[PATCH,c++] fix PR 45330, suggest alternatives for failed name lookups

[Nathan Froyd <froydnj at codesourcery dot com>]

The testcase in PR 45330 is:

namespace N
{
 int foo;
}

int bar()
{
  return foo;
}

and the perceived problem is that GCC should suggest `N::foo' for the
unqualified `foo' in `bar'.  The below patch does just that: when name
lookup fails, we grovel through all known namespaces for potential
matches and suggest them to the user.

I put the declaration for the function in cp-tree.h rather than
name-lookup.h because it seemed like a better place than including
name-lookup.h in lex.c.  I'm happy to move the declaration to
name-lookup.h and add the include.  (Or, more radically, move
unqualified_name_lookup_error and unqualified_fn_lookup_error to
name-lookup.c and adjust includes appropriately.)

The error.c change is to avoid dump_expr complaining (as occurs in
g++.dg/lookup/koenig5.C).

I didn't include a testcase, as the testcase tweaks indicated there are
a number of testcases testing similar things.
(g++.old-deja/g++.mike/ns5.C is almost identical to the testcase in the
PR, for instance).

Tested on x86_64-unknown-linux-gnu.  OK to commit?

-Nathan

gcc/cp/
	PR c++/45330
	* cp-tree.h (suggest_alternatives_for): Declare.
	* error.c (dump_expr): Handle TYPE_DECL.
	* lex.c (unqualified_name_lookup_error): Call it.
	* name-lookup.c (suggest_alternatives_for_1): New function.
	(suggest_alternatives_for): New function.

gcc/testsuite/
	PR c++/45330
	* g++.dg/ext/builtin3.C: Adjust.
	* g++.dg/lookup/error1.C: Adjust.
	* g++.dg/lookup/koenig5.C: Adjust.
	* g++.dg/overload/koenig1.C: Adjust.
	* g++.dg/parse/decl-specifier-1.C: Adjust.
	* g++.dg/template/static10.C: Adjust.
	* g++.old-deja/g++.mike/ns5.C: Adjust.
	* g++.old-deja/g++.mike/ns7.C: Adjust.
	* g++.old-deja/g++.ns/koenig5.C: Adjust.
	* g++.old-deja/g++.ns/koenig9.C: Adjust.
	* g++.old-deja/g++.other/lineno5.C: Adjust.

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 67f4f93..a323501 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5639,6 +5639,9 @@ extern tree cxx_omp_clause_dtor			(tree, tree);
 extern void cxx_omp_finish_clause		(tree);
 extern bool cxx_omp_privatize_by_reference	(const_tree);
 
+/* in name-lookup.c */
+extern void suggest_alternatives_for (tree);
+
 /* -- end of C++ */
 
 #endif /* ! GCC_CP_TREE_H */
diff --git a/gcc/cp/lex.c b/gcc/cp/lex.c
index c583d7d..9c6be41 100644
--- a/gcc/cp/lex.c
+++ b/gcc/cp/lex.c
@@ -450,7 +450,10 @@ unqualified_name_lookup_error (tree name)
   else
     {
       if (!objc_diagnose_private_ivar (name))
-        error ("%qD was not declared in this scope", name);
+	{
+	  error ("%qD was not declared in this scope", name);
+	  suggest_alternatives_for (name);
+	}
       /* Prevent repeated error messages by creating a VAR_DECL with
 	 this NAME in the innermost block scope.  */
       if (current_function_decl)
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 1560fc6..de45efe 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -1700,6 +1700,7 @@ dump_expr (tree t, int flags)
     case NAMESPACE_DECL:
     case LABEL_DECL:
     case OVERLOAD:
+    case TYPE_DECL:
     case IDENTIFIER_NODE:
       dump_decl (t, (flags & ~TFF_DECL_SPECIFIERS) | TFF_NO_FUNCTION_ARGUMENTS);
       break;
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index 0a93da8..1f2f4e5 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -30,6 +30,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "timevar.h"
 #include "toplev.h"
 #include "diagnostic-core.h"
+#include "intl.h"
 #include "debug.h"
 #include "c-family/c-pragma.h"
 
@@ -3919,6 +3920,62 @@ remove_hidden_names (tree fns)
   return fns;
 }
 
+/* Helper function for suggest_alternatives_for: lookup NAME in
+   namespace SCOPE and record any matches in CANDIDATES.  */
+
+static VEC(tree,heap) *
+suggest_alternatives_for_1 (tree name, tree scope,
+			    VEC(tree,heap) *candidates)
+{
+  struct scope_binding binding = EMPTY_SCOPE_BINDING;
+  struct cp_binding_level *level = NAMESPACE_LEVEL (scope);
+  tree t;
+
+  /* Look in this namespace.  */
+  qualified_lookup_using_namespace (name, scope, &binding, 0);
+
+  if (binding.value)
+    VEC_safe_push (tree, heap, candidates, binding.value);
+
+  /* Lookup in child namespaces.  */
+  for (t = level->namespaces; t; t = DECL_CHAIN (t))
+    candidates = suggest_alternatives_for_1 (name, t, candidates);
+
+  return candidates;
+}
+
+/* Suggest alternatives for NAME, an IDENTIFIER_NODE for which name
+   lookup failed.  Search through all available namespaces and print out
+   possible candidates.  */
+
+void
+suggest_alternatives_for (tree name)
+{
+  VEC(tree,heap) *candidates
+    = suggest_alternatives_for_1 (name, global_namespace, NULL);
+  const char *str;
+  char *spaces;
+  tree t;
+  unsigned ix;
+
+  /* Nothing useful to report.  */
+  if (VEC_empty (tree, candidates))
+    return;
+
+  str = (VEC_length(tree, candidates) > 1
+	 ? _("suggested alternatives:")
+	 : _("suggested alternative:"));
+  spaces = NULL;
+
+  FOR_EACH_VEC_ELT (tree, candidates, ix, t)
+    {
+      inform (input_location, "%s %qE", (spaces ? spaces : str), t);
+      spaces = spaces ? spaces : get_spaces (str);
+    }
+
+  VEC_free (tree, heap, candidates);
+}
+
 /* Unscoped lookup of a global: iterate over current namespaces,
    considering using-directives.  */
 
diff --git a/gcc/testsuite/g++.dg/ext/builtin3.C b/gcc/testsuite/g++.dg/ext/builtin3.C
index 3d06dd7..a9ebce0 100644
--- a/gcc/testsuite/g++.dg/ext/builtin3.C
+++ b/gcc/testsuite/g++.dg/ext/builtin3.C
@@ -10,4 +10,5 @@ extern "C" int printf(char*, ...);
 
 void foo() {
   printf("abc"); 		// { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 12 }
 }
diff --git a/gcc/testsuite/g++.dg/lookup/error1.C b/gcc/testsuite/g++.dg/lookup/error1.C
index 2264b23..3b34ee3 100644
--- a/gcc/testsuite/g++.dg/lookup/error1.C
+++ b/gcc/testsuite/g++.dg/lookup/error1.C
@@ -4,6 +4,7 @@
 
 namespace N { int i; }
 void foo() { i; }   // { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 6 }
 
 using namespace N;
 void bar() { i; }
diff --git a/gcc/testsuite/g++.dg/lookup/koenig5.C b/gcc/testsuite/g++.dg/lookup/koenig5.C
index 6ecc25d..bc1dc8c 100644
--- a/gcc/testsuite/g++.dg/lookup/koenig5.C
+++ b/gcc/testsuite/g++.dg/lookup/koenig5.C
@@ -32,10 +32,12 @@ void g (N::A *a, M::B *b, O::C *c)
   One (a); // ok
   One (a, b); // ok
   One (b); // { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 34 }
 
   Two (c); // ok
   Two (a, c); // ok
   Two (a); // { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 39 }
   Two (a, a); // error masked by earlier error
   Two (b); // error masked by earlier error
   Two (a, b); // error masked by earlier error
@@ -43,4 +45,5 @@ void g (N::A *a, M::B *b, O::C *c)
   Three (b); // ok
   Three (a, b); // ok
   Three (a); // { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 47 }
 }
diff --git a/gcc/testsuite/g++.dg/overload/koenig1.C b/gcc/testsuite/g++.dg/overload/koenig1.C
index 1ed7bce..be0be69 100644
--- a/gcc/testsuite/g++.dg/overload/koenig1.C
+++ b/gcc/testsuite/g++.dg/overload/koenig1.C
@@ -14,5 +14,6 @@ void g ()
   B *bp;
   N::A *ap;
   f (bp);			// { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 16 }
   f (ap);
 }
diff --git a/gcc/testsuite/g++.dg/parse/decl-specifier-1.C b/gcc/testsuite/g++.dg/parse/decl-specifier-1.C
index e81fbab..48fc7fa 100644
--- a/gcc/testsuite/g++.dg/parse/decl-specifier-1.C
+++ b/gcc/testsuite/g++.dg/parse/decl-specifier-1.C
@@ -13,4 +13,5 @@ N::X X;                           // { dg-error "" "" }
 int main()
 {
     return sizeof(X);             // { dg-error "" "" }
+    // { dg-message "note" "suggested alternative" { target *-*-* } 15 }
 }
diff --git a/gcc/testsuite/g++.dg/template/static10.C b/gcc/testsuite/g++.dg/template/static10.C
index ab857bd..2f60f0c 100644
--- a/gcc/testsuite/g++.dg/template/static10.C
+++ b/gcc/testsuite/g++.dg/template/static10.C
@@ -20,4 +20,5 @@ namespace std
 {
   template<> void
   vector<int, allocator<int> >::swap(vector<int, allocator<int> >&) { } // { dg-error "" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 22 }
 }
diff --git a/gcc/testsuite/g++.old-deja/g++.mike/ns5.C b/gcc/testsuite/g++.old-deja/g++.mike/ns5.C
index 9d806ca..f13da04 100644
--- a/gcc/testsuite/g++.old-deja/g++.mike/ns5.C
+++ b/gcc/testsuite/g++.old-deja/g++.mike/ns5.C
@@ -4,3 +4,4 @@ namespace A {
 }
 
 int j = i;		// { dg-error "" } 
+  // { dg-message "note" "suggested alternative" { target *-*-* } 6 }
diff --git a/gcc/testsuite/g++.old-deja/g++.mike/ns7.C b/gcc/testsuite/g++.old-deja/g++.mike/ns7.C
index 57008db..31a71dd 100644
--- a/gcc/testsuite/g++.old-deja/g++.mike/ns7.C
+++ b/gcc/testsuite/g++.old-deja/g++.mike/ns7.C
@@ -6,4 +6,5 @@ namespace A {
 
 namespace B {
   int j = i;	// { dg-error "" } 
+  // { dg-message "note" "suggested alternative" { target *-*-* } 8 }
 }
diff --git a/gcc/testsuite/g++.old-deja/g++.ns/koenig5.C b/gcc/testsuite/g++.old-deja/g++.ns/koenig5.C
index 33061ad..67b781d 100644
--- a/gcc/testsuite/g++.old-deja/g++.ns/koenig5.C
+++ b/gcc/testsuite/g++.old-deja/g++.ns/koenig5.C
@@ -15,4 +15,5 @@ void g()
 			 // foo variable first, and therefore do not
 			 // perform argument-dependent lookup.
   bar(new X);            // { dg-error "not declared" }
+  // { dg-message "note" "suggested alternative" { target *-*-* } 17 }
 }
diff --git a/gcc/testsuite/g++.old-deja/g++.ns/koenig9.C b/gcc/testsuite/g++.old-deja/g++.ns/koenig9.C
index 78b0e8b..f246639 100644
--- a/gcc/testsuite/g++.old-deja/g++.ns/koenig9.C
+++ b/gcc/testsuite/g++.old-deja/g++.ns/koenig9.C
@@ -10,4 +10,5 @@ void foo(const char*,...);
 inline void
 bar() {
   foo("",count);    //  { dg-error "" } multiple overloaded count functions
+  // { dg-message "note" "suggested alternative" { target *-*-* } 12 }
 }
diff --git a/gcc/testsuite/g++.old-deja/g++.other/lineno5.C b/gcc/testsuite/g++.old-deja/g++.other/lineno5.C
index d14bd90..20e49bc 100644
--- a/gcc/testsuite/g++.old-deja/g++.other/lineno5.C
+++ b/gcc/testsuite/g++.old-deja/g++.other/lineno5.C
@@ -16,4 +16,5 @@ namespace tmp {
 class A {
   public:
   int kaka(tmp::B = b);		// { dg-error "" } no b in scope
+  // { dg-message "note" "suggested alternative" { target *-*-* } 18 }
 };