Re: [PATCH] c++: Fix pretty printing of context of local class [PR99213]

[Jason Merrill via Gcc-patches]

On 2/25/21 1:37 AM, Patrick Palka wrote:

My r10-7705 patch for PR94521 made us set TFF_NO_FUNCTION_ARGUMENTS when
pretty printing the function scope of a local class type in order to
eliminate infinite recursion with a function signature that contains
decltype([]{}).  But due to the way dump_function_decl works, this
change regressed our pretty printing of local class types whose context
contains a class template specialization, as in the testcase below, in
which we wrongly pretty print the two local types as 'A<T>::f<char>::S1'
and 'B<T>::f<int>::S2'.

This patch makes dump_scope pass TFF_NO_TEMPLATE_BINDINGS instead of
TFF_NO_FUNCTION_ARGUMENTS when pretty printing a function scope.  It
appears this is the strictly better flag to use: it avoids the infinite
recursion issue, it restores pretty printing of the function parameter
list, and it stops dump_function_decl from trying to print a function
template specialization in its own weird way.

Summary of pretty printing differences for the below testcase:

   r10-7704:   A<T>::f() [with U = char; T = int]::S1
               B<T>::f() [with T = int]::S2

   r10-7705:   A<T>::f<char>::S1
               B<T>::f<int>::S2

   this patch: A<int>::f<char>()::S1
               B<int>::f()::S2

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

OK.

gcc/cp/ChangeLog:

        PR c++/99213
        PR c++/94521
        * error.c (dump_scope): Pass TFF_NO_TEMPLATE_BINDINGS instead of
        TFF_NO_FUNCTION_ARGUMENTS when dumping a function scope.

gcc/testsuite/ChangeLog:

        PR c++/99213
        PR c++/94521
        * g++.dg/diagnostic/local1.C: New test.
---
  gcc/cp/error.c                           |  4 +---
  gcc/testsuite/g++.dg/diagnostic/local1.C | 25 ++++++++++++++++++++++++
  2 files changed, 26 insertions(+), 3 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/diagnostic/local1.C

diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 5213a8030ca..ff4ae6f4b23 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -243,9 +243,7 @@ dump_scope (cxx_pretty_printer *pp, tree scope, int flags)
      }
    else if ((flags & TFF_SCOPE) && TREE_CODE (scope) == FUNCTION_DECL)
      {
-      if (DECL_USE_TEMPLATE (scope))
-       f |= TFF_NO_FUNCTION_ARGUMENTS;
-      dump_function_decl (pp, scope, f);
+      dump_function_decl (pp, scope, f | TFF_NO_TEMPLATE_BINDINGS);
        pp_cxx_colon_colon (pp);
      }
  }
diff --git a/gcc/testsuite/g++.dg/diagnostic/local1.C 
b/gcc/testsuite/g++.dg/diagnostic/local1.C
new file mode 100644
index 00000000000..5905b571a44
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/local1.C
@@ -0,0 +1,25 @@
+// PR c++/99213
+// { dg-do compile { target c++14 } }
+
+template <class T>
+struct A {
+  template <class U>
+  static auto f() {
+    struct S1{};
+    return S1{};
+  }
+};
+
+using type = void;
+using type = decltype(A<int>::f<char>()); // { dg-error 
"A<int>::f<char>\\(\\)::S1"  }
+
+template <class T>
+struct B {
+  static auto f() {
+    struct S2{};
+    return S2{};
+  }
+};
+
+using type = void;
+using type = decltype(B<int>::f()); // { dg-error "B<int>::f\\(\\)::S2"  }