Add TOML formatter (prettier)

.prettierrc.js

@@ -0,0 +1,3 @@
+module.exports = {
+  "plugins": ["prettier-plugin-toml"],
+};

flake.nix

@@ -25,12 +25,18 @@
           in
           {
 
-            treefmt = stdenv.mkDerivation {
+            treefmt =
+              let
+                devShell = devShells.default;
+              in
+              stdenv.mkDerivation {
                 name = "treefmt-check";
                 src = self;
-              nativeBuildInputs = devShells.default.nativeBuildInputs;
+                nativeBuildInputs = devShell.nativeBuildInputs;
                 dontConfigure = true;
 
+                inherit (devShell) NODE_PATH;
+
                 buildPhase = ''
                   env HOME=$(mktemp -d) treefmt --fail-on-change
                 '';

shell.nix

@@ -29,6 +29,7 @@ in
     pkgs.treefmt
     pkgs.llvmPackages.clang # clang-format
     pkgs.nixpkgs-fmt
+    pkgs.nodePackages.prettier
 
     (pkgs.python3.withPackages (ps: [
       ps.pytest
@@ -36,6 +37,8 @@ in
 
   ];
 
+  NODE_PATH = "${pkgs.nodePackages.prettier-plugin-toml}/lib/node_modules";
+
   shellHook = lib.optionalString stdenv.isLinux ''
     export NIX_DEBUG_INFO_DIRS="${pkgs.curl.debug}/lib/debug:${nix.debug}/lib/debug''${NIX_DEBUG_INFO_DIRS:+:$NIX_DEBUG_INFO_DIRS}"
   '';

treefmt.toml

@@ -1,8 +1,17 @@
 [formatter."c++"]
 command = "clang-format"
-options = [ "-i", "-style", "{BasedOnStyle: llvm, IndentWidth: 4, SortIncludes: false}" ]
+options = [
+  "-i",
+  "-style",
+  "{BasedOnStyle: llvm, IndentWidth: 4, SortIncludes: false}"
+]
 includes = ["*.c", "*.cpp", "*.cc", "*.h", "*.hpp"]
 
 [formatter.nix]
 command = "nixpkgs-fmt"
 includes = ["*.nix"]
+
+[formatter.toml]
+command = "prettier"
+options = ["--write"]
+includes = ["*.toml"]