Skip building C extensions for the target

(except for numpy)

pyodide_build/pywasmcross.py

@@ -59,10 +59,43 @@ def collect_args(basename):
         path = path.replace(str(ROOTDIR) + ':', '')
     env['PATH'] = path
 
+    # determine the package name from the current directory
+    re_res = re.match('.*packages/(?P<name>[\w\-]+)/build.*',
+                      env['PWD'])
+    if re_res:
+        package_name = re_res.group('name')
+    else:
+        package_name = None
+
+    # Skip compilations of C/Fortran extensions for the target environement.
+    # We still need to generate the output files for distutils to continue
+    # the build.
+    # TODO: This may need slight tuning for new projects. In particular,
+    #       currently ar is not skipped, so a known failure would happen when
+    #       we create some object files (that are empty as gcc is skipped), on
+    #       which we run the actual ar command.
+    skip = False
+    if (basename in ['gcc', 'cc', 'c++', 'gfortran', 'ld']
+            and '-o' in sys.argv[1:]
+            # do not skip numpy as it is needed as build time
+            # dependency by other packages (e.g. matplotlib)
+            and package_name != 'numpy'):
+        out_idx = sys.argv.index('-o')
+        if (out_idx + 1) < len(sys.argv):
+            # get the index of the output file path
+            out_idx += 1
+            with open(sys.argv[out_idx], 'wb') as fh:
+                fh.write(b'')
+            skip = True
     with open('build.log', 'a') as fd:
+        if skip:
+            fd.write('SKIP\n')
         json.dump([basename] + sys.argv[1:], fd)
         fd.write('\n')
 
+    if skip:
+        sys.exit(0)
+
     sys.exit(
         subprocess.run(
             [basename] + sys.argv[1:],