Consider explicit conversions before aggregate fallback [GH #222]

src/Changes

@@ -1,3 +1,20 @@
+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 f(S s) {
+    D d(s);       // Previously an error in C++20 mode.  Now okay.
+    return D(s);  // Likewise.
+  }
+
+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.
 Version 7.1
 
 10/9/26  [GH #27]

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

@@ -27551,7 +27551,9 @@ will be an lvalue instead of the usual prvalue.
                                   (a_param_type_ptr)NULL,
                                   /*param_type_is_deduced=*/FALSE,
                                   try_user_conversions_in_ovl_res,
-                                  /*allow_expl_conv_funcs=*/FALSE,
+                                  /*allow_expl_conv_funcs=*/
+                                    (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 +1,20 @@
+//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:Explicit conversion functions before aggregate fallback [GH #281]
+// Core issue 899 permits these conversions in C++11 and later.  Previously,
+// C++20 parenthesized aggregate initialization caused spurious errors.
+
+struct D { float x, y; };
+struct S {
+  float x, y;
+  explicit constexpr operator D() const { return D{x, y}; }
+};
+
+D f(S s) {
+  D d(s);       // Previously an error in C++20 mode.  Now okay.
+  return D(s);  // Likewise.
+}
+
+constexpr S s = {1.0f, 2.0f};
+static_assert(D(s).x == 1.0f && D(s).y == 2.0f, "functional cast");

tests/tests/cwg/.899.rto/default.1.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=1 -tused --c++11 Test_name.c
+"Test_name.c", line 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/.899.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 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/.899.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 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/.899.rto/default.4.1.txt

@@ -0,0 +1,10 @@
+fe_only -DTEST_NUMBER=4 -tused --c++20 Test_name.c
+"Test_name.c", line 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/.899.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 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/.899.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 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/.899.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 18: error: no suitable conversion function from "A" to "int" exists
+    int i = a;  // Error: copy-initialization.
+            ^
+
+"Test_name.c", line 20: 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/899.sft.cpp

@@ -0,0 +1,22 @@
+//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 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 i = a;  // Error: copy-initialization.
+  int j(a);   // Okay: direct-initialization.
+  C c = a;    // Error: copy-initialization.
+  C c2(a);    // Okay: direct-initialization (Core issue 899).
+}

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".