Consider explicit conversions before aggregate fallback [GH #222]

src/Changes

@@ -1,5 +1,21 @@
 Version 7.1
 
+10/12/26  [GH #281]
+Explicit conversion functions before parenthesized aggregate initialization
+
+The front end could incorrectly attempt parenthesized aggregate initialization
+instead of considering an explicit conversion function when directly
+initializing an aggregate in C++20 mode.  For example:
+
+  struct D { float x, y; };
+  struct S { explicit operator D() const; };
+  D d(S{});  // Previously an error in C++20 mode.  Now okay.
+
+That is now fixed.  The rule allowing explicit conversion functions in this
+context comes from Core issue 899 and applies in C++11 and later modes.  The
+failure occurred when C++20 parenthesized aggregate initialization was enabled.
+
+
 10/9/26  [GH #27]
 Clearer diagnostic when auto is deduced from an incomplete type
 

src/expr.c

@@ -30702,11 +30702,16 @@ parentheses do not themselves correspond to aggregate initialization).
     an_arg_match_summary  arg_match;
     an_operand            opnd;
     clear_arg_match_summary(&arg_match);
+    /* When matching the first reference parameter of a copy constructor
+       called with one argument in a direct-initialization context, explicit
+       conversion functions are considered (N3092 [over.match.copy]/1,
+       Core issue 899). */
     prep_list_initializer(arg_list, dest_type, /*is_direct_init=*/TRUE,
                           /*check_narrowing=*/FALSE,
                           /*warning_on_narrowing=*/FALSE,
                           CCO_CAST | CCO_FUNC_NOTATION_CAST |
-                          CCO_EXPLICIT_CAST | CCO_DIRECT_INITIALIZATION,
+                          CCO_EXPLICIT_CAST | CCO_DIRECT_INITIALIZATION |
+                          CCO_ALLOW_EXPLICIT_CONV_FUNCTIONS,
                           /*fill_in_dtor=*/TRUE, /*force_temp=*/FALSE,
                           /*make_lvalue_temp=*/FALSE,
                           &opnd, (an_init_state*)NULL, &arg_match);

src/overload.c

@@ -27545,13 +27545,18 @@ will be an lvalue instead of the usual prvalue.
            in this context. */
         arg_match_err = TRUE;
       } else {
+        /* For this tentative match, explicit conversion functions are only
+           considered for direct initialization.  In particular, a temporary
+           created for a braced reference argument is copy-list-initialized. */
         determine_arg_match_level(operand_of_arg_list_elem(icp),
                                   (a_type_ptr)NULL,
                                   dest_type,
                                   (a_param_type_ptr)NULL,
                                   /*param_type_is_deduced=*/FALSE,
                                   try_user_conversions_in_ovl_res,
-                                  /*allow_expl_conv_funcs=*/FALSE,
+                                  is_direct_init &&
+                                  (conv_context &
+                                      CCO_ALLOW_EXPLICIT_CONV_FUNCTIONS) != 0,
                                   arg_match);
       }  /* if */
     } else {

tests/tests/changes/.GH281.rto/default.1.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=1 -tused --c++11 Test_name.c

tests/tests/changes/.GH281.rto/default.2.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=2 -tused --c++11 --gnu_version 160200 Test_name.c

tests/tests/changes/.GH281.rto/default.3.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=3 -tused --c++11 --clang_version 230100 Test_name.c

tests/tests/changes/.GH281.rto/default.4.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=4 -tused --c++20 Test_name.c

tests/tests/changes/.GH281.rto/default.5.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=5 -tused --c++20 --gnu_version 160200 Test_name.c

tests/tests/changes/.GH281.rto/default.6.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=6 -tused --c++20 --clang_version 230100 Test_name.c

tests/tests/changes/.GH281.rto/default.7.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=7 -tused --ms_c++20 --microsoft_version 1950 Test_name.c

tests/tests/changes/GH281.sft.cpp

@@ -0,0 +1,8 @@
+//type:fp
+//options:--c++11:--c++11 --gnu_version 160200:--c++11 --clang_version 230100:--c++20:--c++20 --gnu_version 160200:--c++20 --clang_version 230100:--ms_c++20 --microsoft_version 1950
+//options_all:-tused
+//remark:Explicit conversion functions before aggregate fallback [GH #281]
+
+struct D { float x, y; };
+struct S { explicit operator D() const; };
+D d(S{});  // Error, now okay.

tests/tests/cwg/.cwg899.rto/default.1.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=1 -tused --c++11 Test_name.c

tests/tests/cwg/.cwg899.rto/default.2.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=2 -tused --c++11 --gnu_version 160200 Test_name.c

tests/tests/cwg/.cwg899.rto/default.3.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=3 -tused --c++11 --clang_version 230100 Test_name.c

tests/tests/cwg/.cwg899.rto/default.4.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=4 -tused --c++20 Test_name.c

tests/tests/cwg/.cwg899.rto/default.5.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=5 -tused --c++20 --gnu_version 160200 Test_name.c

tests/tests/cwg/.cwg899.rto/default.6.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=6 -tused --c++20 --clang_version 230100 Test_name.c

tests/tests/cwg/.cwg899.rto/default.7.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=7 -tused --ms_c++20 --microsoft_version 1950 Test_name.c

tests/tests/cwg/.cwg899b.rto/default.1.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=1 -tused --c++11 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/.cwg899b.rto/default.2.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=2 -tused --c++11 --gnu_version 160200 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/.cwg899b.rto/default.3.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=3 -tused --c++11 --clang_version 230100 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/.cwg899b.rto/default.4.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=4 -tused --c++20 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/.cwg899b.rto/default.5.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=5 -tused --c++20 --gnu_version 160200 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/.cwg899b.rto/default.6.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=6 -tused --c++20 --clang_version 230100 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/.cwg899b.rto/default.7.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=7 -tused --ms_c++20 --microsoft_version 1950 Test_name.c
+"Test_name.c", line 13: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 14: error: no suitable user-defined conversion from "A" to "C" exists
+    C c = a;    // Error: copy-initialization.
+          ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/cwg/cwg899.sft.cpp

@@ -0,0 +1,20 @@
+//type:fp
+//options:--c++11:--c++11 --gnu_version 160200:--c++11 --clang_version 230100:--c++20:--c++20 --gnu_version 160200:--c++20 --clang_version 230100:--ms_c++20 --microsoft_version 1950
+//options_all:-tused
+//remark:Core issue 899: Explicit conversion functions in direct class initialization
+
+struct C { };
+struct A {
+  explicit operator int() const;
+  explicit operator C() const;
+};
+
+struct B {
+  int i;
+  B(const A& a): i(a) { }  // Okay.
+};
+
+void f(A a) {
+  int j(a);   // Okay: direct-initialization.
+  C c2(a);    // Okay: direct-initialization (Core issue 899).
+}

tests/tests/cwg/cwg899b.sft.cpp

@@ -0,0 +1,15 @@
+//type:fn
+//options:--c++11:--c++11 --gnu_version 160200:--c++11 --clang_version 230100:--c++20:--c++20 --gnu_version 160200:--c++20 --clang_version 230100:--ms_c++20 --microsoft_version 1950
+//options_all:-tused
+//remark:Core issue 899: Explicit conversion functions in copy-initialization
+
+struct C { };
+struct A {
+  explicit operator int() const;
+  explicit operator C() const;
+};
+
+void f(A a) {
+  int i = a;  // Error: copy-initialization.
+  C c = a;    // Error: copy-initialization.
+}

tests/tests/imported/clang/cpp/SemaCXX/.cxx2a-explicit-bool.rto/default.2.1.txt

@@ -476,14 +476,6 @@ fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
   Y y2 = z; // expected-error {{no viable conversion}}
          ^
 
-"Test_name.c", line 530: error: too many initializer values
-  Y y2b(z);
-        ^
-
-"Test_name.c", line 532: error: too many initializer values
-  Y y4 = Y(z);
-           ^
-
 "Test_name.c", line 540: error: no suitable user-defined conversion from "conversion3::Z<true>" to "const conversion3::Y" exists
   const Y& y6 = z; // expected-error {{no viable conversion}}
                 ^
@@ -683,4 +675,4 @@ fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     explicit(ptr) S(long);             // expected-error {{conversion from 'const int *' to 'bool' is not allowed in a converted constant expression}}
              ^
 
-121 errors detected in the compilation of "Test_name.c".
+119 errors detected in the compilation of "Test_name.c".

tests/tests/imported/clang/cpp/SemaCXX/.explicit.rto/default.2.1.txt

@@ -23,14 +23,6 @@ fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
       Y y2 = z; // expected-error {{no viable conversion from 'Z' to 'Y'}}
              ^
 
-"Test_name.c", line 90: error: too many initializer values
-      Y y2b(z);
-            ^
-
-"Test_name.c", line 92: error: too many initializer values
-      Y y4 = Y(z);
-               ^
-
 "Test_name.c", line 100: error: no suitable user-defined conversion from "Z" to "const Y" exists
       const Y& y6 = z; // expected-error {{no viable conversion from 'Z' to 'const Y'}}
                     ^
@@ -171,4 +163,4 @@ fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
         switch(EC){}
                ^
 
-31 errors detected in the compilation of "Test_name.c".
+29 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-222.rto/default.1.1.txt

@@ -0,0 +1,24 @@
+fe_only -DTEST_NUMBER=1 -tused --c++11 Test_name.c
+"Test_name.c", line 15: error: no instance of overloaded function "f" matches the argument list
+            argument types are: ({...})
+  int i = f({A{}});  // Error: cannot copy-list-initialize the temporary int.
+          ^
+"Test_name.c", line 7: note: function "f(int *)" does not match because argument #1 does not match parameter
+  int f(int*);
+      ^
+"Test_name.c", line 6: note: function "f(int &&)" does not match because argument #1 does not match parameter
+  int f(int&&);
+      ^
+
+"Test_name.c", line 16: error: no instance of overloaded function "g" matches the argument list
+            argument types are: ({...})
+  int j = g({A{}});  // Likewise for a const lvalue reference.
+          ^
+"Test_name.c", line 9: note: function "g(int *)" does not match because argument #1 does not match parameter
+  int g(int*);
+      ^
+"Test_name.c", line 8: note: function "g(const int &)" does not match because argument #1 does not match parameter
+  int g(const int&);
+      ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-222.rto/default.2.1.txt

@@ -0,0 +1,24 @@
+fe_only -DTEST_NUMBER=2 -tused --c++11 --gnu_version 160200 Test_name.c
+"Test_name.c", line 15: error: no instance of overloaded function "f" matches the argument list
+            argument types are: ({...})
+  int i = f({A{}});  // Error: cannot copy-list-initialize the temporary int.
+          ^
+"Test_name.c", line 7: note: function "f(int *)" does not match because argument #1 does not match parameter
+  int f(int*);
+      ^
+"Test_name.c", line 6: note: function "f(int &&)" does not match because argument #1 does not match parameter
+  int f(int&&);
+      ^
+
+"Test_name.c", line 16: error: no instance of overloaded function "g" matches the argument list
+            argument types are: ({...})
+  int j = g({A{}});  // Likewise for a const lvalue reference.
+          ^
+"Test_name.c", line 9: note: function "g(int *)" does not match because argument #1 does not match parameter
+  int g(int*);
+      ^
+"Test_name.c", line 8: note: function "g(const int &)" does not match because argument #1 does not match parameter
+  int g(const int&);
+      ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-222.rto/default.3.1.txt

@@ -0,0 +1,24 @@
+fe_only -DTEST_NUMBER=3 -tused --c++11 --clang_version 230100 Test_name.c
+"Test_name.c", line 15: error: no instance of overloaded function "f" matches the argument list
+            argument types are: ({...})
+  int i = f({A{}});  // Error: cannot copy-list-initialize the temporary int.
+          ^
+"Test_name.c", line 7: note: function "f(int *)" does not match because argument #1 does not match parameter
+  int f(int*);
+      ^
+"Test_name.c", line 6: note: function "f(int &&)" does not match because argument #1 does not match parameter
+  int f(int&&);
+      ^
+
+"Test_name.c", line 16: error: no instance of overloaded function "g" matches the argument list
+            argument types are: ({...})
+  int j = g({A{}});  // Likewise for a const lvalue reference.
+          ^
+"Test_name.c", line 9: note: function "g(int *)" does not match because argument #1 does not match parameter
+  int g(int*);
+      ^
+"Test_name.c", line 8: note: function "g(const int &)" does not match because argument #1 does not match parameter
+  int g(const int&);
+      ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-222.rto/default.4.1.txt

@@ -0,0 +1,24 @@
+fe_only -DTEST_NUMBER=4 -tused --c++20 Test_name.c
+"Test_name.c", line 15: error: no instance of overloaded function "f" matches the argument list
+            argument types are: ({...})
+  int i = f({A{}});  // Error: cannot copy-list-initialize the temporary int.
+          ^
+"Test_name.c", line 7: note: function "f(int *)" does not match because argument #1 does not match parameter
+  int f(int*);
+      ^
+"Test_name.c", line 6: note: function "f(int &&)" does not match because argument #1 does not match parameter
+  int f(int&&);
+      ^
+
+"Test_name.c", line 16: error: no instance of overloaded function "g" matches the argument list
+            argument types are: ({...})
+  int j = g({A{}});  // Likewise for a const lvalue reference.
+          ^
+"Test_name.c", line 9: note: function "g(int *)" does not match because argument #1 does not match parameter
+  int g(int*);
+      ^
+"Test_name.c", line 8: note: function "g(const int &)" does not match because argument #1 does not match parameter
+  int g(const int&);
+      ^
+
+2 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-222.rto/default.5.1.txt

@@ -0,0 +1,24 @@
+fe_only -DTEST_NUMBER=5 -tused --c++20 --gnu_version 160200 Test_name.c
+"Test_name.c", line 15: error: no instance of overloaded function "f" matches the argument list
+            argument types are: ({...})
+  int i = f({A{}});  // Error: cannot copy-list-initialize the temporary int.
+          ^
+"Test_name.c", line 7: note: function "f(int *)" does not match because argument #1 does not match parameter
+  int f(int*);
+      ^
+"Test_name.c", line 6: note: function "f(int &&)" does not match because argument #1 does not match parameter
+  int f(int&&);
+      ^
+
+"Test_name.c", line 16: error: no instance of overloaded function "g" matches the argument list
+            argument types are: ({...})
+  int j = g({A{}});  // Likewise for a const lvalue reference.
+          ^
+"Test_name.c", line 9: note: function "g(int *)" does not match because argument #1 does not match parameter
+  int g(int*);
+      ^
+"Test_name.c", line 8: note: function "g(const int &)" does not match because argument #1 does not match parameter
+  int g(const int&);
+      ^
+
+2 errors detected in the compilation of "Test_name.c".