clangml provides bindings to call the Clang API from OCaml.
Published: 07 Sep 2022
clangml: OCaml bindings for Clang.
clangml provides bindings for all versions of Clang, from 3.4 to 15.0.0.
This library is a complete rewritting of the previous clangml (clangml versions <4.0.0): the bindings now rely on automatically generated C stubs to libclang, with some extensions when libclang is incomplete. Contrary to old clangml versions, the versions of clangml from 4.0.0 are independent from the version of the Clang library: any version of clangml from 4.0.0 can be built with any version of the Clang library in the supported interval. Currently, all versions of Clang, from 3.4 to 15.0.0, are supported.
However, clangml is statically linked to libclang, and clangml needs to be rebuilt for every version of libclang to run with. In addition, the low-level bindings are automatically generated from libclang's header and their signature can change from one version of libclang to another.
The high-level bindings (
Clang.Enum_constant) provide abstractions that are essentially independent from libclang version. These abstractions aim mainly to provide an algebraic datatype representation of Clang abstract syntax tree (AST). It is worth noticing that there can be some differences in the way clang parses file from one version to another (in particular, some features of the C/C++ languages are only supported by recent versions of clang, see some examples in
Clang__ast module documentation).
clangml is installable via
opam. Since the library relies on external dependencies, we suggest to use the depext plugin to install it together with the packages needed for your system:
opam depext -i clangml
Manual installation requires a bootstrapped source directory. Commits from branch
snapshot are bootstrapped: a new snapshot is committed by continuous integration after every successful build from
Snapshot tarball: https://github.com/thierry-martinez/clangml/archive/refs/heads/snapshot.tar.gz
To build clangml from snapshot or from a bootstrapped source directory, you may either:
./configure && make && make install(this method is recommended if you have to pass some options to configure);
opam pin add git+https://github.com/thierry-martinez/clangml.git#snapshot.
To bootstrap the repository from a development branch (e.g.,
./bootstrap.sh first, then
./configure && make && make install as usual.
configure relies on
llvm-config to find clang's library. By default,
llvm-config is searched in
PATH, and you may specify a path with
clangml requires some dependencies:
opam install dune refl. Additionnally, to run
opam install ocamlcodoc pattern.
libclang and other external dependencies can be installed with opam depext plugin:
opam pin add -n git+https://github.com/thierry-martinez/clangml.git#snapshot opam depext -i clangml
-n option asks
opam pin not to install clangml directly, and
-i option asks
opam depext to install clangml once dependencies are installed.)
Clang provides direct bindings to most of the symbols defined by libclang. To match OCaml conventions, camel-case symbols have been renamed to snake case (lower-case symbols with underscores), and
clang_ prefixes have been removed. Additional bindings have been defined in
libclang_extensions.h for some parts of clang's API that have not been covered by libclang.
Clang.Ast provides a higher-level interface to clang's AST. The function
Clang.Ast.parse_file returns the AST from a file and
Clang.Ast.parse_string returns the AST from a string. You may try these functions in OCaml toplevel to discover the resulting data structure.
Clang.Ast includes in particular the module
Clang__ast which declares the algebraic data types that represent the AST. The documentation of most of the nodes contains examples that can be used as references for how syntactic constructions are parsed, and that are extracted with
ocamlcodoc and serve as unit tests with
dune runtest (or, equivalently,
make test). Moreover, the git branch
norms contains the AST corresponding to the examples automatically extracted from C++14, C++17, and C++20 norms.
given an expression node
e : Clang.Expr.t, the type of
ecan be obtained by
t : Clang.Type.tis a
typedef, the underlying type declared for
tcan be obtained by
t : Clang.Type.tis a record (
union), the list of fields can by
C/C++ attributes are defined in a separate (auto-generated) module
Clang.Lazy.Enum_constant mirror their non-lazy counterparts, by replacing eagerly constructed
desc fields by
lazy values, that are computed on demand. This is useful to explore large ASTs efficiently (note that Clang parsing itself can still be slow; the lazy part only concerns the conversion into the
Generating a new seed
clang__bindings.mli, are generated for each version of LLVM by the
stubgen tool (sub-directory
To generate these files for a given version of LLVM, you may run:
stubgen --llvm-config=$PATH_TO_LLVM_CONFIG $TARGET_PATH
stubgen depends on
Additionnally, three files,
attributes.ml are generated by the
generate_attrs tool (sub-directory
To generate these files, you may run
generate_attrs --llvm-config=$PATH_TO_LLVM_CONFIG $PATH_TO_BOOTSTRAP_DIR. The tool enumerates all the attributes supported by the given version of Clang, and uses the bootstrap directory both as target path and to determine in which version of Clang each attribute has been introduced.