[clang] 9cfb138 - [Clang][Sema] Defer instantiation of exception specification until after partial ordering when determining primary template (#82417)
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cfe-commits at lists.llvm.org
Mon Feb 26 06:59:00 PST 2024
Author: Krystian Stasiowski
Date: 2024-02-26T09:58:55-05:00
New Revision: 9cfb138eccb83b5876928b08be346fde5ca78b47
URL: https://github.com/llvm/llvm-project/commit/9cfb138eccb83b5876928b08be346fde5ca78b47
DIFF: https://github.com/llvm/llvm-project/commit/9cfb138eccb83b5876928b08be346fde5ca78b47.diff
LOG: [Clang][Sema] Defer instantiation of exception specification until after partial ordering when determining primary template (#82417)
Consider the following:
```
struct A {
static constexpr bool x = true;
};
template<typename T, typename U>
void f(T, U) noexcept(T::y); // #1, error: no member named 'y' in 'A'
template<typename T, typename U>
void f(T, U*) noexcept(T::x); // #2
template<>
void f(A, int*) noexcept; // explicit specialization of #2
```
We currently instantiate the exception specification of all candidate
function template specializations when deducting template arguments for
an explicit specialization, which results in a error despite `#1` not
being selected by partial ordering as the most specialized template.
According to [except.spec] p13:
> An exception specification is considered to be needed when:
> - [...]
> - the exception specification is compared to that of another
declaration (e.g., an explicit specialization or an overriding virtual
function);
Assuming that "comparing declarations" means "determining whether the
declarations correspond and declare the same entity" (per [basic.scope.scope] p4 and
[basic.link] p11.1, respectively), the exception specification does _not_ need to be
instantiated until _after_ partial ordering, at which point we determine
whether the implicitly instantiated specialization and the explicit
specialization declare the same entity (the determination of whether two
functions/function templates correspond does not consider the exception
specifications).
This patch defers the instantiation of the exception specification until
a single function template specialization is selected via partial
ordering, matching the behavior of GCC, EDG, and
MSVC: see https://godbolt.org/z/Ebb6GTcWE.
Added:
clang/test/CXX/except/except.spec/p13.cpp
Modified:
clang/docs/ReleaseNotes.rst
clang/lib/Sema/SemaTemplate.cpp
clang/lib/Sema/SemaTemplateDeduction.cpp
clang/test/SemaTemplate/class-template-noexcept.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 529dd783ab7382..9e67bbb7895040 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -281,6 +281,8 @@ Bug Fixes to C++ Support
a requires-clause lie at the same depth as those of the surrounding lambda. This,
in turn, results in the wrong template argument substitution during constraint checking.
(`#78524 <https://github.com/llvm/llvm-project/issues/78524>`_)
+- Clang no longer instantiates the exception specification of discarded candidate function
+ templates when determining the primary template of an explicit specialization.
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index c95c08c0422ed2..e91033dd886891 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -9709,6 +9709,40 @@ bool Sema::CheckFunctionTemplateSpecialization(
// Ignore access information; it doesn't figure into redeclaration checking.
FunctionDecl *Specialization = cast<FunctionDecl>(*Result);
+ // C++23 [except.spec]p13:
+ // An exception specification is considered to be needed when:
+ // - [...]
+ // - the exception specification is compared to that of another declaration
+ // (e.g., an explicit specialization or an overriding virtual function);
+ // - [...]
+ //
+ // The exception specification of a defaulted function is evaluated as
+ // described above only when needed; similarly, the noexcept-specifier of a
+ // specialization of a function template or member function of a class
+ // template is instantiated only when needed.
+ //
+ // The standard doesn't specify what the "comparison with another declaration"
+ // entails, nor the exact circumstances in which it occurs. Moreover, it does
+ // not state which properties of an explicit specialization must match the
+ // primary template.
+ //
+ // We assume that an explicit specialization must correspond with (per
+ // [basic.scope.scope]p4) and declare the same entity as (per [basic.link]p8)
+ // the declaration produced by substitution into the function template.
+ //
+ // Since the determination whether two function declarations correspond does
+ // not consider exception specification, we only need to instantiate it once
+ // we determine the primary template when comparing types per
+ // [basic.link]p11.1.
+ auto *SpecializationFPT =
+ Specialization->getType()->castAs<FunctionProtoType>();
+ // If the function has a dependent exception specification, resolve it after
+ // we have selected the primary template so we can check whether it matches.
+ if (getLangOpts().CPlusPlus17 &&
+ isUnresolvedExceptionSpec(SpecializationFPT->getExceptionSpecType()) &&
+ !ResolveExceptionSpec(FD->getLocation(), SpecializationFPT))
+ return true;
+
FunctionTemplateSpecializationInfo *SpecInfo
= Specialization->getTemplateSpecializationInfo();
assert(SpecInfo && "Function template specialization info missing?");
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 47cc22310c4eec..563491f76f5478 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -4632,11 +4632,9 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
Info.getLocation()))
return TemplateDeductionResult::MiscellaneousDeductionFailure;
- // If the function has a dependent exception specification, resolve it now,
- // so we can check that the exception specification matches.
auto *SpecializationFPT =
Specialization->getType()->castAs<FunctionProtoType>();
- if (getLangOpts().CPlusPlus17 &&
+ if (IsAddressOfFunction && getLangOpts().CPlusPlus17 &&
isUnresolvedExceptionSpec(SpecializationFPT->getExceptionSpecType()) &&
!ResolveExceptionSpec(Info.getLocation(), SpecializationFPT))
return TemplateDeductionResult::MiscellaneousDeductionFailure;
@@ -4662,11 +4660,11 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
// specialization with respect to arguments of compatible pointer to function
// types, template argument deduction fails.
if (!ArgFunctionType.isNull()) {
- if (IsAddressOfFunction
- ? !isSameOrCompatibleFunctionType(
- Context.getCanonicalType(SpecializationType),
- Context.getCanonicalType(ArgFunctionType))
- : !Context.hasSameType(SpecializationType, ArgFunctionType)) {
+ if (IsAddressOfFunction ? !isSameOrCompatibleFunctionType(
+ Context.getCanonicalType(SpecializationType),
+ Context.getCanonicalType(ArgFunctionType))
+ : !Context.hasSameFunctionTypeIgnoringExceptionSpec(
+ SpecializationType, ArgFunctionType)) {
Info.FirstArg = TemplateArgument(SpecializationType);
Info.SecondArg = TemplateArgument(ArgFunctionType);
return TemplateDeductionResult::NonDeducedMismatch;
diff --git a/clang/test/CXX/except/except.spec/p13.cpp b/clang/test/CXX/except/except.spec/p13.cpp
new file mode 100644
index 00000000000000..61cdb74f21ec51
--- /dev/null
+++ b/clang/test/CXX/except/except.spec/p13.cpp
@@ -0,0 +1,74 @@
+// RUN: %clang_cc1 -fexceptions -fcxx-exceptions -fsyntax-only -verify %s
+
+struct A {
+ static constexpr bool x = true;
+};
+
+namespace N0 {
+
+template<typename T, typename U>
+void f(T, U) noexcept(T::y); // #1
+
+template<typename T, typename U> // #2
+void f(T, U*) noexcept(T::x);
+
+// Deduction should succeed for both candidates, and #2 should be selected as the primary template.
+// Only the exception specification of #2 should be instantiated.
+template<>
+void f(A, int*) noexcept;
+
+}
+
+namespace N1 {
+
+template<typename T, typename U>
+void f(T, U) noexcept(T::x); // #1
+
+template<typename T, typename U>
+void f(T, U*) noexcept(T::y); // #2
+// expected-error at -1 {{no member named 'y' in 'A'}}
+
+// Deduction should succeed for both candidates, and #2 should be selected as the primary template.
+// Only the exception specification of #2 should be instantiated.
+template<>
+void f(A, int*) noexcept; // expected-error {{exception specification in declaration does not match previous declaration}}
+ // expected-note at -1 {{in instantiation of exception specification for 'f<A, int>' requested here}}
+ // expected-note at -2 {{previous declaration is here}}
+}
+
+namespace N2 {
+
+template<typename T, typename U>
+void f(T, U) noexcept(T::x);
+
+template<typename T, typename U>
+void f(T, U*) noexcept(T::x);
+
+template<typename T, typename U>
+void f(T, U**) noexcept(T::y); // expected-error {{no member named 'y' in 'A'}}
+
+template<typename T, typename U>
+void f(T, U***) noexcept(T::x);
+
+template<>
+void f(A, int*) noexcept; // expected-note {{previous declaration is here}}
+
+template<>
+void f(A, int*); // expected-error {{'f<A, int>' is missing exception specification 'noexcept'}}
+
+template<>
+void f(A, int**) noexcept; // expected-error {{exception specification in declaration does not match previous declaration}}
+ // expected-note at -1 {{in instantiation of exception specification for 'f<A, int>' requested here}}
+ // expected-note at -2 {{previous declaration is here}}
+
+// FIXME: Exception specification is currently set to EST_None if instantiation fails.
+template<>
+void f(A, int**);
+
+template<>
+void f(A, int***) noexcept; // expected-note {{previous declaration is here}}
+
+template<>
+void f(A, int***); // expected-error {{'f<A, int>' is missing exception specification 'noexcept'}}
+
+}
diff --git a/clang/test/SemaTemplate/class-template-noexcept.cpp b/clang/test/SemaTemplate/class-template-noexcept.cpp
index 5c4ac090f3166d..14d2e36bc0bfae 100644
--- a/clang/test/SemaTemplate/class-template-noexcept.cpp
+++ b/clang/test/SemaTemplate/class-template-noexcept.cpp
@@ -2,9 +2,7 @@
// RUN: %clang_cc1 -std=c++11 -verify %s
// RUN: %clang_cc1 -std=c++17 -verify %s
// RUN: %clang_cc1 -std=c++1z -verify %s
-#if __cplusplus >= 201703
-// expected-no-diagnostics
-#endif
+
class A {
public:
static const char X;
@@ -14,19 +12,9 @@ const char A::X = 0;
template<typename U> void func() noexcept(U::X);
template<class... B, char x>
-#if __cplusplus >= 201703
-void foo(void(B...) noexcept(x)) {}
-#else
void foo(void(B...) noexcept(x)) {} // expected-note{{candidate template ignored}}
-#endif
void bar()
{
-#if __cplusplus >= 201703
- foo(func<A>);
-#else
foo(func<A>); // expected-error{{no matching function for call}}
-#endif
}
-
-
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