How can I automatically download the dependencies of an external Rust crate (similar to Cargo)? #14096

bertulli · 2025-01-08T18:20:46Z

bertulli
Jan 8, 2025

Hi! I'm trying to port a fairly complex project to Rust, and since I need to heavily interface with existing C/C++ libraries, I'm trying to use a polyglot build system, in this case Meson. I managed to make it compile Rust, and link against one of the C libraries I'm using. Now, I want to use an external crate (for the sake of MWE, let's say rand). How can I make Meson automatically download and compile the crate and its dependencies, like Cargo does?

I managed to write a rand.wrap file

[wrap-git]
url = https://github.com/rust-random/rand.git
revision = 0.8.5
depth = 1
method = cargo

[provide]
dependency_names = rand-0.8-rs

and my relevant meson.build is

project('meson-test', ['rust', 'c'],
  version : '0.1',
  default_options : ['warning_level=3'],
  meson_version: '>=1.0.0')

c_lib = static_library('utils', 'utils.c')

# build cJSON lib with CMake
cjson = dependency('cJSON')

# generate cJSON Rust bindings
rust = import('rust')

generated = rust.bindgen(
    input : 'cJSON/cJSON.h',
    output : 'generated-cJSON.rs',
    dependencies : cjson,
    args : ['--no-rustfmt-bindings'],
)

rand = dependency('rand')

exe = executable('meson_test',
                 'main.rs', generated,
                 link_with: [c_lib],
                 dependencies: [cjson])

but I get the error

Run-time dependency rand found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency rand
WARNING: Subproject rand's revision may be out of date; its wrap file has changed since it was first configured

Executing subproject rand method cargo

meson.build:21: WARNING: Project targets '>=1.0.0' but uses feature introduced in '1.3.0': Cargo subproject.
meson.build:21: WARNING: Cargo subproject is an experimental feature and has no backwards compatibility guarantees.
rand| Generated Meson AST: /home/abertulli/meson-test/build/subprojects/rand/meson.build
rand| Project name: rand
rand| Project version: 0.8.5
rand| Rust compiler for the host machine: rustc -C linker=cc (rustc 1.83.0)
rand| Rust linker for the host machine: rustc -C linker=cc ld.bfd 2.38
rand| Message: Enabled features: ['alloc', 'default', 'getrandom', 'libc', 'rand_chacha', 'std', 'std_rng']
rand| Run-time dependency rand_core-0.6-rs found: NO (tried pkgconfig and cmake)

subprojects/rand/meson.build:77:-1: ERROR: Dependency "rand_core-0.6-rs" not found, tried pkgconfig and cmake

A full log can be found at /home/abertulli/meson-test/build/meson-logs/meson-log.txt

and in case it's useful, the complete log is

Determining dependency 'rand' with pkg-config executable '/usr/bin/pkg-config'
env[PKG_CONFIG_PATH]: 
env[PKG_CONFIG]: /usr/bin/pkg-config
-----------
Called: `/usr/bin/pkg-config --modversion rand` -> 1
stderr:
Package rand was not found in the pkg-config search path.
Perhaps you should add the directory containing `rand.pc'
to the PKG_CONFIG_PATH environment variable
No package 'rand' found
-----------
CMake binary for host machine is cached.
Preliminary CMake check failed. Aborting.
Run-time dependency rand found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency rand
WARNING: Subproject rand's revision may be out of date; its wrap file has changed since it was first configured

Executing subproject rand method cargo 

meson.build:21: WARNING: Project targets '>=1.0.0' but uses feature introduced in '1.3.0': Cargo subproject.
meson.build:21: WARNING: Cargo subproject is an experimental feature and has no backwards compatibility guarantees.
Generated Meson AST: /home/abertulli/meson-test/build/subprojects/rand/meson.build
Project name: rand
Project version: 0.8.5
Rust compiler for the host machine: rustc -C linker=cc (rustc 1.83.0)
Rust linker for the host machine: rustc -C linker=cc ld.bfd 2.38
Rust compiler for the build machine: rustc -C linker=cc (rustc 1.83.0)
Rust linker for the build machine: rustc -C linker=cc ld.bfd 2.38
Message: Enabled features: ['alloc', 'default', 'getrandom', 'libc', 'rand_chacha', 'std', 'std_rng']
Determining dependency 'rand_core-0.6-rs' with pkg-config executable '/usr/bin/pkg-config'
env[PKG_CONFIG_PATH]: 
env[PKG_CONFIG]: /usr/bin/pkg-config
-----------
Called: `/usr/bin/pkg-config --modversion rand_core-0.6-rs` -> 1
stderr:
Package rand_core-0.6-rs was not found in the pkg-config search path.
Perhaps you should add the directory containing `rand_core-0.6-rs.pc'
to the PKG_CONFIG_PATH environment variable
No package 'rand_core-0.6-rs' found
-----------
CMake binary for host machine is cached.
Preliminary CMake check failed. Aborting.
Run-time dependency rand_core-0.6-rs found: NO (tried pkgconfig and cmake)

subprojects/rand/meson.build:77:-1: ERROR: Dependency "rand_core-0.6-rs" not found, tried pkgconfig and cmake

What am doing wrong? think this may be related to #13466 . Thanks!

eli-schwartz · 2025-01-08T18:28:42Z

eli-schwartz
Jan 8, 2025
Maintainer

Since dependency_names is rand-0.8-rs you should also use that in dependency().

0 replies

eli-schwartz · 2025-01-08T18:31:34Z

eli-schwartz
Jan 8, 2025
Maintainer

Meson can synthesize new *.wrap files for you automatically by parsing a Cargo.lock but iirc this only kicks in for the main project, not subprojects.

My understanding is the eventual goal is to plumb this into meson wrap install, /cc @xclaesse

5 replies

bertulli Jan 9, 2025
Author

Thanks! I tried changing my meson.build to rand = dependency('rand-0.8-rs') but it doesn't help.

For what I understand from the manual, Meson can automatically download crate dependencies, even for subprojects, :

When a (sub)project has a Cargo.lock file at its root, it is loaded to provide an automatic fallback for dependencies it defines, fetching code from https://crates.io or git. This is identical as providing subprojects/*.wrap, see cargo wraps dependency naming convention.

I would interpret this as: if one of your subprojects is a Cargo one, Meson can derive the dependencies automatically. I tried using a simpler crate, humansize, that has only one dependency, libm, and that in turn has no further dependency, but it fails with subprojects/humansize/meson.build:30:-1: ERROR: Dependency "libm-0.2-rs" not found.

By contrast, it works with a crate that has no dependencies, for instance if I try using libm directly. For what I read in the manual, this feature for subprojects should already be implemented? I'm using Meson 1.6.0, do I need to use a special CLI flag or something? Thanks

bertulli Jan 9, 2025
Author

Update: I misread, Meson searches for the lock file, not the toml. So I cd into the subproject, did a cargo build to populate the Cargo.lock, and retried with Meson. Now it downloads the dependent libm, but fails with a Python exception:

Run-time dependency humansize-2-rs found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency humansize-2-rs

Executing subproject humansize method cargo

meson.build:22: WARNING: Cargo subproject is an experimental feature and has no backwards compatibility guarantees.
humansize| Generated Meson AST: /home/abertulli/meson-test/build/subprojects/humansize/meson.build
humansize| Project name: humansize
humansize| Project version: 2.1.3
humansize| Rust compiler for the host machine: rustc -C linker=cc (rustc 1.83.0)
humansize| Rust linker for the host machine: rustc -C linker=cc ld.bfd 2.38
humansize| Message: Enabled features: ['default']
humansize| Run-time dependency libm-0.2-rs found: NO (tried pkgconfig and cmake)
humansize| Looking for a fallback subproject for the dependency libm-0.2-rs

Executing subproject humansize:libm-0.2-rs method cargo

Traceback (most recent call last):
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/mesonmain.py", line 193, in run
    return options.run_func(options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/msetup.py", line 365, in run
    app.generate()
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/msetup.py", line 188, in generate
    return self._generate(env, capture, vslite_ctx)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/msetup.py", line 227, in _generate
    intr.run()
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 3063, in run
    super().run()
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 169, in run
    self.evaluate_codeblock(self.ast, start=1)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 195, in evaluate_codeblock
    raise e
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 187, in evaluate_codeblock
    self.evaluate_statement(cur)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 205, in evaluate_statement
    self.assignment(cur)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 642, in assignment
    value = self.evaluate_statement(node.value)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 201, in evaluate_statement
    return self.function_call(cur)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 528, in function_call
    res = func(node, func_args, kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 806, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 806, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 806, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  [Previous line repeated 4 more times]
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 85, in wrapped
    ret = f(*wrapped_args, **wrapped_kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 103, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 237, in wrapper
    return f(*nargs, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 556, in wrapper
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 1825, in func_dependency
    d = df.lookup(kwargs)
        ^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/dependencyfallbacks.py", line 355, in lookup
    dep = func(kwargs, func_args, func_kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/dependencyfallbacks.py", line 131, in _do_subproject
    self.interpreter.do_subproject(subp_name, func_kwargs)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 951, in do_subproject
    raise e
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 939, in do_subproject
    return methods_map[method](subp_name, subdir, default_options, kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 1051, in _do_subproject_cargo
    return self._do_subproject_meson(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 990, in _do_subproject_meson
    subi.run()
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 3063, in run
    super().run()
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 169, in run
    self.evaluate_codeblock(self.ast, start=1)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 195, in evaluate_codeblock
    raise e
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 187, in evaluate_codeblock
    self.evaluate_statement(cur)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 205, in evaluate_statement
    self.assignment(cur)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 642, in assignment
    value = self.evaluate_statement(node.value)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 201, in evaluate_statement
    return self.function_call(cur)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/interpreterbase.py", line 528, in function_call
    res = func(node, func_args, kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 806, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 806, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 806, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  [Previous line repeated 4 more times]
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 85, in wrapped
    ret = f(*wrapped_args, **wrapped_kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 103, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 237, in wrapper
    return f(*nargs, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreterbase/decorators.py", line 556, in wrapper
    return f(*wrapped_args, **wrapped_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 1825, in func_dependency
    d = df.lookup(kwargs)
        ^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/dependencyfallbacks.py", line 355, in lookup
    dep = func(kwargs, func_args, func_kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/dependencyfallbacks.py", line 131, in _do_subproject
    self.interpreter.do_subproject(subp_name, func_kwargs)
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 951, in do_subproject
    raise e
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 939, in do_subproject
    return methods_map[method](subp_name, subdir, default_options, kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/interpreter/interpreter.py", line 1049, in _do_subproject_cargo
    ast, options = cargo.interpret(subp_name, subdir, self.environment)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/cargo/interpreter.py", line 713, in interpret
    manifests = _load_manifests(os.path.join(env.source_dir, subdir))
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/cargo/interpreter.py", line 343, in _load_manifests
    manifest_ = _convert_manifest(raw_manifest, subdir)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/abertulli/.local/lib/python3.12/site-packages/mesonbuild/cargo/interpreter.py", line 317, in _convert_manifest
    Package(**pkg),
    ^^^^^^^^^^^^^^
TypeError: Package.__init__() got an unexpected keyword argument 'autolib'

subprojects/humansize/meson.build:30:-1: ERROR: Unhandled python exception

    This is a Meson bug and should be reporte!

I use Python 3.12.3, so it shouldn't be a problem of the parser. Is it a bug, or did i do something wrong? Thanks

eli-schwartz Jan 9, 2025
Maintainer

Aha, that one I definitely know the answer to. It is a meson bug that was reported in #13826 and got fixed and backported into meson 1.6.1 -- you said you have 1.6.0 installed, so try updating to the latest bugfix release with pip install --upgrade meson

bertulli Jan 9, 2025
Author

Thanks, it worked! 🎉 Now, iiuc, this means that to use crates dependencies in the main project meson is building, we need to provide a wrap file for each one. Is it planned for the future to simply list them, in a Cargo.toml or in the meson.build? I'm thinking of something like

rust = import('rust')

rand = rust.cratesio('rand', '0.8.0')

executable('test_project', 'main.rs', dependencies : rand)

eli-schwartz Jan 9, 2025
Maintainer

I think so but @xclaesse would know better (I'm not the main driver of rust support in meson).

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