[C++] Fix interaction between aka changes and DR1558 (PR92206)

One of the changes in r277281 was to make the typedef variant
handling in strip_typedefs pass the raw DECL_ORIGINAL_TYPE to the
recursive call, instead of applying TYPE_MAIN_VARIANT first.
This PR shows that that interacts badly with the implementation
of DR1558, because we then refuse to strip aliases with dependent
template parameters and trip:

  gcc_assert (!typedef_variant_p (result)
	      || ((flags & STF_USER_VISIBLE)
		  && !user_facing_original_type_p (result)));

Keeping the current behaviour but suppressing the ICE leads to a
duplicate error (the dg-bogus in the first test), so that didn't
seem like a good fix.

I assume keeping the alias should never actually be necessary for
DECL_ORIGINAL_TYPEs, because it will already have been checked
somewhere, even for implicit TYPE_DECLs.  This patch therefore
passes a flag to say that we can safely strip aliases with
dependent template parameters.

2019-11-13  Richard Sandiford  <richard.sandiford@arm.com>

gcc/cp/
	PR c++/92206
	* cp-tree.h (STF_STRIP_DEPENDENT): New constant.
	* tree.c (strip_typedefs): Add STF_STRIP_DEPENDENT to the flags
	when calling strip_typedefs recursively on a DECL_ORIGINAL_TYPE.
	Don't apply the fix for DR1558 in that case; allow aliases with
	dependent template parameters to be stripped instead.

gcc/testsuite/
	PR c++/92206
	* g++.dg/cpp0x/alias-decl-pr92206-1.C: New test.
	* g++.dg/cpp0x/alias-decl-pr92206-2.C: Likewise.
	* g++.dg/cpp0x/alias-decl-pr92206-3.C: Likewise.

From-SVN: r278119

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index bf50b1bcfa97d569e0a730c9fc551b90abaa2e46..5dcf13bbc89c23dbe35e845b5c5dd4a5099c22bc 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,12 @@
+2019-11-13  Richard Sandiford  <richard.sandiford@arm.com>
+
+       PR c++/92206
+       * cp-tree.h (STF_STRIP_DEPENDENT): New constant.
+       * tree.c (strip_typedefs): Add STF_STRIP_DEPENDENT to the flags
+       when calling strip_typedefs recursively on a DECL_ORIGINAL_TYPE.
+       Don't apply the fix for DR1558 in that case; allow aliases with
+       dependent template parameters to be stripped instead.
+
 2019-11-12  Nathan Sidwell  <nathan@acm.org>
 
        * name-lookup.c (lookup_using_decl): New function, merged from ...

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index adc021b2a5c169a40f827470f4f37e96a201c6e7..42afe1bd5cb86f15fcc940b8dc2380438e827033 100644 (file)
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5759,8 +5759,13 @@ enum auto_deduction_context
 
    STF_USER_VISIBLE: use heuristics to try to avoid stripping user-facing
        aliases of internal details.  This is intended for diagnostics,
-       where it should (for example) give more useful "aka" types.  */
+       where it should (for example) give more useful "aka" types.
+
+   STF_STRIP_DEPENDENT: allow the stripping of aliases with dependent
+       template parameters, relying on code elsewhere to report any
+       appropriate diagnostics.  */
 const unsigned int STF_USER_VISIBLE = 1U;
+const unsigned int STF_STRIP_DEPENDENT = 1U << 1;
 
 /* Returns the TEMPLATE_DECL associated to a TEMPLATE_TEMPLATE_PARM
    node.  */

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index ba635d4ddbd9996f0da04d7856d5bd2b37944813..6c39c004b011d1d0ff0332caf1cdfdf914741717 100644 (file)
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1488,7 +1488,8 @@ strip_typedefs (tree t, bool *remove_attributes, unsigned int flags)
   if (t == TYPE_CANONICAL (t))
     return t;
 
-  if (dependent_alias_template_spec_p (t))
+  if (!(flags & STF_STRIP_DEPENDENT)
+      && dependent_alias_template_spec_p (t))
     /* DR 1558: However, if the template-id is dependent, subsequent
        template argument substitution still applies to the template-id.  */
     return t;
@@ -1673,7 +1674,8 @@ strip_typedefs (tree t, bool *remove_attributes, unsigned int flags)
              && !user_facing_original_type_p (t))
            return t;
          result = strip_typedefs (DECL_ORIGINAL_TYPE (TYPE_NAME (t)),
-                                  remove_attributes, flags);
+                                  remove_attributes,
+                                  flags | STF_STRIP_DEPENDENT);
        }
       else
        result = TYPE_MAIN_VARIANT (t);

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 19243cfb6bf147420d8880a791e0c97970b805cc..a253a5397cc006a34c041dd80b4d8db2db45b8ba 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2019-11-13  Richard Sandiford  <richard.sandiford@arm.com>
+
+       PR c++/92206
+       * g++.dg/cpp0x/alias-decl-pr92206-1.C: New test.
+       * g++.dg/cpp0x/alias-decl-pr92206-2.C: Likewise.
+       * g++.dg/cpp0x/alias-decl-pr92206-3.C: Likewise.
+
 2019-11-13  Martin Liska  <mliska@suse.cz>
 
        * gcc.dg/params/params.exp: Restore test by parsing output

diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-1.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-1.C
new file mode 100644 (file)
index 0000000..c3f7b19
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-1.C
@@ -0,0 +1,9 @@
+// { dg-require-effective-target c++11 }
+
+template<typename> struct A {};
+template<typename T1, typename T2 = typename T1::value> using alias1 = A<T1>;
+template<typename T> class B {
+  using alias2 = alias1<A<T>>; // { dg-error {no type named 'value'} }
+  A<alias2> a; // { dg-bogus {no type named 'value'} }
+};
+B<int> b;

diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-2.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-2.C
new file mode 100644 (file)
index 0000000..31d73d6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-2.C
@@ -0,0 +1,14 @@
+// { dg-require-effective-target c++11 }
+
+template <bool> struct A;
+class Vector {
+  template <typename> struct TypeIsGCThing {
+    template <typename T, typename A<T ::value>::Type> using Vector = Vector;
+    struct B;
+    template <typename> class ContainerIter {
+      using Action = B;
+      using ActionVector = Vector<Action, 0>;
+      ContainerIter<ActionVector> a;
+    };
+  };
+};

diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-3.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-3.C
new file mode 100644 (file)
index 0000000..6698a36
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-pr92206-3.C
@@ -0,0 +1,8 @@
+// { dg-require-effective-target c++11 }
+
+template <typename> void a();
+template <typename> struct b;
+template <bool> using c = int;
+template <typename d, typename e = decltype(a<d>)> using f = e;
+template <typename e> using g = f<e>;
+template <typename h> c<b<g<h>>::i> j;