lib.applyToOverridable: init

lib/customisation.nix

@@ -107,6 +107,61 @@ rec {
         }
       else result);
 
+  /*
+    Apply arbitrary customization to an overridable attribute set and its overriding results.
+
+    This function apply the specified customization *modify*
+    to an [overridable](#chap-overrides) attribute set *overridable*
+    and update common attributes that perform overriding
+    to automatically re-apply the customization to future overriding results.
+
+    Attributes [`override`](#sec-pkg-override),
+    [`overrideAttributes`](#sec-pkg-overrideAttrs) and
+    [`overrideDerivation`](#sec-pkg-overrideDerivation) are chosen
+    to cover most of the use cases.
+
+    Example:
+      helloWithAns1 = lib.extendDerivation true { ans = 42; } pkgs.hello
+
+      helloWithAns1.ans
+      => 42
+      (helloWithAns1.override { }).ans
+      => error: attribute 'ans' missing
+
+      helloWithAns2 = lib.applyToOverridable (lib.extendDerivation true { ans = 42; }) pkgs.hello
+
+      helloWithAns2.ans
+      => 42
+      (helloWithAns2.override { }).ans
+      => 42
+
+      helloFive1 = lib.extendDerivation (2 + 2 == 5) { } pkgs.hello
+
+      helloFive1
+      => error: assertion 'condition' failed
+      helloFive1.override { }
+      => «derivation /nix/store/4f4rwzm6s707ify0yqgib2lckp4dw8as-hello-2.12.1.drv»
+
+      helloFive2 = lib.applyToOverridable (lib.extendDerivation (2 + 2 == 5) { }) pkgs.hello
+
+      helloFive2
+      => error: assertion 'condition' failed
+      helloFive2.override { }
+      => error: assertion 'condition' failed
+
+    Type:
+      applyToOverridable :: (AttrSet -> AttrSet) -> AttrSet -> AttrSet
+  */
+  applyToOverridable = modify: overridable:
+    let
+      r = modify overridable;
+    in
+    r // {
+      ${if r ? override then "override" else null} = lib.mirrorFunctionArgs r.override (fdrv: applyToOverridable modify (r.override fdrv));
+      ${if r ? overrideAttrs then "overrideAttrs" else null} = fdrv: applyToOverridable modify (r.overrideAttrs fdrv);
+      ${if r ? overrideDerivation then "overrideDerivation" else null} = fdrv: applyToOverridable modify (r.overrideDerivation fdrv);
+    };
+
 
   /* Call the package function in the file `fn` with the required
     arguments automatically.  The function is called with the

lib/default.nix

@@ -114,6 +114,7 @@ let
     inherit (self.stringsWithDeps) textClosureList textClosureMap
       noDepEntry fullDepEntry packEntry stringAfter;
     inherit (self.customisation) overrideDerivation makeOverridable
+      applyToOverridable
       callPackageWith callPackagesWith extendDerivation hydraJob
       makeScope makeScopeWithSplicing makeScopeWithSplicing';
     inherit (self.derivations) lazyDerivation;

pkgs/development/compilers/cudatoolkit/stdenv.nix

@@ -26,8 +26,10 @@ let
   };
   assertCondition = true;
 in
-lib.extendDerivation
-  assertCondition
-  passthruExtra
+lib.applyToOverridable
+  (lib.extendDerivation
+    assertCondition
+    passthruExtra
+  )
   cudaStdenv
 

pkgs/test/overriding.nix

@@ -31,6 +31,43 @@ let
         expr = ((stdenvNoCC.mkDerivation { pname = "hello-no-final-attrs"; }).overrideAttrs { pname = "hello-no-final-attrs-overridden"; }).pname == "hello-no-final-attrs-overridden";
         expected = true;
       })
+      ({
+        name = "extendDerivation-passthru";
+        expr = helloWithAns.ans == 42;
+        expected = true;
+      })
+    ]
+    ++ getTestsApplyToOverridable { }
+    ;
+
+  getTestsApplyToOverridable =
+    { applyToOverridable ? lib.applyToOverridable
+    , fname ? "applyToOverridable"
+    }:
+    let
+      helloWithAnsOverridable = applyToOverridable (lib.extendDerivation true { ans = 42; }) pkgs.hello;
+    in
+    [
+      ({
+        name = fname + "-self";
+        expr = helloWithAnsOverridable.ans == 42;
+        expected = true;
+      })
+      ({
+        name = fname + "-override";
+        expr = (helloWithAnsOverridable.override { stdenv = pkgs.clangStdenv; }).ans == 42;
+        expected = true;
+      })
+      ({
+        name = fname + "-overrideAttrs";
+        expr = (helloWithAnsOverridable.overrideAttrs (previousAttrs: { FOO = "bar"; })).ans == 42;
+        expected = true;
+      })
+      ({
+        name = fname + "-overrideDerivation";
+        expr = (helloWithAnsOverridable.overrideDerivation (previousDrv: { FOO = "bar"; })).ans == 42;
+        expected = true;
+      })
     ];
 
   addEntangled = origOverrideAttrs: f:
@@ -55,6 +92,8 @@ let
   overrides1 = example.overrideAttrs (_: super: { pname = "a-better-${super.pname}"; });
 
   repeatedOverrides = overrides1.overrideAttrs (_: super: { pname = "${super.pname}-with-blackjack"; });
+
+  helloWithAns = lib.extendDerivation true { ans = 42; } pkgs.hello;
 in
 
 stdenvNoCC.mkDerivation {