This patch corrects our handling of array new-expression with ()-init:

  new int[4](1, 2, 3, 4);

should work even with the explicit array bound, and

  new char[3]("so_sad");

should cause an error, but we weren't giving any.

Fixed by handling array new-expressions with ()-init in the same spot
where we deduce the array bound in array new-expression.  I'm now
always passing STRING_CSTs to build_new_1 wrapped in { } which allowed
me to remove the special handling of STRING_CSTs in build_new_1.  And
since the DIRECT_LIST_INIT_P block in build_new_1 calls digest_init, we
report errors about too short arrays.

I took a stab at cp_complete_array_type's "FIXME: this code is duplicated
from reshape_init", but calling reshape_init there, I ran into issues
with has_designator_problem: when we reshape an already reshaped
CONSTRUCTOR again, d.cur.index has been filled, so we think that we
have a user-provided designator (though there was no designator in the
source code), and report an error.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

gcc/cp/ChangeLog:

        PR c++/77841
        * init.c (build_new_1): Don't handle string-initializers here.
        (build_new): Handle new-expression with paren-init when the
        array bound is known.  Always pass string constants to build_new_1
        enclosed in braces.

gcc/testsuite/ChangeLog:

        PR c++/77841
        * g++.old-deja/g++.ext/arrnew2.C: Expect the error only in C++17
        and less.
        * g++.old-deja/g++.robertl/eb58.C: Adjust dg-error.
        * g++.dg/cpp2a/paren-init36.C: New test.
---
 gcc/cp/init.c                                 | 37 ++++++++++---------
 gcc/testsuite/g++.dg/cpp2a/paren-init36.C     | 14 +++++++
 gcc/testsuite/g++.old-deja/g++.ext/arrnew2.C  |  2 +-
 gcc/testsuite/g++.old-deja/g++.robertl/eb58.C |  2 +-
 4 files changed, 35 insertions(+), 20 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/paren-init36.C

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 3268ae4ad3f..537651778b9 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -3596,15 +3596,6 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, 
tree nelts,
                  vecinit = digest_init (arraytype, vecinit, complain);
                }
            }
-         /* This handles code like new char[]{"foo"}.  */
-         else if (len == 1
-                  && char_type_p (TYPE_MAIN_VARIANT (type))
-                  && TREE_CODE (tree_strip_any_location_wrapper ((**init)[0]))
-                     == STRING_CST)
-           {
-             vecinit = (**init)[0];
-             STRIP_ANY_LOCATION_WRAPPER (vecinit);
-           }
          else if (*init)
             {
               if (complain & tf_error)
@@ -3944,9 +3935,9 @@ build_new (location_t loc, vec<tree, va_gc> **placement, 
tree type,
     }
 
   /* P1009: Array size deduction in new-expressions.  */
-  if (TREE_CODE (type) == ARRAY_TYPE
-      && !TYPE_DOMAIN (type)
-      && *init)
+  const bool deduce_array_p = (TREE_CODE (type) == ARRAY_TYPE
+                              && !TYPE_DOMAIN (type));
+  if (*init && (deduce_array_p || (nelts && cxx_dialect >= cxx20)))
     {
       /* This means we have 'new T[]()'.  */
       if ((*init)->is_empty ())
@@ -3955,16 +3946,20 @@ build_new (location_t loc, vec<tree, va_gc> 
**placement, tree type,
          CONSTRUCTOR_IS_DIRECT_INIT (ctor) = true;
          vec_safe_push (*init, ctor);
        }
+      tree array_type = deduce_array_p ? TREE_TYPE (type) : type;
       tree &elt = (**init)[0];
       /* The C++20 'new T[](e_0, ..., e_k)' case allowed by P0960.  */
       if (!DIRECT_LIST_INIT_P (elt) && cxx_dialect >= cxx20)
        {
-         /* Handle new char[]("foo").  */
+         /* Handle new char[]("foo"): turn it into new char[]{"foo"}.  */
          if (vec_safe_length (*init) == 1
-             && char_type_p (TYPE_MAIN_VARIANT (TREE_TYPE (type)))
+             && char_type_p (TYPE_MAIN_VARIANT (array_type))
              && TREE_CODE (tree_strip_any_location_wrapper (elt))
                 == STRING_CST)
-           /* Leave it alone: the string should not be wrapped in {}.  */;
+           {
+             elt = build_constructor_single (init_list_type_node, NULL_TREE, 
elt);
+             CONSTRUCTOR_IS_DIRECT_INIT (elt) = true;
+           }
          else
            {
              tree ctor = build_constructor_from_vec (init_list_type_node, 
*init);
@@ -3977,9 +3972,15 @@ build_new (location_t loc, vec<tree, va_gc> **placement, 
tree type,
            }
        }
       /* Otherwise we should have 'new T[]{e_0, ..., e_k}'.  */
-      if (BRACE_ENCLOSED_INITIALIZER_P (elt))
-       elt = reshape_init (type, elt, complain);
-      cp_complete_array_type (&type, elt, /*do_default*/false);
+      if (deduce_array_p)
+       {
+         /* Don't reshape ELT itself: we want to pass a list-initializer to
+            build_new_1, even for STRING_CSTs.  */
+         tree e = elt;
+         if (BRACE_ENCLOSED_INITIALIZER_P (e))
+           e = reshape_init (type, e, complain);
+         cp_complete_array_type (&type, e, /*do_default*/false);
+       }
     }
 
   /* The type allocated must be complete.  If the new-type-id was
diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init36.C 
b/gcc/testsuite/g++.dg/cpp2a/paren-init36.C
new file mode 100644
index 00000000000..996249515bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/paren-init36.C
@@ -0,0 +1,14 @@
+// PR c++/77841
+// { dg-do compile { target c++20 } }
+
+int *p0 = new int[1]();
+int *p1 = new int[1](1);
+int *p2 = new int[4](1, 2, 3, 4);
+int *p3 = new int[2](1, 2, 3, 4); // { dg-error "too many initializers" }
+
+char *c1 = new char[]("foo");
+char *c2 = new char[4]("foo");
+char *c3 = new char[]{"foo"};
+char *c4 = new char[4]{"foo"};
+char *c5 = new char[3]("so_sad"); // { dg-error "too long" }
+char *c6 = new char[3]{"so_sad"}; // { dg-error "too long" }
diff --git a/gcc/testsuite/g++.old-deja/g++.ext/arrnew2.C 
b/gcc/testsuite/g++.old-deja/g++.ext/arrnew2.C
index aff6b9c7c63..fceb95e9ee5 100644
--- a/gcc/testsuite/g++.old-deja/g++.ext/arrnew2.C
+++ b/gcc/testsuite/g++.old-deja/g++.ext/arrnew2.C
@@ -1,7 +1,7 @@
 // { dg-do compile }
 // { dg-options "-w -fpermissive" }
 
-int *foo = new int[1](42); // { dg-error "parenthesized" }
+int *foo = new int[1](42); // { dg-error "parenthesized" "" { target 
c++17_down } }
 int main ()
 {
   return foo[0] != 42;
diff --git a/gcc/testsuite/g++.old-deja/g++.robertl/eb58.C 
b/gcc/testsuite/g++.old-deja/g++.robertl/eb58.C
index d702296bdc7..1e51e14c51d 100644
--- a/gcc/testsuite/g++.old-deja/g++.robertl/eb58.C
+++ b/gcc/testsuite/g++.old-deja/g++.robertl/eb58.C
@@ -11,5 +11,5 @@ private:
 
 main()
 {
-  A *list = new A[10](4); // { dg-error "parenthesized" }
+  A *list = new A[10](4); // { dg-error "parenthesized|could not convert" }
 }

base-commit: 0dc80505562c89df617ea11c733ee2cfab53c3f7
-- 
2.26.2

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