---
language:
  - code
license: mit
base_model: microsoft/graphcodebert-base
tags:
  - code-search
  - semantic-search
  - graphcodebert
  - erlang
  - cpp
library_name: transformers
pipeline_tag: feature-extraction
---

# GraphCode-CErl — Semantic Code Search for Erlang & C++

Fine-tuned [GraphCodeBERT](https://huggingface.co/microsoft/graphcodebert-base) for semantic code search over **Erlang** and **C++** codebases. Given a natural language query, the model retrieves the most semantically relevant functions from an indexed repository.

## Model Description

This is a bi-encoder trained with contrastive learning. It encodes both natural language queries and code snippets into a shared embedding space, enabling efficient cosine-similarity-based retrieval at search time.

- **Base model:** `microsoft/graphcodebert-base`
- **Architecture:** GraphCodeBERT encoder with mean pooling + L2 normalization (no LM head)
- **Languages trained on:** Erlang, C++
- **Task:** Semantic code search / function retrieval

### Architecture detail

The model wraps the GraphCodeBERT encoder in a lightweight `CodeSearchModel`:

```python
# Mean pooling over all token positions (not CLS)
def mean_pooling(last_hidden_state, attention_mask):
    mask = attention_mask.unsqueeze(-1).expand(last_hidden_state.size()).float()
    return torch.sum(last_hidden_state * mask, 1) / torch.clamp(mask.sum(1), min=1e-9)
```

Embeddings are L2-normalized, so retrieval is a plain dot product (equivalent to cosine similarity).

---

## Training

### Data

Training triplets were constructed from two sources:

| Language | Source | Records |
|----------|--------|---------|
| C++ | [`codeparrot/xlcost-text-to-code`](https://huggingface.co/datasets/codeparrot/xlcost-text-to-code) (C++-program-level) | 8,650 |
| Erlang | Private dataset (not released) | — |

Each record is a `(code, good_docstring, bad1_docstring, bad2_docstring)` tuple. Negatives were mined as follows:
- **60% hard negatives** — BM25-retrieved docstrings that are lexically similar to the positive but semantically wrong (top-20 BM25 candidates, sampled randomly)
- **30% cross-language negatives** — docstrings sampled from the opposite language to discourage language-specific shortcuts
- **10% random negatives** — uniform random docstrings as easy negatives

### Loss

Temperature-scaled cross-entropy over augmented scores. For each batch the score matrix is extended with both negatives:

```
augmented_scores = [good_scores | bad1_scores | bad2_scores]
loss = CrossEntropyLoss(augmented_scores / τ, diagonal_labels)
```

where `τ = 0.05`.

### Hyperparameters

| Parameter | Value |
|-----------|-------|
| Base model | `microsoft/graphcodebert-base` |
| Batch size | 32 |
| Epochs | 10 |
| Learning rate | 2e-5 |
| LR schedule | Linear warmup (10%) → linear decay to 0 |
| Optimizer | AdamW |
| Gradient clipping | 1.0 |
| Code max length | 256 tokens |
| NL max length | 128 tokens |
| Temperature (τ) | 0.05 |
| Early stopping patience | 3 (not triggered) |
| Seed | 42 |

### Training curve

| Epoch | Loss |
|-------|------|
| 1 | 1.4135 |
| 2 | 0.4685 |
| 3 | 0.3438 |
| 4 | 0.2738 |
| 5 | 0.2308 |
| 6 | 0.1997 |
| 7 | 0.1671 |
| 8 | 0.1507 |
| 9 | 0.1425 |
| **10** | **0.1348** ← best |

Training ran for all 10 epochs without triggering early stopping (patience = 3). Best model saved at epoch 10.

---

## Usage

This model is intended to be used with [`code_search.py`](https://github.com/MatthewsO3/GraphCode-CErl-base/tree/main/Code%20Search), a unified indexing and search tool included in the repository.

### Quick start

```bash
git clone https://github.com/MatthewsO3/GraphCode-CErl-base
cd "GraphCode-CErl-base/Code Search/Evaluation"
python setup.py          # creates .venv, installs deps, builds erlang.so
source .venv/bin/activate

# Index a repository (auto-discovers Erlang + C++ + Python)
python code_search.py index \
    --repo /path/to/your/repo \
    --model MatthewsO3/GraphCode-CErl-codesearch \
    --output corpus.jsonl \
    --index corpus_index.pt

# Search interactively
python code_search.py search \
    --model MatthewsO3/GraphCode-CErl-codesearch \
    --jsonl corpus.jsonl \
    --index corpus_index.pt \
    --top 5
```

Language-specific flags are also available and can be combined freely:

```bash
# Erlang only
python code_search.py index --erlang /path/to/erl_repo ...

# C++ only
python code_search.py index --cpp /path/to/cpp_repo ...

# Explicit mix
python code_search.py index --erlang /path/erl --cpp /path/cpp --python /path/py ...
```

### Using the model directly

```python
from transformers import AutoTokenizer, AutoModel
import torch

tokenizer = AutoTokenizer.from_pretrained("microsoft/graphcodebert-base")
model = AutoModel.from_pretrained("MatthewsO3/GraphCode-CErl-codesearch")
model.eval()

def encode(texts):
    enc = tokenizer(texts, return_tensors="pt", truncation=True,
                    padding=True, max_length=256)
    with torch.no_grad():
        out = model(**enc)
    # Mean pooling
    mask = enc["attention_mask"].unsqueeze(-1).float()
    emb = (out.last_hidden_state * mask).sum(1) / mask.sum(1).clamp(min=1e-9)
    return emb / emb.norm(dim=1, keepdim=True)

query = encode(["handle TCP connection timeout"])
code  = encode(["handle_timeout(Socket, State) -> gen_tcp:close(Socket), {stop, timeout, State}."])

score = (query @ code.T).item()
print(f"Similarity: {score:.4f}")
```

> **Note:** The tokenizer is loaded from `microsoft/graphcodebert-base` since it is identical to the fine-tuned model's tokenizer and avoids a redundant download.

---

## Supported Languages

| Language | Extractor | Extensions |
|----------|-----------|------------|
| Erlang | tree-sitter (WhatsApp grammar) + custom `ErlangParser` + regex fallback | `.erl`, `.hrl` |
| C++ | tree-sitter + regex fallback | `.cpp`, `.cc`, `.cxx`, `.c`, `.h`, `.hpp` |
| Python | tree-sitter + regex fallback | `.py` |

> **Note:** Python indexing is supported by `code_search.py` but the model was not trained on Python data. Results for Python queries may be less accurate.

---

## Limitations

- Not trained on Python — cross-language transfer to Python is best-effort
- The Erlang training set is private and not released
- Functions without docstrings or comments are embedded on code tokens alone, which may reduce retrieval accuracy for ambiguous natural language queries
- Running on CPU is fully supported but slow for large corpora at index-build time; a GPU is recommended

---

## Repository

Training code, indexing tool, and setup scripts are available at:
[github.com/MatthewsO3/GraphCode-CErl-base](https://github.com/MatthewsO3/GraphCode-CErl-base)

---

## Citation

If you use this model, please cite the original GraphCodeBERT paper:

```bibtex
@inproceedings{guo2021graphcodebert,
  title     = {GraphCodeBERT: Pre-training Code Representations with Data Flow},
  author    = {Guo, Daya and Ren, Shuo and Lu, Shuai and Feng, Zhangyin and Tang, Duyu
               and Liu, Shujie and Zhou, Long and Duan, Nan and Svyatkovskiy, Alexey
               and Fu, Shengyu and others},
  booktitle = {International Conference on Learning Representations},
  year      = {2021}
}
```