[clang] 07008a8 - CWG2635: Disallow constrained structured bindings.
Erich Keane via cfe-commits
cfe-commits at lists.llvm.org
Mon Nov 28 14:41:20 PST 2022
Author: Erich Keane
Date: 2022-11-28T14:41:14-08:00
New Revision: 07008a8df57f8eb75e934a3a01ed0a4a76ae92ce
URL: https://github.com/llvm/llvm-project/commit/07008a8df57f8eb75e934a3a01ed0a4a76ae92ce
DIFF: https://github.com/llvm/llvm-project/commit/07008a8df57f8eb75e934a3a01ed0a4a76ae92ce.diff
LOG: CWG2635: Disallow constrained structured bindings.
CWG2635 prohibits adding a constraint to a structured as a defect
report. This patch implements that restriction.
Differential Revision: https://reviews.llvm.org/D138852
Added:
clang/test/FixIt/fixit-constrained-structured-binding.cpp
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaDeclCXX.cpp
clang/test/CXX/drs/dr26xx.cpp
clang/www/cxx_dr_status.html
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3f99bc2f7c939..86911bd3b1a1e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -655,6 +655,7 @@ C++20 Feature Support
- Do not hide templated base members introduced via using-decl in derived class
(useful specially for constrained members). Fixes `GH50886 <https://github.com/llvm/llvm-project/issues/50886>`_.
+- Implemented CWG2635 as a Defect Report, which prohibits structured bindings from being constrained.
C++2b Feature Support
^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9678fd58b997c..71093da21b0d5 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -492,6 +492,8 @@ def warn_cxx17_compat_decomp_decl_spec : Warning<
def err_decomp_decl_type : Error<
"decomposition declaration cannot be declared with type %0; "
"declared type must be 'auto' or reference to 'auto'">;
+def err_decomp_decl_constraint : Error<
+ "decomposition declaration cannot be declared with constrained 'auto'">;
def err_decomp_decl_parens : Error<
"decomposition declaration cannot be declared with parentheses">;
def err_decomp_decl_template : Error<
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index e714ffec87592..174fe43a2cd51 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -760,11 +760,16 @@ Sema::ActOnDecompositionDeclarator(Scope *S, Declarator &D,
// C++17 [dcl.dcl]/8:
// The decl-specifier-seq shall contain only the type-specifier auto
// and cv-qualifiers.
- // C++2a [dcl.dcl]/8:
+ // C++20 [dcl.dcl]/8:
// If decl-specifier-seq contains any decl-specifier other than static,
// thread_local, auto, or cv-qualifiers, the program is ill-formed.
+ // C++2b [dcl.pre]/6:
+ // Each decl-specifier in the decl-specifier-seq shall be static,
+ // thread_local, auto (9.2.9.6 [dcl.spec.auto]), or a cv-qualifier.
auto &DS = D.getDeclSpec();
{
+ // Note: While constrained-auto needs to be checked, we do so separately so
+ // we can emit a better diagnostic.
SmallVector<StringRef, 8> BadSpecifiers;
SmallVector<SourceLocation, 8> BadSpecifierLocs;
SmallVector<StringRef, 8> CPlusPlus20Specifiers;
@@ -791,6 +796,7 @@ Sema::ActOnDecompositionDeclarator(Scope *S, Declarator &D,
BadSpecifiers.push_back("inline");
BadSpecifierLocs.push_back(DS.getInlineSpecLoc());
}
+
if (!BadSpecifiers.empty()) {
auto &&Err = Diag(BadSpecifierLocs.front(), diag::err_decomp_decl_spec);
Err << (int)BadSpecifiers.size()
@@ -851,6 +857,20 @@ Sema::ActOnDecompositionDeclarator(Scope *S, Declarator &D,
D.setInvalidType();
}
+ // Constrained auto is prohibited by [decl.pre]p6, so check that here.
+ if (DS.isConstrainedAuto()) {
+ TemplateIdAnnotation *TemplRep = DS.getRepAsTemplateId();
+ assert(TemplRep->Kind == TNK_Concept_template &&
+ "No other template kind should be possible for a constrained auto");
+
+ SourceRange TemplRange{TemplRep->TemplateNameLoc,
+ TemplRep->RAngleLoc.isValid()
+ ? TemplRep->RAngleLoc
+ : TemplRep->TemplateNameLoc};
+ Diag(TemplRep->TemplateNameLoc, diag::err_decomp_decl_constraint)
+ << TemplRange << FixItHint::CreateRemoval(TemplRange);
+ }
+
// Build the BindingDecls.
SmallVector<BindingDecl*, 8> Bindings;
diff --git a/clang/test/CXX/drs/dr26xx.cpp b/clang/test/CXX/drs/dr26xx.cpp
index 7f590ca4cc1b2..7e8866045a7cd 100644
--- a/clang/test/CXX/drs/dr26xx.cpp
+++ b/clang/test/CXX/drs/dr26xx.cpp
@@ -27,6 +27,34 @@ void f() {
// expected-note@#DR2628_CTOR {{marked deleted here}}
}
+}
+
+namespace dr2635 { // dr2635: yes
+template<typename T>
+concept UnaryC = true;
+template<typename T, typename U>
+concept BinaryC = true;
+
+struct S{ int i, j; };
+S get_S();
+
+template<typename T>
+T get_T();
+
+void use() {
+ // expected-error at +1{{decomposition declaration cannot be declared with constrained 'auto'}}
+ UnaryC auto [a, b] = get_S();
+ // expected-error at +1{{decomposition declaration cannot be declared with constrained 'auto'}}
+ BinaryC<int> auto [c, d] = get_S();
+}
+
+template<typename T>
+void TemplUse() {
+ // expected-error at +1{{decomposition declaration cannot be declared with constrained 'auto'}}
+ UnaryC auto [a, b] = get_T<T>();
+ // expected-error at +1{{decomposition declaration cannot be declared with constrained 'auto'}}
+ BinaryC<T> auto [c, d] = get_T<T>();
+}
}
// dr2636: na
diff --git a/clang/test/FixIt/fixit-constrained-structured-binding.cpp b/clang/test/FixIt/fixit-constrained-structured-binding.cpp
new file mode 100644
index 0000000000000..3f21c1da45a4a
--- /dev/null
+++ b/clang/test/FixIt/fixit-constrained-structured-binding.cpp
@@ -0,0 +1,33 @@
+// RUN: not %clang_cc1 -std=c++20 -fdiagnostics-parseable-fixits -x c++ %s 2> %t
+// RUN: FileCheck %s < %t
+
+template<typename T>
+concept UnaryC = true;
+template<typename T, typename U>
+concept BinaryC = true;
+
+struct S{ int i, j; };
+S get_S();
+
+template<typename T>
+T get_T();
+
+void use() {
+ UnaryC auto [a, b] = get_S();
+ // CHECK: error: decomposition declaration cannot be declared with constrained 'auto'
+ // CHECK: fix-it:{{.*}}:{16:3-16:10}:""
+ BinaryC<int> auto [c, d] = get_S();
+ // CHECK: error: decomposition declaration cannot be declared with constrained 'auto'
+ // CHECK: fix-it:{{.*}}:{19:3-19:16}:""
+}
+
+template<typename T>
+void TemplUse() {
+ UnaryC auto [a, b] = get_T<T>();
+ // CHECK: error: decomposition declaration cannot be declared with constrained 'auto'
+ // XCHECK: fix-it:{{.*}}:{26:3-26:10}:""
+ BinaryC<T> auto [c, d] = get_T<T>();
+ // CHECK: error: decomposition declaration cannot be declared with constrained 'auto'
+ // XCHECK: fix-it:{{.*}}:{29:3-29:14}:""
+}
+
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index a85b966a9f955..678c91313a47e 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -15618,7 +15618,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
<td><a href="https://wg21.link/cwg2635">2635</a></td>
<td>DR</td>
<td>Constrained structured bindings</td>
- <td class="none" align="center">Unknown</td>
+ <td class="unreleased" align="center">Clang 16</td>
</tr>
<tr id="2636">
<td><a href="https://wg21.link/cwg2636">2636</a></td>
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