FIX Use response file for EXPORTED_FUNCTIONS (#4717)

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

docs/project/changelog.md

@@ -16,6 +16,9 @@ myst:
 
 ## Unreleased
 
+- {{ Fix }} pyodide-build now use response file when passing list of exported symbols to `emcc`.
+  This Fixes "Argument list too long" error.
+
 - {{ Fix }} Pass through `-E` (command mode) arguments in CMake wrapper {pr}`4705`.
 
 - {{ Fix }} Fix exception handling in dynamic linking of int64 functions {pr}`4698`.

packages/awkward-cpp/meta.yaml

@@ -11,7 +11,7 @@ source:
 build:
   script: |
     export CMAKE_ARGS="${CMAKE_ARGS} -DEMSCRIPTEN=1"
-  exports: whole_archive
+  exports: requested
 
 requirements:
   run:

packages/lightgbm/meta.yaml

@@ -6,7 +6,7 @@ source:
   sha256: 006f5784a9bcee43e5a7e943dc4f02de1ba2ee7a7af1ee5f190d383f3b6c9ebe
 build:
   backend-flags: cmake.define.USE_OPENMP=OFF
-  exports: whole_archive # FIXME: using "requested" fails with SIGKILL, not sure why
+  exports: requested
 requirements:
   run:
     - numpy

pyodide-build/pyodide_build/pywasmcross.py

@@ -427,8 +427,16 @@ def get_export_flags(
         export_list = calculate_exports(line, exports == "requested")
     else:
         export_list = exports
+
     prefixed_exports = ["_" + x for x in export_list]
-    yield f"-sEXPORTED_FUNCTIONS={prefixed_exports!r}"
+
+    import tempfile
+
+    with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
+        # Use a response file to avoid command line length limits
+        f.write(json.dumps(prefixed_exports))
+
+    yield f"-sEXPORTED_FUNCTIONS=@{f.name}"
 
 
 def handle_command_generate_args(  # noqa: C901