1 files changed, 43 insertions, 0 deletions
diff --git a/modules/home-manager/assert-valid-neovim-config/default.nix b/modules/home-manager/assert-valid-neovim-config/default.nix
new file mode 100644
index 0000000..218436a
--- /dev/null
+++ b/modules/home-manager/assert-valid-neovim-config/default.nix
@@ -0,0 +1,43 @@
+# This HM module asserts the nvim configuration has valid syntax during
+# building. This shortens the iteration cycle a bit when working on the Lua
+# config as it means I don't have to launch `nvim` only to discover I missed a
+# comma.
+#
+# This approach uses import-from-derivation which _does_ slow down evaluation.
+#
+# This approach should not affect the final closure size as there is no
+# reference to `checkDerivation` in `build.toplevel`. It does however generate
+# a bit of garbage in the Nix store every time the Neovim configuration
+# changes.
+{
+  pkgs,
+  config,
+  ...
+}: let
+  checkDerivation =
+    pkgs.runCommand "successful-syntax-check.nix" {
+      passAsFile = ["luaConfig"];
+      luaConfig = config.programs.neovim.generatedConfigs.lua;
+    } ''
+      # Print listing to give context to error messages when viewing logs (as
+      # suggested by the assertion's message).
+      nl -b a $luaConfigPath
+
+      # `luac` compiles Lua to bytecode, but we can ask it to only parse the input file with `-p`.
+      # Result is exported via import-from-derivation.
+      if ${pkgs.lua}/bin/luac -p -- $luaConfigPath; then
+        echo true >$out
+      else
+        echo false >$out
+      fi
+    '';
+
+  isValidSyntax = import "${checkDerivation}";
+in {
+  assertions = [
+    {
+      assertion = isValidSyntax;
+      message = "Syntax error in Neovim configuration. Run `nix log ${checkDerivation.drvPath}` for more information.";
+    }
+  ];
+}