build-clang.py
==============

A script to build clang from source.

```
usage: build-clang.py [-h] -c CONFIG [--clean]

optional arguments:
  -h, --help            show this help message and exit
  -c CONFIG, --config CONFIG
                        Clang configuration file
  --clean               Clean the build directory
```

Pre-requisites
--------------
* Working build toolchain.
* git
* CMake
* Ninja
* Python 2.7 and 3

Please use the latest available CMake for your platform to avoid surprises.

Config file format
------------------

build-clang.py accepts a JSON config format with the following fields:

* stages: Use 1, 2, 3 or 4 to select different compiler stages.  The default is 3.
* python_path: Path to the Python 2.7 installation on the machine building clang.
* gcc_dir: Path to the gcc toolchain installation, only required on Linux.
* cc: Path to the bootsraping C Compiler.
* cxx: Path to the bootsraping C++ Compiler.
* as: Path to the assembler tool.
* ar: Path to the library archiver tool.
* ranlib: Path to the ranlib tool (optional).
* libtool: Path to the libtool tool (optional).
* ld: Path to the linker.
* patches: Optional list of patches to apply.
* build_type: The type of build to make.  Supported types: Release, Debug, RelWithDebInfo or MinSizeRel.
* build_libcxx: Whether to build with libcxx.  The default is false.
* build_clang_tidy: Whether to build clang-tidy with the Mozilla checks imported.  The default is false.
* osx_cross_compile: Whether to invoke CMake for OS X cross compile builds.
* assertions: Whether to enable LLVM assertions.  The default is false.
* pgo: Whether to build with PGO (requires stages == 4).  The default is false.

The revisions are defined in taskcluster/ci/fetch/toolchains.yml. They are usually commit sha1s corresponding to upstream tags.

Environment Variables
---------------------

The following environment variables are used for cross-compile builds targeting OS X on Linux.

* CROSS_CCTOOLS_PATH: Path to the cctools directory where the cross compiler toolchain is located.
* CROSS_SYSROOT: Path to the OS X SDK directory for cross compile builds.