to overwrite whatever is
specified in the toolchain file, can be useful to overwrite variables
like CMAKE_SYSTEM_PROCESSOR, which is used by projects to detect if
system is ARM. This way we can exercise both Emscripten's SSE headers
and NEON headers.
diff --git a/emcmake.py b/emcmake.py
@@ -29,13 +29,14 @@ def run():
   def has_substr(args, substr):
     return any(substr in s for s in args)
 
-  # Append the Emscripten toolchain file if the user didn't specify one.
+  # Insert arg for the Emscripten toolchain file if the user didn't specify one.
+  # User specified arguments come afterwards so they can overwrite variables defined in toolchain file.
   if not has_substr(args, '-DCMAKE_TOOLCHAIN_FILE'):
-    args.append('-DCMAKE_TOOLCHAIN_FILE=' + utils.path_from_root('cmake/Modules/Platform/Emscripten.cmake'))
+    args.insert(1, '-DCMAKE_TOOLCHAIN_FILE=' + utils.path_from_root('cmake/Modules/Platform/Emscripten.cmake'))
 
   if not has_substr(args, '-DCMAKE_CROSSCOMPILING_EMULATOR'):
     node_js = config.NODE_JS[0]
-    args.append(f'-DCMAKE_CROSSCOMPILING_EMULATOR={node_js}')
+    args.insert(1, f'-DCMAKE_CROSSCOMPILING_EMULATOR={node_js}')
 
   # On Windows specify MinGW Makefiles or ninja if we have them and no other
   # toolchain was specified, to keep CMake from pulling in a native Visual
