On 6/29/21 3:25 PM, Marek Polacek wrote:
This patch implements DR2397, which removes the restriction in
[dcl.array]p4 that the array element type may not be a placeholder
type. We don't need to worry about decltype(auto) here, so this
allows code like
int a[3];
auto (*p)[3] = &a;
auto (&r)[3] = a;
However, note that
auto (&&r)[2] = { 1, 2 };
auto arr[2] = { 1, 2 };
still doesn't work (although one day it might) and neither does
int arr[5];
auto x[5] = arr;
given that auto deduction is performed in terms of function template
argument deduction, so the array decays to *.
Bootstrapped/regtested on x86_64-pc-linux-gnu. Does this look OK or
have I missed a case we want to support?
PR c++/100975
DR 2397
gcc/cp/ChangeLog:
* decl.c (create_array_type_for_decl): Allow array of auto.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/auto24.C: Remove dg-error.
* g++.dg/cpp0x/auto3.C: Adjust dg-error.
* g++.dg/cpp0x/auto42.C: Likewise.
* g++.dg/cpp0x/initlist75.C: Likewise.
* g++.dg/cpp0x/initlist80.C: Likewise.
* g++.dg/diagnostic/auto1.C: Remove dg-error.
* g++.dg/cpp23/auto-array.C: New test.
---
gcc/cp/decl.c | 11 --------
gcc/testsuite/g++.dg/cpp0x/auto24.C | 3 ++-
gcc/testsuite/g++.dg/cpp0x/auto3.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/auto42.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/initlist75.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/initlist80.C | 2 +-
gcc/testsuite/g++.dg/cpp23/auto-array.C | 36 +++++++++++++++++++++++++
gcc/testsuite/g++.dg/diagnostic/auto1.C | 3 ++-
8 files changed, 44 insertions(+), 17 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-array.C
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index fa6af6fec11..7672947e64a 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -10969,17 +10969,6 @@ create_array_type_for_decl (tree name, tree type, tree
size, location_t loc)
if (type == error_mark_node || size == error_mark_node)
return error_mark_node;
- /* 8.3.4/1: If the type of the identifier of D contains the auto
- type-specifier, the program is ill-formed. */
- if (type_uses_auto (type))
- {
- if (name)
- error_at (loc, "%qD declared as array of %qT", name, type);
- else
- error ("creating array of %qT", type);
- return error_mark_node;
- }
-
/* If there are some types which cannot be array elements,
issue an error-message and return. */
switch (TREE_CODE (type))
diff --git a/gcc/testsuite/g++.dg/cpp0x/auto24.C
b/gcc/testsuite/g++.dg/cpp0x/auto24.C
index 193f92e977a..ac1ba24f72d 100644
--- a/gcc/testsuite/g++.dg/cpp0x/auto24.C
+++ b/gcc/testsuite/g++.dg/cpp0x/auto24.C
@@ -1,5 +1,6 @@
// PR c++/48599
// { dg-do compile { target c++11 } }
+// Allowed since DR2397.
int v[1];
-auto (*p)[1] = &v; // { dg-error "8:.p. declared as array of .auto" }
+auto (*p)[1] = &v;
diff --git a/gcc/testsuite/g++.dg/cpp0x/auto3.C
b/gcc/testsuite/g++.dg/cpp0x/auto3.C
index 2cd0520023d..56439408a0b 100644
--- a/gcc/testsuite/g++.dg/cpp0x/auto3.C
+++ b/gcc/testsuite/g++.dg/cpp0x/auto3.C
@@ -10,7 +10,7 @@ auto x; // { dg-error "auto" }
auto i = 42, j = 42.0; // { dg-error "auto" }
// New CWG issue
Let's at least update this comment to quote [dcl.type.auto.deduct]/2: "T
shall not be an array type". I guess "unable to deduce" is a suitable
diagnostic for that error.
-auto a[2] = { 1, 2 }; // { dg-error "6:.a. declared as array of
.auto" }
+auto a[2] = { 1, 2 }; // { dg-error "20:unable to deduce" }
template<class T>
struct A { };
diff --git a/gcc/testsuite/g++.dg/cpp0x/auto42.C
b/gcc/testsuite/g++.dg/cpp0x/auto42.C
index 8d15fc96f09..5b2f6779aaf 100644
--- a/gcc/testsuite/g++.dg/cpp0x/auto42.C
+++ b/gcc/testsuite/g++.dg/cpp0x/auto42.C
@@ -5,5 +5,5 @@
void foo(int i)
{
- auto x[1] = { 0 }; // { dg-error "8:.x. declared as array of
.auto" }
+ auto x[1] = { 0 }; // { dg-error "19:unable to deduce" }
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist75.C
b/gcc/testsuite/g++.dg/cpp0x/initlist75.C
index 9a45087c5e4..f572f5181ad 100644
--- a/gcc/testsuite/g++.dg/cpp0x/initlist75.C
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist75.C
@@ -3,4 +3,4 @@
#include <initializer_list>
-auto foo[] = {}; // { dg-error "6:.foo. declared as array of .auto" }
+auto foo[] = {}; // { dg-error "15:unable to deduce" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist80.C
b/gcc/testsuite/g++.dg/cpp0x/initlist80.C
index 15723be16f8..a6ab40ca349 100644
--- a/gcc/testsuite/g++.dg/cpp0x/initlist80.C
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist80.C
@@ -3,4 +3,4 @@
#include <initializer_list>
-auto x[2] = {}; // { dg-error "6:.x. declared as array of .auto" }
+auto x[2] = {}; // { dg-error "14:unable to deduce" }
diff --git a/gcc/testsuite/g++.dg/cpp23/auto-array.C
b/gcc/testsuite/g++.dg/cpp23/auto-array.C
new file mode 100644
index 00000000000..42f2b0c5cf4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/auto-array.C
@@ -0,0 +1,36 @@
+// PR c++/100975
+// DR 2397 - auto specifier for pointers and references to arrays
+// { dg-do compile { target c++11 } }
+
+struct false_type { static constexpr bool value = false; };
+struct true_type { static constexpr bool value = true; };
+template<class T, class U>
+struct is_same : false_type {};
+template<class T>
+struct is_same<T, T> : true_type {};
+
+using U = int[3];
+
+void
+g ()
+{
+ int a[3];
+ auto (*p)[3] = &a;
+ auto (&r)[3] = a;
+ int aa[3][3];
+ auto (*pp)[3][3] = &aa;
+ auto (&rr)[3][3] = aa;
+
+ auto (&&rv)[3] = U{};
+
+ static_assert (is_same<decltype (p), int(*)[3]>::value, "");
+ static_assert (is_same<decltype (pp), int(*)[3][3]>::value, "");
+ static_assert (is_same<decltype (r), int(&)[3]>::value, "");
+ static_assert (is_same<decltype (rv), int(&&)[3]>::value, "");
+ static_assert (is_same<decltype (rr), int(&)[3][3]>::value, "");
+
+#if __cplusplus >= 201402L
+ // In a generic lambda parameter this was OK even before.
+ auto l = [](auto (&arr)[5]) { return arr[0]; };
+#endif
+}
diff --git a/gcc/testsuite/g++.dg/diagnostic/auto1.C
b/gcc/testsuite/g++.dg/diagnostic/auto1.C
index ee2eefd59aa..9d9979e3fdc 100644
--- a/gcc/testsuite/g++.dg/diagnostic/auto1.C
+++ b/gcc/testsuite/g++.dg/diagnostic/auto1.C
@@ -1,4 +1,5 @@
// PR c++/86915
// { dg-do compile { target c++17 } }
+// Allowed since DR2397.
Well, not really; any attempt to use this template should hit the same
problem as above of trying to do auto deduction where T is an array
type. Please add to the testcase to get the error.
-template<auto [1]> struct S; // { dg-error "creating array of .auto." }
+template<auto [1]> struct S;
base-commit: 8a8a7d332d5d01db5aea7336a36d9fd71a679fb1
