Fix up dev shell in a few ways

- Skip packages that don't build for Windows when building for windows
- Automatically disable kaitai / json schema, fixing todo
- Skip native build of Nix for manual

packaging/dev-shell.nix

@@ -148,6 +148,15 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
     isInternal =
       dep: internalDrvs ? ${builtins.unsafeDiscardStringContext dep.drvPath or "_non-existent_"};
 
+    activeComponentNames = lib.listToAttrs (
+      map (c: {
+        name = c.pname or c.name;
+        value = null;
+      }) activeComponents
+    );
+
+    isActiveComponent = name: activeComponentNames ? ${name};
+
   in
   {
     pname = "shell-for-nix";
@@ -190,8 +199,7 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
           }
         );
 
-      small =
+      small = finalAttrs.finalPackage.withActiveComponents (
-        (finalAttrs.finalPackage.withActiveComponents (
         c:
         lib.intersectAttrs (lib.genAttrs [
           "nix-cli"
@@ -203,14 +211,7 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
           "nix-functional-tests"
           "nix-perl-bindings"
         ] (_: null)) c
-        )).overrideAttrs
+      );
-          (o: {
-            mesonFlags = o.mesonFlags ++ [
-              # TODO: infer from activeComponents or vice versa
-              "-Dkaitai-struct-checks=false"
-              "-Djson-schema-checks=false"
-            ];
-          });
     };
 
     # Remove the version suffix to avoid unnecessary attempts to substitute in nix develop
@@ -278,8 +279,11 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
 
     dontUseCmakeConfigure = true;
 
-    mesonFlags =
+    mesonFlags = [
-      map (transformFlag "libutil") (ignoreCrossFile pkgs.nixComponents2.nix-util.mesonFlags)
+      (lib.mesonBool "kaitai-struct-checks" (isActiveComponent "nix-kaitai-struct-checks"))
+      (lib.mesonBool "json-schema-checks" (isActiveComponent "nix-json-schema-checks"))
+    ]
+    ++ map (transformFlag "libutil") (ignoreCrossFile pkgs.nixComponents2.nix-util.mesonFlags)
     ++ map (transformFlag "libstore") (ignoreCrossFile pkgs.nixComponents2.nix-store.mesonFlags)
     ++ map (transformFlag "libfetchers") (ignoreCrossFile pkgs.nixComponents2.nix-fetchers.mesonFlags)
     ++ lib.optionals havePerl (
@@ -292,7 +296,16 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
       let
         inputs =
           dedupByString (v: "${v}") (
-            lib.filter (x: !isInternal x) (lib.lists.concatMap (c: c.nativeBuildInputs) activeComponents)
+            lib.filter (x: !isInternal x) (
+              lib.lists.concatMap (
+                # Nix manual has a build-time dependency on nix, but we
+                # don't want to do a native build just to enter the ross
+                # dev shell.
+                #
+                # TODO: think of a more principled fix for this.
+                c: lib.filter (f: f.pname or null != "nix") c.nativeBuildInputs
+              ) activeComponents
+            )
           )
           ++ lib.optional (
             !buildCanExecuteHost
@@ -308,8 +321,8 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
             pkgs.buildPackages.nixfmt-rfc-style
             pkgs.buildPackages.shellcheck
             pkgs.buildPackages.include-what-you-use
-            pkgs.buildPackages.gdb
           ]
+          ++ lib.optional pkgs.hostPlatform.isUnix pkgs.buildPackages.gdb
           ++ lib.optional (stdenv.cc.isClang && stdenv.hostPlatform == stdenv.buildPlatform) (
             lib.hiPrio pkgs.buildPackages.clang-tools
           )
@@ -325,9 +338,9 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
       )
     );
 
-    buildInputs = [
+    buildInputs =
-      pkgs.gbenchmark
+      # TODO change Nixpkgs to mark gbenchmark as building on Windows
-    ]
+      lib.optional pkgs.hostPlatform.isUnix pkgs.gbenchmark
       ++ dedupByString (v: "${v}") (
         lib.filter (x: !isInternal x) (lib.lists.concatMap (c: c.buildInputs) activeComponents)
       )