buck2: reduce number of parallel jobs for cargo on Windows

Summary:
Cargo doesn't have good mechanism to limit parallerism to avoid OOMs: rust-lang/cargo#12912

Reduce number of parallel jobs to save some memory. Default is number of logical processors, so this will run twice less jobs.

If it keeps failing, we may need to reduce it further as it's still using over 25 GB .

Reviewed By: blackm00n

Differential Revision: D59054227

fbshipit-source-id: 708265891d69c0264392d0b24e29ac1f6b9818dd

test.py

@@ -40,6 +40,10 @@ def is_macos() -> bool:
     return sys.platform == "darwin"
 
 
+def is_windows() -> bool:
+    return sys.platform == "win32"
+
+
 class Colors(Enum):
     # Copied from https://stackoverflow.com/questions/287871/how-to-print-colored-text-to-the-terminal
     HEADER = "\033[95m"
@@ -366,8 +370,14 @@ def rustdoc(package_args: List[str]) -> None:
 
 
 def test(package_args: List[str]) -> None:
-    print_running("cargo test")
-    run(["cargo", "test", *package_args])
+    print_running("cargo test --lib")
+    extra_args = []
+    # Limit number of parallel jobs to prevent OOMs
+    if is_windows():
+        extra_args = ["--jobs", str(os.cpu_count() // 2)]
+    run(["cargo", "test", "--lib", *extra_args, *package_args])
+    print_running("cargo test --doc")
+    run(["cargo", "test", "--doc", *extra_args, *package_args])
 
 
 def main() -> None: