[Clang][Diagnostics] Use "structured binding" instead of "decomposition" (#163101)

[P0615R0](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0615r0.html)
changed the term "decomposition" to "structured binding". Some
diagnostic messages were created before this paper. These messages
should be updated using "structured binding" to avoid making users
confused.

Closes #157880

---------

Co-authored-by: foxfromabyss <[email protected]>
Co-authored-by: Sirraide <[email protected]>

Author: 3 people

clang-tools-extra/test/clang-tidy/checkers/misc/misplaced-const-cxx17.cpp

@@ -3,7 +3,7 @@
 // This test previously would cause a failed assertion because the structured
 // binding declaration had no valid type associated with it. This ensures the
 // expected clang diagnostic is generated instead.
-// CHECK-MESSAGES: :[[@LINE+1]]:6: error: decomposition declaration '[x]' requires an initializer [clang-diagnostic-error]
+// CHECK-MESSAGES: :[[@LINE+1]]:6: error: structured binding declaration '[x]' requires an initializer [clang-diagnostic-error]
 auto [x];
 
 struct S { int a; };

clang/docs/ReleaseNotes.rst

@@ -304,6 +304,8 @@ Attribute Changes in Clang
 
 Improvements to Clang's diagnostics
 -----------------------------------
+- Diagnostics messages now refer to ``structured binding`` instead of ``decomposition``,
+  to align with `P0615R0 <https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0615r0.html>`_ changing the term. (#GH157880)
 - Added a separate diagnostic group ``-Wfunction-effect-redeclarations``, for the more pedantic
   diagnostics for function effects (``[[clang::nonblocking]]`` and ``[[clang::nonallocating]]``).
   Moved the warning for a missing (though implied) attribute on a redeclaration into this group.

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -505,7 +505,7 @@ def err_expected_coloncolon_after_super : Error<
   "expected '::' after '__super'">;
 
 def ext_decomp_decl_empty : ExtWarn<
-  "ISO C++17 does not allow a decomposition group to be empty">,
+  "ISO C++17 does not allow a structured binding group to be empty">,
   InGroup<DiagGroup<"empty-decomposition">>;
 
 def err_function_parameter_limit_exceeded : Error<

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -31,12 +31,12 @@ defm constexpr_body_multiple_return : CXX14Compat<
 defm variable_template : CXX14Compat<"variable templates are">;
 
 // C++17 compatibility with C++14 and earlier.
-defm decomp_decl : CXX17Compat<"decomposition declarations are">;
+defm decomp_decl : CXX17Compat<"structured binding declarations are">;
 defm inline_variable : CXX17Compat<"inline variables are">;
 
 // C++20 compatibility with C++17 and earlier.
 defm decomp_decl_spec
-    : CXX20Compat<"decomposition declaration declared '%0' is">;
+    : CXX20Compat<"structured binding declaration declared '%0' is">;
 defm constexpr_local_var_no_init : CXX20Compat<
   "uninitialized variable in a constexpr %select{function|constructor}0 is">;
 defm constexpr_function_try_block : CXX20Compat<
@@ -591,58 +591,58 @@ def warn_modifying_shadowing_decl :
 
 // C++ decomposition declarations
 def err_decomp_decl_context : Error<
-  "decomposition declaration not permitted in this context">;
+  "structured binding declaration not permitted in this context">;
 def err_decomp_decl_spec
-    : Error<"decomposition declaration cannot be declared '%0'">;
+    : Error<"structured binding declaration cannot be declared '%0'">;
 def err_decomp_decl_type : Error<
-  "decomposition declaration cannot be declared with type %0; "
+  "structured binding 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'">;
+  "structured binding declaration cannot be declared with constrained 'auto'">;
 def err_decomp_decl_parens : Error<
-  "decomposition declaration cannot be declared with parentheses">;
+  "structured binding declaration cannot be declared with parentheses">;
 def err_decomp_decl_template : Error<
-  "decomposition declaration cannot be a template">;
+  "structured binding declaration cannot be a template">;
 def err_decomp_decl_not_alone : Error<
-  "decomposition declaration must be the only declaration in its group">;
+  "structured binding declaration must be the only declaration in its group">;
 def err_decomp_decl_requires_init : Error<
-  "decomposition declaration %0 requires an initializer">;
+  "structured binding declaration %0 requires an initializer">;
 def err_decomp_decl_wrong_number_bindings : Error<
-  "type %0 decomposes into %3 %plural{1:element|:elements}2, but "
+  "type %0 binds to %3 %plural{1:element|:elements}2, but "
   "%select{%plural{0:no|:only %1}1|%1}4 "
   "%plural{1:name was|:names were}1 provided">;
 def err_decomp_decl_unbindable_type : Error<
-  "cannot decompose %select{union|non-class, non-array}1 type %2">;
+  "cannot bind %select{union|non-class, non-array}1 type %2">;
 def err_decomp_decl_multiple_bases_with_members : Error<
-  "cannot decompose class type %1: "
+  "cannot bind class type %1: "
   "%select{its base classes %2 and|both it and its base class}0 %3 "
   "have non-static data members">;
 def err_decomp_decl_ambiguous_base : Error<
-  "cannot decompose members of ambiguous base class %1 of %0:%2">;
+  "cannot bind members of ambiguous base class %1 of %0:%2">;
 def err_decomp_decl_inaccessible_base : Error<
-  "cannot decompose members of inaccessible base class %1 of %0">,
+  "cannot bind members of inaccessible base class %1 of %0">,
   AccessControl;
 def err_decomp_decl_inaccessible_field : Error<
-  "cannot decompose %select{private|protected}0 member %1 of %3">,
+  "cannot bind %select{private|protected}0 member %1 of %3">,
   AccessControl;
 def err_decomp_decl_lambda : Error<
-  "cannot decompose lambda closure type">;
+  "cannot bind lambda closure type">;
 def err_decomp_decl_anon_union_member : Error<
-  "cannot decompose class type %0 because it has an anonymous "
+  "cannot bind class type %0 because it has an anonymous "
   "%select{struct|union}1 member">;
 def err_decomp_decl_std_tuple_element_not_specialized : Error<
-  "cannot decompose this type; 'std::tuple_element<%0>::type' "
+  "cannot bind this type; 'std::tuple_element<%0>::type' "
   "does not name a type">;
 def err_decomp_decl_std_tuple_size_not_constant : Error<
-  "cannot decompose this type; 'std::tuple_size<%0>::value' "
+  "cannot bind this type; 'std::tuple_size<%0>::value' "
   "is not a valid integral constant expression">;
 def err_decomp_decl_std_tuple_size_invalid
-    : Error<"cannot decompose this type; 'std::tuple_size<%0>::value' "
+    : Error<"cannot bind this type; 'std::tuple_size<%0>::value' "
             "is not a valid size: %1">;
 def note_in_binding_decl_init : Note<
   "in implicit initialization of binding declaration %0">;
 def err_arg_is_not_destructurable : Error<
-  "type %0 cannot be decomposed">;
+  "type %0 cannot be bound">;
 
 def err_std_type_trait_not_class_template : Error<
   "unsupported standard library implementation: "
@@ -2620,7 +2620,7 @@ def err_auto_variable_cannot_appear_in_own_initializer
           "declared with deduced type %2 cannot appear in its own initializer">;
 def err_binding_cannot_appear_in_own_initializer : Error<
   "binding %0 cannot appear in the initializer of its own "
-  "decomposition declaration">;
+  "structured binding declaration">;
 def err_new_array_of_auto : Error<
   "cannot allocate array of 'auto'">;
 def err_auto_not_allowed : Error<

clang/test/Analysis/zero-size-non-pod-array.cpp

@@ -95,7 +95,7 @@ void zeroSizeArrayBinding() {
     // Note: This is an error in gcc but a warning in clang.
     // In MSVC the declaration of 'S arr[0]' is already an error
     // and it doesn't recognize this syntax as a structured binding.
-    auto [] = arr; //expected-warning{{ISO C++17 does not allow a decomposition group to be empty}}
+    auto [] = arr; //expected-warning{{ISO C++17 does not allow a structured binding group to be empty}}
 
     clang_analyzer_eval(S::CtorInvocationCount == 0); //expected-warning{{TRUE}}
 }

clang/test/CXX/dcl.decl/dcl.decomp/p2.cpp

@@ -16,8 +16,8 @@ int array() {
   using X3 = X[3];
   auto [a3, b3, c3] = X3{1, 2, 3};
 
-  auto &[d, e] = arr; // expected-error {{type 'int[3]' decomposes into 3 elements, but only 2 names were provided}}
-  auto &[f, g, h, i] = arr; // expected-error {{type 'int[3]' decomposes into 3 elements, but 4 names were provided}}
+  auto &[d, e] = arr; // expected-error {{type 'int[3]' binds to 3 elements, but only 2 names were provided}}
+  auto &[f, g, h, i] = arr; // expected-error {{type 'int[3]' binds to 3 elements, but 4 names were provided}}
 
   auto &[r0, r1, r2] = arr;
   const auto &[cr0, cr1, cr2] = arr;

clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp

@@ -5,26 +5,26 @@ using size_t = decltype(sizeof(0));
 struct A { int x, y; };
 struct B { int x, y; };
 
-void no_tuple_size_1() { auto [x, y] = A(); } // ok, decompose elementwise
+void no_tuple_size_1() { auto [x, y] = A(); } // ok, bind elementwise
 
 namespace std { template<typename T> struct tuple_size; }
-void no_tuple_size_2() { auto [x, y] = A(); } // ok, decompose elementwise
+void no_tuple_size_2() { auto [x, y] = A(); } // ok, bind elementwise
 
 struct Bad1 { int a, b; };
 template<> struct std::tuple_size<Bad1> {};
 void no_tuple_size_3() { auto [x, y] = Bad1(); } // ok, omitting value is valid after DR2386
 
 struct Bad2 {};
 template<> struct std::tuple_size<Bad2> { const int value = 5; };
-void no_tuple_size_4() { auto [x, y] = Bad2(); } // expected-error {{cannot decompose this type; 'std::tuple_size<Bad2>::value' is not a valid integral constant expression}}
+void no_tuple_size_4() { auto [x, y] = Bad2(); } // expected-error {{cannot bind this type; 'std::tuple_size<Bad2>::value' is not a valid integral constant expression}}
 
 template<> struct std::tuple_size<A> { static const int value = 3; };
 template<> struct std::tuple_size<B> { enum { value = 3 }; };
 
 void no_get_1() {
   {
-    auto [a0, a1] = A(); // expected-error {{decomposes into 3 elements}}
-    auto [b0, b1] = B(); // expected-error {{decomposes into 3 elements}}
+    auto [a0, a1] = A(); // expected-error {{binds to 3 elements}}
+    auto [b0, b1] = B(); // expected-error {{binds to 3 elements}}
   }
   auto [a0, a1, a2] = A(); // expected-error {{undeclared identifier 'get'}} expected-note {{in implicit initialization of binding declaration 'a0'}}
 }

clang/test/CXX/dcl.decl/dcl.decomp/p4.cpp

@@ -25,10 +25,10 @@ namespace NonPublicMembers {
   struct NonPublic4 : NonPublic2 {};
 
   void test() {
-    auto [a1] = NonPublic1(); // expected-error {{cannot decompose protected member 'a' of 'NonPublicMembers::NonPublic1'}}
-    auto [a2] = NonPublic2(); // expected-error {{cannot decompose private member 'a' of 'NonPublicMembers::NonPublic2'}}
-    auto [a3] = NonPublic3(); // expected-error {{cannot decompose members of inaccessible base class 'A' of 'NonPublicMembers::NonPublic3'}}
-    auto [a4] = NonPublic4(); // expected-error {{cannot decompose private member 'a' of 'NonPublicMembers::NonPublic2'}}
+    auto [a1] = NonPublic1(); // expected-error {{cannot bind protected member 'a' of 'NonPublicMembers::NonPublic1'}}
+    auto [a2] = NonPublic2(); // expected-error {{cannot bind private member 'a' of 'NonPublicMembers::NonPublic2'}}
+    auto [a3] = NonPublic3(); // expected-error {{cannot bind members of inaccessible base class 'A' of 'NonPublicMembers::NonPublic3'}}
+    auto [a4] = NonPublic4(); // expected-error {{cannot bind private member 'a' of 'NonPublicMembers::NonPublic2'}}
   }
 }
 
@@ -46,8 +46,8 @@ namespace AnonymousMember {
   };
 
   void test() {
-    auto [a1] = Struct(); // expected-error {{cannot decompose class type 'Struct' because it has an anonymous struct member}}
-    auto [a2] = Union(); // expected-error {{cannot decompose class type 'Union' because it has an anonymous union member}}
+    auto [a1] = Struct(); // expected-error {{cannot bind class type 'Struct' because it has an anonymous struct member}}
+    auto [a2] = Union(); // expected-error {{cannot bind class type 'Union' because it has an anonymous union member}}
   }
 }
 
@@ -73,12 +73,12 @@ namespace MultipleClasses {
   struct M : virtual J, L {};
 
   void test() {
-    auto [b] = B(); // expected-error {{cannot decompose class type 'B': both it and its base class 'A' have non-static data members}}
-    auto [d] = D(); // expected-error {{cannot decompose class type 'D': its base classes 'A' and 'C' have non-static data members}}
+    auto [b] = B(); // expected-error {{cannot bind class type 'B': both it and its base class 'A' have non-static data members}}
+    auto [d] = D(); // expected-error {{cannot bind class type 'D': its base classes 'A' and 'C' have non-static data members}}
     auto [e] = E();
-    auto [f] = F(); // expected-error-re {{cannot decompose members of ambiguous base class 'A' of 'F':{{.*}}struct MultipleClasses::F -> A{{.*}}struct MultipleClasses::F -> E -> A}}
+    auto [f] = F(); // expected-error-re {{cannot bind members of ambiguous base class 'A' of 'F':{{.*}}struct MultipleClasses::F -> A{{.*}}struct MultipleClasses::F -> E -> A}}
     auto [h] = H(); // ok, only one (virtual) base subobject even though there are two paths to it
-    auto [k] = K(); // expected-error {{cannot decompose members of ambiguous base class 'I'}}
+    auto [k] = K(); // expected-error {{cannot bind members of ambiguous base class 'I'}}
     auto [m] = M(); // ok, all paths to I are through the same virtual base subobject J
 
     same<decltype(m), int>();
@@ -214,7 +214,7 @@ namespace p0969r0 {
     auto &[x, y] = b;
   }
   void test_external(B b) {
-    auto &[x, y] = b; // expected-error {{cannot decompose members of inaccessible base class 'A' of 'p0969r0::B'}}
+    auto &[x, y] = b; // expected-error {{cannot bind members of inaccessible base class 'A' of 'p0969r0::B'}}
   }
 
   struct C {
@@ -229,13 +229,13 @@ namespace p0969r0 {
   struct D : C {
     static void test_member(D d, C c) {
       auto &[x1, y1] = d;
-      auto &[x2, y2] = c; // expected-error {{cannot decompose protected member 'y' of 'p0969r0::C'}}
+      auto &[x2, y2] = c; // expected-error {{cannot bind protected member 'y' of 'p0969r0::C'}}
     }
   };
   void test_friend(D d) {
     auto &[x, y] = d;
   }
   void test_external(D d) {
-    auto &[x, y] = d; // expected-error {{cannot decompose protected member 'y' of 'p0969r0::C'}}
+    auto &[x, y] = d; // expected-error {{cannot bind protected member 'y' of 'p0969r0::C'}}
   }
 }

clang/test/CXX/drs/cwg22xx.cpp

@@ -202,7 +202,7 @@ namespace cwg2285 { // cwg2285: 4
   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}}
+    // since-cxx17-error@-1 {{binding 'a' cannot appear in the initializer of its own structured binding declaration}}
   }
 #endif
 } // namespace cwg2285

clang/test/CXX/drs/cwg23xx.cpp

@@ -440,7 +440,7 @@ template <> struct tuple_size<cwg2386::Bad2> {
 namespace cwg2386 {
 void no_value() { auto [x, y] = Bad1(); }
 void wrong_value() { auto [x, y] = Bad2(); }
-// since-cxx17-error@-1 {{type 'Bad2' decomposes into 42 elements, but only 2 names were provided}}
+// since-cxx17-error@-1 {{type 'Bad2' binds to 42 elements, but only 2 names were provided}}
 #endif
 } // namespace cwg2386