Save symlinks directory when building with recipe builder (#96)

Instead of putting the symlinks directory in a temp directory and
deleting after the build is finished, put it under the build directory.
This makes reproducing compile errors much easier, and the `build`
directory is already just scratch files.

pyodide_build/pypabuild.py

@@ -242,6 +242,23 @@ def make_command_wrapper_symlinks(symlink_dir: Path) -> dict[str, str]:
     return env
 
 
+@contextmanager
+def _create_symlink_dir(env: dict[str, str], build_dir: Path | None):
+    if build_dir:
+        # If we're running under build-recipes, leave the symlinks in
+        # the build directory. This helps with reproducing.
+        symlink_dir = build_dir / "pywasmcross_symlinks"
+        shutil.rmtree(symlink_dir, ignore_errors=True)
+        symlink_dir.mkdir()
+        yield symlink_dir
+        return
+
+    # Running from "pyodide build". Put symlinks in a temporary directory.
+    # TODO: Add a debug option to save the symlinks.
+    with TemporaryDirectory() as symlink_dir_str:
+        yield Path(symlink_dir_str)
+
+
 @contextmanager
 def get_build_env(
     env: dict[str, str],
@@ -252,6 +269,7 @@ def get_build_env(
     ldflags: str,
     target_install_dir: str,
     exports: _BuildSpecExports,
+    build_dir: Path | None = None,
 ) -> Iterator[dict[str, str]]:
     """
     Returns a dict of environment variables that should be used when building
@@ -267,14 +285,11 @@ def get_build_env(
     }
 
     args = common.environment_substitute_args(kwargs, env)
-    args["builddir"] = str(Path(".").absolute())
     args["exports"] = exports
     env = env.copy()
 
-    with TemporaryDirectory() as symlink_dir_str:
-        symlink_dir = Path(symlink_dir_str)
+    with _create_symlink_dir(env, build_dir) as symlink_dir:
         env.update(make_command_wrapper_symlinks(symlink_dir))
-
         sysconfig_dir = Path(get_build_flag("TARGETINSTALLDIR")) / "sysconfigdata"
         args["PYTHONPATH"] = sys.path + [str(symlink_dir), str(sysconfig_dir)]
         args["orig__name__"] = __name__

pyodide_build/recipe/builder.py

@@ -367,6 +367,7 @@ def _compile(
             ldflags=ldflags,
             target_install_dir=self.build_args.target_install_dir,
             exports=self.build_metadata.exports,
+            build_dir=self.build_dir,
         )
         config_settings = pypabuild.parse_backend_flags(
             self.build_metadata.backend_flags

pyodide_build/tests/test_pypabuild.py

@@ -95,4 +95,3 @@ def test_get_build_env(tmp_path, dummy_xbuildenv):
         assert "cxxflags" in wasmcross_args
         assert "ldflags" in wasmcross_args
         assert "exports" in wasmcross_args
-        assert "builddir" in wasmcross_args