feat: added assertions for automatically validation related options

Some programs and their configurations may depend on other programs.
For a truly portable configuration users must be able to get appropriate error messages if a options is enabled but its requirements (like a dependent option) is not met.
The build crashes for those and keeps the config concise.

6 files changed, 51 insertions, 0 deletions

diff --git a/modules/programs/aerc/assertions.nix b/modules/programs/aerc/assertions.nix
new file mode 100644
index 0000000..a2b49c1
--- /dev/null
+++ b/modules/programs/aerc/assertions.nix
@@ -0,0 +1,19 @@
+{ config, ... }:
+{
+  assertions = [
+    {
+      assertion = !config.programs.aerc.enable || config.programs.less.enable;
+      message = ''
+        programs.aerc is enabled but programs.less.enable is not.
+        aerc requires less as its pager. Please enable programs.less.
+      '';
+    }
+    {
+      assertion = !config.programs.aerc.enable || config.programs.bat.enable;
+      message = ''
+        programs.aerc is enabled but programs.bat.enable is not.
+        aerc requires bat for text/html filtering. Please enable programs.bat.
+      '';
+    }
+  ];
+}
diff --git a/modules/programs/aerc/default.nix b/modules/programs/aerc/default.nix
index 7c69999..2a1361d 100644
--- a/modules/programs/aerc/default.nix
+++ b/modules/programs/aerc/default.nix
@@ -6,6 +6,8 @@
 }:
 
 {
+  imports = [ ./assertions.nix ];
+
   config = lib.mkIf config.programs.aerc.enable {
     programs.aerc = {
       extraConfig = {
diff --git a/modules/programs/fzf/assertions.nix b/modules/programs/fzf/assertions.nix
new file mode 100644
index 0000000..7c2e79c
--- /dev/null
+++ b/modules/programs/fzf/assertions.nix
@@ -0,0 +1,13 @@
+{ config, ... }:
+{
+  assertions = [
+    {
+      assertion =
+        !config.programs.fzf.enable || config.programs.zsh.enable || config.programs.bash.enable;
+      message = ''
+        programs.fzf is enabled but neither programs.zsh.enable nor programs.bash.enable is set.
+        fzf shell integration requires zsh or bash. Please enable at least one.
+      '';
+    }
+  ];
+}
diff --git a/modules/programs/fzf/default.nix b/modules/programs/fzf/default.nix
index 8816ddd..7671b3c 100644
--- a/modules/programs/fzf/default.nix
+++ b/modules/programs/fzf/default.nix
@@ -2,6 +2,8 @@
 
 # FZF - Fuzzy finder, CLI fuzzy search tool
 {
+  imports = [ ./assertions.nix ];
+
   config =
     let
       shellIntegration = ''
diff --git a/modules/programs/git/assertions.nix b/modules/programs/git/assertions.nix
new file mode 100644
index 0000000..fbe5d3c
--- /dev/null
+++ b/modules/programs/git/assertions.nix
@@ -0,0 +1,13 @@
+{ config, ... }:
+{
+  assertions = [
+    {
+      assertion =
+        !config.programs.git.useSSH || (config.programs.git.enable && config.programs.ssh.enable);
+      message = ''
+        programs.git.useSSH is enabled but programs.ssh.enable is not.
+        SSH must be enabled (programs.ssh.enable = true) to use SSH for git.
+      '';
+    }
+  ];
+}
diff --git a/modules/programs/git/default.nix b/modules/programs/git/default.nix
index 2c4303b..133c063 100644
--- a/modules/programs/git/default.nix
+++ b/modules/programs/git/default.nix
@@ -6,6 +6,8 @@
 
 # Git - Distributed version control system
 {
+  imports = [ ./assertions.nix ];
+
   options.programs.git = {
     username = lib.mkOption {
       type = lib.types.str;