build-support/rust: add cargoPurityFlag parameter

pkgs/build-support/rust/build-rust-package/default.nix

@@ -7,6 +7,7 @@
 , cacert
 , git
 , cargoBuildHook
+, cargoBuildHookOffline
 , cargoCheckHook
 , cargoInstallHook
 , cargoNextestHook
@@ -43,6 +44,7 @@
 , checkFeatures ? buildFeatures
 , useNextest ? false
 , depsExtraArgs ? {}
+, cargoPurityFlag ? "--frozen"
 
 # Toggles whether a custom sysroot is created when the target is a .json file.
 , __internal_dontAddSysroot ? false
@@ -119,6 +121,10 @@ stdenv.mkDerivation ((removeAttrs args [ "depsExtraArgs" "cargoUpdateHook" "carg
     cacert
     git
     cargoBuildHook
+    ({ "--frozen"  = cargoBuildHook;
+       "--offline" = cargoBuildHookOffline;
+    }.${cargoPurityFlag}
+      or (throw "unrecognized cargoPurityFlag \"${cargoPurityFlag}\""))
     (if useNextest then cargoNextestHook else cargoCheckHook)
     cargoInstallHook
     cargoSetupHook

pkgs/build-support/rust/hooks/cargo-build-hook.sh

@@ -33,7 +33,7 @@ cargoBuildHook() {
       "CXX_@rustTargetPlatform@=@cxxForHost@" \
       cargo build -j $NIX_BUILD_CORES \
         --target @rustTargetPlatformSpec@ \
-        --frozen \
+        @cargoPurityFlag@ \
         ${cargoBuildProfileFlag} \
         ${cargoBuildNoDefaultFeaturesFlag} \
         ${cargoBuildFeaturesFlag} \

pkgs/build-support/rust/hooks/default.nix

@@ -27,16 +27,29 @@ let
   rustBuildPlatform = rust.toRustTarget stdenv.buildPlatform;
   rustTargetPlatform = rust.toRustTarget stdenv.hostPlatform;
   rustTargetPlatformSpec = rust.toRustTargetSpec stdenv.hostPlatform;
-in {
-  cargoBuildHook = callPackage ({ }:
+  cargoBuildHookFlexible = { cargoPurityFlag }: callPackage ({ }:
     makeSetupHook {
       name = "cargo-build-hook.sh";
       deps = [ cargo ];
       substitutions = {
-        inherit ccForBuild ccForHost cxxForBuild cxxForHost
+        inherit ccForBuild ccForHost cxxForBuild cxxForHost cargoPurityFlag
           rustBuildPlatform rustTargetPlatform rustTargetPlatformSpec;
       };
     } ./cargo-build-hook.sh) {};
+in {
+
+  # "requires that the Cargo.lock file is up-to-date. If the lock file
+  # is missing, or it needs to be updated, Cargo will exit with an
+  # error. The --frozen flag also prevents Cargo from attempting to
+  # access the network to determine if it is out-of-date."
+  cargoBuildHook = cargoBuildHookFlexible { cargoPurityFlag = "--frozen"; };
+
+  # "Prevents Cargo from accessing the network for any reason.  Beware
+  # that this may result in different dependency resolution than
+  # online mode. Cargo will restrict itself to crates that are
+  # downloaded locally, even if there might be a newer version as
+  # indicated in the local copy of the index."
+  cargoBuildHookOffline = cargoBuildHookFlexible { cargoPurityFlag = "--offline"; };
 
   cargoCheckHook = callPackage ({ }:
     makeSetupHook {

pkgs/development/compilers/rust/make-rust-platform.nix

@@ -14,7 +14,7 @@ rec {
 
   buildRustPackage = callPackage ../../../build-support/rust/build-rust-package {
     git = buildPackages.gitMinimal;
-    inherit stdenv cargoBuildHook cargoCheckHook cargoInstallHook cargoNextestHook cargoSetupHook
+    inherit stdenv cargoBuildHook cargoBuildHookOffline cargoCheckHook cargoInstallHook cargoNextestHook cargoSetupHook
       fetchCargoTarball importCargoLock rustc;
   };
 
@@ -31,5 +31,5 @@ rec {
   # Hooks
   inherit (callPackage ../../../build-support/rust/hooks {
     inherit stdenv cargo rustc;
-  }) cargoBuildHook cargoCheckHook cargoInstallHook cargoNextestHook cargoSetupHook maturinBuildHook bindgenHook;
+  }) cargoBuildHook cargoBuildHookOffline cargoCheckHook cargoInstallHook cargoNextestHook cargoSetupHook maturinBuildHook bindgenHook;
 }