commit 877e622383fc633385e407bac68f3d949dcefb38
author Lukasz Anforowicz <lukasza@chromium.org> Fri Nov 26 00:03:23 2021
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Fri Nov 26 00:03:23 2021
tree f961d532a94999d0d0d7f78ab41d50d6dcfc0fae
parent c088a0d9ef5a08eae01e10b25737dc6fd011539f

Inline, next-to-field-decl comments explaining raw_ptr exclusions.

Before this CL, some fields were excluded from the Big MiraclePtr
Rewrite (i.e. kept as `SomeClass* field_` rather than rewritten into
`raw_ptr<SomeClass> field_`), because earlier analysis has shown that
rewriting these particular fields would either 1) have an unusually big,
negative impact on performance or 2) result in runtime crashes because
of violating stricter raw_ptr usage rules [1].

After this CL, these exclusions will also be documented in inline
comments, next to the pointer fields that shouldn't use raw_ptr<T>.

This CL should prevent backsliding (and unintentional performance and/or
stability regressions).  This is important, because there are currently
no plans for automated detection and enforcement to disallow using
raw_ptr<T> in performance-sensitive fields (or fields that use more
complex casts or memory operations).

This CL should also prevent surprises and communicate upfront to omit
these fields from future manual rewrites (e.g. suppressing the somewhat
natural and desirable urge to make all fields raw_ptr<T> wherever the
compiler doesn't complain).

[1] See //base/memory/raw_ptr.md#Extra-pointer-rules

Bug: 1073933
Change-Id: Ic58973da003dd54fb11635d7c57f02cf2d197276
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3298431
Auto-Submit: Łukasz Anforowicz <lukasza@chromium.org>
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Owners-Override: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/main@{#945508}