{home-environment,bash,zsh}: support ignoring null sessionVariables

Some applications consider environment variables to be “true” simply if
they are set. Previously it was not possible to have a var set and later
override (e.g. with `lib.mkForce`) to *unset* it. This makes that
possible. The filtering must be done in the `exportAll` as attempting to
do it in the option’s `apply` causing infinite recursion (likely why it
is `lazyAttrsOf`).

modules/home-environment.nix

@@ -266,12 +266,14 @@ in
       default = { };
       type =
         with types;
-        lazyAttrsOf (oneOf [
-          str
-          path
-          int
-          float
-        ]);
+        lazyAttrsOf (
+          nullOr (oneOf [
+            str
+            path
+            int
+            float
+          ])
+        );
       example = {
         EDITOR = "emacs";
         GS_OPTIONS = "-sPAPERSIZE=a4";
@@ -307,6 +309,9 @@ in
           BAR = "''${config.home.sessionVariables.FOO} World!";
         };
         ```
+
+        Setting a value to `null` will skip setting the variable at all, which
+        may be useful when overriding.
       '';
     };
 

modules/lib/shell.nix

@@ -69,7 +69,9 @@ in
   # Given an attribute set containing shell variable names and their
   # assignment, this function produces a string containing an export
   # statement for each set entry.
-  exportAll = vars: lib.concatStringsSep "\n" (lib.mapAttrsToList export vars);
+  exportAll =
+    vars:
+    lib.concatStringsSep "\n" (lib.mapAttrsToList export (lib.filterAttrs (_k: v: v != null) vars));
 
   # Formats a list of items for shell array content with intelligent width optimization.
   # IMPORTANT: This formats the CONTENTS of an array (what goes inside parentheses),

modules/lib/zsh.nix

@@ -38,5 +38,7 @@ rec {
     let
       separator = if indent == "" then "\n" else "\n" + indent;
     in
-    lib.concatStringsSep separator (lib.mapAttrsToList export vars);
+    lib.concatStringsSep separator (
+      lib.mapAttrsToList export (lib.filterAttrs (_k: v: v != null) vars)
+    );
 }

modules/programs/bash.nix

@@ -135,17 +135,22 @@ in
         default = { };
         type =
           with types;
-          lazyAttrsOf (oneOf [
-            str
-            path
-            int
-            float
-          ]);
+          lazyAttrsOf (
+            nullOr (oneOf [
+              str
+              path
+              int
+              float
+            ])
+          );
         example = {
           MAILCHECK = 30;
         };
         description = ''
           Environment variables that will be set for the Bash session.
+
+          Setting a value to `null` will skip setting the variable at all, which
+          may be useful when overriding.
         '';
       };
 

modules/programs/zsh/default.nix

@@ -249,16 +249,23 @@ in
           default = { };
           type =
             with types;
-            lazyAttrsOf (oneOf [
-              str
-              path
-              int
-              float
-            ]);
+            lazyAttrsOf (
+              nullOr (oneOf [
+                str
+                path
+                int
+                float
+              ])
+            );
           example = {
             MAILCHECK = 30;
           };
-          description = "Environment variables that will be set for zsh session.";
+          description = ''
+            Environment variables that will be set for zsh session.
+
+            Setting a value to `null` will skip setting the variable at all, which
+            may be useful when overriding.
+          '';
         };
 
         initContent = mkOption {

tests/modules/home-environment/session-variables.nix

@@ -9,6 +9,7 @@ let
     if [ -n "$__HM_SESS_VARS_SOURCED" ]; then return; fi
     export __HM_SESS_VARS_SOURCED=1
 
+    export IS_EMPTY=""
     export LOCALE_ARCHIVE_2_27="${config.i18n.glibcLocales}/lib/locale/locale-archive"
     export V1="v1"
     export V2="v2-v1"
@@ -25,6 +26,7 @@ let
     if [ -n "$__HM_SESS_VARS_SOURCED" ]; then return; fi
     export __HM_SESS_VARS_SOURCED=1
 
+    export IS_EMPTY=""
     export TERMINFO_DIRS="/home/hm-user/.nix-profile/share/terminfo:$TERMINFO_DIRS''${TERMINFO_DIRS:+:}/usr/share/terminfo"
     export V1="v1"
     export V2="v2-v1"
@@ -45,6 +47,8 @@ in
   home.sessionVariables = {
     V1 = "v1";
     V2 = "v2-${config.home.sessionVariables.V1}";
+    IS_EMPTY = "";
+    IS_NULL = null;
   };
 
   nmt.script = ''

tests/modules/programs/bash/session-variables.nix

@@ -8,6 +8,8 @@
     sessionVariables = {
       V1 = "v1";
       V2 = "v2-${config.programs.bash.sessionVariables.V1}";
+      IS_EMPTY = "";
+      IS_NULL = null;
     };
   };
 
@@ -18,6 +20,7 @@
       ${builtins.toFile "session-variables-expected" ''
         . "/nix/store/00000000000000000000000000000000-hm-session-vars.sh/etc/profile.d/hm-session-vars.sh"
 
+        export IS_EMPTY=""
         export V1="v1"
         export V2="v2-v1"
 

tests/modules/programs/zsh/session-variables.nix

@@ -8,6 +8,8 @@
       PATH = "$HOME/bin:$PATH";
       V1 = "v1";
       V2 = "v2-${config.programs.zsh.sessionVariables.V1}";
+      IS_EMPTY = "";
+      IS_NULL = null;
     };
   };
 

tests/modules/programs/zsh/session-variables.zshenv

@@ -4,6 +4,7 @@
 # Only source this once
 if [[ -z "$__HM_ZSH_SESS_VARS_SOURCED" ]]; then
   export __HM_ZSH_SESS_VARS_SOURCED=1
+  export IS_EMPTY=""
   export PATH="$HOME/bin:$PATH"
   export V1="v1"
   export V2="v2-v1"