https://github.com/adityak2006 updated https://github.com/llvm/llvm-project/pull/167224
>From f24e5b8d0c9c9a3cea91d1671bf956e0a9285176 Mon Sep 17 00:00:00 2001 From: Aditya <[email protected]> Date: Sun, 9 Nov 2025 14:49:24 +0000 Subject: [PATCH] [Clang][Diagnostics] Simplify 'decltype(T{})' to 'T' in diagnostics Clang's type printer would verbosely print `decltype(T{})` in diagnostics, even though this is equivalent to just `T`. This made error messages unnecessarily long and harder to read. This commit modifies `TypePrinter::printDecltypeBefore` to detect this specific pattern. It checks if the underlying expression of a `DecltypeType` is a default `CXXConstructExpr` (i.e., `T{}`) and, if so, prints the constructor's type (`T`) directly instead of the full `decltype`. Fixes #96638. --- clang/lib/AST/TypePrinter.cpp | 13 ++++++++++ .../SemaCXX/decltype-diagnostic-print.cpp | 25 +++++++++++++++++++ 2 files changed, 38 insertions(+) create mode 100644 clang/test/SemaCXX/decltype-diagnostic-print.cpp diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp index c18b2eafc722c..510923229ea11 100644 --- a/clang/lib/AST/TypePrinter.cpp +++ b/clang/lib/AST/TypePrinter.cpp @@ -18,6 +18,7 @@ #include "clang/AST/DeclObjC.h" #include "clang/AST/DeclTemplate.h" #include "clang/AST/Expr.h" +#include "clang/AST/ExprCXX.h" #include "clang/AST/NestedNameSpecifier.h" #include "clang/AST/PrettyPrinter.h" #include "clang/AST/TemplateBase.h" @@ -1321,6 +1322,18 @@ void TypePrinter::printTypeOfBefore(const TypeOfType *T, raw_ostream &OS) { void TypePrinter::printTypeOfAfter(const TypeOfType *T, raw_ostream &OS) {} void TypePrinter::printDecltypeBefore(const DecltypeType *T, raw_ostream &OS) { + // Check for the 'decltype(T{})' pattern and simplify it to 'T'. + if (const Expr *E = T->getUnderlyingExpr()) { + E = E->IgnoreParenImpCasts(); + if (const CXXConstructExpr *CE = dyn_cast<CXXConstructExpr>(E)) { + // Check if it's a default constructor (T{}) and not a list init (T{...}) + if (CE->getNumArgs() == 0 && !CE->isListInitialization()) { + CE->getType().print(OS, Policy); + spaceBeforePlaceHolder(OS); + return; // Skip the default 'decltype(...)' printing + } + } + } OS << "decltype("; if (const Expr *E = T->getUnderlyingExpr()) { PrintingPolicy ExprPolicy = Policy; diff --git a/clang/test/SemaCXX/decltype-diagnostic-print.cpp b/clang/test/SemaCXX/decltype-diagnostic-print.cpp new file mode 100644 index 0000000000000..c4b075ef4ea33 --- /dev/null +++ b/clang/test/SemaCXX/decltype-diagnostic-print.cpp @@ -0,0 +1,25 @@ +// clang/test/SemaCXX/decltype-diagnostic-print.cpp +// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s + +template <typename T> +struct TestAssert { + // This static_assert will fail, forcing the compiler to print the name + // of the template instantiation in its diagnostic "note". + static_assert(sizeof(T) == 0, "Static assert to check type printing"); +}; + +struct MySimpleType {}; +struct MyOtherType {}; + +void test() { + // This will fail the static_assert. + TestAssert<decltype(MySimpleType{})> test1; + // expected-error@6 {{Static assert to check type printing}} + // expected-note@16 {{in instantiation of template class 'TestAssert<MySimpleType>' requested here}} + // CHECK-NOT: decltype(MySimpleType{}) + + TestAssert<decltype(MyOtherType{})> test2; + // expected-error@6 {{Static assert to check type printing}} + // expected-note@22 {{in instantiation of template class 'TestAssert<MyOtherType>' requested here}} + // CHECK-NOT: decltype(MyOtherType{}) +} \ No newline at end of file _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
