Function _build_ast_json_and_chunks

src/pyspector/ast_cache.py:129–180

Serialise *tree* to AST JSON, reusing encoded subtrees from *old_chunks* for any chunk whose content hash AND start_line are both unchanged. Skips encode_node() for every unchanged top-level function/class — typically 80-100 % of body nodes when only a few lines change. Return

(
    tree: ast.Module,
    source: str,
    old_chunks: Dict[str, AstChunk],
)

def _build_ast_json_and_chunks(
    tree: ast.Module,
    source: str,
    old_chunks: Dict[str, AstChunk],
) -> Tuple[str, Dict[str, AstChunk]]:
    """
    Serialise *tree* to AST JSON, reusing encoded subtrees from *old_chunks*
    for any chunk whose content hash AND start_line are both unchanged.

    Skips encode_node() for every unchanged top-level function/class —
    typically 80-100 % of body nodes when only a few lines change.

    Returns (full_ast_json, new_chunks_dict).
    """
    lines = source.splitlines(keepends=True)
    seen: Dict[str, int] = {}
    new_chunks: Dict[str, AstChunk] = {}
    body_parts: List[str] = []

    for node in tree.body:
        cid = _make_chunk_id(node, seen)
        src = _source_slice(lines, node)
        end = getattr(node, "end_lineno", node.lineno)
        new_hash = hashlib.sha256(src.encode()).hexdigest()

        old = old_chunks.get(cid)
        reuse = (
            old is not None
            and old.content_hash == new_hash
            and old.start_line == node.lineno
        )

        if reuse:
            assert old is not None  # type narrowing
            node_json = zlib.decompress(old.ast_json_z).decode()
            chunk_z = old.ast_json_z
        else:
            node_json = encode_node(node)
            chunk_z = zlib.compress(node_json.encode(), _ZLIB_LEVEL)

        new_chunks[cid] = AstChunk(
            chunk_id=cid,
            start_line=node.lineno,
            end_line=end,
            content_hash=new_hash,
            ast_json_z=chunk_z,
        )
        body_parts.append(node_json)

    type_ignore_parts = [encode_node(ti) for ti in tree.type_ignores]
    full_json = _assemble_module_json(body_parts, type_ignore_parts)
    return full_json, new_chunks


# ── Disk serialization — JSON + base64, no executable deserialization ─────────