c++: Function found via ADL when it should not [PR95074]

I noticed that we don't implement [basic.lookup.argdep]/3: quite correctly;
it says "If X (the lookup set produced by unqualified lookup) contains
-- a block-scope function declaration that is not a using-declaration
[...]
then Y (the lookup set produced by ADL) is empty."
but we were still performing ADL in fn1 in the attached test.  The
problem was that we were only looking at the first function in the
overload set which in this case happened to be a using-declaration, and
those don't suppress ADL.  We have to look through the whole set to find
out if unqualified lookup found a block-scope function declaration, or
a member function declaration.

	PR c++/95074
	* parser.c (cp_parser_postfix_expression) <case CPP_OPEN_PAREN>: When
	looking for a block-scope function declaration, look through the whole
	set, not just the first function in the overload set.

	* g++.dg/lookup/koenig15.C: New test.

4 files changed, 73 insertions, 10 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index db80907..7515827 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2020-05-12  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/95074
+	* parser.c (cp_parser_postfix_expression) <case CPP_OPEN_PAREN>: When
+	looking for a block-scope function declaration, look through the whole
+	set, not just the first function in the overload set.
+
 2020-05-12  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/95063
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 10627cb..f1ddef2 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -7385,19 +7385,25 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
 		else if (!args->is_empty ()
 			 && is_overloaded_fn (postfix_expression))
 		  {
-		    /* We only need to look at the first function,
-		       because all the fns share the attribute we're
-		       concerned with (all member fns or all local
-		       fns).  */
-		    tree fn = get_first_fn (postfix_expression);
-		    fn = STRIP_TEMPLATE (fn);
-
 		    /* Do not do argument dependent lookup if regular
 		       lookup finds a member function or a block-scope
 		       function declaration.  [basic.lookup.argdep]/3  */
-		    if (!((TREE_CODE (fn) == USING_DECL && DECL_DEPENDENT_P (fn))
-			  || DECL_FUNCTION_MEMBER_P (fn)
-			  || DECL_LOCAL_FUNCTION_P (fn)))
+		    bool do_adl_p = true;
+		    tree fns = get_fns (postfix_expression);
+		    for (lkp_iterator iter (fns); iter; ++iter)
+		      {
+			tree fn = STRIP_TEMPLATE (*iter);
+			if ((TREE_CODE (fn) == USING_DECL
+			     && DECL_DEPENDENT_P (fn))
+			    || DECL_FUNCTION_MEMBER_P (fn)
+			    || DECL_LOCAL_FUNCTION_P (fn))
+			  {
+			    do_adl_p = false;
+			    break;
+			  }
+		      }
+
+		    if (do_adl_p)
 		      {
 			koenig_p = true;
 			if (!any_type_dependent_arguments_p (args))
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 34f48e7..24a4276 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-12  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/95074
+	* g++.dg/lookup/koenig15.C: New test.
+
 2020-05-12  Jakub Jelinek  <jakub@redhat.com>
 
 	PR sanitizer/95051
diff --git a/gcc/testsuite/g++.dg/lookup/koenig15.C b/gcc/testsuite/g++.dg/lookup/koenig15.C
new file mode 100644
index 0000000..f317c01
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/koenig15.C
@@ -0,0 +1,45 @@
+// PR c++/95074 - Function found via ADL when it should not.
+// { dg-do compile }
+
+namespace N {
+  struct S { };
+  void f(S);
+}
+
+namespace M {
+  void f(int);
+}
+
+void
+fn0 ()
+{
+  N::S s;
+  using M::f;
+  f (s);
+}
+
+void
+fn1 ()
+{
+  N::S s;
+  extern void f(char);
+  using M::f;
+  f (s); // { dg-error "no matching function" }
+}
+
+void
+fn2 ()
+{
+  N::S s;
+  using M::f;
+  extern void f(char);
+  f (s); // { dg-error "no matching function" }
+}
+
+void
+fn3 ()
+{
+  N::S s;
+  extern void (*f)(char);
+  f (s); // { dg-error "cannot convert" }
+}