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* [PATCH] c++: Relax rules for non-type arguments in partial specs [CWG1315]
@ 2021-05-26 23:36 Patrick Palka
  2021-05-27 13:22 ` Jason Merrill
  0 siblings, 1 reply; 2+ messages in thread
From: Patrick Palka @ 2021-05-26 23:36 UTC (permalink / raw)
  To: gcc-patches

This implements the wording changes of CWG 1315, which permits non-type
template arguments in a partial specialization to use template
parameters more freely.  Delightfully, it seems the only change needed
is to remove a few checks from process_partial_specialization.

But that change alone revealed a latent problem with
for_each_template_parm: it ends up looking into some non-deduced
contexts even when include_nondeduced_p is false.  This causes us to
silently accept some partial specializations within the testsuite that
contain non-deducible non-type template parameters (and that were
previously rejected due to the rule that CWG 1315 removed).  For now
this patch makes a minimal amount of changes to for_each_template_parm_r
so we continue to reject existing ill-formed partial specializations
within the testsuite.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?  Patch generated with -w to hide noisy whitespace changes.

	DR 1315
	PR c++/96555
	PR c++/100779

gcc/cp/ChangeLog:

	* pt.c (process_partial_specialization): Don't error on a
	non-simple non-type template argument that involves template
	parameters.
	(for_each_template_parm_r): Don't walk TRAIT_EXPR, PLUS_EXPR,
	MULT_EXPR, or SCOPE_REF when include_nondeduced_p is unset.

gcc/testsuite/ChangeLog:

	* g++.dg/template/partial16.C: New test.
	* g++.dg/template/partial17.C: New test.
	* g++.dg/template/partial18.C: New test.
	* g++.dg/cpp0x/pr68724.C: Adjust expected diagnostic for
	  ill-formed partial specialization.
	* g++.dg/cpp0x/variadic38.C: Likewise.
	* g++.dg/cpp1z/pr81016.C: Likewise.
	* g++.dg/template/partial5.C: Likewise.
	* g++.old-deja/g++.pt/spec21.C: Likewise.
---
 gcc/cp/pt.c                                | 28 ++++++++--------------
 gcc/testsuite/g++.dg/cpp0x/pr68724.C       |  2 +-
 gcc/testsuite/g++.dg/cpp0x/variadic38.C    |  3 ++-
 gcc/testsuite/g++.dg/cpp1z/pr81016.C       |  2 +-
 gcc/testsuite/g++.dg/template/partial16.C  |  8 +++++++
 gcc/testsuite/g++.dg/template/partial17.C  | 14 +++++++++++
 gcc/testsuite/g++.dg/template/partial18.C  | 19 +++++++++++++++
 gcc/testsuite/g++.dg/template/partial5.C   |  2 +-
 gcc/testsuite/g++.old-deja/g++.pt/spec21.C |  3 +--
 9 files changed, 57 insertions(+), 24 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/partial16.C
 create mode 100644 gcc/testsuite/g++.dg/template/partial17.C
 create mode 100644 gcc/testsuite/g++.dg/template/partial18.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index f3fa9c192ad..6b0bc815404 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -5157,11 +5157,7 @@ process_partial_specialization (tree decl)
 		maintmpl);
     }
 
-  /* [temp.class.spec]
-
-     A partially specialized non-type argument expression shall not
-     involve template parameters of the partial specialization except
-     when the argument expression is a simple identifier.
+  /* [temp.spec.partial]
 
      The type of a template parameter corresponding to a specialized
      non-type argument shall not be dependent on a parameter of the
@@ -5221,13 +5217,6 @@ process_partial_specialization (tree decl)
 	      && !((REFERENCE_REF_P (arg)
 		    || TREE_CODE (arg) == VIEW_CONVERT_EXPR)
 		   && TREE_CODE (TREE_OPERAND (arg, 0)) == TEMPLATE_PARM_INDEX))
-            {
-              if ((!packed_args && tpd.arg_uses_template_parms[i])
-                  || (packed_args && uses_template_parms (arg)))
-		error_at (cp_expr_loc_or_input_loc (arg),
-			  "template argument %qE involves template "
-			  "parameter(s)", arg);
-              else 
             {
 	      /* Look at the corresponding template parameter,
 		 marking which template parameters its type depends
@@ -5281,7 +5270,6 @@ process_partial_specialization (tree decl)
             }
         }
     }
-    }
 
   /* We should only get here once.  */
   if (TREE_CODE (decl) == TYPE_DECL)
@@ -10502,6 +10490,15 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
 	return error_mark_node;
       break;
 
+    case TRAIT_EXPR:
+    case PLUS_EXPR:
+    case MULT_EXPR:
+    case SCOPE_REF:
+      /* These are always non-deduced contexts.  */
+      if (!pfd->include_nondeduced_p)
+	*walk_subtrees = 0;
+      break;
+
     case MODOP_EXPR:
     case CAST_EXPR:
     case IMPLICIT_CONV_EXPR:
@@ -10517,11 +10514,6 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
 	return error_mark_node;
       break;
 
-    case SCOPE_REF:
-      if (pfd->include_nondeduced_p)
-	WALK_SUBTREE (TREE_OPERAND (t, 0));
-      break;
-
     case REQUIRES_EXPR:
       {
 	if (!fn)
diff --git a/gcc/testsuite/g++.dg/cpp0x/pr68724.C b/gcc/testsuite/g++.dg/cpp0x/pr68724.C
index 4e99d53d5a9..6df7f718a7e 100644
--- a/gcc/testsuite/g++.dg/cpp0x/pr68724.C
+++ b/gcc/testsuite/g++.dg/cpp0x/pr68724.C
@@ -9,7 +9,7 @@ struct integral_constant
 integral_constant<bool, true> inst;
 
 template <typename _Tp>
-struct integral_constant<bool, __is_enum(_Tp)> // { dg-error "32:template argument" }
+struct integral_constant<bool, __is_enum(_Tp)> // { dg-error "not deducible" }
 {
 };
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic38.C b/gcc/testsuite/g++.dg/cpp0x/variadic38.C
index b569404cdf2..9155445dce1 100644
--- a/gcc/testsuite/g++.dg/cpp0x/variadic38.C
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic38.C
@@ -3,4 +3,5 @@ template<int... Values>
 struct int_vec {};
 
 template<int... Values>
-struct int_vec<0, (Values+1)...> {}; // { dg-error "26:template argument" }
+struct int_vec<0, (Values+1)...> {}; // { dg-error "not deducible" }
+
diff --git a/gcc/testsuite/g++.dg/cpp1z/pr81016.C b/gcc/testsuite/g++.dg/cpp1z/pr81016.C
index 358b12056c0..a17afcc6b65 100644
--- a/gcc/testsuite/g++.dg/cpp1z/pr81016.C
+++ b/gcc/testsuite/g++.dg/cpp1z/pr81016.C
@@ -1,4 +1,4 @@
 // { dg-do compile { target c++17 } }
 
 template <typename a, a> struct b;
-template <typename c> struct b<bool, c::d>; // { dg-error "template parameter" }
+template <typename c> struct b<bool, c::d>; // { dg-error "not deducible" }
diff --git a/gcc/testsuite/g++.dg/template/partial16.C b/gcc/testsuite/g++.dg/template/partial16.C
new file mode 100644
index 00000000000..30c34c3e0d9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial16.C
@@ -0,0 +1,8 @@
+// [temp.spec.partial.general]/9
+
+template <class T, T t> struct C {};
+template <class T> struct C<T, 1>;              // { dg-error "depends on a template parameter" }
+
+template< int X, int (*array_ptr)[X] > class A {};
+int array[5];
+template< int X > class A<X,&array> { };        // { dg-error "depends on a template parameter" }
diff --git a/gcc/testsuite/g++.dg/template/partial17.C b/gcc/testsuite/g++.dg/template/partial17.C
new file mode 100644
index 00000000000..d5c82d26db3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial17.C
@@ -0,0 +1,14 @@
+// [temp.spec.partial.match]/3
+
+template <int I, int J> struct A;
+template <int I> struct A<I+5, I*2> {};     // { dg-error "not deducible" }
+
+template <int I> struct A<I, I> {};         // OK
+
+template <int I, int J, int K> struct B;
+template <int I> struct B<I, I*2, I> {};    // OK
+template <int I> struct B<I, I*2, 2> { typedef int type; };    // OK
+
+B<1, 2, 1> b1;
+B<1, 2, 2>::type b2;
+B<1, 2, 3> b3; // { dg-error "incomplete" }
diff --git a/gcc/testsuite/g++.dg/template/partial18.C b/gcc/testsuite/g++.dg/template/partial18.C
new file mode 100644
index 00000000000..7b7614ebc6b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial18.C
@@ -0,0 +1,19 @@
+// PR c++/96555
+
+template<class T, int i>
+struct X;
+
+template<class T>
+struct X<T, sizeof(T)> {};
+
+X<int, sizeof(int)> x1;
+X<int, sizeof(int)+1> x2; // { dg-error "incomplete" }
+
+
+struct A { int x; } a;
+template<int, int> struct B;
+template<int y>
+struct B<y, sizeof(a.x)> { };
+
+B<0, sizeof(int)> b1;
+B<0, sizeof(int)+1> b2; // { dg-error "incomplete" }
diff --git a/gcc/testsuite/g++.dg/template/partial5.C b/gcc/testsuite/g++.dg/template/partial5.C
index 40d8c45b087..037f684cbd2 100644
--- a/gcc/testsuite/g++.dg/template/partial5.C
+++ b/gcc/testsuite/g++.dg/template/partial5.C
@@ -21,4 +21,4 @@ template<typename T, T V>
 struct Z { };
 
 template<typename T>
-struct Z<T, (T)0> { }; // { dg-error "13:template argument" }
+struct Z<T, (T)0> { }; // { dg-error "depends on a template parameter" }
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/spec21.C b/gcc/testsuite/g++.old-deja/g++.pt/spec21.C
index cf89d6b325a..bf25c0ebb39 100644
--- a/gcc/testsuite/g++.old-deja/g++.pt/spec21.C
+++ b/gcc/testsuite/g++.old-deja/g++.pt/spec21.C
@@ -4,8 +4,7 @@ template <class T> struct S {};
 template <class T = int> struct S<T*> {}; // { dg-error "" } default argument
 
 template <int I, int J> struct A {};
-template <int I> struct A<I+5, I*2> {}; // { dg-error "28:template argument" }
-// { dg-error "33:template argument" "" { target *-*-* } .-1 }
+template <int I> struct A<I+5, I*2> {}; // { dg-error "not deducible" }
 template <class T, T t> struct C {};
 template <class T> struct C<T, 1>;  // { dg-error "" } type depends on parameter
 int i;
-- 
2.32.0.rc0


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