clang-format does not handle semicolons in template argument lists

[JohelEGP]

Bugzilla Link	47161
Version	trunk
OS	Linux
CC	@JohelEGP,@mydeveloperday

Extended Description

This is how semicolons in template argument lists are formatted with the default configuration:

template <auto> struct X {};

struct Y : X < [] {
  return 0;
} > {};

struct Z : X < decltype([]
{
  return 0;
}){} > {};

struct W : X < requires {
  ill - formed;
} > {};

These uses will become more common in C++20 thanks to the used features.

[mydeveloperday]

Sorry I'm struggling to understand the before/after?

[JohelEGP]

The before would look something like this:

template <auto> struct X {};

struct Y : X<[] { return 0; }> {};

struct Z : X<decltype([] { return 0; }){}> {};

struct W : X<requires { ill - formed; }> {};

[mydeveloperday]

I'm not saying one way or another but being able to format in both ways seems equally desirable right? I mean these could get very complex and long and we'd need to break them somewhere eventually.

We may be missing some sort of options like AllowShortTemplateDeclarationsOnOneLine

struct Z : X < decltype([]
{
  return 0;
}){} > {};

struct Z : X<decltype([] { return 0; }){}> {};

[JohelEGP]

There's AllowShortLambdasOnASingleLine. The important part is to handle semicolons within template argument lists, or everywhere else since now you can use lambdas everywhere.

[JohelEGP]

It works fine in other contexts: https://godbolt.org/z/o7b1G9.

template <auto L> constexpr auto A{L()};

struct B {
  int : A<[] { return 1; }>;
  int : A<[] {
    return 4;
    return 2;
  }>;
};

template <auto = A<[] { return B{}; }>> struct C {};
template <auto = A<[] {
            return B{};
            return B{};
          }>>
struct D {};

template <auto L> constexpr auto E{A<[] { L; }>};

[mydeveloperday]

Could you please clearly state what it is that you see and what it is that you expect, we can't be expected to understand where the difference you are seeing is.

please also tell us which version of clang-format you are using and provide the smallest .clang-format file that produces your problem.

I can tell you from experience bugs that don't explain what you want, get quickly ignored.

[JohelEGP]

Thank you. The following uses the default settings, so no .clang-format or an empty .clang-format.

Here's the result:

struct Y : X < [] {
  return 0;
} > {};

The input and also expected result of the formatted code:

struct Y : X <[] { return 0; }> {};

[mydeveloperday]

https://reviews.llvm.org/D116806

[llvmbot]

@llvm/issue-subscribers-bug

[JohelEGP]

Awesome, thank you.