home/neovim: Add pyls-black

Black’s integrated vim plugin does some virtualenv wizardry that does
not work on nixos.

users/simon/modules/neovim.nix

@@ -30,6 +30,41 @@ let
       sha256 = "1ss065b2psalli46bs3v13fhaplqydh13bg3jg3zr98wbdn70cws";
     };
   };
+  pyls-black = pkgs.python3Packages.buildPythonPackage rec {
+    pname = "pyls-black";
+    version = "0.4.6";
+
+    src = pkgs.python3Packages.fetchPypi {
+      inherit pname version;
+      sha256 = "0qsnjrpqhws7ajwg5y01fcpn1y6jc89ql61rpaknwqq5srg0ww1k";
+    };
+
+    propagatedBuildInputs = with pkgs.python3Packages; [
+      black
+      toml
+    ];
+
+    # circular dependency
+    doCheck = false;
+    postPatch = ''
+      sed -i 's/python-language-server; //' setup.cfg
+    '';
+  };
+  pyls = (pkgs.python3Packages.python-language-server.override {
+    providers = [
+      # everything except autopep8 and yapf (conflicts with black)
+      "mccabe"
+      "pycodestyle"
+      "pydocstyle"
+      "pyflakes"
+      "pylint"
+      "rope"
+    ];
+  }).overrideAttrs (oldAttrs: oldAttrs // {
+    propagatedBuildInputs = oldAttrs.propagatedBuildInputs ++ [
+      pyls-black
+    ];
+  });
 in
 {
   programs.neovim = {
@@ -119,7 +154,7 @@ in
           let g:LanguageClient_serverCommands = {
               \ 'rust': ['rustup', 'run', 'stable', 'rls'],
               \ 'go': ['${pkgs.gopls}/bin/gopls'],
-              \ 'python': ['${pkgs.python3Packages.python-language-server}/bin/pyls'],
+              \ 'python': ['${pyls}/bin/pyls'],
               \ 'typescript': ['${pkgs.nodePackages.javascript-typescript-langserver}/bin/javascript-typescript-stdio'],
               \ 'javascript': ['${pkgs.nodePackages.javascript-typescript-langserver}/bin/javascript-typescript-stdio'],
               \ 'haskell': ['${pkgs.haskellPackages.haskell-language-server}/bin/haskell-language-server', '--lsp'],
@@ -134,7 +169,9 @@ in
               nnoremap <buffer> <silent> K :call LanguageClient#textDocument_hover()<CR>
               nnoremap <buffer> <silent> gd :call LanguageClient#textDocument_definition()<CR>
               nnoremap <buffer> <silent> <F2> :call LanguageClient#textDocument_rename()<CR>
-              set formatexpr=LanguageClient#textDocument_rangeFormatting_sync()
+              nnoremap <buffer> <silent> <Leader>f :call LanguageClient#textDocument_formatting()<CR>
+              " disable since it breaks most code
+              "set formatexpr=LanguageClient#textDocument_rangeFormatting_sync()
             endif
           endfunction
 
@@ -226,7 +263,6 @@ in
       rainbow_csv
       vim-openscad
     ];
-    # TODO: add psf/black
   };
 
   xdg.configFile = {