Pin down the current nixpkgs version.

default.nix

@@ -19,6 +19,5 @@
 # @end:license
 
 let
-  nixpkgs = import <nixpkgs> {};
-  noisicaa = nixpkgs.callPackage ./noisicaa.nix {};
+  noisicaa = import ./noisicaa.nix {};
 in noisicaa

noisicaa.nix

@@ -18,24 +18,14 @@
 #
 # @end:license
 
-{ lib,
-  stdenv,
-  fetchFromGitHub,
-  python38,
-  python38Packages,
-  lcov,
-  cmake,
-  wafHook,
-  pkg-config,
-  gtest,
-  protobuf,
-  grpc,
-  libjack2,
-  ffmpeg,
-  fmt,
-  withTests ? false
+{ withTests ? false
 }:
 let
+  nixpkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/d14d83a3691121642be1b0579cf3408a83c558d7.tar.gz") {};
+  lib = nixpkgs.lib;
+  stdenv = nixpkgs.stdenv;
+  fetchFromGitHub = nixpkgs.fetchFromGitHub;
+
   # mach-nix: Create highly reproducible python environments
   # https://github.com/DavHau/mach-nix
   mach-nix = import (builtins.fetchGit {
@@ -60,7 +50,7 @@ let
     # system libraries are missing. Using the nixpkgs provider seems to work, but requires building
     # Qt5 from source.
     providers.pyside2 = "nixpkgs";
-    _.pyside2.buildInputs.add = [ python38Packages.shiboken2 ];
+    _.pyside2.buildInputs.add = [ nixpkgs.python38Packages.shiboken2 ];
   };
 
   # gitignoreSource: Nix functions for filtering local git sources
@@ -86,7 +76,7 @@ let
       sha256 = "sha256:1j2l5nm4lhkfymhv5qd5gi8760df7khvdvw174lzc9fjzs3a42af";
     };
 
-    nativeBuildInputs = [cmake python38];
+    nativeBuildInputs = [nixpkgs.cmake nixpkgs.python38];
 
     patchPhase = ''
       patchShebangs test/dependencies/cxxtest/bin/cxxtestgen
@@ -137,7 +127,7 @@ let
       sha256 = "sha256:1a7cj068vap1m3sq9wvzyjjj0vgnk7bxm18mfwvvadl68yh9ij1f";
     };
 
-    nativeBuildInputs = [ cmake ];
+    nativeBuildInputs = [ nixpkgs.cmake ];
 
     cmakeFlags = [ "-DFLATBUFFERS_BUILD_TESTS=OFF" ];
     doCheck = false;
@@ -151,20 +141,23 @@ in stdenv.mkDerivation {
 
   nativeBuildInputs = [
     python
-    wafHook
-    pkg-config
-    protobuf
+    nixpkgs.wafHook
+    nixpkgs.pkg-config
+    nixpkgs.protobuf
     flatbuffers
-    grpc
-    libjack2
+    nixpkgs.grpc
+    nixpkgs.libjack2
     subprocess
-    ffmpeg.dev
+    nixpkgs.ffmpeg.dev
     dep_sort
-    fmt
+    nixpkgs.fmt
   ] ++ lib.lists.optional withTests [
-    gtest.dev
-    lcov
+    nixpkgs.gtest.dev
+    nixpkgs.lcov
   ];
 
   wafConfigureFlags = if withTests then "--with-tests" else "--without-tests";
+
+  # https://discourse.nixos.org/t/how-can-i-build-a-python-package-that-uses-qt/7657
+  QT_QPA_PLATFORM_PLUGIN_PATH="${nixpkgs.qt5.qtbase.bin}/lib/qt-${nixpkgs.qt5.qtbase.version}/plugins";
 }

shell.nix

@@ -19,8 +19,8 @@
 # @end:license
 
 let
-  nixpkgs = import <nixpkgs> {};
-  noisicaa = nixpkgs.callPackage ./noisicaa.nix {
+  nixpkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/d14d83a3691121642be1b0579cf3408a83c558d7.tar.gz") {};
+  noisicaa = import ./noisicaa.nix {
     withTests = true;
   };
 in nixpkgs.mkShell {
@@ -29,7 +29,6 @@ in nixpkgs.mkShell {
   ];
   inputsFrom = [ noisicaa ];
 
-  # https://discourse.nixos.org/t/how-can-i-build-a-python-package-that-uses-qt/7657
-  QT_QPA_PLATFORM_PLUGIN_PATH="${nixpkgs.qt5.qtbase.bin}/lib/qt-${nixpkgs.qt5.qtbase.version}/plugins";
+  inherit (noisicaa) QT_QPA_PLATFORM_PLUGIN_PATH;
 }