[PATCH] D44883: [Sema] Extend -Wself-assign with -Wself-assign-overloaded to warn on overloaded self-assignment (classes)

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: aaron.ballman, rsmith, rtrieu, nikola, chandlerc, rjmccall.

This has just bit me, so i though it would be nice to avoid that next time :)
Motivational case:

  https://godbolt.org/g/cq9UNk

Basically, it's likely to happen if you don't like shadowing issues,
and use `-Wshadow` and friends. And it won't be diagnosed by clang.

The reason is, these self-assign diagnostics only work for builtin assignment
operators. Which makes sense, one could have a very special operator=,
that does something unusual in case of self-assignment,
so it may make sense to not warn on that.

But while it may be intentional in some cases, it may be a bug in other cases,
so it would be really great to have some [opt-in] diagnostic about it...

For now, this diff restructures `SelfAssignment` diag group, splits it into
`SelfAssignmentBuiltin` (as what is already in trunk),
and the new `SelfAssignmentOverloaded`, which is not enabled by default/`-Wall`.
For now i have put it into `-Wextra`, but i don't know if it should be there.

Additionally, a question: what should be done for trivial assignment operators?
Perhaps this should be split even more, and if the operator is trivial implicit
(or even trivial user-defined =default ?), it should even warn in `-Wall`?

I'm guessing the self-move, and self-field-assign warnings should also be adjusted
to work for overloaded operators, but i did not want to bloat this diff.


Repository:
  rC Clang

https://reviews.llvm.org/D44883

Files:
  include/clang/Basic/DiagnosticGroups.td
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaExpr.cpp
  test/SemaCXX/warn-self-assign-builtin.cpp
  test/SemaCXX/warn-self-assign-overloaded.cpp
  test/SemaCXX/warn-self-assign.cpp

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