C++ PATCH for c++/81180, ICE with C++17 member class template deduction

C++ PATCH for c++/81180, ICE with C++17 member class template deduction

[Jason Merrill]

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The substitution we do in build_deduction_guide needs
processing_template_decl set, since it's only partial instantiation,
and also needs to be done on the template; substituting the
FUNCTION_DECL pattern doesn't properly adjust the template parameters
on the template, which we will use in building the deduction guide.

Tested x86_64-pc-linux-gnu, applying to trunk and 7.

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commit a1ecbf88833602a7d37fd44f831d4c1efd6ffaf8
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Jun 29 14:12:09 2017 -0400

            PR c++/81180 - ICE with C++17 deduction of member class template.
    
            * pt.c (build_deduction_guide): Correct member template handling.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 047d3ba..3ecacbd 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -25216,17 +25216,16 @@ build_deduction_guide (tree ctor, tree outer_args, tsubst_flags_t complain)
     }
   else
     {
+      ++processing_template_decl;
+
+      tree fn_tmpl
+	= (TREE_CODE (ctor) == TEMPLATE_DECL ? ctor
+	   : DECL_TI_TEMPLATE (ctor));
       if (outer_args)
-	ctor = tsubst (ctor, outer_args, complain, ctor);
+	fn_tmpl = tsubst (fn_tmpl, outer_args, complain, ctor);
+      ctor = DECL_TEMPLATE_RESULT (fn_tmpl);
+
       type = DECL_CONTEXT (ctor);
-      tree fn_tmpl;
-      if (TREE_CODE (ctor) == TEMPLATE_DECL)
-	{
-	  fn_tmpl = ctor;
-	  ctor = DECL_TEMPLATE_RESULT (fn_tmpl);
-	}
-      else
-	fn_tmpl = DECL_TI_TEMPLATE (ctor);
 
       tparms = DECL_TEMPLATE_PARMS (fn_tmpl);
       /* If type is a member class template, DECL_TI_ARGS (ctor) will have
@@ -25248,7 +25247,6 @@ build_deduction_guide (tree ctor, tree outer_args, tsubst_flags_t complain)
 	  /* For a member template constructor, we need to flatten the two
 	     template parameter lists into one, and then adjust the function
 	     signature accordingly.  This gets...complicated.  */
-	  ++processing_template_decl;
 	  tree save_parms = current_template_parms;
 
 	  /* For a member template we should have two levels of parms/args, one
@@ -25309,8 +25307,8 @@ build_deduction_guide (tree ctor, tree outer_args, tsubst_flags_t complain)
 	    ci = tsubst_constraint_info (ci, tsubst_args, complain, ctor);
 
 	  current_template_parms = save_parms;
-	  --processing_template_decl;
 	}
+      --processing_template_decl;
     }
 
   if (!memtmpl)
diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction40.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction40.C
new file mode 100644
index 0000000..eeffa69
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction40.C
@@ -0,0 +1,19 @@
+// PR c++/81180
+// { dg-options -std=c++1z }
+
+template < int I > struct int_{};
+
+template < typename T >
+struct A{
+    template < typename U, int I >
+    struct B{
+        B(U u, int_< I >){}
+    };
+};
+
+
+int main(){
+    A< int >::B v(0, int_< 0 >());
+    (void)v;
+}
+