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Prepare backwards compatible usage of optional C++ toolchain
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By adding an alias and a no-op keyword argument now, rulesets can start using the new optional form of `find_cpp_toolchain` now and benefit from the toolchain actually being optional once that has been implemented in a future version of Bazel.

Work towards bazelbuild#16966

Closes bazelbuild#17308.

PiperOrigin-RevId: 504501621
Change-Id: I549fea6290195aadad4ccbd045c0aa3c180946d2
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fmeum authored and copybara-github committed Jan 25, 2023
1 parent c162166 commit 942ddda
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Showing 2 changed files with 12 additions and 1 deletion.
8 changes: 8 additions & 0 deletions tools/cpp/BUILD.tools
Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,14 @@ constraint_value(

cc_toolchain_alias(name = "current_cc_toolchain")

# In future versions of Bazel, this target will not fail if no C++ toolchain is
# available. Instead, it will not advertise the cc_common.CcToolchainInfo
# provider.
alias(
name = "optional_current_cc_toolchain",
actual = ":current_cc_toolchain",
)

cc_host_toolchain_alias(name = "current_cc_host_toolchain")

cc_libc_top_alias(name = "current_libc_top")
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5 changes: 4 additions & 1 deletion tools/cpp/toolchain_utils.bzl
Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ Utilities to help work with c++ toolchains.

CPP_TOOLCHAIN_TYPE = "@bazel_tools//tools/cpp:toolchain_type"

def find_cpp_toolchain(ctx):
def find_cpp_toolchain(ctx, *, mandatory = True):
"""
Finds the c++ toolchain.
Expand All @@ -29,6 +29,9 @@ def find_cpp_toolchain(ctx):
Args:
ctx: The rule context for which to find a toolchain.
mandatory: This is currently a no-op. In future releases of Bazel, if this
is set to False, this function will return None rather than fail if no
toolchain is found.
Returns:
A CcToolchainProvider.
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