[Bug middle-end/77696] Confusing wording for -Wformat-overflow

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77696

--- Comment #12 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #5)
> I brainstormed some ideas on making these kinds of warning easier for
> the user to understand.

Copying a string to a buffer allocated with strlen(), rather than
strlen() + 1:

  |                  |          |
  |+----------------+|+--------+|
  ||0...strlen() - 1||   NUL   ||
  |+----------------+|+--------+|
  vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
  |<---   ok      -->|<overflow>|
  |                  |          |
  to 'buf':
  |                  |
  |+----------------+|
  ||0...strlen() - 1||
  |+----------------+|

(drawing the user's attention to the NUL terminator, because it's such
a common source of mistakes)

FWIW, I have some classes for laying out ASCII art drawings which could be
reused for this, as part of this vectorization RFC:
  https://gcc.gnu.org/ml/gcc-patches/2018-07/msg01576.html