Help GraalPy discover build tools on Windows

Author: timfel

cibuildwheel/platforms/windows.py

@@ -346,6 +346,46 @@ def setup_python(
         setup_setuptools_cross_compile(tmp, python_configuration, python_libs_base, env)
         setup_rust_cross_compile(tmp, python_configuration, python_libs_base, env)
 
+    if implementation_id.startswith("gp"):
+        # GraalPy fails to discover compilers, setup the relevant environment
+        # variables. Adapted from
+        # https://github.com/microsoft/vswhere/wiki/Start-Developer-Command-Prompt
+        vcpath = subprocess.check_output(
+            [
+                Path(os.environ["PROGRAMFILES(X86)"])
+                / "Microsoft Visual Studio"
+                / "Installer"
+                / "vswhere.exe",
+                "-products",
+                "*",
+                "-latest",
+                "-property",
+                "installationPath",
+            ],
+            text=True,
+        ).strip()
+        log.notice(f"Discovering Visual Studio for GraalPy at {vcpath}")
+        vcenv = dict(
+            [
+                envvar.strip().split("=", 1)
+                for envvar in subprocess.check_output(
+                    [
+                        f"{vcpath}\\Common7\\Tools\\vsdevcmd.bat",
+                        "-no_logo",
+                        "-arch=amd64",
+                        "-host_arch=amd64",
+                        "&&",
+                        "set",
+                    ],
+                    shell=True,
+                    text=True,
+                )
+                .strip()
+                .split("\n")
+            ]
+        )
+        env.update(vcenv)
+
     return base_python, env