[clang] bc93131 - [Clang] Implement CWG2517 Useless restriction on use of parameter in constraint-expression (#132919)
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Sat Jun 7 02:31:07 PDT 2025
Author: Imad Aldij
Date: 2025-06-07T11:31:04+02:00
New Revision: bc931318a2880360f3970e1e6906adc9c90eb698
URL: https://github.com/llvm/llvm-project/commit/bc931318a2880360f3970e1e6906adc9c90eb698
DIFF: https://github.com/llvm/llvm-project/commit/bc931318a2880360f3970e1e6906adc9c90eb698.diff
LOG: [Clang] Implement CWG2517 Useless restriction on use of parameter in constraint-expression (#132919)
Remove `[expr.prim.req.nested]` check which restrict that local
parameters in constraint-expressions can only appear as unevaluated
operands. This change makes the treatment of examples like `requires`
expressions and other constant expression contexts uniform, consistent
with the adoption of P2280.
References: https://cplusplus.github.io/CWG/issues/2517.html
Fixes #132825
---------
Co-authored-by: cor3ntin <corentinjabot at gmail.com>
Added:
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaExpr.cpp
clang/test/CXX/drs/cwg25xx.cpp
clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
clang/test/CXX/expr/expr.prim/expr.prim.req/simple-requirement.cpp
clang/www/cxx_dr_status.html
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 9ab69320f0368..74a205a85da5c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -153,6 +153,8 @@ Resolutions to C++ Defect Reports
- Bumped the ``__cpp_constexpr`` feature-test macro to ``202002L`` in C++20 mode as indicated in
`P2493R0 <https://wg21.link/P2493R0>`_.
+- Implemented `CWG2517 Useless restriction on use of parameter in `
+ `constraint-expression <https://cplusplus.github.io/CWG/issues/2517.html>`_.
- Implemented `CWG3005 Function parameters should never be name-independent <https://wg21.link/CWG3005>`_.
C Language Changes
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index e963612f387ef..5f44d503580b9 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3108,8 +3108,6 @@ def err_reference_to_function_with_unsatisfied_constraints : Error<
"invalid reference to function %0: constraints not satisfied">;
def err_requires_expr_local_parameter_default_argument : Error<
"default arguments not allowed for parameters of a requires expression">;
-def err_requires_expr_parameter_referenced_in_evaluated_context : Error<
- "constraint variable %0 cannot be used in an evaluated context">;
def note_expr_requirement_expr_substitution_error : Note<
"%select{and|because}0 '%1' would be invalid: %2">;
def note_expr_requirement_expr_unknown_substitution_error : Note<
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 9c322deb55e00..c7abbbd6993de 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -397,17 +397,6 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
targetDiag(*Locs.begin(), diag::err_thread_unsupported);
}
- if (isa<ParmVarDecl>(D) && isa<RequiresExprBodyDecl>(D->getDeclContext()) &&
- !isUnevaluatedContext()) {
- // C++ [expr.prim.req.nested] p3
- // A local parameter shall only appear as an unevaluated operand
- // (Clause 8) within the constraint-expression.
- Diag(Loc, diag::err_requires_expr_parameter_referenced_in_evaluated_context)
- << D;
- Diag(D->getLocation(), diag::note_entity_declared_at) << D;
- return true;
- }
-
return false;
}
diff --git a/clang/test/CXX/drs/cwg25xx.cpp b/clang/test/CXX/drs/cwg25xx.cpp
index d9a7d2bbb2671..5c2948f67d0ee 100644
--- a/clang/test/CXX/drs/cwg25xx.cpp
+++ b/clang/test/CXX/drs/cwg25xx.cpp
@@ -32,6 +32,26 @@ enum E2 : S<E2>::I { e };
#endif
} // namespace cwg2516
+namespace cwg2517 { // cwg2517: 21
+#if __cplusplus >= 202002L
+template<typename ArrayType>
+concept LargeArray = requires (ArrayType my_array) {
+ requires my_array.size() > 5;
+};
+
+struct Big {
+ constexpr int size() const { return 100; }
+};
+
+struct Small {
+ constexpr int size() const { return 3; }
+};
+
+static_assert(LargeArray<Big>);
+static_assert(!LargeArray<Small>);
+#endif
+} // namespace cwg2517
+
namespace cwg2518 { // cwg2518: 17
#if __cplusplus >= 201103L
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
index 19145f68b2f75..033ae349a02e5 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
@@ -41,9 +41,17 @@ namespace std_example {
template<typename T>
concept C2 = requires (T a) {
requires sizeof(a) == 4; // OK
- requires a == 0; // expected-note{{because 'a == 0' would be invalid: constraint variable 'a' cannot be used in an evaluated context}}
+ requires a == 0; // expected-error{{substitution into constraint expression resulted in a non-constant expression}}
+ // expected-note at -1{{while checking the satisfaction of nested requirement requested here}}
+ // expected-note at -2{{in instantiation of requirement here}}
+ // expected-note at -3{{while checking the satisfaction of nested requirement requested here}}
+ // expected-note at -6{{while substituting template arguments into constraint expression here}}
+ // expected-note at -5{{function parameter 'a' with unknown value cannot be used in a constant expression}}
+ // expected-note at -8{{declared here}}
};
- static_assert(C2<int>); // expected-note{{because 'int' does not satisfy 'C2'}} expected-error{{static assertion failed}}
+ static_assert(C2<int>); // expected-error{{static assertion failed}}
+ // expected-note at -1{{while checking the satisfaction of concept 'C2<int>' requested here}}
+ // expected-note at -2{{because 'int' does not satisfy 'C2'}}
}
template<typename T>
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.req/simple-requirement.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.req/simple-requirement.cpp
index 7515f5c62d5ea..5199708cd8166 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.req/simple-requirement.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.req/simple-requirement.cpp
@@ -102,8 +102,10 @@ namespace std_example {
// of a polymorphic type.
class X { virtual ~X(); };
constexpr bool b = requires (X &x) { static_cast<int(*)[(typeid(x), 0)]>(nullptr); };
-// expected-error at -1{{constraint variable 'x' cannot be used in an evaluated context}}
-// expected-note at -2{{'x' declared here}}
+// expected-warning at -1 {{left operand of comma operator has no effect}}
+// expected-warning at -2 {{variable length arrays in C++ are a Clang extension}}
+// expected-note at -3{{function parameter 'x' with unknown value cannot be used in a constant expression}}
+// expected-note at -4{{declared here}}
namespace access_checks {
namespace in_requires_expression {
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 58286db165077..d06eb4a0ed23e 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -14937,7 +14937,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
<td><a href="https://cplusplus.github.io/CWG/issues/2517.html">2517</a></td>
<td>C++23</td>
<td>Useless restriction on use of parameter in <I>constraint-expression</I></td>
- <td class="unknown" align="center">Unknown</td>
+ <td class="unreleased" align="center">Clang 21</td>
</tr>
<tr id="2518">
<td><a href="https://cplusplus.github.io/CWG/issues/2518.html">2518</a></td>
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