[PATCH] c++: Ignore default arguments for friend functions that cannot have any [PR118319]

[Simon Martin]

We segfault upon the following invalid code

=== cut here ===
template <int> struct S {
  friend void foo (int a = []{}());
};
void foo (int a) {}
int main () {
  S<0> t;
  foo ();
}
=== cut here ===

The problem is that we end up with a LAMBDA_EXPR callee in
set_flags_from_callee, and dereference its NULL_TREE
TREE_TYPE (TREE_TYPE ( )).

This patch simply sets the default argument to error_mark_node for
friend functions that do not meet the requirement in C++17 11.3.6/4.

Successfully tested on x86_64-pc-linux-gnu.

        PR c++/118319

gcc/cp/ChangeLog:

        * decl.cc (grokfndecl): Inspect all friend function parameters,
        and set them to error_mark_node if invalid.

gcc/testsuite/ChangeLog:

        * g++.dg/parse/defarg18.C: New test.

---
 gcc/cp/decl.cc                        | 13 +++++---
 gcc/testsuite/g++.dg/parse/defarg18.C | 48 +++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/parse/defarg18.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 503ecd9387e..b2761c23d3e 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -11134,14 +11134,19 @@ grokfndecl (tree ctype,
      expression, that declaration shall be a definition..."  */
   if (friendp && !funcdef_flag)
     {
+      bool has_permerrored = false;
       for (tree t = FUNCTION_FIRST_USER_PARMTYPE (decl);
           t && t != void_list_node; t = TREE_CHAIN (t))
        if (TREE_PURPOSE (t))
          {
-           permerror (DECL_SOURCE_LOCATION (decl),
-                      "friend declaration of %qD specifies default "
-                      "arguments and isn%'t a definition", decl);
-           break;
+           if (!has_permerrored)
+             {
+               has_permerrored = true;
+               permerror (DECL_SOURCE_LOCATION (decl),
+                          "friend declaration of %qD specifies default "
+                          "arguments and isn%'t a definition", decl);
+             }
+           TREE_PURPOSE (t) = error_mark_node;
          }
     }
 
diff --git a/gcc/testsuite/g++.dg/parse/defarg18.C 
b/gcc/testsuite/g++.dg/parse/defarg18.C
new file mode 100644
index 00000000000..a087d45bf34
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/defarg18.C
@@ -0,0 +1,48 @@
+// PR c++/118319
+// { dg-do "compile" { target c++11 } }
+
+// Template case, that used to crash.
+
+template <int>
+struct S {
+  friend void foo1 (int a = []{}());  // { dg-error "specifies default|only 
declaration" }
+  friend void foo3 (int a,           // { dg-error "specifies default|only 
declaration" }
+                   int b = []{}(),
+                   int c = []{}());
+};
+
+void foo1 (int a) {}
+void foo3 (int a, int b, int c) {}
+
+void hello (){
+  S<0> t;
+  foo1 ();
+  foo3 (1, 2);
+}
+
+
+// Template case, that already worked.
+
+template <int>
+struct T {
+  friend void bar (int a = []{}()); // { dg-error "specifies default|only 
declaration" }
+};
+
+void hallo (){
+  T<0> t;
+  bar (); // { dg-error "not declared" }
+}
+
+
+// Non template case, that already worked.
+
+struct NoTemplate {
+  friend void baz (int a = []{}()); // { dg-error "specifies default" }
+};
+
+void baz (int a) {} // { dg-error "only declaration" }
+
+void ola (){
+  NoTemplate t;
+  baz ();
+}
-- 
2.44.0