[build] Fix script for conda MacOS

Author: vepadulano

cmake/scripts/std_modulemap_darwin_fix.py

@@ -25,6 +25,13 @@ def main():
     output_path = sys.argv[1]
     sdk = get_sdk_path()
     cpp_modulemap = os.path.join(sdk, "usr/include/c++/v1/module.modulemap")
+    if not os.path.exists(cpp_modulemap):
+        # Try again if we are running a conda build. conda-forge ships the MacOS SDK stripped of libc++.
+        # Instead, the standard libraries are shipped as a separate package which must be declared as a build
+        # dependency and thus ends up in the $BUILD_PREFIX path. For explanation, see
+        # https://conda-forge.zulipchat.com/#narrow/channel/516932-compilers/topic/Organisation.20of.20libc.2B.2B.20and.20SDKs.20on.20MacOS
+        if (os.environ.get("CONDA_BUILD", "0") == "1") and (os.environ.get("BUILD_PREFIX", None) is not None):
+            cpp_modulemap = os.path.join(os.environ["BUILD_PREFIX"], "include/c++/v1/module.modulemap")
 
     if not os.path.exists(cpp_modulemap):
         raise FileNotFoundError(f"Cannot find libc++ modulemap at {cpp_modulemap}")