Update build system to depend on Nix 2.26

flake.nix

@@ -81,7 +81,12 @@
           inherit (nixpkgs.lib) fileset;
           inherit (self.packages.${system}) nix-eval-jobs;
           rawSrc = self;
-          nix = nix.packages.${system}.nix;
+          inherit (nix.packages.${system})
+            nix-util
+            nix-store
+            nix-main
+            nix-cli
+            ;
           nix-perl-bindings = nix.hydraJobs.perlBindings.${system};
         };
         default = self.packages.${system}.hydra;

meson.build

@@ -8,22 +8,22 @@ project('hydra', 'cpp',
   ],
 )
 
+nix_util_dep = dependency('nix-util', required: true)
 nix_store_dep = dependency('nix-store', required: true)
 nix_main_dep = dependency('nix-main', required: true)
-nix_expr_dep = dependency('nix-expr', required: true)
-nix_flake_dep = dependency('nix-flake', required: true)
-nix_cmd_dep = dependency('nix-cmd', required: true)
 
 # Nix need extra flags not provided in its pkg-config files.
 nix_dep = declare_dependency(
   dependencies: [
+    nix_util_dep,
     nix_store_dep,
     nix_main_dep,
-    nix_expr_dep,
-    nix_flake_dep,
-    nix_cmd_dep,
   ],
-  compile_args: ['-include', 'nix/config.h'],
+  compile_args: [
+    '-include', 'nix/config-util.hh',
+    '-include', 'nix/config-store.hh',
+    '-include', 'nix/config-main.hh',
+  ],
 )
 
 pqxx_dep = dependency('libpqxx', required: true)

package.nix

@@ -8,7 +8,10 @@
 
 , perlPackages
 
-, nix
+, nix-util
+, nix-store
+, nix-main
+, nix-cli
 , nix-perl-bindings
 , git
 
@@ -162,7 +165,7 @@ stdenv.mkDerivation (finalAttrs: {
     nukeReferences
     pkg-config
     mdbook
-    nix
+    nix-cli
     perlDeps
     perl
     unzip
@@ -172,7 +175,9 @@ stdenv.mkDerivation (finalAttrs: {
     libpqxx
     openssl
     libxslt
-    nix
+    nix-util
+    nix-store
+    nix-main
     perlDeps
     perl
     boost
@@ -199,13 +204,14 @@ stdenv.mkDerivation (finalAttrs: {
     glibcLocales
     libressl.nc
     python3
+    nix-cli
   ];
 
   hydraPath = lib.makeBinPath (
     [
       subversion
       openssh
-      nix
+      nix-cli
       coreutils
       findutils
       pixz
@@ -266,13 +272,13 @@ stdenv.mkDerivation (finalAttrs: {
             --prefix PATH ':' $out/bin:$hydraPath \
             --set HYDRA_RELEASE ${version} \
             --set HYDRA_HOME $out/libexec/hydra \
-            --set NIX_RELEASE ${nix.name or "unknown"} \
+            --set NIX_RELEASE ${nix-cli.name or "unknown"} \
             --set NIX_EVAL_JOBS_RELEASE ${nix-eval-jobs.name or "unknown"}
     done
   '';
 
   dontStrip = true;
 
   meta.description = "Build of Hydra on ${stdenv.system}";
-  passthru = { inherit perlDeps nix; };
+  passthru = { inherit perlDeps; };
 })

t/meson.build

@@ -27,6 +27,7 @@ testenv.prepend('PERL5LIB',
   separator: ':'
 )
 testenv.prepend('PATH',
+  fs.parent(find_program('nix').full_path()),
   fs.parent(hydra_evaluator.full_path()),
   fs.parent(hydra_queue_runner.full_path()),
   meson.project_source_root() / 'src/script',