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Summary: In the case of a coroutine that takes no arguments, `Sema::buildCoroutinePromise` constructs a list-initialization (`clang::InitializationKind::InitKind::IK_DirectList`) of the promise variable, using a list of empty arguments. So, if one were to dump the promise `VarDecl` immediately after `Sema::ActOnCoroutineBodyStart` calls `checkCoroutineContext`, for a coroutine function that takes no arguments, they'd see the following: ``` VarDecl 0xb514490 <test.cpp:26:3> col:3 __promise '<dependent type>' callinit `-ParenListExpr 0xb514510 <col:3> 'NULL TYPE' ``` But after this patch, the `ParenListExpr` is no longer constructed, and the promise variable uses default initialization (`clang::InitializationKind::InitKind::IK_Default`): ``` VarDecl 0x63100012dae0 <test.cpp:26:3> col:3 __promise '<dependent type>' ``` As far as I know, there's no case in which list-initialization with no arguments differs from default initialization, but if I'm wrong please let me know (and I'll add a test case that demonstrates the change -- but as-is I can't think of a functional test case for this). I think both comply with the wording of C++20 `[dcl.fct.def.coroutine]p5`: > _promise-constructor-arguments_ is determined as follows: overload resolution is performed on a promise constructor call created by assembling an argument list with lvalues `p1 ... pn`. If a viable constructor is found (12.4.2), then _promise-constructor-arguments_ is `(p1, ... , pn)`, otherwise _promise-constructor-arguments_ is empty. Still, I think this patch is an improvement regardless, because it reduces the size of the AST. Reviewers: GorNishanov, rsmith, lewissbaker Subscribers: EricWF, cfe-commits Tags: #clang Differential Revision: https://reviews.llvm.org/D70555
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