Merge pull request #50212 from matthewbauer/host-emulator

Add "emulator" function to systems

lib/systems/default.nix

@@ -66,6 +66,46 @@ rec {
          # uname -r
          release = null;
       };
+
+      qemuArch =
+        if final.isArm then "arm"
+        else if final.isx86_64 then "x86_64"
+        else if final.isx86 then "i386"
+        else {
+          "powerpc" = "ppc";
+          "powerpc64" = "ppc64";
+          "powerpc64le" = "ppc64";
+          "mips64" = "mips";
+          "mipsel64" = "mipsel";
+        }.${final.parsed.cpu.name} or final.parsed.cpu.name;
+
+      emulator = pkgs: let
+        qemu-user = pkgs.qemu.override {
+          smartcardSupport = false;
+          spiceSupport = false;
+          openGLSupport = false;
+          virglSupport = false;
+          vncSupport = false;
+          gtkSupport = false;
+          sdlSupport = false;
+          pulseSupport = false;
+          smbdSupport = false;
+          seccompSupport = false;
+          hostCpuTargets = ["${final.qemuArch}-linux-user"];
+        };
+        wine-name = "wine${toString final.parsed.cpu.bits}";
+        wine = (pkgs.winePackagesFor wine-name).minimal;
+      in
+        if final.parsed.kernel.name == pkgs.stdenv.hostPlatform.parsed.kernel.name &&
+           (final.parsed.cpu.name == pkgs.stdenv.hostPlatform.parsed.cpu.name ||
+            (final.platform.isi686 && pkgs.stdenv.hostPlatform.isx86_64))
+        then pkgs.runtimeShell
+        else if final.isWindows
+        then "${wine}/bin/${wine-name}"
+        else if final.isLinux && pkgs.stdenv.hostPlatform.isLinux
+        then "${qemu-user}/bin/qemu-${final.qemuArch}"
+        else throw "Don't know how to run ${final.config} executables.";
+
     } // mapAttrs (n: v: v final.parsed) inspect.predicates
       // args;
   in assert final.useAndroidPrebuilt -> final.isAndroid;

lib/systems/examples.nix

@@ -2,7 +2,14 @@
 # `crossSystem`. They are put here for user convenience, but also used by cross
 # tests and linux cross stdenv building, so handle with care!
 { lib }:
-let platforms = import ./platforms.nix { inherit lib; }; in
+let
+  platforms = import ./platforms.nix { inherit lib; };
+
+  riscv = bits: {
+    config = "riscv${bits}-unknown-linux-gnu";
+    platform = platforms.riscv-multiplatform bits;
+  };
+in
 
 rec {
   #
@@ -92,10 +99,6 @@ rec {
   musl64 = { config = "x86_64-unknown-linux-musl"; };
   musl32  = { config = "i686-unknown-linux-musl"; };
 
-  riscv = bits: {
-    config = "riscv${bits}-unknown-linux-gnu";
-    platform = platforms.riscv-multiplatform bits;
-  };
   riscv64 = riscv "64";
   riscv32 = riscv "32";