commit b0d26ea54748bf6dc869d60d1ddfc97bb045966e
author David Benjamin <davidben@chromium.org> Mon Mar 11 12:33:16 2024
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Mar 11 12:33:16 2024
tree 39c817bbca7a5d142e0fbd1c321b1778ca8162ac
parent 075afa69f190f0de30e89250f5a236e2aa37c5b0

Fix some more incompatibilities with std::variant from narrowing

std::variant does not allow narrowing conversions. absl::variant didn't
quite get this right, which means narrowing conversions sometimes sneak
in.

The main non-obvious consequence is that variant<size_t, ...> cannot be
constructed from literals like 0 or 2. Such literals have type int, and
an int may be negative. These ints will not be negative, but the
language has lost this information by the time it calls the std::variant
constructor. Writing 0u or 2u works because those have type unsigned,
which can convert to size_t without narrowing. In C++23, we'll have 0uz
and 2uz which even have type size_t, but we're not there yet and no
supported platform has unsigned larger than size_t.

Conversely, a variant<int, ...> cannot be constructed from a size_t
because size_t may not fit in int. That need a checked_cast. There was
also one instance of Persistent<T>, where I used an in_place_type.

Bug: 40242126
Change-Id: I0b6c16f120553284545451df5aaf5d550824b5d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5352774
Reviewed-by: Thomas Nguyen <tungnh@chromium.org>
Reviewed-by: Aya Elsayed <ayaelattar@chromium.org>
Reviewed-by: Steinar H Gunderson <sesse@chromium.org>
Commit-Queue: Aya Elsayed <ayaelattar@chromium.org>
Auto-Submit: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1270890}