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This allows `static_assert(false)` to not be ill-formed
in template definitions.
This change is applied as a DR in all C++ modes.
Of notes, a couple of tests were relying of the eager nature
of static_assert
- test/SemaTemplate/instantiation-dependence.cpp
- test/SemaTemplate/instantiate-var-template.cpp
I don't know if the changes to `static_assert`
still allow that sort of tests to be expressed.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D144285
Files:
clang/docs/ReleaseNotes.rst
clang/lib/Sema/SemaDeclCXX.cpp
clang/test/CXX/drs/dr25xx.cpp
clang/test/SemaCXX/access-base-class.cpp
clang/test/SemaCXX/coroutines-exp-namespace.cpp
clang/test/SemaCXX/coroutines.cpp
clang/test/SemaCXX/static-assert.cpp
clang/test/SemaTemplate/instantiate-var-template.cpp
clang/test/SemaTemplate/instantiation-dependence.cpp
clang/www/cxx_dr_status.html
Index: clang/www/cxx_dr_status.html
===================================================================
--- clang/www/cxx_dr_status.html
+++ clang/www/cxx_dr_status.html
@@ -14915,7 +14915,7 @@
<td><a href="https://wg21.link/cwg2518";>2518</a></td>
<td>review</td>
<td>Conformance requirements and <TT>#error</TT>/<TT>#warning</TT></td>
- <td align="center">Not resolved</td>
+ <td class="unreleased" align="center">Clang 17</td>
</tr>
<tr class="open" id="2519">
<td><a href="https://wg21.link/cwg2519";>2519</a></td>
Index: clang/test/SemaTemplate/instantiation-dependence.cpp
===================================================================
--- clang/test/SemaTemplate/instantiation-dependence.cpp
+++ clang/test/SemaTemplate/instantiation-dependence.cpp
@@ -38,7 +38,7 @@
template<class T> void foo() {
static_assert(!__is_void(indirect_void_t<T>)); // "ok", dependent
- static_assert(!__is_void(void_t<T>)); // expected-error {{failed}}
+ static_assert(!__is_void(void_t<T>)); // fixme: can we check a type is dependant?
}
}
Index: clang/test/SemaTemplate/instantiate-var-template.cpp
===================================================================
--- clang/test/SemaTemplate/instantiate-var-template.cpp
+++ clang/test/SemaTemplate/instantiate-var-template.cpp
@@ -31,9 +31,9 @@
static_assert(b<char> == 1, ""); // expected-note {{in instantiation of}}
template<typename T> void f() {
- static_assert(a<sizeof(sizeof(f(T())))> == 0, ""); // expected-error {{static assertion failed due to requirement 'a<sizeof (sizeof (f(type-parameter-0-0())))> == 0'}} \
- // expected-note {{evaluates to '1 == 0'}}
+ static_assert(a<sizeof(sizeof(f(T())))> == 0, ""); // fixme: can we check a var is dependant?
}
+
}
namespace PR24483 {
Index: clang/test/SemaCXX/static-assert.cpp
===================================================================
--- clang/test/SemaCXX/static-assert.cpp
+++ clang/test/SemaCXX/static-assert.cpp
@@ -54,7 +54,7 @@
// Only give one error here.
static_assert(false, ""); // expected-error {{static assertion failed}}
};
-AlwaysFails<int> alwaysFails;
+AlwaysFails<int> alwaysFails; // expected-note {{instantiation}}
template<typename T> struct StaticAssertProtected {
static_assert(__is_literal(T), ""); // expected-error {{static assertion failed}}
Index: clang/test/SemaCXX/coroutines.cpp
===================================================================
--- clang/test/SemaCXX/coroutines.cpp
+++ clang/test/SemaCXX/coroutines.cpp
@@ -1309,7 +1309,7 @@
}
};
-template struct DepTestType<int>; // expected-note {{requested here}}
+template struct DepTestType<int>; // expected-note 2{{requested here}}
template CoroMemberTag DepTestType<int>::test_member_template(long, const char *) const &&;
template CoroMemberTag DepTestType<int>::test_static_template<void>(const char *volatile &, unsigned);
Index: clang/test/SemaCXX/coroutines-exp-namespace.cpp
===================================================================
--- clang/test/SemaCXX/coroutines-exp-namespace.cpp
+++ clang/test/SemaCXX/coroutines-exp-namespace.cpp
@@ -1288,7 +1288,7 @@
}
};
-template struct DepTestType<int>; // expected-note {{requested here}}
+template struct DepTestType<int>; // expected-note 2{{requested here}}
template CoroMemberTag DepTestType<int>::test_member_template(long, const char *) const &&;
template CoroMemberTag DepTestType<int>::test_static_template<void>(const char *volatile &, unsigned);
Index: clang/test/SemaCXX/access-base-class.cpp
===================================================================
--- clang/test/SemaCXX/access-base-class.cpp
+++ clang/test/SemaCXX/access-base-class.cpp
@@ -96,14 +96,14 @@
};
template <class T>
-struct trait : flag<sizeof(T)> {};
+struct trait : flag<sizeof(T)> {}; // expected-note 2{{here}}
-template <class T, bool Inferred = trait<T>::value>
+template <class T, bool Inferred = trait<T>::value> // expected-note {{here}}
struct a {};
template <class T>
class b {
- a<T> x;
+ a<T> x; // expected-note {{here}}
using U = a<T>;
};
@@ -113,5 +113,5 @@
};
// verify "no member named 'value'" bogus diagnostic is not emitted.
-trait<b<Impossible<0>>>::value;
+trait<b<Impossible<0>>>::value; // expected-note {{here}}
} // namespace T8
Index: clang/test/CXX/drs/dr25xx.cpp
===================================================================
--- clang/test/CXX/drs/dr25xx.cpp
+++ clang/test/CXX/drs/dr25xx.cpp
@@ -1,5 +1,33 @@
// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-unknown %s -verify
+namespace dr2518 { // dr2518: 17 review
+
+#error one
+// expected-error@-1 {{one}}
+#if 0
+#error skip
+#warning skip // expected-error {{skip}}
+#endif
+#error two
+// expected-error@-1 {{two}}
+#warning warn
+// expected-warning@-1 {{warn}}
+
+template <class T>
+void f(T t) {
+ if constexpr (sizeof(T) != sizeof(int)) {
+ static_assert(false, "must be int-sized"); // expected-error {{must be int-size}}
+ }
+}
+
+void g(char c) {
+ f(0);
+ f(c); // expected-note {{requested here}}
+}
+
+}
+
+
namespace dr2565 { // dr2565: 16 open
template<typename T>
concept C = requires (typename T::type x) {
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -16799,7 +16799,13 @@
FoldKind).isInvalid())
Failed = true;
- if (!Failed && !Cond) {
+ // CWG2518
+ // [dcl.pre]/p10 If [...] the expression is evaluated in the context of a template
+ // definition, the declaration has no effect.
+ bool InTemplateDefinition = getLangOpts().CPlusPlus && getTemplateDepth(getCurScope()) != 0;
+
+ if (!Failed && !Cond && !InTemplateDefinition) {
+
SmallString<256> MsgBuffer;
llvm::raw_svector_ostream Msg(MsgBuffer);
if (AssertMessage) {
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -59,6 +59,8 @@
- Improved ``-O0`` code generation for calls to ``std::forward_like``. Similarly to
``std::move, std::forward`` et al. it is now treated as a compiler builtin and implemented
directly rather than instantiating the definition from the standard library.
+- Implemented `CWG2518 <https://wg21.link/CWG2518>`_ which allows ``static_assert(false)``
+ not to be ill-formed when its condition is evaluated in a non-instantiated templates.
C++20 Feature Support
^^^^^^^^^^^^^^^^^^^^^
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