fish: support simple key bindings

support simple keybinds of the form "SEQUENCE" -> COMMAND,
as described in the fish docs: https://fishshell.com/docs/current/cmds/bind.html

modules/programs/fish.nix

@@ -213,6 +213,9 @@ let
   aliasesStr = concatStringsSep "\n"
     (mapAttrsToList (k: v: "alias ${k} ${escapeShellArg v}") cfg.shellAliases);
 
+  bindsStr = concatStringsSep "\n"
+    (mapAttrsToList (k: v: "bind ${k} ${escapeShellArg v}") cfg.shellBinds);
+
   fishIndent = name: text:
     pkgs.runCommand name {
       nativeBuildInputs = [ cfg.package ];
@@ -288,6 +291,20 @@ in {
         '';
       };
 
+      shellBinds = mkOption {
+        type = with types; attrsOf str;
+        default = { };
+        example = literalExpression ''
+          {
+            "\cg" = "git diff; commandline -f repaint";
+          }
+        '';
+        description = ''
+          An attribute set that maps a key bindings (the top level attribute names
+          in this option) to command strings or directly to build outputs.
+        '';
+      };
+
       shellInit = mkOption {
         type = types.lines;
         default = "";
@@ -474,6 +491,9 @@ in {
           # Aliases
           ${aliasesStr}
 
+          # Binds
+          ${bindsStr}
+
           # Interactive shell initialisation
           ${cfg.interactiveShellInit}
 

tests/modules/programs/fish/bindings.nix

@@ -0,0 +1,29 @@
+{ config, ... }: {
+  config = {
+    programs.fish = {
+      enable = true;
+
+      shellBinds = {
+        "\\cd" = "exit";
+        "." = "rationalise-dot";
+        "\\cg" = "git diff; commandline -f repaint";
+        "\\cz" = "foo && bar";
+      };
+    };
+
+    nmt = {
+      description =
+        "if fish.shellBinds is set, check fish.config contains bindings";
+      script = ''
+        assertFileContains home-files/.config/fish/config.fish \
+          "bind \cd exit"
+        assertFileContains home-files/.config/fish/config.fish \
+          "bind . rationalise-dot"
+        assertFileContains home-files/.config/fish/config.fish \
+          "bind \cg 'git diff; commandline -f repaint'"
+        assertFileContains home-files/.config/fish/config.fish \
+          "bind \cz 'foo && bar'"
+      '';
+    };
+  };
+}

tests/modules/programs/fish/default.nix

@@ -4,4 +4,5 @@
   fish-functions = ./functions.nix;
   fish-no-functions = ./no-functions.nix;
   fish-plugins = ./plugins.nix;
+  fish-bindings = ./bindings.nix;
 }