Overview

This updates <variant> to make a C++20 behavioral change unconditional, updates our LLVM submodule yet again to pick up small improvements, and finally performs a large overhaul of our LLVM-derived tests for variant, any, and optional. This overhaul picks up newly-added test coverage (e.g. for spaceship comparisons), cleans up test coverage that was unintentionally missing, and splits the extremely large variant test into LLVM-derived and MSVC-specific parts.

Product code

• Unconditionally implement WG21-P0608R3 Improving variant's Converting Constructor/Assignment.
  • Originally implemented by <variant>: P0608R3 Improving variant's converting constructor/assignment #1629.
  • Previous discussion: <variant>: Should we treat P0608R3 as a DR against C++17? #4412
  • Fixes DevCom-10606398 VSO-1988387 "MSVC accepts invalid std::variant<bool> b(1)".

I originally worried about the source-breaking impact of extending this C++20 behavioral change down to C++17. However, libc++ and libstdc++ have implemented this downlevel, the ecosystem has had some time to adapt (for projects that are portable, or compiled with MSVC C++20), and I think the remaining cleanup costs will be manageable.

I thought about guarding this with an escape hatch macro, but I'd like to try just ripping off the bandage. Unlike (for example) header-inclusion escape hatches, supporting both the old and new modes would require the old mode to be tested, and test coverage is what finally pushed me to make this change (as libc++'s tests started assuming this new behavior).

LLVM

• llvm-project Micro-Update, to pick up:
  • [libc++] [test] Fix __has_include usage, expand condvarany and spaceship coverage llvm/llvm-project#94120
  • [libc++][test] Mark optional test functions as TEST_CONSTEXPR_CXX20 llvm/llvm-project#94172
• cgmanifest.json: Update llvm-project commitHash.

transform_llvm.sh

• Extract script.
  • Use extended regular expressions (sed -E).
  • Use FI[X]ME to avoid any literal occurrences in the repo.
  • Filter out REQUIRES, UNSUPPORTED, and XFAIL, as they would affect the consolidated test.
  • We don't need to use -a in find; logical AND is the default.
  • We can skip nothing_to_do tests for all three.
  • Improve do ... done style.

P0088R3_variant

• Replace LLVM SOURCES with script output, no manual changes yet.
• Add namespaces, update run_test() calls.
  • I renamed some of the namespaces to be more consistent.
  • ctor::in_place_type_args::run_test(); is now called in order.
• Handle std::hash, std::get specializations.
• Restore EDG and /clr workarounds.
  • With updated "no workaround" arrow comments.
• Add MSVC workaround, also affects EDG (not yet reported).
  • Also appears in libcxx expected_results.txt:

    STL/tests/libcxx/expected_results.txt

    Lines 304 to 305 in e36ee6c

    	std/utilities/variant/variant.relops/three_way.pass.cpp:0 FAIL
    	std/utilities/variant/variant.relops/three_way.pass.cpp:1 FAIL

• Add Clang workarounds, not yet investigated.
  • These also appear in libcxx expected_results.txt:

    STL/tests/libcxx/expected_results.txt

    Lines 726 to 727 in e36ee6c

    	# Not analyzed. Clang instantiates BoomOnAnything during template argument substitution.
    	std/utilities/variant/variant.variant/variant.ctor/T.pass.cpp:2 FAIL

    STL/tests/libcxx/expected_results.txt

    Lines 1093 to 1094 in e36ee6c

    	# Not analyzed. Clang emits a -Wundefined-inline warning.
    	std/utilities/variant/variant.relops/three_way.pass.cpp:2 FAIL

• Guard relops::three_way, visit::return_type with _HAS_CXX20.
  • We were previously guarding plain visit, which was unnecessary.
• Guard WG21-P2637R3 Member visit.
  • Tracking issue: P2637R3 Member visit #3808
• Use usual_17_matrix.lst and is_permissive.
  • is_permissive allows us to detect the mode without needing the matrix to define macros.
  • This significantly extends test coverage - we previously skipped all of the visit and visit::return_type tests for permissive mode, when only has_visit<BadVariant> was affected.
• Update instructions to record what we did.

P0220R1_any

• Cleanup instructions to reduce unnecessary divergence.
• Replace LLVM SOURCES with script output, no manual changes yet.
• Restore namespaces, update run_test() calls.
  • I renamed ctor::in_place_type to be more consistent.
  • not_literal::run_test() has been removed.
• Silence warning C4640: construction of local static object is not thread-safe
• Add /clr workaround, update instructions to record what we did.

P0220R1_optional

• Replace LLVM SOURCES with script output, no manual changes yet.
• Add namespaces, update run_test() calls.
  • I renamed some of the namespaces to be more consistent.
  • The run_test() calls are now exhaustive and ordered; e.g. assign::const_optional_U was previously missing.
• Handle std::hash specialization.
• Restore EDG workarounds.
  • With updated "no workaround" arrow comments.
• Add/restore _HAS_CXX20/_HAS_CXX23 guards.
• Update instructions to record what we did.

Escape hatches

• Drop unnecessary deprecation/removal escape hatches.

P0088R3_variant_msvc

• Extract, part 1. Pure movement, no changes.
• Extract, part 2. Transfer <msvc_stdlib_force_include.h> preamble.

x64 /std:c++latest compiler memory consumption as reported by /d1reportMemorySummary:

This improved total test runtime from 72.5s to 56.4s (1.29x speedup). Presumably this was caused by better parallelism (splitting up long-tail /analyze configurations) and won't significantly impact full test runs.