logan-5 added a comment.
Hi @Quuxplusone, glad you found your way here. I thought of adding you as a
reviewer out the gate but then I didn't.
================
Comment at: clang-tools-extra/clang-tidy/bugprone/UnintendedADLCheck.cpp:43
+ Whitelist(
+ utils::options::parseStringList(Options.get("Whitelist", "swap"))) {}
+
----------------
Quuxplusone wrote:
> JonasToth wrote:
> > JonasToth wrote:
> > > logan-5 wrote:
> > > > JonasToth wrote:
> > > > > do you mean `std::swap`? If you it should be fully qualified.
> > > > > Doesn't `std::error_code` rely on adl, too? I think `std::cout <<`
> > > > > and other streams of the STL rely on it too, and probably many more
> > > > > code-constructs that are commonly used.
> > > > >
> > > > > That means, the list should be extended to at least all
> > > > > standard-library facilities that basically required ADL to work. And
> > > > > then we need data on different code bases (e.g. LLVM is a good start)
> > > > > how much noise gets generated.
> > > > I distinctly //don't// mean `std::swap` -- I want to whitelist any
> > > > unqualified function call spelled simply `swap`.
> > > >
> > > > Overloaded operators are the poster child for ADL's usefulness, so
> > > > that's why this check has a special default-on
> > > > `IgnoreOverloadedOperators` option. That whitelists a whole ton of
> > > > legitimate stuff including `std::cout << x` and friends.
> > > >
> > > > I don't see a ton of discussion online about
> > > > `error_code`/`make_error_code` and ADL being very much intertwined. I'm
> > > > not particularly familiar with those constructs myself though, and I
> > > > could just be out of the loop. I do see a fair number of unqualified
> > > > calls to `make_error_code` within LLVM, though most of those resolve to
> > > > `llvm::make_error_code`, the documentation for which says it exists
> > > > because `std::make_error_code` can't be reliably/portably used with
> > > > ADL. That makes me think `make_error_code` would belong in LLVM's
> > > > project-specific whitelist configuration, not the check's default.
> > > >
> > > > Speaking of which, I did run this check over LLVM while developing and
> > > > found it not particularly noisy as written. That is, it generated a
> > > > fair number of warnings, but only on constructs that, when examined
> > > > closely, //were// a little suspicious or non-obvious.
> > > I don't have a solid understanding of the `error_code` world as well. All
> > > I know is, that you specialize some templates with your own types in
> > > order to use the generic `error_code`-world.
> > > AFAIK that needs some form of ADL at some point, but that could even
> > > happen through the overloaded operators (`==` and `!=`), in which case
> > > that would already be handled. (maybe @aaron.ballman knows more?)
> > >
> > > But overloaded operators being ignored by default is good and that point
> > > is gone :)
> > Yes, `make_error_code` is used via ADL. -->
> > https://www.boost.org/doc/libs/1_72_0/libs/outcome/doc/html/motivation/plug_error_code.html
> > I think that should be in the default list for ignored functions, as it is
> > a standard facility.
> +1, both `make_error_code` and `make_error_condition` should be on the
> whitelist. (I am the author of [P0824 "Summary of SG14 discussion of
> `<system_error>`"](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0824r1.html#best-arthur).
> I also confirm that libc++ `<system_error>` does call them unqualified on
> purpose.)
>
> I would like to see some discussion and/or TODO-comments about the other
> standard [designated customization
> points](http://eel.is/c++draft/iterator.range#1.sentence-2): `data`, `begin`,
> `end`, `rbegin`, `rend`, `crbegin`, `crend`, `size`, `ssize`, and `empty`.
> This might deserve input from the libc++ implementors.
Added `make_error_condition` to the whitelist.
My inclination would be to just add all those standard customization points to
the default whitelist. Users can easily supply a smaller whitelist if they want.
================
Comment at:
clang-tools-extra/test/clang-tidy/checkers/bugprone-unintended-adl.cpp:54
+ move(a);
+ // CHECK-MESSAGES: [[@LINE-1]]:3: warning: expression calls 'ns::move'
through ADL [bugprone-unintended-adl]
+ forward(a);
----------------
Quuxplusone wrote:
> This is awesome. :) Please also consider ADL where there's more than one
> associated namespace, something like this: https://godbolt.org/z/S73Gzy
> ```
> template<class T> struct Templated { };
> Templated<std::byte> testX() {
> Templated<std::byte> x;
> using std::move;
> return move(x); // "correctly" resolves to std::move today, but still
> does unintended ADL
> }
> ```
> Please add a test isomorphic to the above, unless you think it's already
> covered by one of the existing tests.
It's interesting, that code only triggers the check (i.e. my AST matchers only
think it's doing ADL) without the `using std::move`. I admit I'm a bit confused
as to why.
================
Comment at:
clang-tools-extra/test/clang-tidy/checkers/bugprone-unintended-adl.cpp:61
+void templateFunction(T t) {
+ swap(t, t);
+
----------------
Quuxplusone wrote:
> This is not the idiomatic way of calling `swap`: there is no ADL swap for
> `int`, for example (so `templateFunction<int>` will hard-error during
> instantiation). It would probably be scope-creep to try to handle the
> "std::swap two-step", but can you leave a TODO comment somewhere to revisit
> this issue?
>
I believe this addressed by my juggling the tests around a bit.
Repository:
rG LLVM Github Monorepo
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https://reviews.llvm.org/D72282/new/
https://reviews.llvm.org/D72282
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