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This let's you point Bazel at an installed toolchain or download one of our release archives. When you do, it will configure itself as a C++ Bazel toolchain. This toolchain works reasonably well, but doesn't cache the C++ runtimes, and so linking is inefficient. The next step will be to pivot the runtimes from the implicitly on-demand (which can't cache when using a sandboxed build system like Bazel) to _explicit_ on-demand runtimes directly with Bazel support. I've included an example Bazel project that uses this and provides a bunch of documentation and an example script that should let folks try this out easily. --------- Co-authored-by: Geoff Romer <gromer@google.com> Co-authored-by: David Blaikie <dblaikie@gmail.com>
57 lines
2.1 KiB
Python
57 lines
2.1 KiB
Python
# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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# Exceptions. See /LICENSE for license information.
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# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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"""Example Bazel module that builds C++ with the Carbon toolchain.
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Note that this is at the root of an example Bazel project, not part of the
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larger Carbon Bazel project. To interact with this example, you'll want to
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`cd examples/bazel` so that you can operate Bazel entirely within this example
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(sub-)project.
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Once interacting with this subdirectory's project, you can use this and build
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with the Carbon toolchain in a few different ways:
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1) Override the module with a local installation on the command line:
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`bazel build --override_module=carbon_toolchain=/path/to/carbon_toolchain/installation/lib/carbon`
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2) Encode a local override into this file:
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```
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local_path_override(
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module_name = "carbon_toolchain",
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path = "/path/to/carbon_toolchain/installation/lib/carbon",
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)
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```
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3) Encode a archive override into this file:
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```
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version = "0.0.0-0.nightly.YYYY.MM.DD"
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archive_override(
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module_name = "carbon_toolchain",
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strip_prefix = "carbon_toolchain-{0}/lib/carbon".format(version),
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urls = ["https://github.com/carbon-language/carbon-lang/releases/download/v{0}/carbon_toolchain-{0}.tar.gz".format(version)],
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)
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```
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Note: Initially, Bazel will warn about the lack of an `integrity` field,
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and will print the value it found by downloading the archive which you can
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verify on GitHub before encoding.
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You can use the provided script `update_module_to_nightly.py` to generate and
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add an `archive_override` of the current nightly release, including integrity
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from GitHub.
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Once the Carbon toolchain has established releases in the Bazel central
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registry, this file will work with an updated version out of the box.
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"""
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module(name = "example")
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bazel_dep(name = "rules_cc", version = "0.2.14")
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# Declare the `carbon_toolchain` module. This is needed even if it will be
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# overridden with a local path or archive.
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bazel_dep(name = "carbon_toolchain", version = "0.0.0")
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register_toolchains("@carbon_toolchain//:all")
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