Cannot call lambda defined in immediate lambda

[LHLaurini]

The following code compiles on both GCC and MSVC, but is refused by Clang (Godbolt link):

void func_1(auto)
{
    [](auto) consteval
    {
        [](auto)
        {
        }(123);
    };
}

auto func_2()
{
    func_1(123);
}

The error message:

<source>:6:9: error: no matching function for call to object of type '(lambda at <source>:6:9)'
    6 |         [](auto)
      |         ^~~~~~~~
    7 |         {
      |         ~
    8 |         }(123);
      |         ~
<source>:5:5: note: while substituting into a lambda expression here
    5 |     {
      |     ^
<source>:14:5: note: in instantiation of function template specialization 'func_1<int>' requested here
   14 |     func_1(123);
      |     ^
<source>:6:9: note: candidate template ignored: couldn't infer template argument 'auto:1'
    6 |         [](auto)
      |         ^
1 error generated.

From my experimentation:

• func_1 must be a function template;
• The outer lambda must be immediate;
• The outer lambda must be either polymorphic or a lambda template;
• The inner lambda must be either polymorphic or a lambda template.

Note: the code from which I wrote this test-case is almost the same where I originally found #117676, so there could be some relation (or not).

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Luiz Henrique Laurini (LHLaurini)

The following code compiles on both GCC and MSVC, but is refused by Clang ([Godbolt link](https://godbolt.org/z/M7KdM36YE)): ```c++ void func_1(auto) { [](auto) consteval { [](auto) { }(123); }; }

auto func_2()
{
func_1(123);
}

The error message:

<source>:6:9: error: no matching function for call to object of type '(lambda at <source>:6:9)'
6 |
| ^~~~~~~~
7 | {
| ~
8 | }(123);
| ~
<source>:5:5: note: while substituting into a lambda expression here
5 | {
| ^
<source>:14:5: note: in instantiation of function template specialization 'func_1<int>' requested here
14 | func_1(123);
| ^
<source>:6:9: note: candidate template ignored: couldn't infer template argument 'auto:1'
6 |
| ^
1 error generated.

From my experimentation:
- `func_1` must be a function template;
- The outer lambda must be immediate;
- The outer lambda must be either polymorphic or a lambda template;
- The inner lambda must be either polymorphic or a lambda template.

Note: the code from which I wrote this test-case is almost the same where I originally found #<!-- -->117676, so there could be some relation (or not).
</details>

[shafik]

clang-19 regression: https://godbolt.org/z/hW5a1aqeW

CC @cor3ntin

[shafik]

@katzdm git bisect points to this commit as to the cause of this regression: 5e767bd

[katzdm]

@shafik Sorry for ignoring this for a while - The changes from my commit looks to have been fully rolled back by a recent change by @cor3ntin , but the bug remains. I have some time this week, so I'll dig a bit to try to understand it.

[katzdm]

@shafik Sorry for ignoring this for a while - The changes from my commit looks to have been fully rolled back by a recent change by @cor3ntin , but the bug remains. I have some time this week, so I'll dig a bit to try to understand it.

Nevermind; I see that the logic I had added is now encapsulated by PushExpressionEvaluationContextForFunction.