[clang] [clang-tools-extra] [clangd] show lambda name instead of operator() in signature help (PR #101857)

[Timothy Akintilo via cfe-commits]

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@@ -6292,11 +6298,16 @@ SemaCodeCompletion::ProduceCallSignatureHelp(Expr *Fn, ArrayRef<Expr *> Args,
         SmallVector<Expr *, 12> ArgExprs(1, NakedFn);
         ArgExprs.append(ArgsWithoutDependentTypes.begin(),
                         ArgsWithoutDependentTypes.end());
+        auto *const LambdaName =
+            DC->isLambda() ? cast<VarDecl>(NakedFn->getReferencedDeclOfCallee())
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tilobyte wrote:

@erichkeane stepping through the test i added for a lambda returned from a function, `NakedFn->getReferencedDeclOfCallee()` returns `nullptr` in the case of a lambda returned from a function. i believe this is because `NakedFn` is an rvalue, so there is no referenced decl to get.
using `cast_if_present`/`dyn_cast_if_present` seems to cover that case.

@zyn0217 yes, you are correct that `NakedFn` is a `DeclRefExpr` referring to the `VarDecl` of the declaration. `dyn_cast_if_present` indeed works, though i wonder--if `NakedFn->getReferencedDeclOfCallee()` returns `nullptr` in the case of a lambda returned from a function, could we get away with just `cast_if_present`?

https://github.com/llvm/llvm-project/pull/101857