Count the characters, not the bytes, of a string literal initializer of an array new-expression in constant evaluation [GH #501]

src/interpret.c

@@ -26825,8 +26825,10 @@ Evaluate the given new-expression.
               a_constant_ptr  cp = init_cp->variant.aggregate.first_constant;
               for (; cp != NULL; cp = cp->next) ++n_init_elems;
             } else {
-              /* ck_string case. */
-              n_init_elems = init_cp->variant.string.length;
+              /* ck_string case (whose length is in bytes). */
+              a_type_ptr  etp = skip_typerefs(
+                                         init_tp->variant.array.element_type);
+              n_init_elems = init_cp->variant.string.length / etp->size;
             }  /* if */
             if (n_init_elems > orig_alloc_length) {
               info_with_pos_num(ec_constexpr_alloc_too_small,

src/pending_changes/gh-501-array-new-wide-string.txt

@@ -0,0 +1,15 @@
+[GH #501]
+Array new with a wide string literal initializer in constant evaluation
+
+During constant evaluation, the initializer of an array new-expression that is
+a string literal of a character type wider than one byte (e.g., wchar_t) was
+treated as having as many elements as the literal has bytes, so a large enough
+array could be diagnosed as too small for it.  For example:
+
+  constexpr int f(int n) {
+    auto p = new wchar_t[n]{L"ab"};
+    int r = p[1];
+    delete[] p;
+    return r;
+  }
+  static_assert(f(3) == L'b');  // Previously an error; now okay.

tests/tests/regressions/.gh-501-neg.rto/default.1.1.txt

@@ -0,0 +1,9 @@
+fe_only -DTEST_NUMBER=1 --c++20 Test_name.c
+"Test_name.c", line 11: error: expression must have a constant value
+  static_assert(g(2) == L'b');  // Error: too few elements for the initializer.
+                ^
+"Test_name.c", line 6: note: number of dynamically-allocated elements (2) too small for initializer
+    auto p = new wchar_t[n]{L"ab"};
+                         ^
+
+1 error detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-501.rto/default.1.1.txt

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

tests/tests/regressions/gh-501-neg.sft.cpp

@@ -0,0 +1,11 @@
+//type:fn
+//options_all:--c++20
+//remark:Array new with a too-long wide string literal initializer
+
+constexpr int g(int n) {
+  auto p = new wchar_t[n]{L"ab"};
+  int r = p[1];
+  delete[] p;
+  return r;
+}
+static_assert(g(2) == L'b');  // Error: too few elements for the initializer.

tests/tests/regressions/gh-501.sft.cpp

@@ -0,0 +1,26 @@
+//type:fp
+//options_all:--c++20
+//remark:Constexpr array new with a wide string literal initializer
+
+// The number of elements of a string literal initializer is compared with the
+// number of allocated elements, regardless of the character size.
+constexpr int g(int n) {
+  auto p = new wchar_t[n]{L"ab"};
+  int r = p[1] + p[n - 1];
+  delete[] p;
+  return r;
+}
+static_assert(g(3) == L'b');
+static_assert(g(4) == L'b');
+
+constexpr int h(int n) {
+  auto p16 = new char16_t[n]{u"ab"};
+  auto p32 = new char32_t[n]{U"ab"};
+  auto p8 = new char8_t[n]{u8"ab"};
+  int r = (p16[1] == u'b') + (p32[1] == U'b') + (p8[1] == u8'b');
+  delete[] p16;
+  delete[] p32;
+  delete[] p8;
+  return r;
+}
+static_assert(h(3) == 3);