buildFHSUserEnv: add version arg

This lets you set the version for the derivation produced from
`buildFHSUserEnvChroot` and `buildFHSUserEnvBubblewrap`.

This can help to make it more clear to end-users to see the versions of
the packages they are using.

pkgs/build-support/build-fhs-userenv-bubblewrap/default.nix

@@ -2,6 +2,7 @@
 
 args @ {
   name
+, version ? null
 , runScript ? "bash"
 , extraInstallCommands ? ""
 , meta ? {}
@@ -24,6 +25,7 @@ let
   env = buildFHSEnv (removeAttrs args [
     "runScript" "extraInstallCommands" "meta" "passthru" "extraBwrapArgs" "dieWithParent"
     "unshareUser" "unshareCgroup" "unshareUts" "unshareNet" "unsharePid" "unshareIpc"
+    "version"
   ]);
 
   etcBindFlags = let
@@ -192,7 +194,11 @@ let
 
   bin = writeShellScriptBin name (bwrapCmd { initArgs = ''"$@"''; });
 
-in runCommandLocal name {
+  versionStr = lib.optionalString (! isNull version) ("-" + version);
+
+  nameAndVersion = name + versionStr;
+
+in runCommandLocal nameAndVersion {
   inherit meta;
 
   passthru = passthru // {

pkgs/build-support/build-fhs-userenv/default.nix

@@ -1,11 +1,11 @@
-{ callPackage, runCommandLocal, writeScript, stdenv, coreutils }:
+{ lib, callPackage, runCommandLocal, writeScript, stdenv, coreutils }:
 
 let buildFHSEnv = callPackage ./env.nix { }; in
 
-args@{ name, runScript ? "bash", extraInstallCommands ? "", meta ? {}, passthru ? {}, ... }:
+args@{ name, version ? null, runScript ? "bash", extraInstallCommands ? "", meta ? {}, passthru ? {}, ... }:
 
 let
-  env = buildFHSEnv (removeAttrs args [ "runScript" "extraInstallCommands" "meta" "passthru" ]);
+  env = buildFHSEnv (removeAttrs args [ "version" "runScript" "extraInstallCommands" "meta" "passthru" ]);
 
   chrootenv = callPackage ./chrootenv {};
 
@@ -23,7 +23,11 @@ let
     exec ${run} "$@"
   '';
 
-in runCommandLocal name {
+  versionStr = lib.optionalString (! isNull version) ("-" + version);
+
+  nameAndVersion = name + versionStr;
+
+in runCommandLocal nameAndVersion {
   inherit meta;
 
   passthru = passthru // {