Use an allow-list of platforms that support std.

Use a fall-through for no_std targets.

1 files changed, 23 insertions, 3 deletions

diff --git a/src/libstd/build.rs b/src/libstd/build.rs
index 8317eedd53f..eb2753d6245 100644
--- a/src/libstd/build.rs
+++ b/src/libstd/build.rs
@@ -62,9 +62,29 @@ fn main() {
         }
         println!("cargo:rustc-link-lib=c");
         println!("cargo:rustc-link-lib=compiler_rt");
-    }
-    println!("cargo:rustc-env=STD_ENV_ARCH={}", env::var("CARGO_CFG_TARGET_ARCH").unwrap());
-    if target.contains("-none") || target.contains("nvptx") {
+    } else if (target.contains("sgx") && target.contains("fortanix"))
+        || target.contains("hermit")
+        || target.contains("l4re")
+        || target.contains("redox")
+        || target.contains("haiku")
+        || target.contains("vxworks")
+        || target.contains("wasm32")
+        || target.contains("asmjs")
+    {
+        // These platforms don't have any special requirements.
+    } else {
+        // This is for Cargo's build-std support, to mark std as unstable for
+        // typically no_std platforms.
+        // This covers:
+        // - os=none ("bare metal" targets)
+        // - mipsel-sony-psp
+        // - nvptx64-nvidia-cuda
+        // - avr-unknown-unknown
+        // - tvos (aarch64-apple-tvos, x86_64-apple-tvos)
+        // - uefi (x86_64-unknown-uefi, i686-unknown-uefi)
+        // - JSON targets
+        // - Any new targets that have not been explicitly added above.
         println!("cargo:rustc-cfg=feature=\"restricted-std\"");
     }
+    println!("cargo:rustc-env=STD_ENV_ARCH={}", env::var("CARGO_CFG_TARGET_ARCH").unwrap());
 }