nixpkgs/pkgs/development/compilers/swift/swift-driver/patches/linux-fix-linking.patch

--- a/Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift
+++ b/Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+import Foundation
 import SwiftOptions
 
 import func TSCBasic.lookupExecutablePath
@@ -120,7 +121,20 @@ extension GenericUnixToolchain {
       // just using `clang` and avoid a dependency on the C++ runtime.
       let clangTool: Tool =
         parsedOptions.hasArgument(.enableExperimentalCxxInterop) ? .clangxx : .clang
-      var clangPath = try getToolPath(clangTool)
+
+      // For Nix, prefer linking using the wrapped system clang, instead of using
+      // the unwrapped clang packaged with swift. The latter is unable to link, but
+      // we still want to use it for other purposes (clang importer).
+      var clangPath: AbsolutePath
+      let env = ProcessInfo.processInfo.environment
+      if let nixCC = env["NIX_CC"],
+         let binPath = try? AbsolutePath(validating: "\(nixCC)/bin"),
+         let tool = lookupExecutablePath(filename: parsedOptions.hasArgument(.enableExperimentalCxxInterop)
+                                                        ? "clang++" : "clang",
+                                         searchPaths: [binPath]) {
+        clangPath = tool
+      } else {
+      clangPath = try getToolPath(clangTool)
       if let toolsDirPath = parsedOptions.getLastArgument(.toolsDirectory) {
         // FIXME: What if this isn't an absolute path?
         let toolsDir = try AbsolutePath(validating: toolsDirPath.asSingle)
@@ -136,6 +150,7 @@ extension GenericUnixToolchain {
         commandLine.appendFlag("-B")
         commandLine.appendPath(toolsDir)
       }
+      } // nixCC
 
       // Executables on Linux get -pie
       if targetTriple.os == .linux && linkerOutputType == .executable {