[Clang] Add test for CWG2285 "Issues with structured bindings"

[zwuis]

The resolution of CWG2285 adds the point of declaration of a structured binding, and was implemented in bdb84f3 .

Drive-by changes: modify comment and diagnostic messages mentioned in CWG2285.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Yanzuo Liu (zwuis)

Changes

The resolution of CWG2285 adds the point of declaration of a structured binding, and was implemented in bdb84f3 .

Drive-by changes: modify comment mentioned in CWG2285.

---

Full diff: https://github.com/llvm/llvm-project/pull/126421.diff

3 Files Affected:

• (modified) clang/lib/Sema/SemaDeclCXX.cpp (+5-2)
• (modified) clang/test/CXX/drs/cwg22xx.cpp (+14-4)
• (modified) clang/www/cxx_dr_status.html (+1-1)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 0cf02fe6407c24c..7cc67598e4c819f 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -733,8 +733,11 @@ Sema::ActOnDecompositionDeclarator(Scope *S, Declarator &D,
   }
 
   if (!TemplateParamLists.empty()) {
-    // FIXME: There's no rule against this, but there are also no rules that
-    // would actually make it usable, so we reject it for now.
+    // C++17 [temp]/1:
+    //   A template defines a family of class, functions, or variables, or an
+    //   alias for a family of types.
+    //
+    // Structured bindings are not included.
     Diag(TemplateParamLists.front()->getTemplateLoc(),
          diag::err_decomp_decl_template);
     return nullptr;
diff --git a/clang/test/CXX/drs/cwg22xx.cpp b/clang/test/CXX/drs/cwg22xx.cpp
index d93070ef3804dd9..62988e35b963741 100644
--- a/clang/test/CXX/drs/cwg22xx.cpp
+++ b/clang/test/CXX/drs/cwg22xx.cpp
@@ -1,10 +1,10 @@
 // RUN: %clang_cc1 -std=c++98 -triple x86_64-unknown-unknown %s -verify=expected -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11 -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++14 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11 -fexceptions -fcxx-exceptions -pedantic-errors
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11 -fexceptions -fcxx-exceptions -pedantic-errors
-// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11 -fexceptions -fcxx-exceptions -pedantic-errors
-// RUN: %clang_cc1 -std=c++23 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11 -fexceptions -fcxx-exceptions -pedantic-errors
-// RUN: %clang_cc1 -std=c++2c -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11 -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11,since-cxx17 -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11,since-cxx17 -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++23 -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11,since-cxx17 -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -std=c++2c -triple x86_64-unknown-unknown %s -verify=expected,since-cxx11,since-cxx17 -fexceptions -fcxx-exceptions -pedantic-errors
 
 
 namespace cwg2211 { // cwg2211: 8
@@ -196,6 +196,16 @@ void g() {
 #endif
 } // namespace cwg2277
 
+namespace cwg2285 { // cwg2285: 4
+#if __cplusplus >= 201703L
+  void test() {
+    using T = int[1];
+    auto [a] = T{a};
+    // since-cxx17-error@-1 {{binding 'a' cannot appear in the initializer of its own decomposition declaration}}
+  }
+#endif
+} // namespace cwg2285
+
 namespace cwg2292 { // cwg2292: 9
 #if __cplusplus >= 201103L
   template<typename T> using id = T;
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 69ddd5e58b921a8..3fae1c6c6a0620d 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -13537,7 +13537,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/2285.html">2285</a></td>
     <td>CD5</td>
     <td>Issues with structured bindings</td>
-    <td class="unknown" align="center">Unknown</td>
+    <td class="full" align="center">Clang 4</td>
   </tr>
   <tr id="2286">
     <td><a href="https://cplusplus.github.io/CWG/issues/2286.html">2286</a></td>

[Endilll]

It seems that Clang 5 was the first release which exhibits the correct behavior: https://godbolt.org/z/qabGrdvPq

[zwuis]

It seems that Clang 5 was the first release which exhibits the correct behavior: https://godbolt.org/z/qabGrdvPq

-std=c++1z set __cplusplus to 201406L in Clang 4. It was changed to 201703L in 4b0cad0 (Clang 5). We need to remove the #if condition to test corresponding behaviour in Clang 4.

Do I need to add this note in test file?

[Endilll]

You're right, Clang 4 behaves as expected without #if __cplusplus.

Do I need to add this note in test file?

Yes, leave a comment somewhere that Clang 4 doesn't pass the test because of the wrong value of __cplusplus, even though it implements the DR.

[cor3ntin]

LGTM