fish: add binds option (#7121)

binds options is a wrapper of fish_user_key_bindings that contains
custom binds

tests/modules/programs/fish/binds.nix

@@ -0,0 +1,46 @@
+{ lib, ... }:
+{
+  config = {
+    programs.fish = {
+      enable = true;
+
+      binds = {
+        "ctrl-d".command = "exit";
+
+        "ctrl-c" = {
+          mode = "insert";
+          command = [
+            "kill-whole-line"
+            "repaint"
+          ];
+        };
+
+        "ctrl-g" = {
+          command = [
+            "git diff"
+            "repaint"
+          ];
+        };
+      };
+    };
+
+    # Needed to avoid error with dummy fish package.
+    xdg.dataFile."fish/home-manager_generated_completions".source = lib.mkForce (
+      builtins.toFile "empty" ""
+    );
+
+    nmt = {
+      description = "if fish.binds is set, check function exists and contains valid binds";
+      script = ''
+        assertFileExists home-files/.config/fish/functions/fish_user_key_bindings.fish
+
+        assertFileContains home-files/.config/fish/functions/fish_user_key_bindings.fish \
+          "bind ctrl-d exit"
+        assertFileContains home-files/.config/fish/functions/fish_user_key_bindings.fish \
+          "bind --mode insert ctrl-c kill-whole-line repaint"
+        assertFileContains home-files/.config/fish/functions/fish_user_key_bindings.fish \
+          "bind ctrl-g 'git diff' repaint"
+      '';
+    };
+  };
+}

tests/modules/programs/fish/default.nix

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