diff --git a/pkgs/tools/package-management/nix/2_26/componentized.nix b/pkgs/tools/package-management/nix/2_26/componentized.nix
index 48f2d052d36f9..d22741427faf3 100644
--- a/pkgs/tools/package-management/nix/2_26/componentized.nix
+++ b/pkgs/tools/package-management/nix/2_26/componentized.nix
@@ -25,7 +25,7 @@ let
       {
         otherSplices = generateSplicesForMkScope "nixComponents";
         f = import ./packaging/components.nix {
-          inherit lib officialRelease src;
+          inherit lib officialRelease pkgs src stdenv;
         };
       };
 
@@ -42,8 +42,7 @@ let
         f = import ./dependencies.nix {
           inherit pkgs;
           inherit stdenv;
-          inherit src;
         };
       };
 in
-nixComponents.nix-everything
+(nixComponents.overrideSource src).nix-everything
diff --git a/pkgs/tools/package-management/nix/2_26/dependencies.nix b/pkgs/tools/package-management/nix/2_26/dependencies.nix
index 73739e2edcc5b..0e874d990188c 100644
--- a/pkgs/tools/package-management/nix/2_26/dependencies.nix
+++ b/pkgs/tools/package-management/nix/2_26/dependencies.nix
@@ -1,8 +1,6 @@
 # These overrides are applied to the dependencies of the Nix components.
 
 {
-  src,
-
   # The raw Nixpkgs, not affected by this scope
   pkgs,
 
@@ -14,10 +12,6 @@ let
 in
 
 let
-  inherit (pkgs) lib;
-
-  root = ./.;
-
   stdenv = if prevStdenv.isDarwin && prevStdenv.isx86_64 then darwinStdenv else prevStdenv;
 
   # Fix the following error with the default x86_64-darwin SDK:
@@ -28,113 +22,6 @@ let
   # allocation function Clang uses with this setting actually works
   # all the way back to 10.6.
   darwinStdenv = pkgs.overrideSDK prevStdenv { darwinMinVersion = "10.13"; };
-
-  resolveRelPath = p: lib.path.removePrefix root p;
-  resolvePath = p: src + "/${resolveRelPath p}";
-
-  # Indirection for Nixpkgs to override when package.nix files are vendored
-  # fileset filtering is not possible without IFD on src, so we ignore the fileset
-  # and produce a path containing _more_, but the extra files generally won't be
-  # accessed.
-  # The Nix flake uses fileset.toSource for this.
-  filesetToSource = { root, fileset }: resolvePath root;
-
-  /**
-    Given a set of layers, create a mkDerivation-like function
-  */
-  mkPackageBuilder =
-    exts: userFn: stdenv.mkDerivation (lib.extends (lib.composeManyExtensions exts) userFn);
-
-  localSourceLayer =
-    finalAttrs: prevAttrs:
-    let
-      workDirPath =
-        # Ideally we'd pick finalAttrs.workDir, but for now `mkDerivation` has
-        # the requirement that everything except passthru and meta must be
-        # serialized by mkDerivation, which doesn't work for this.
-        prevAttrs.workDir;
-
-      workDirSubpath = resolveRelPath workDirPath;
-      # sources = assert prevAttrs.fileset._type == "fileset"; prevAttrs.fileset;
-      # src = lib.fileset.toSource { fileset = sources; inherit root; };
-
-    in
-    {
-      sourceRoot = "${src.name}/" + workDirSubpath;
-      inherit src;
-
-      # Clear what `derivation` can't/shouldn't serialize; see prevAttrs.workDir.
-      fileset = null;
-      workDir = null;
-    };
-
-  mesonLayer = finalAttrs: prevAttrs: {
-    # NOTE:
-    # As of https://github.com/NixOS/nixpkgs/blob/8baf8241cea0c7b30e0b8ae73474cb3de83c1a30/pkgs/by-name/me/meson/setup-hook.sh#L26,
-    # `mesonBuildType` defaults to `plain` if not specified. We want our Nix-built binaries to be optimized by default.
-    # More on build types here: https://mesonbuild.com/Builtin-options.html#details-for-buildtype.
-    mesonBuildType = "release";
-    # NOTE:
-    # Users who are debugging Nix builds are expected to set the environment variable `mesonBuildType`, per the
-    # guidance in https://github.com/NixOS/nix/blob/8a3fc27f1b63a08ac983ee46435a56cf49ebaf4a/doc/manual/source/development/debugging.md?plain=1#L10.
-    # For this reason, we don't want to refer to `finalAttrs.mesonBuildType` here, but rather use the environment variable.
-    preConfigure =
-      prevAttrs.preConfigure or ""
-      +
-        lib.optionalString
-          (
-            !stdenv.hostPlatform.isWindows
-            # build failure
-            && !stdenv.hostPlatform.isStatic
-            # LTO breaks exception handling on x86-64-darwin.
-            && stdenv.system != "x86_64-darwin"
-          )
-          ''
-            case "$mesonBuildType" in
-            release|minsize) appendToVar mesonFlags "-Db_lto=true"  ;;
-            *)               appendToVar mesonFlags "-Db_lto=false" ;;
-            esac
-          '';
-    nativeBuildInputs = [
-      pkgs.buildPackages.meson
-      pkgs.buildPackages.ninja
-    ] ++ prevAttrs.nativeBuildInputs or [ ];
-    mesonCheckFlags = prevAttrs.mesonCheckFlags or [ ] ++ [
-      "--print-errorlogs"
-    ];
-  };
-
-  mesonBuildLayer = finalAttrs: prevAttrs: {
-    nativeBuildInputs = prevAttrs.nativeBuildInputs or [ ] ++ [
-      pkgs.buildPackages.pkg-config
-    ];
-    separateDebugInfo = !stdenv.hostPlatform.isStatic;
-    hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
-    env =
-      prevAttrs.env or { }
-      // lib.optionalAttrs (
-        stdenv.isLinux
-        && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")
-        && !(stdenv.hostPlatform.useLLVM or false)
-      ) { LDFLAGS = "-fuse-ld=gold"; };
-  };
-
-  mesonLibraryLayer = finalAttrs: prevAttrs: {
-    outputs = prevAttrs.outputs or [ "out" ] ++ [ "dev" ];
-  };
-
-  # Work around weird `--as-needed` linker behavior with BSD, see
-  # https://github.com/mesonbuild/meson/issues/3593
-  bsdNoLinkAsNeeded =
-    finalAttrs: prevAttrs:
-    lib.optionalAttrs stdenv.hostPlatform.isBSD {
-      mesonFlags = [ (lib.mesonBool "b_asneeded" false) ] ++ prevAttrs.mesonFlags or [ ];
-    };
-
-  miscGoodPractice = finalAttrs: prevAttrs: {
-    strictDeps = prevAttrs.strictDeps or true;
-    enableParallelBuilding = true;
-  };
 in
 scope: {
   inherit stdenv;
@@ -156,27 +43,4 @@ scope: {
   boehmgc = pkgs.boehmgc.override {
     enableLargeConfig = true;
   };
-
-  inherit resolvePath filesetToSource;
-
-  mkMesonDerivation = mkPackageBuilder [
-    miscGoodPractice
-    localSourceLayer
-    mesonLayer
-  ];
-  mkMesonExecutable = mkPackageBuilder [
-    miscGoodPractice
-    bsdNoLinkAsNeeded
-    localSourceLayer
-    mesonLayer
-    mesonBuildLayer
-  ];
-  mkMesonLibrary = mkPackageBuilder [
-    miscGoodPractice
-    bsdNoLinkAsNeeded
-    localSourceLayer
-    mesonLayer
-    mesonBuildLayer
-    mesonLibraryLayer
-  ];
 }
diff --git a/pkgs/tools/package-management/nix/2_26/packaging/components.nix b/pkgs/tools/package-management/nix/2_26/packaging/components.nix
index 57932617f827e..8b027591e6ed8 100644
--- a/pkgs/tools/package-management/nix/2_26/packaging/components.nix
+++ b/pkgs/tools/package-management/nix/2_26/packaging/components.nix
@@ -1,13 +1,22 @@
 {
   lib,
+  pkgs,
   src,
+  stdenv,
   officialRelease,
 }:
 
 scope:
 
 let
-  inherit (scope) callPackage;
+  inherit (scope)
+    callPackage
+    ;
+  inherit (pkgs.buildPackages)
+    meson
+    ninja
+    pkg-config
+    ;
 
   baseVersion = lib.fileContents ../.version;
 
@@ -20,6 +29,165 @@ let
       }_${src.shortRev or "dirty"}";
 
   fineVersion = baseVersion + fineVersionSuffix;
+
+  root = ../.;
+
+  # Indirection for Nixpkgs to override when package.nix files are vendored
+  filesetToSource = lib.fileset.toSource;
+
+  /**
+    Given a set of layers, create a mkDerivation-like function
+  */
+  mkPackageBuilder =
+    exts: userFn: stdenv.mkDerivation (lib.extends (lib.composeManyExtensions exts) userFn);
+
+  setVersionLayer = finalAttrs: prevAttrs: {
+    preConfigure =
+      prevAttrs.prevAttrs or ""
+      +
+        # Update the repo-global .version file.
+        # Symlink ./.version points there, but by default only workDir is writable.
+        ''
+          chmod u+w ./.version
+          echo ${finalAttrs.version} > ./.version
+        '';
+  };
+
+  localSourceLayer =
+    finalAttrs: prevAttrs:
+    let
+      workDirPath =
+        # Ideally we'd pick finalAttrs.workDir, but for now `mkDerivation` has
+        # the requirement that everything except passthru and meta must be
+        # serialized by mkDerivation, which doesn't work for this.
+        prevAttrs.workDir;
+
+      workDirSubpath = lib.path.removePrefix root workDirPath;
+      sources =
+        assert prevAttrs.fileset._type == "fileset";
+        prevAttrs.fileset;
+      src = lib.fileset.toSource {
+        fileset = sources;
+        inherit root;
+      };
+
+    in
+    {
+      sourceRoot = "${src.name}/" + workDirSubpath;
+      inherit src;
+
+      # Clear what `derivation` can't/shouldn't serialize; see prevAttrs.workDir.
+      fileset = null;
+      workDir = null;
+    };
+
+  resolveRelPath = p: lib.path.removePrefix root p;
+
+  makeFetchedSourceLayer =
+    finalScope: finalAttrs: prevAttrs:
+    let
+      workDirPath =
+        # Ideally we'd pick finalAttrs.workDir, but for now `mkDerivation` has
+        # the requirement that everything except passthru and meta must be
+        # serialized by mkDerivation, which doesn't work for this.
+        prevAttrs.workDir;
+
+      workDirSubpath = resolveRelPath workDirPath;
+
+    in
+    {
+      sourceRoot = "${finalScope.patchedSrc.name}/" + workDirSubpath;
+      src = finalScope.patchedSrc;
+      version =
+        let
+          n = lib.length finalScope.patches;
+        in
+        if n == 0 then prevAttrs.version else prevAttrs.version + "+${toString n}";
+
+      # Clear what `derivation` can't/shouldn't serialize; see prevAttrs.workDir.
+      fileset = null;
+      workDir = null;
+    };
+
+  mesonLayer = finalAttrs: prevAttrs: {
+    # NOTE:
+    # As of https://github.com/NixOS/nixpkgs/blob/8baf8241cea0c7b30e0b8ae73474cb3de83c1a30/pkgs/by-name/me/meson/setup-hook.sh#L26,
+    # `mesonBuildType` defaults to `plain` if not specified. We want our Nix-built binaries to be optimized by default.
+    # More on build types here: https://mesonbuild.com/Builtin-options.html#details-for-buildtype.
+    mesonBuildType = "release";
+    # NOTE:
+    # Users who are debugging Nix builds are expected to set the environment variable `mesonBuildType`, per the
+    # guidance in https://github.com/NixOS/nix/blob/8a3fc27f1b63a08ac983ee46435a56cf49ebaf4a/doc/manual/source/development/debugging.md?plain=1#L10.
+    # For this reason, we don't want to refer to `finalAttrs.mesonBuildType` here, but rather use the environment variable.
+    preConfigure =
+      prevAttrs.preConfigure or ""
+      +
+        lib.optionalString
+          (
+            !stdenv.hostPlatform.isWindows
+            # build failure
+            && !stdenv.hostPlatform.isStatic
+            # LTO breaks exception handling on x86-64-darwin.
+            && stdenv.system != "x86_64-darwin"
+          )
+          ''
+            case "$mesonBuildType" in
+            release|minsize) appendToVar mesonFlags "-Db_lto=true"  ;;
+            *)               appendToVar mesonFlags "-Db_lto=false" ;;
+            esac
+          '';
+    nativeBuildInputs = [
+      meson
+      ninja
+    ] ++ prevAttrs.nativeBuildInputs or [ ];
+    mesonCheckFlags = prevAttrs.mesonCheckFlags or [ ] ++ [
+      "--print-errorlogs"
+    ];
+  };
+
+  mesonBuildLayer = finalAttrs: prevAttrs: {
+    nativeBuildInputs = prevAttrs.nativeBuildInputs or [ ] ++ [
+      pkg-config
+    ];
+    separateDebugInfo = !stdenv.hostPlatform.isStatic;
+    hardeningDisable = lib.optional stdenv.hostPlatform.isStatic "pie";
+    env =
+      prevAttrs.env or { }
+      // lib.optionalAttrs (
+        stdenv.isLinux
+        && !(stdenv.hostPlatform.isStatic && stdenv.system == "aarch64-linux")
+        && !(stdenv.hostPlatform.useLLVM or false)
+      ) { LDFLAGS = "-fuse-ld=gold"; };
+  };
+
+  mesonLibraryLayer = finalAttrs: prevAttrs: {
+    outputs = prevAttrs.outputs or [ "out" ] ++ [ "dev" ];
+  };
+
+  # Work around weird `--as-needed` linker behavior with BSD, see
+  # https://github.com/mesonbuild/meson/issues/3593
+  bsdNoLinkAsNeeded =
+    finalAttrs: prevAttrs:
+    lib.optionalAttrs stdenv.hostPlatform.isBSD {
+      mesonFlags = [ (lib.mesonBool "b_asneeded" false) ] ++ prevAttrs.mesonFlags or [ ];
+    };
+
+  miscGoodPractice = finalAttrs: prevAttrs: {
+    strictDeps = prevAttrs.strictDeps or true;
+    enableParallelBuilding = true;
+  };
+
+  /**
+    Append patches to the source layer.
+  */
+  appendPatches =
+    scope: patches:
+    scope.overrideScope (
+      finalScope: prevScope: {
+        patches = prevScope.patches ++ patches;
+      }
+    );
+
 in
 
 # This becomes the pkgs.nixComponents attribute set
@@ -27,6 +195,113 @@ in
   version = baseVersion + versionSuffix;
   inherit versionSuffix;
 
+  inherit filesetToSource;
+
+  /**
+    A user-provided extension function to apply to each component derivation.
+  */
+  mesonComponentOverrides = finalAttrs: prevAttrs: { };
+
+  /**
+    An overridable derivation layer for handling the sources.
+  */
+  sourceLayer = localSourceLayer;
+
+  /**
+    Resolve a path value to either itself or a path in the `src`, depending
+    whether `overrideSource` was called.
+  */
+  resolvePath = p: p;
+
+  /**
+    Apply an extension function (i.e. overlay-shaped) to all component derivations.
+  */
+  overrideAllMesonComponents =
+    f:
+    scope.overrideScope (
+      finalScope: prevScope: {
+        mesonComponentOverrides = lib.composeExtensions scope.mesonComponentOverrides f;
+      }
+    );
+
+  /**
+    Provide an alternate source. This allows the expressions to be vendored without copying the sources,
+    but it does make the build non-granular; all components will use a complete source.
+
+    Packaging expressions will be ignored.
+  */
+  overrideSource =
+    src:
+    scope.overrideScope (
+      finalScope: prevScope: {
+        sourceLayer = makeFetchedSourceLayer finalScope;
+        /**
+          Unpatched source for the build of Nix. Packaging expressions will be ignored.
+        */
+        src = src;
+        /**
+          Patches for the whole Nix source. Changes to packaging expressions will be ignored.
+        */
+        patches = [ ];
+        /**
+          Fetched and patched source to be used in component derivations.
+        */
+        patchedSrc =
+          if finalScope.patches == [ ] then
+            src
+          else
+            pkgs.buildPackages.srcOnly (
+              pkgs.buildPackages.stdenvNoCC.mkDerivation {
+                name = "${finalScope.src.name or "nix-source"}-patched";
+                inherit (finalScope) src patches;
+              }
+            );
+
+        resolvePath = p: finalScope.patchedSrc + "/${resolveRelPath p}";
+        filesetToSource = { root, fileset }: finalScope.resolvePath root;
+
+        appendPatches = appendPatches finalScope;
+      }
+    );
+
+  /**
+    Append patches to be applied to the whole Nix source.
+    This affects all components.
+
+    Changes to the packaging expressions will be ignored.
+  */
+  appendPatches =
+    patches:
+    # switch to "fetched" source first, so that patches apply to the whole tree.
+    (scope.overrideSource "${./..}").appendPatches patches;
+
+  mkMesonDerivation = mkPackageBuilder [
+    miscGoodPractice
+    scope.sourceLayer
+    setVersionLayer
+    mesonLayer
+    scope.mesonComponentOverrides
+  ];
+  mkMesonExecutable = mkPackageBuilder [
+    miscGoodPractice
+    bsdNoLinkAsNeeded
+    scope.sourceLayer
+    setVersionLayer
+    mesonLayer
+    mesonBuildLayer
+    scope.mesonComponentOverrides
+  ];
+  mkMesonLibrary = mkPackageBuilder [
+    miscGoodPractice
+    bsdNoLinkAsNeeded
+    scope.sourceLayer
+    mesonLayer
+    setVersionLayer
+    mesonBuildLayer
+    mesonLibraryLayer
+    scope.mesonComponentOverrides
+  ];
+
   nix-util = callPackage ../src/libutil/package.nix { };
   nix-util-c = callPackage ../src/libutil-c/package.nix { };
   nix-util-test-support = callPackage ../src/libutil-test-support/package.nix { };
@@ -56,7 +331,9 @@ in
 
   nix-cli = callPackage ../src/nix/package.nix { version = fineVersion; };
 
-  nix-functional-tests = callPackage ../tests/functional/package.nix { version = fineVersion; };
+  nix-functional-tests = callPackage ../tests/functional/package.nix {
+    version = fineVersion;
+  };
 
   nix-manual = callPackage ../doc/manual/package.nix { version = fineVersion; };
   nix-internal-api-docs = callPackage ../src/internal-api-docs/package.nix { version = fineVersion; };
@@ -64,5 +341,33 @@ in
 
   nix-perl-bindings = callPackage ../src/perl/package.nix { };
 
-  nix-everything = callPackage ../packaging/everything.nix { };
+  nix-everything = callPackage ../packaging/everything.nix { } // {
+    # Note: no `passthru.overrideAllMesonComponents`
+    #       This would propagate into `nix.overrideAttrs f`, but then discard
+    #       `f` when `.overrideAllMesonComponents` is used.
+    #       Both "methods" should be views on the same fixpoint overriding mechanism
+    #       for that to work. For now, we intentionally don't support the broken
+    #       two-fixpoint solution.
+    /**
+      Apply an extension function (i.e. overlay-shaped) to all component derivations, and return the nix package.
+    */
+    overrideAllMesonComponents = f: (scope.overrideAllMesonComponents f).nix-everything;
+
+    /**
+      Append patches to be applied to the whole Nix source.
+      This affects all components.
+
+      Changes to the packaging expressions will be ignored.
+    */
+    appendPatches = ps: (scope.appendPatches ps).nix-everything;
+
+    /**
+      Provide an alternate source. This allows the expressions to be vendored without copying the sources,
+      but it does make the build non-granular; all components will use a complete source.
+
+      Packaging expressions will be ignored.
+    */
+    overrideSource = src: (scope.overrideSource src).nix-everything;
+
+  };
 }
diff --git a/pkgs/tools/package-management/nix/2_26/packaging/everything.nix b/pkgs/tools/package-management/nix/2_26/packaging/everything.nix
index 7ac7a156d2269..d8fc835f235d1 100644
--- a/pkgs/tools/package-management/nix/2_26/packaging/everything.nix
+++ b/pkgs/tools/package-management/nix/2_26/packaging/everything.nix
@@ -39,6 +39,8 @@
 
   testers,
   runCommand,
+
+  patchedSrc ? null,
 }:
 
 let
@@ -68,52 +70,50 @@ let
           ;
       };
 
-  dev =
-    nixAttrs:
-    stdenv.mkDerivation (finalAttrs: {
-      name = "nix-${nix-cli.version}-dev";
-      pname = "nix";
-      version = nix-cli.version;
-      dontUnpack = true;
-      dontBuild = true;
-      libs = map lib.getDev (lib.attrValues libs);
-      installPhase = ''
-        mkdir -p $out/nix-support
-        echo $libs >> $out/nix-support/propagated-build-inputs
-        echo ${nixAttrs.finalPackage} >> $out/nix-support/propagated-build-inputs
-      '';
-      passthru = {
-        tests = {
-          # TODO: is this supposed to work for a dev output?
-          # pkg-config = testers.hasPkgConfigModules {
-          #   package = finalAttrs.finalPackage;
-          # };
+  dev = stdenv.mkDerivation (finalAttrs: {
+    name = "nix-${nix-cli.version}-dev";
+    pname = "nix";
+    version = nix-cli.version;
+    dontUnpack = true;
+    dontBuild = true;
+    libs = map lib.getDev (lib.attrValues libs);
+    nix = nix-cli;
+    installPhase = ''
+      mkdir -p $out/nix-support
+      echo $libs >> $out/nix-support/propagated-build-inputs
+      echo $nix >> $out/nix-support/propagated-build-inputs
+    '';
+    passthru = {
+      tests = {
+        pkg-config = testers.hasPkgConfigModules {
+          package = finalAttrs.finalPackage;
         };
+      };
 
-        # If we were to fully emulate output selection here, we'd confuse the Nix CLIs,
-        # because they rely on `drvPath`.
-        dev = finalAttrs.finalPackage.out;
-        out = nixAttrs.finalPackage.out;
+      # If we were to fully emulate output selection here, we'd confuse the Nix CLIs,
+      # because they rely on `drvPath`.
+      dev = finalAttrs.finalPackage.out;
 
-        libs = throw "`nix.dev.libs` is not meant to be used; use `nix.libs` instead.";
-      };
-      meta = {
-        pkgConfigModules = [
-          "nix-cmd"
-          "nix-expr"
-          "nix-expr-c"
-          "nix-fetchers"
-          "nix-flake"
-          "nix-flake-c"
-          "nix-main"
-          "nix-main-c"
-          "nix-store"
-          "nix-store-c"
-          "nix-util"
-          "nix-util-c"
-        ];
-      };
-    });
+      libs = throw "`nix.dev.libs` is not meant to be used; use `nix.libs` instead.";
+    };
+    meta = {
+      mainProgram = "nix";
+      pkgConfigModules = [
+        "nix-cmd"
+        "nix-expr"
+        "nix-expr-c"
+        "nix-fetchers"
+        "nix-flake"
+        "nix-flake-c"
+        "nix-main"
+        "nix-main-c"
+        "nix-store"
+        "nix-store-c"
+        "nix-util"
+        "nix-util-c"
+      ];
+    };
+  });
   devdoc = buildEnv {
     name = "nix-${nix-cli.version}-devdoc";
     paths = [
@@ -122,87 +122,141 @@ let
     ];
   };
 
+  /**
+    Produce a set of derivation outputs that implement the multiple outputs interface.
+
+    The multiple outputs interface was originally designed for derivations with
+    multiple outputs, but it can also be used for packages which do not correspond
+    1:1 to a single derivation and whose outputs come from distinct derivations.
+  */
+  makeOutputs =
+    {
+      outputs,
+      defaultOutput ? "out",
+      extraAttrs ? outputName: value: { },
+    }:
+
+    let
+      prepOutput =
+        outputName: value:
+        {
+          _type = "package";
+          /**
+            For compatibility. The outputs of this package may not actually be implemented using a single derivation.
+          */
+          type = "derivation";
+          outputName = outputName;
+          outPath = value.outPath or value;
+        }
+        // extraAttrs outputName value;
+
+      outputAttrs = lib.mapAttrs (
+        outputName: value: { outputSpecified = true; } // prepOutput outputName value // commonAttrs
+      ) outputs;
+
+      # This is without `outputSpecified`, but otherwise matches the `outputAttrs` above.
+      defaultOutputValue = prepOutput defaultOutput outputs.${defaultOutput} // commonAttrs;
+
+      commonAttrs = {
+        outputs = builtins.attrNames outputs;
+      } // outputAttrs;
+
+    in
+    defaultOutputValue;
+
 in
-(buildEnv {
-  name = "nix-${nix-cli.version}";
-  paths = [
-    nix-cli
-    nix-manual.man
-  ];
-
-  meta.mainProgram = "nix";
-}).overrideAttrs
-  (
-    finalAttrs: prevAttrs: {
-      doCheck = true;
-      doInstallCheck = true;
-
-      checkInputs =
-        [
-          # Make sure the unit tests have passed
-          nix-util-tests.tests.run
-          nix-store-tests.tests.run
-          nix-expr-tests.tests.run
-          nix-fetchers-tests.tests.run
-          nix-flake-tests.tests.run
-
-          # Make sure the functional tests have passed
-          nix-functional-tests
-        ]
-        ++ lib.optionals
-          (!stdenv.hostPlatform.isStatic && stdenv.buildPlatform.canExecute stdenv.hostPlatform)
-          [
-            # Perl currently fails in static build
-            # TODO: Split out tests into a separate derivation?
-            nix-perl-bindings
-          ];
-      passthru = prevAttrs.passthru // {
-        inherit (nix-cli) version;
-
-        /**
-          These are the libraries that are part of the Nix project. They are used
-          by the Nix CLI and other tools.
-
-          If you need to use these libraries in your project, we recommend to use
-          the `-c` C API libraries exclusively, if possible.
-
-          We also recommend that you build the complete package to ensure that the unit tests pass.
-          You could do this in CI, or by passing it in an unused environment variable. e.g in a `mkDerivation` call:
-
-          ```nix
-            buildInputs = [ nix.libs.nix-util-c nix.libs.nix-store-c ];
-            # Make sure the nix libs we use are ok
-            unusedInputsForTests = [ nix ];
-            disallowedReferences = nix.all;
-          ```
-        */
-        inherit libs;
-
-        tests = prevAttrs.passthru.tests or { } // {
-          pkg-config = testers.hasPkgConfigModules {
-            package = finalAttrs.finalPackage;
-          };
-        };
 
-        /**
-          A derivation referencing the `dev` outputs of the Nix libraries.
-        */
-        dev = dev finalAttrs;
-        inherit devdoc;
-        doc = nix-manual;
-        outputs = [
-          "out"
-          "dev"
-          "devdoc"
-          "doc"
+makeOutputs {
+  extraAttrs = outputName: drv: {
+    meta = drv.meta // {
+      description = "The Nix package manager";
+      pkgConfigModules = dev.meta.pkgConfigModules;
+      outputsToInstall = [
+        # man is symlinked
+        "out"
+      ];
+    };
+    internals = drv;
+    name = "nix";
+    overrideAttrs =
+      _:
+      throw "The nix package does not support overrideAttrs, because it has been split into multiple derivations. Instead, you may call attributes such as overrideSource, appendPatches or overrideAllMesonComponents.";
+    inherit (nix-cli) version;
+    # Should not be required
+    inherit (drv) drvPath;
+    tests = drv.tests or {};
+    src = patchedSrc;
+  };
+  outputs = {
+    inherit dev devdoc;
+    doc = nix-manual;
+    out =
+      (buildEnv {
+        name = "nix-${nix-cli.version}";
+        paths = [
+          nix-cli
+          nix-manual.man
         ];
-        all = lib.attrValues (
-          lib.genAttrs finalAttrs.passthru.outputs (outName: finalAttrs.finalPackage.${outName})
+        meta.mainProgram = "nix";
+      }).overrideAttrs
+        (
+          finalAttrs: prevAttrs: {
+            doCheck = true;
+            doInstallCheck = true;
+
+            checkInputs =
+              [
+                # Make sure the unit tests have passed
+                nix-util-tests.tests.run
+                nix-store-tests.tests.run
+                nix-expr-tests.tests.run
+                nix-fetchers-tests.tests.run
+                nix-flake-tests.tests.run
+
+                # Make sure the functional tests have passed
+                nix-functional-tests
+
+                # dev bundle is ok
+                # (checkInputs must be empty paths??)
+                (runCommand "check-pkg-config" { checked = dev.tests.pkg-config; } "mkdir $out")
+              ]
+              ++ lib.optionals
+                (!stdenv.hostPlatform.isStatic && stdenv.buildPlatform.canExecute stdenv.hostPlatform)
+                [
+                  # Perl currently fails in static build
+                  # TODO: Split out tests into a separate derivation?
+                  nix-perl-bindings
+                ];
+            passthru = prevAttrs.passthru // {
+              inherit (nix-cli) version;
+
+              /**
+                These are the libraries that are part of the Nix project. They are used
+                by the Nix CLI and other tools.
+
+                If you need to use these libraries in your project, we recommend to use
+                the `-c` C API libraries exclusively, if possible.
+
+                We also recommend that you build the complete package to ensure that the unit tests pass.
+                You could do this in CI, or by passing it in an unused environment variable. e.g in a `mkDerivation` call:
+
+                ```nix
+                  buildInputs = [ nix.libs.nix-util-c nix.libs.nix-store-c ];
+                  # Make sure the nix libs we use are ok
+                  unusedInputsForTests = [ nix ];
+                  disallowedReferences = nix.all;
+                ```
+              */
+              inherit libs;
+
+              tests = prevAttrs.passthru.tests or { } // {
+                # TODO: create a proper fixpoint and:
+                pkg-config = testers.hasPkgConfigModules {
+                  package = finalAttrs.finalPackage;
+                };
+              };
+            };
+          }
         );
-      };
-      meta = prevAttrs.meta // {
-        description = "The Nix package manager";
-        pkgConfigModules = (dev finalAttrs).meta.pkgConfigModules;
-      };
-    }
-  )
+  };
+}
diff --git a/pkgs/tools/package-management/nix/2_26/src/libcmd/package.nix b/pkgs/tools/package-management/nix/2_26/src/libcmd/package.nix
index d155d9f1e620d..d459d1c20fb54 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libcmd/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libcmd/package.nix
@@ -64,14 +64,6 @@ mkMesonLibrary (finalAttrs: {
     nlohmann_json
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
     (lib.mesonEnable "markdown" enableMarkdown)
     (lib.mesonOption "readline-flavor" readlineFlavor)
diff --git a/pkgs/tools/package-management/nix/2_26/src/libexpr-c/package.nix b/pkgs/tools/package-management/nix/2_26/src/libexpr-c/package.nix
index ad1ea371c2d7c..694fbc1fe7893 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libexpr-c/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libexpr-c/package.nix
@@ -36,14 +36,6 @@ mkMesonLibrary (finalAttrs: {
     nix-expr
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libexpr-test-support/package.nix b/pkgs/tools/package-management/nix/2_26/src/libexpr-test-support/package.nix
index 5628d606a4524..44b0ff3863137 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libexpr-test-support/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libexpr-test-support/package.nix
@@ -40,14 +40,6 @@ mkMesonLibrary (finalAttrs: {
     rapidcheck
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libexpr-tests/package.nix b/pkgs/tools/package-management/nix/2_26/src/libexpr-tests/package.nix
index bb5acb7c873da..51d52e935bf5c 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libexpr-tests/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libexpr-tests/package.nix
@@ -46,14 +46,6 @@ mkMesonExecutable (finalAttrs: {
     gtest
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libexpr/package.nix b/pkgs/tools/package-management/nix/2_26/src/libexpr/package.nix
index afd01c3846e94..533dae9f253c7 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libexpr/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libexpr/package.nix
@@ -77,14 +77,6 @@ mkMesonLibrary (finalAttrs: {
     nlohmann_json
   ] ++ lib.optional enableGC boehmgc;
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
     (lib.mesonEnable "gc" enableGC)
   ];
diff --git a/pkgs/tools/package-management/nix/2_26/src/libfetchers-tests/package.nix b/pkgs/tools/package-management/nix/2_26/src/libfetchers-tests/package.nix
index f2680e9b3c1f7..1e379fc5ade24 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libfetchers-tests/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libfetchers-tests/package.nix
@@ -44,14 +44,6 @@ mkMesonExecutable (finalAttrs: {
     gtest
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libfetchers/package.nix b/pkgs/tools/package-management/nix/2_26/src/libfetchers/package.nix
index b0aecd04979e2..3f52e987800e3 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libfetchers/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libfetchers/package.nix
@@ -41,14 +41,6 @@ mkMesonLibrary (finalAttrs: {
     nlohmann_json
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   meta = {
     platforms = lib.platforms.unix ++ lib.platforms.windows;
   };
diff --git a/pkgs/tools/package-management/nix/2_26/src/libflake-c/package.nix b/pkgs/tools/package-management/nix/2_26/src/libflake-c/package.nix
index f0615a42798ee..1149508523e9f 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libflake-c/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libflake-c/package.nix
@@ -38,14 +38,6 @@ mkMesonLibrary (finalAttrs: {
     nix-flake
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libflake-tests/package.nix b/pkgs/tools/package-management/nix/2_26/src/libflake-tests/package.nix
index f9d9b0bc0c6bd..714f3791ad904 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libflake-tests/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libflake-tests/package.nix
@@ -46,14 +46,6 @@ mkMesonExecutable (finalAttrs: {
     gtest
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libflake/package.nix b/pkgs/tools/package-management/nix/2_26/src/libflake/package.nix
index ebd38e140d302..5240ce5e39656 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libflake/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libflake/package.nix
@@ -40,14 +40,6 @@ mkMesonLibrary (finalAttrs: {
     nlohmann_json
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   meta = {
     platforms = lib.platforms.unix ++ lib.platforms.windows;
   };
diff --git a/pkgs/tools/package-management/nix/2_26/src/libmain-c/package.nix b/pkgs/tools/package-management/nix/2_26/src/libmain-c/package.nix
index cf710e03b0d07..f019a917d360c 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libmain-c/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libmain-c/package.nix
@@ -40,14 +40,6 @@ mkMesonLibrary (finalAttrs: {
     nix-main
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libmain/package.nix b/pkgs/tools/package-management/nix/2_26/src/libmain/package.nix
index 046b505dfd46d..c03697c48dab6 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libmain/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libmain/package.nix
@@ -37,14 +37,6 @@ mkMesonLibrary (finalAttrs: {
     openssl
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   meta = {
     platforms = lib.platforms.unix ++ lib.platforms.windows;
   };
diff --git a/pkgs/tools/package-management/nix/2_26/src/libstore-c/package.nix b/pkgs/tools/package-management/nix/2_26/src/libstore-c/package.nix
index 89abeaab87063..fde17c78e0176 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libstore-c/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libstore-c/package.nix
@@ -36,14 +36,6 @@ mkMesonLibrary (finalAttrs: {
     nix-store
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libstore-test-support/package.nix b/pkgs/tools/package-management/nix/2_26/src/libstore-test-support/package.nix
index 7cc29795c1903..ccac25ee16a21 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libstore-test-support/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libstore-test-support/package.nix
@@ -40,14 +40,6 @@ mkMesonLibrary (finalAttrs: {
     rapidcheck
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libstore-tests/package.nix b/pkgs/tools/package-management/nix/2_26/src/libstore-tests/package.nix
index 670386c4a6ff3..b39ee7fa73c07 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libstore-tests/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libstore-tests/package.nix
@@ -52,14 +52,6 @@ mkMesonExecutable (finalAttrs: {
     nix-store-test-support
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libstore/package.nix b/pkgs/tools/package-management/nix/2_26/src/libstore/package.nix
index c982b44f0b738..31867d331b92b 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libstore/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libstore/package.nix
@@ -69,14 +69,6 @@ mkMesonLibrary (finalAttrs: {
     nlohmann_json
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags =
     [
       (lib.mesonEnable "seccomp-sandboxing" stdenv.hostPlatform.isLinux)
diff --git a/pkgs/tools/package-management/nix/2_26/src/libutil-c/package.nix b/pkgs/tools/package-management/nix/2_26/src/libutil-c/package.nix
index 72f57d6f9c62e..f26f57775d4f8 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libutil-c/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libutil-c/package.nix
@@ -34,14 +34,6 @@ mkMesonLibrary (finalAttrs: {
     nix-util
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libutil-test-support/package.nix b/pkgs/tools/package-management/nix/2_26/src/libutil-test-support/package.nix
index 33cd5217defaf..fafd47c86c5e0 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libutil-test-support/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libutil-test-support/package.nix
@@ -38,14 +38,6 @@ mkMesonLibrary (finalAttrs: {
     rapidcheck
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libutil-tests/package.nix b/pkgs/tools/package-management/nix/2_26/src/libutil-tests/package.nix
index d4eea3a8dc260..b8d54b76c42f5 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libutil-tests/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libutil-tests/package.nix
@@ -46,14 +46,6 @@ mkMesonExecutable (finalAttrs: {
     gtest
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
   ];
 
diff --git a/pkgs/tools/package-management/nix/2_26/src/libutil/package.nix b/pkgs/tools/package-management/nix/2_26/src/libutil/package.nix
index 586119a6e5d5e..47dcb54a26f85 100644
--- a/pkgs/tools/package-management/nix/2_26/src/libutil/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/libutil/package.nix
@@ -52,17 +52,6 @@ mkMesonLibrary (finalAttrs: {
     nlohmann_json
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    #
-    # TODO: change release process to add `pre` in `.version`, remove it
-    # before tagging, and restore after.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../.version
-    '';
-
   mesonFlags = [
     (lib.mesonEnable "cpuid" stdenv.hostPlatform.isx86_64)
   ];
diff --git a/pkgs/tools/package-management/nix/2_26/src/nix/package.nix b/pkgs/tools/package-management/nix/2_26/src/nix/package.nix
index 89c52c3bb0506..40a2804378504 100644
--- a/pkgs/tools/package-management/nix/2_26/src/nix/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/src/nix/package.nix
@@ -91,18 +91,11 @@ mkMesonExecutable (finalAttrs: {
     nix-cmd
   ];
 
-  preConfigure =
-    # "Inline" .version so it's not a symlink, and includes the suffix.
-    # Do the meson utils, without modification.
-    ''
-      chmod u+w ./.version
-      echo ${version} > ../../../.version
-    '';
-
   mesonFlags = [
   ];
 
   meta = {
+    mainProgram = "nix";
     platforms = lib.platforms.unix ++ lib.platforms.windows;
   };
 
diff --git a/pkgs/tools/package-management/nix/2_26/tests/functional/package.nix b/pkgs/tools/package-management/nix/2_26/tests/functional/package.nix
index 74c034196fde7..c479d6ca38d3a 100644
--- a/pkgs/tools/package-management/nix/2_26/tests/functional/package.nix
+++ b/pkgs/tools/package-management/nix/2_26/tests/functional/package.nix
@@ -75,16 +75,10 @@ mkMesonDerivation (
     ];
 
     preConfigure =
-      # "Inline" .version so it's not a symlink, and includes the suffix.
-      # Do the meson utils, without modification.
-      ''
-        chmod u+w ./.version
-        echo ${version} > ../../../.version
-      ''
       # TEMP hack for Meson before make is gone, where
       # `src/nix-functional-tests` is during the transition a symlink and
       # not the actual directory directory.
-      + ''
+      ''
         cd $(readlink -e $PWD)
         echo $PWD | grep tests/functional
       '';
@@ -106,5 +100,6 @@ mkMesonDerivation (
   }
   // lib.optionalAttrs (test-daemon != null) {
     NIX_DAEMON_PACKAGE = test-daemon;
+    _NIX_TEST_CLIENT_VERSION = nix-cli.version;
   }
 )
diff --git a/pkgs/tools/package-management/nix/default.nix b/pkgs/tools/package-management/nix/default.nix
index 23b11f1c62857..38583c18eabee 100644
--- a/pkgs/tools/package-management/nix/default.nix
+++ b/pkgs/tools/package-management/nix/default.nix
@@ -137,6 +137,29 @@ let
     }
     pkg;
 
+  # (meson based packaging)
+  # Add passthru tests to the package, and re-expose package set overriding
+  # functions. This will not incorporate the tests into the package set.
+  # TODO (roberth): add package-set level overriding to the "everything" package.
+  addTests = selfAttributeName: pkg:
+    let
+      tests =
+        pkg.tests or {}
+        // import ./tests.nix {
+          inherit runCommand lib stdenv pkgs pkgsi686Linux pkgsStatic nixosTests;
+          inherit (pkg) version src;
+          nix = pkg;
+          self_attribute_name = selfAttributeName;
+        };
+    in
+    # preserve old pkg, including overrideSource, etc
+    pkg // {
+      tests = pkg.tests or {} // tests;
+      passthru = pkg.passthru or {} // {
+        tests = lib.warn "nix.passthru.tests is deprecated. Use nix.tests instead." pkg.passthru.tests or {} // tests;
+      };
+    };
+
 in lib.makeExtensible (self: ({
   nix_2_3 = ((common {
     version = "2.3.18";
@@ -164,18 +187,7 @@ in lib.makeExtensible (self: ({
     self_attribute_name = "nix_2_25";
   };
 
-  nix_2_26 = (callPackage ./2_26/componentized.nix { }).overrideAttrs (this: old: {
-    passthru = old.passthru or {} // {
-      tests =
-        old.passthru.tests or {}
-        // import ./tests.nix {
-          inherit runCommand lib stdenv pkgs pkgsi686Linux pkgsStatic nixosTests;
-          inherit (old) version src;
-          nix = this.finalPackage;
-          self_attribute_name = "nix_2_26";
-        };
-    };
-  });
+  nix_2_26 = addTests "nix_2_26" (callPackage ./2_26/componentized.nix { });
 
   git = common rec {
     version = "2.25.0";