[PATCH] D119670: [clang] Warn on unqualified calls to std::move and std::forward

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added a comment.

Tangential data point: I hacked up this check to find //all// unqualified `std` functions and ran it on libc++'s tests and also on some of my own codebase (including re2, asio, protobuf). I'm fixing the issues it turned up in libc++'s tests. In the other codebases, there was a lot of `min` and `max` in multiple codebases; several uses of `back_inserter` and `getline` across different codebases; scattered probably-accidental use of algorithms in protobuf (`sort`, `stable_sort`, `binary_search`); one file contained `using std::setw` etc.; and asio makes very heavy use of unqualified `declval`.
This is irrelevant to Corentin's interests with this PR; I'm just dumping the finding here in case anyone's ever interested in generalizing this check and wants to know what it would find.



================
Comment at: clang/lib/Sema/SemaExpr.cpp:6437
+  NamedDecl *D = dyn_cast_or_null<NamedDecl>(Call->getCalleeDecl());
+  if (!D || !D->isInStdNamespace())
+    return;
----------------
erichkeane wrote:
> Do we really want this?  I guess I would think doing:
> 
> 
> ```
> void MyFunc(auto whatever) {
>   auto X = move(whatever);
> ```
> 
> when I MEAN std::move, just for it to pick up a non-std::move the 1st time is likely the same problem?  Or should it get a separate warning?
That's a good point (IMHO). Perhaps instead of making this a specific case of "warn for unqualified call to things in `std` (namely `move` and `forward`)," we should make it a specific case of "warn for any unqualified use of //this identifier// (namely `move` and `forward`)." That's closer in spirit to Nico Josuttis's comment that `move` is almost like a keyword in modern C++, and therefore shouldn't be thrown around willy-nilly. Either you mean `std::move` (in which case qualify it), or you mean some other `my::move` (in which case qualify it), but using the bare word `move` is inappropriate in modern C++ no matter whether it //currently// finds something out of `std` or not.
I'm ambivalent between these two ways of looking at the issue. Maybe someone can think up a reason to prefer one or the other?

libc++'s tests do include several recently-added instances of `move` as a //variable name//, e.g. `auto copy(x); auto move(std::move(x));`. This confuses grep but would not confuse Clang, for better and worse. I don't expect that real code would ever do this, either.

@erichkeane's specific example is a //template//, which means it's going to be picked up by D72282 `clang-tidy bugprone-unintended-adl` also. Using ADL inside templates triggers multiple red flags simultaneously. Whereas this D119670 is the only thing that's going to catch unqualified `move` in //non-template// code.


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  https://reviews.llvm.org/D119670/new/

https://reviews.llvm.org/D119670