gptel-cpp-complete

gptel-cpp-complete is an experimental package that provides Copilot-style, context-aware C++ code completion using:

• eglot + clangd for authoritative semantic information
• tree-sitter for correct current function retrieval
• rg/ag for repository-wide pattern retrieval
• gptel for LLM-powered code continuation
• inline ghost text overlays for a VS Code–like UX

Unlike generic AI assistants, this package is designed to behave like a language-server–style completion engine, not a chat bot. Its sole purpose is accurate, minimal, inline code continuation.

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Features

• Context-aware C++ code completion inside functions
• Uses real in-scope symbols from clangd (via eglot)
• Retrieves similar usage patterns from your repository with rg/ag
• Uses real call-hierarchy data from clangd (via eglot)
• Strict system prompt to avoid hallucinated APIs
• Inline “ghost text” suggestions
• Regenerates completion as you type (except when accepting with RET)
• Support both local and remote LLM with gptel

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Requirements

• Emacs 30+
• eglot/clangd
• tree-sitter
• gptel
• rg
• ag

Recommended eglot configuration:

(use-package eglot
   :ensure t
   :hook (((c-mode c++-mode c-ts-mode c++-ts-mode) . eglot-ensure))
   :init
   (setq eglot-stay-out-of '(imenu)
         read-process-output-max (* 1024 1024) ; 1MB
         eglot-autoshutdown t
         eglot-events-buffer-size 0
         eglot-send-changes-idle-time 0.5)
   :config
   (add-to-list 'eglot-server-programs
                '((c-mode c-ts-mode c++-mode c++-ts-mode objc-mode)
                  . ("clangd"
                     "--compile-commands-dir=./build/"
                     "--background-index"
                     "--clang-tidy"
                     "--completion-style=detailed"
                     "--header-insertion=never"
                     "--pch-storage=memory"
                     "--malloc-trim"))))

Recommended tree-sitter configuration:

 (when (treesit-available-p)
   (use-package treesit
     :ensure t
     :init (setq treesit-extra-load-path
                 (gptel-cpp-complete--get-treesit-extra-load-path)
                 major-mode-remap-alist
                 '((c-mode          . c-ts-mode)
                   (c++-mode        . c++-ts-mode))
                 treesit-font-lock-level 4)))

Recommended gptel configuration:

(use-package gptel
   :ensure t
   :config
   (setq gptel-model 'deepseek-ai/DeepSeek-V3.2
         ;; Randomness in response text, 0 to 2
         gptel-temperature 0
         gptel-backend
         ;; free 2000 request per-day, each model 500
         (gptel-make-openai "Free"
           :host "api-inference.modelscope.cn"
           :stream t
           :key ""
           :models '(Qwen/Qwen2.5-32B-Instruct
                     deepseek-ai/DeepSeek-V3.2))))

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Installation

Clone the repository and add it to your load path:

(add-to-list 'load-path "/path/to/gptel-cpp-complete")
(require 'gptel-cpp-complete)
(when (display-graphic-p)
  ;; gptel-cpp-complete-mode not work well in terminal mode
  (dolist (c-mode-hook '(c-mode-common-hook c-ts-mode-hook c++-ts-mode-hook))
    (add-hook c-mode-hook #'gptel-cpp-complete-mode)))

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Screenshots

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Contributing

Yes, please do! See CONTRIBUTING for guidelines.

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License

See LICENSE. Copyright (c) 2025 Huming Chen chenhuming@gmail.com