Support C++20 modules in the rules-based toolchain API#750
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FYI @dzbarsky |
The rules-based cc/toolchains toolchain API was missing several pieces needed to drive Bazel's C++20 modules pipeline (clang-scan-deps -> .ddi -> aggregate-ddi -> generate-modmap -> module compile): - Add a cpp20_module_actions action type set grouping the module interface compile, codegen and dependency scanning actions. These are deliberately kept out of compile_actions/source_compile_actions so that flags incompatible with C++20 modules can keep targeting only the non-module compiles. - Register the cpp_module_output_file and cpp_module_modmap_file build variables and make dependency_file, output_file, source_file and user_compile_flags available to the C++20 module actions. - Extend the legacy compile features (compiler_input_flags, compiler_output_flags, dependency_file, user_compile_flags) to the C++20 module actions, so the generic -c / -o / -MD -MF / user-copt flags are emitted for module interface compile, codegen and dependency scanning the same way they are for ordinary compiles. Toolchains that use these features then need no module-specific source/output/dependency/copt args of their own. - Include the C++20 module actions in the compiler_files legacy file group so their tools (e.g. the dependency scanner) are available to the compile actions. The C++20 modules pipeline lives only in rules_cc's compile.bzl (Bazel's native rules do not implement it), and was previously untested here: Bazel's CppModulesConfiguredTargetTest only checks the --experimental_cpp_modules / cpp_modules gating, and the shell integration test self-skips unless a host clang >= 17 is present. Add an analysis test that drives the module interface compile + dependency scanning actions with a mock toolchain (no real compiler needed) and asserts the scanning action emits both the P1689 .ddi file and the Make-style .ddi.d dependency file. This test fails without the fixes in the preceding commit.
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Add toolchain variables and and an action type set for C++20 module actions, allowing them to be configured in a rule-based toolchain.