Python Bindings for libclang

Warnings

• gotcha The `clang` PyPI package provides Python bindings ONLY. It does NOT include the `libclang` C++ shared library, which is a fundamental dependency. You must install `libclang` separately on your operating system.
  Fix: Install `libclang` via your system's package manager (e.g., `apt install libclang-dev` on Debian/Ubuntu, `brew install llvm` on macOS, or LLVM installer on Windows) before running Python code.
• gotcha After installing `libclang`, the Python bindings might not find it automatically. You may need to explicitly tell the bindings where to find `libclang.so` (Linux), `libclang.dylib` (macOS), or `libclang.dll` (Windows).
  Fix: Set the `CLANG_LIBRARY_PATH` environment variable to the directory containing `libclang` before running your Python script, or call `clang.cindex.Config.set_library_path('/path/to/libclang/directory')` in your code.
• gotcha There can be compatibility issues if the version of the `clang` Python package does not match the version of the system `libclang` installed. Mismatches can lead to crashes, incorrect parsing, or unexpected behavior.
  Fix: Try to keep the Python `clang` package version in sync with your system's `libclang` version. For example, `pip install 'clang==18.*'` if you have LLVM 18 installed. Downgrade/upgrade `libclang` or the Python bindings if problems persist.
• breaking The `clang.cindex` API, being a binding to a C++ library, can have subtle breaking changes between major LLVM versions (e.g., how AST nodes are iterated, new cursor kinds, or changes in diagnostic information structure).
  Fix: Always refer to the official LLVM `libclang` Python binding documentation or examples corresponding to your LLVM version when upgrading. Test thoroughly after upgrading major versions.
• gotcha Correctly configuring compiler arguments (e.g., include paths, language standard, preprocessor definitions) is crucial for accurate parsing of C/C++ source code, especially for complex projects.
  Fix: Pass all necessary compiler flags (e.g., `-I`, `-D`, `-std=c++17`, `-x c++`) as a list of strings to the `args` parameter of `index.parse()`.

Install

• pip install clang Install Python bindings

Imports

• Index

  from clang.cindex import Index

• Config

  from clang.cindex import Config

• Cursor

  from clang.cindex import Cursor

• TranslationUnit

  from clang.cindex import TranslationUnit

Quickstart

This quickstart demonstrates how to parse C code from a string, check for diagnostics, and traverse the Abstract Syntax Tree (AST) using `clang.cindex`. The most critical step is ensuring that the underlying `libclang` shared library is installed on your system and discoverable by the Python bindings.

import os
from clang.cindex import Index, Config, TranslationUnit # type: ignore

# CRITICAL: Ensure libclang (the C++ library) is installed and discoverable.
# The 'clang' pip package only provides Python wrappers.
#
# On macOS (with Homebrew LLVM): 
# Config.set_library_path('/usr/local/opt/llvm/lib')
# On Linux (e.g., Ubuntu/Debian LLVM-18): 
# Config.set_library_path('/usr/lib/llvm-18/lib')
# On Windows, ensure 'libclang.dll' is in your PATH or set its full path.
# Alternatively, set the CLANG_LIBRARY_PATH environment variable.

source_code = """
#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int main() {
    printf("Hello from Clang AST!");
    int result = add(5, 7);
    return 0;
}
"""

try:
    index = Index.create()
    # Parse the source code from a string. 'main.c' is a dummy name.
    # args can include compiler flags, e.g., ['-std=c99', '-I/path/to/includes']
    tu = index.parse('main.c', unsaved_files=[('main.c', source_code)], args=['-x', 'c'])

    # Check for diagnostics (errors, warnings) during parsing
    if tu.diagnostics:
        for diag in tu.diagnostics:
            if diag.severity >= 3: # Error or Fatal
                print(f"Diagnostic (Error): {diag.spelling} at {diag.location}")

    # Walk the AST and print top-level declarations
    print("\nTop-level declarations:")
    for cursor in tu.cursor.get_children():
        if cursor.location.file and cursor.location.file.name == 'main.c':
            print(f"- {cursor.kind.name}: {cursor.spelling} at Line {cursor.location.line}")

    # Example: Finding the 'main' function and its call to 'add'
    for cursor in tu.cursor.walk_preorder():
        if cursor.kind.is_function() and cursor.spelling == 'main':
            print(f"\nFound 'main' function at Line {cursor.location.line}")
            for child in cursor.get_children():
                if child.kind.is_call_expr() and child.spelling == 'add':
                    print(f"  -> 'main' calls 'add' at Line {child.location.line}")
            break

except Exception as e:
    print(f"An error occurred: {e}")
    print("Hint: Make sure libclang is installed on your system and its path is correctly configured.")