vscode: add options for keybindings

Adds a new `keybindings` option to the `vscode` configuration.

It contains a list of key bindings, which will be written to
`%vscode-dir%/User/keybindings.json`.

PR #1351

tests/modules/programs/vscode/default.nix

@@ -0,0 +1 @@
+{ vscode-keybindings = ./keybindings.nix; }

tests/modules/programs/vscode/keybindings.nix

@@ -0,0 +1,53 @@
+# Test that keybdinings.json is created correctly.
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  bindings = [
+    {
+      key = "ctrl+c";
+      command = "editor.action.clipboardCopyAction";
+      when = "textInputFocus && false";
+    }
+    {
+      key = "ctrl+c";
+      command = "deleteFile";
+      when = "";
+    }
+    {
+      key = "d";
+      command = "deleteFile";
+      when = "explorerViewletVisible";
+    }
+  ];
+
+  targetPath = if pkgs.stdenv.hostPlatform.isDarwin then
+    "Library/Application Support/Code/User/keybindings.json"
+  else
+    ".config/Code/User/keybindings.json";
+
+  expectedJson = pkgs.writeText "expected.json" (builtins.toJSON bindings);
+in {
+  config = {
+    programs.vscode = {
+      enable = true;
+      keybindings = bindings;
+    };
+
+    nixpkgs.overlays = [
+      (self: super: {
+        vscode = pkgs.runCommandLocal "vscode" { pname = "vscode"; } ''
+          mkdir -p $out/bin
+          touch $out/bin/code
+          chmod +x $out/bin/code;
+        '';
+      })
+    ];
+
+    nmt.script = ''
+      assertFileExists "home-files/${targetPath}"
+      assertFileContent "home-files/${targetPath}" "${expectedJson}"
+    '';
+  };
+}