feat: add dap support for python

modules/languages/python.nix

@@ -36,6 +36,69 @@ with builtins; let
       '';
     };
   };
+
+  defaultDebugger = "debugpy";
+  debuggers = {
+    debugpy = {
+      # idk if this is the best way to install/run debugpy
+      package = pkgs.python3.withPackages (ps: with ps; [debugpy]);
+      dapConfig = ''
+        dap.adapters.python = function(cb, config)
+          if config.request == 'attach' then
+            ---@diagnostic disable-next-line: undefined-field
+            local port = (config.connect or config).port
+            ---@diagnostic disable-next-line: undefined-field
+            local host = (config.connect or config).host or '127.0.0.1'
+            cb({
+              type = 'server',
+              port = assert(port, '`connect.port` is required for a python `attach` configuration'),
+              host = host,
+              options = {
+                source_filetype = 'python',
+              },
+            })
+          else
+            cb({
+              type = 'executable',
+              command = '${getExe cfg.dap.package}',
+              args = { '-m', 'debugpy.adapter' },
+              options = {
+                source_filetype = 'python',
+              },
+            })
+          end
+        end
+
+        dap.configurations.python = {
+          {
+            -- The first three options are required by nvim-dap
+            type = 'python'; -- the type here established the link to the adapter definition: `dap.adapters.python`
+            request = 'launch';
+            name = "Launch file";
+
+            -- Options below are for debugpy, see https://github.com/microsoft/debugpy/wiki/Debug-configuration-settings for supported options
+
+            program = "''${file}"; -- This configuration will launch the current file if used.
+            pythonPath = function()
+              -- debugpy supports launching an application with a different interpreter then the one used to launch debugpy itself.
+              -- The code below looks for a `venv` or `.venv` folder in the current directly and uses the python within.
+              -- You could adapt this - to for example use the `VIRTUAL_ENV` environment variable.
+              local cwd = vim.fn.getcwd()
+              if vim.fn.executable(cwd .. '/venv/bin/python') == 1 then
+                return cwd .. '/venv/bin/python'
+              elseif vim.fn.executable(cwd .. '/.venv/bin/python') == 1 then
+                return cwd .. '/.venv/bin/python'
+              elseif vim.fn.executable("python") == 1 then
+                return vim.fn.exepath("python")
+              else -- WARNING cfg.dap.package probably has NO libraries other than builtins and debugpy
+                return '${getExe cfg.dap.package}'
+              end
+            end;
+          },
+        }
+      '';
+    };
+  };
 in {
   options.vim.languages.python = {
     enable = mkEnableOption "Python language support";
@@ -80,6 +143,29 @@ in {
         default = formats.${cfg.format.type}.package;
       };
     };
+
+    # TODO this implementation is very bare bones, I don't know enough python to implement everything
+    dap = {
+      enable = mkOption {
+        description = "Enable Python Debug Adapter";
+        type = types.bool;
+        default = config.vim.languages.enableDAP;
+      };
+      debugger = mkOption {
+        description = "Python debugger to use";
+        type = with types; enum (attrNames debuggers);
+        default = defaultDebugger;
+      };
+      package = mkOption {
+        description = ''
+          Python debugger package.
+          This is a python package with debugpy installed, see https://nixos.wiki/wiki/Python#Install_Python_Packages.
+        '';
+        example = literalExpression "with pkgs; python39.withPackages (ps: with ps; [debugpy])";
+        type = types.package;
+        default = debuggers.${cfg.dap.debugger}.package;
+      };
+    };
   };
   config = mkIf cfg.enable (mkMerge [
     (mkIf cfg.treesitter.enable {
@@ -96,5 +182,10 @@ in {
       vim.lsp.null-ls.enable = true;
       vim.lsp.null-ls.sources.python-format = formats.${cfg.format.type}.nullConfig;
     })
+
+    (mkIf cfg.dap.enable {
+      vim.debugger.nvim-dap.enable = true;
+      vim.debugger.nvim-dap.sources.python-debugger = debuggers.${cfg.dap.debugger}.dapConfig;
+    })
   ]);
 }