feat: add diagnostic actions and modernize prompts for multi-provider support

- Add {{diagnostic}} and {{diagnostics}} template variables for actions
- Add new actions: fix_diagnostic, explain_diagnostic, fix_diagnostics
- Remove deprecated `stop` parameter from all actions (not supported by modern LLMs)
- Remove `frequency_penalty` from keywords action
- Rewrite prompts to explicitly request raw code output without markdown fences
- Update README with new actions and template variable documentation

Author: jackMort

README.md

@@ -294,6 +294,9 @@ list. Available actions are:
   9. `explain_code`
   10. `roxygen_edit`
   11. `code_readability_analysis` -- see [demo](https://youtu.be/zlU3YGGv2zY)
+  12. `fix_diagnostic` -- fix error under cursor
+  13. `explain_diagnostic` -- explain error under cursor
+  14. `fix_diagnostics` -- fix all errors in selection
 
 All the above actions are using `gpt-5-mini` model.
 
@@ -306,7 +309,7 @@ An example of custom action may look like this: (`#` marks comments)
   "action_name": {
     "type": "chat", # or "completion" or "edit"
     "opts": {
-      "template": "A template using possible variable: {{filetype}} (neovim filetype), {{input}} (the selected text) an {{argument}} (provided on the command line), {{filepath}} (the relative path to the file)",
+      "template": "A template using possible variables",
       "strategy": "replace", # or "display" or "append" or "edit"
       "params": { # parameters according to the official OpenAI API
         "model": "gpt-5-mini", # or any other model supported by `"type"` in the OpenAI API, use the playground for reference
@@ -326,6 +329,14 @@ An example of custom action may look like this: (`#` marks comments)
 }
 ```
 
+Available template variables:
+- `{{input}}` - the selected text
+- `{{filetype}}` - neovim filetype
+- `{{filepath}}` - relative path to the file
+- `{{argument}}` - provided on the command line
+- `{{diagnostic}}` - LSP diagnostic under cursor (format: `[SEVERITY] message (line N)`)
+- `{{diagnostics}}` - all LSP diagnostics in selection (format: `Line N [SEVERITY]: message`)
+
 The `edit` strategy consists in showing the output side by side with the input and
 available for further editing requests.
 For now, `edit` strategy is implemented for `chat` type only.

lua/chatgpt/flows/actions/actions.json

@@ -2,13 +2,10 @@
   "complete_code": {
     "type": "chat",
     "opts": {
-      "template": "Complete the following code written in {{lang}} by pasting the existing code and continuing it.\n\nExisting code:\n```{{filetype}}\n{{input}}\n```\n\n```{{filetype}}\n",
+      "template": "Complete the following {{filetype}} code by continuing it. Respond with the COMPLETE code (existing + new). No markdown fences, no explanations.\n\n{{input}}",
       "strategy": "replace",
       "params": {
-        "model": "gpt-5-mini",
-        "stop": [
-          "```"
-        ]
+        "model": "gpt-5-mini"
       }
     }
   },
@@ -53,48 +50,37 @@
       "template": "Extract the main keywords from the following text.\n\n{{input}}",
       "strategy": "replace",
       "params": {
-        "model": "gpt-5-mini",
-        "temperature": 0.5,
-        "frequency_penalty": 0.8
+        "model": "gpt-5-mini"
       }
     }
   },
   "docstring": {
     "type": "chat",
     "opts": {
-      "template": "# An elaborate, high quality docstring for the above function:\n# Writing a good docstring\n\nThis is an example of writing a really good docstring that follows a best practice for the given language. Attention is paid to detailing things like\n* parameter and return types (if applicable)\n* any errors that might be raised or returned, depending on the language\n\nI received the following code:\n\n```{{filetype}}\n{{input}}\n```\n\nThe code with a really good docstring added is below:\n\n```{{filetype}}",
+      "template": "Add a high quality docstring to the following {{filetype}} code. Include parameter types, return types, and any errors that might be raised.\n\nCode:\n{{input}}\n\nRespond with ONLY the complete code including the docstring. No markdown fences, no explanations.",
       "strategy": "edit",
       "params": {
-        "model": "gpt-5-mini",
-        "stop": [
-          "```"
-        ]
+        "model": "gpt-5-mini"
       }
     }
   },
   "add_tests": {
     "type": "chat",
     "opts": {
-      "template": "Implement tests for the following code.\n\nCode:\n```{{filetype}}\n{{input}}\n```\n\nTests:\n```{{filetype}}",
+      "template": "Implement tests for the following {{filetype}} code.\n\nCode:\n{{input}}\n\nRespond with ONLY the test code. No markdown fences, no explanations.",
       "strategy": "append",
       "params": {
-        "model": "gpt-5-mini",
-        "stop": [
-          "```"
-        ]
+        "model": "gpt-5-mini"
       }
     }
   },
   "optimize_code": {
     "type": "chat",
     "opts": {
-      "template": "Optimize the following code.\n\nCode:\n```{{filetype}}\n{{input}}\n```\n\nOptimized version:\n```{{filetype}}",
+      "template": "Optimize the following {{filetype}} code for better performance and readability.\n\nCode:\n{{input}}\n\nRespond with ONLY the optimized code. No markdown fences, no explanations.",
       "strategy": "edit",
       "params": {
-        "model": "gpt-5-mini",
-        "stop": [
-          "```"
-        ]
+        "model": "gpt-5-mini"
       }
     }
   },
@@ -111,27 +97,21 @@
   "fix_bugs": {
     "type": "chat",
     "opts": {
-      "template": "Fix bugs in the below code\n\nCode:\n```{{filetype}}\n{{input}}\n```\n\nFixed code:\n```{{filetype}}",
+      "template": "Fix bugs in the following {{filetype}} code.\n\nCode:\n{{input}}\n\nRespond with ONLY the fixed code. No markdown fences, no explanations.",
       "strategy": "edit",
       "params": {
-        "model": "gpt-5-mini",
-        "stop": [
-          "```"
-        ]
+        "model": "gpt-5-mini"
       }
     }
   },
   "explain_code": {
     "type": "chat",
     "opts": {
       "title": " Explain Code",
-      "template": "Explain the following code:\n\nCode:\n```{{filetype}}\n{{input}}\n```\n\nUse markdown format.\nHere's what the above code is doing:\n```",
+      "template": "Explain the following {{filetype}} code. Use markdown format with clear sections.\n\nCode:\n{{input}}",
       "strategy": "display",
       "params": {
-        "model": "gpt-5-mini",
-        "stop": [
-          "```"
-        ]
+        "model": "gpt-5-mini"
       }
     }
   },
@@ -187,5 +167,36 @@
         ]
       }
     }
+  },
+  "fix_diagnostic": {
+    "type": "chat",
+    "opts": {
+      "template": "Fix the following error in the {{filetype}} code.\n\nError:\n{{diagnostic}}\n\nCode:\n{{input}}\n\nRespond with ONLY the fixed code. No markdown fences, no explanations.",
+      "strategy": "edit",
+      "params": {
+        "model": "gpt-5-mini"
+      }
+    }
+  },
+  "explain_diagnostic": {
+    "type": "chat",
+    "opts": {
+      "title": " Explain Error",
+      "template": "Explain the following error and how to fix it. Use markdown format.\n\nError:\n{{diagnostic}}\n\nCode:\n{{input}}",
+      "strategy": "display",
+      "params": {
+        "model": "gpt-5-mini"
+      }
+    }
+  },
+  "fix_diagnostics": {
+    "type": "chat",
+    "opts": {
+      "template": "Fix all the following errors in the {{filetype}} code.\n\nErrors:\n{{diagnostics}}\n\nCode:\n{{input}}\n\nRespond with ONLY the fixed code. No markdown fences, no explanations.",
+      "strategy": "edit",
+      "params": {
+        "model": "gpt-5-mini"
+      }
+    }
   }
 }

lua/chatgpt/flows/actions/base.lua

@@ -73,6 +73,48 @@ function BaseAction:get_selected_text_with_line_numbers()
   return table.concat(lines_with_numbers, "\n")
 end
 
+function BaseAction:get_diagnostic()
+  local bufnr = self:get_bufnr()
+  local cursor = vim.api.nvim_win_get_cursor(0)
+  local row = cursor[1] - 1
+
+  local diagnostics = vim.diagnostic.get(bufnr, { lnum = row })
+  if #diagnostics == 0 then
+    return ""
+  end
+
+  local diag = diagnostics[1]
+  local severity = vim.diagnostic.severity[diag.severity] or "UNKNOWN"
+  return string.format("[%s] %s (line %d)", severity, diag.message, diag.lnum + 1)
+end
+
+function BaseAction:get_diagnostics()
+  local bufnr = self:get_bufnr()
+  local _, start_row, _, end_row, _ = self:get_visual_selection()
+
+  local diagnostics = vim.diagnostic.get(bufnr)
+  local filtered = {}
+
+  for _, diag in ipairs(diagnostics) do
+    local line = diag.lnum + 1
+    if line >= start_row and line <= end_row then
+      table.insert(filtered, diag)
+    end
+  end
+
+  if #filtered == 0 then
+    return ""
+  end
+
+  local result = {}
+  for _, diag in ipairs(filtered) do
+    local severity = vim.diagnostic.severity[diag.severity] or "UNKNOWN"
+    table.insert(result, string.format("Line %d [%s]: %s", diag.lnum + 1, severity, diag.message))
+  end
+
+  return table.concat(result, "\n")
+end
+
 function BaseAction:mark_selection_with_signs()
   local bufnr = self:get_bufnr()
   local _, start_row, _, end_row, _ = self:get_visual_selection()

lua/chatgpt/flows/actions/chat/init.lua

@@ -46,6 +46,8 @@ function ChatAction:render_template()
     filetype = self:get_filetype(),
     filepath = self:get_filepath(),
     input = input,
+    diagnostic = self:get_diagnostic(),
+    diagnostics = self:get_diagnostics(),
   }
   data = vim.tbl_extend("force", {}, data, self.variables)
   local result = self.template