Add TOML formatter (prettier)

.prettierrc.js

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

flake.nix

@@ -25,18 +25,24 @@
           in
           {
 
-            treefmt = stdenv.mkDerivation {
-              name = "treefmt-check";
-              src = self;
-              nativeBuildInputs = devShells.default.nativeBuildInputs;
-              dontConfigure = true;
+            treefmt =
+              let
+                devShell = devShells.default;
+              in
+              stdenv.mkDerivation {
+                name = "treefmt-check";
+                src = self;
+                nativeBuildInputs = devShell.nativeBuildInputs;
+                dontConfigure = true;
 
-              buildPhase = ''
-                env HOME=$(mktemp -d) treefmt --fail-on-change
-              '';
+                inherit (devShell) NODE_PATH;
 
-              installPhase = "touch $out";
-            };
+                buildPhase = ''
+                  env HOME=$(mktemp -d) treefmt --fail-on-change
+                '';
+
+                installPhase = "touch $out";
+              };
 
             build = mkVariant pkgs.nix;
             build-unstable = mkVariant pkgs.nixUnstable;

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}" ]
-includes = [ "*.c", "*.cpp", "*.cc", "*.h", "*.hpp" ]
+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"]