Make nix flake check aware of devShells

src/nix/flake-check.md

@@ -33,6 +33,7 @@ The following flake output attributes must be derivations:
 * `checks.`*system*`.`*name*
 * `defaultPackage.`*system*`
 * `devShell.`*system*`
+* `devShells.`*system*`.`*name*`
 * `nixosConfigurations.`*name*`.config.system.build.toplevel
 * `packages.`*system*`.`*name*
 

src/nix/flake.cc

@@ -486,7 +486,7 @@ struct CmdFlakeCheck : FlakeCommand
                             }
                         }
 
-                        else if (name == "packages") {
+                        else if (name == "packages" || name == "devShells") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 checkSystemName(attr.name, *attr.pos);