[PATCH] D93822: [clang-tidy] Add check for implicit widening of multiplication result

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman accepted this revision.
aaron.ballman added a comment.
This revision is now accepted and ready to land.

LGTM aside from some small nits in the documentation.



================
Comment at: clang-tools-extra/clang-tidy/bugprone/ImplicitWideningOfMultiplicationResultCheck.cpp:130
+  StringRef TyAsString =
+      IndexExprType->isSignedIntegerType() ? "ssize_t" : "size_t";
+
----------------
lebedev.ri wrote:
> aaron.ballman wrote:
> > aaron.ballman wrote:
> > > One thing that's awkward about this is that there's no portable `ssize_t` type -- that's a POSIX type but it doesn't exist on all platforms (like Windows). We shouldn't print out a typecast that's going to cause compile errors, but we also shouldn't use the underlying type for `ssize_t` as that may be incorrect for other target architectures.
> > I'm still not quite certain what to do about this. Would it make sense to use the underlying type on platforms that don't have `ssize_t`? Relatedly, if we're going to suggest this as a replacement, we should also insert an include for the correct header file.
> I've been thinking about this, and i really can't come up with a better fix than using `ptrdiff_t`.
I'm not super excited about using `ptrdiff_t` as there are not likely to be pointer subtractions in the vicinity of the code being diagnosed, but at the same time, `ptrdiff_t` is functionally the same as `size_t` except with a sign bit, which is what `ssize_t` is. I'll hold my nose for now, but if we get bug reports about this use, we may want to investigate more involved solutions.


================
Comment at: clang-tools-extra/docs/clang-tidy/checks/bugprone-implicit-widening-of-multiplication-result.rst:40
+   When suggesting fix-its for C++ code, should C++-style ``static_cast<>()``'s
+   be suggested, or C-style casts.
+
----------------
Add info about the default behavior.


================
Comment at: clang-tools-extra/docs/clang-tidy/checks/bugprone-implicit-widening-of-multiplication-result.rst:45
+   When suggesting to include the appropriate header in C++ code,
+   should ``<cstddef>`` header be suggested, or ``<stddef.h>``.
+
----------------
Same here.


Repository:
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  https://reviews.llvm.org/D93822/new/

https://reviews.llvm.org/D93822