buildRustCrateTests: add regression test for #74071

pkgs/build-support/rust/build-rust-crate/test/default.nix

@@ -199,6 +199,27 @@ let
           })
         ];
       };
+      # Regression test for https://github.com/NixOS/nixpkgs/issues/74071
+      # Whenevever a build.rs file is generating files those should not be overlayed onto the actual source dir
+      buildRsOutDirOverlay = {
+        src = symlinkJoin {
+          name = "buildrs-out-dir-overlay";
+          paths = [
+            (mkLib "src/lib.rs")
+            (mkFile "build.rs" ''
+              use std::env;
+              use std::ffi::OsString;
+              use std::fs;
+              use std::path::Path;
+              fn main() {
+                let out_dir = env::var_os("OUT_DIR").expect("OUT_DIR not set");
+                let out_file = Path::new(&out_dir).join("lib.rs");
+                fs::write(out_file, "invalid rust code!").expect("failed to write lib.rs");
+              }
+            '')
+          ];
+        };
+      };
     };
     brotliCrates = (callPackage ./brotli-crates.nix {});
   in lib.mapAttrs (key: value: mkTest (value // lib.optionalAttrs (!value?crateName) { crateName = key; })) cases // {