add option for excluding envs from exposition in devShells

changelog.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+* Allow envs to be excluded from being exposed as `devShells` for specific systems.
+
 # 0.6.0
 
 * Support multiple Cabal libraries in a single package.

lib/doc/prose.nix

@@ -424,6 +424,11 @@ in {
   since it will try to read the file and terminate with an error.
   In that (unlikely) case, you'll have to set `gen-overrides.enable = false` before running it for the first time.
   :::
+
+  Another potential source for `nix flake check` to fail is when an environment with a virtual machine is exposed as a
+  shell.
+  For that purpose, the option [](#opt-env-systems) can be used to define for which systems the environment should be
+  exposed.
   '';
 
   environments = ''

lib/with-config.nix

@@ -130,6 +130,9 @@ let
   ${pkgs.git}/bin/git add flake.lock
   '';
 
+  envSystemAllowed = env:
+  env.systems == null || (elem config.system env.systems);
+
 in basic // {
   inherit
   paramApp
@@ -146,5 +149,6 @@ in basic // {
   downloadStaticCli
   bootstrapWithStaticCli
   bootstrapWithDynamicCli
+  envSystemAllowed
   ;
 }

modules/env.nix

@@ -401,6 +401,20 @@ in {
       readOnly = true;
     };
 
+    systems = mkOption {
+      description = mdDoc ''
+      The architecture/system identifiers like `x86_64-linux` for which this environment works.
+      This is used to exclude environments from being exposed as shells when they are system-specific, for example when
+      using a VM that only works with Linux.
+      If those shells were exposed, the command `nix flake check` would fail while evaluating the `devShells` outputs,
+      since that doesn't only select the current system.
+
+      If set to `null` (the default), all systems are accepted.
+      '';
+      type = nullOr (listOf str);
+      default = null;
+    };
+
     vm = {
 
       enable = mkEnableOption (mdDoc "the service VM for this env");

modules/output.nix

@@ -115,7 +115,7 @@ in {
 
       devShells = let
 
-        shells = mapAttrs (_: e: e.shell) util.visibleEnvs;
+        shells = mapAttrs (_: e: e.shell) (filterAttrs (_: util.envSystemAllowed) util.visibleEnvs);
 
       in shells // { default = shells.dev; };