C++: namespaces and scopes for enum values (PR c++/88121)

Consider this test case:

namespace json
{
  enum { JSON_OBJECT };
}

void test ()
{
  JSON_OBJECT;
}

which erroneously accesses an enum value in another namespace without
qualifying the access.

GCC 6 through 8 issue a suggestion that doesn't mention the namespace:

<source>: In function 'void test()':
<source>:8:3: error: 'JSON_OBJECT' was not declared in this scope
   JSON_OBJECT;
   ^~~~~~~~~~~
<source>:8:3: note: suggested alternative:
<source>:3:10: note:   'JSON_OBJECT'
   enum { JSON_OBJECT };
          ^~~~~~~~~~~

which is suboptimal.

I made the problem worse with r265610, which consolidates the single
suggestion into the error, and emits:

<source>: In function 'void test()':
<source>:8:3: error: 'JSON_OBJECT' was not declared in this scope; did
   you mean 'JSON_OBJECT'?
    8 |   JSON_OBJECT;
      |   ^~~~~~~~~~~
      |   JSON_OBJECT
<source>:3:10: note: 'JSON_OBJECT' declared here
    3 |   enum { JSON_OBJECT };
      |          ^~~~~~~~~~~

where the message:
  'JSON_OBJECT' was not declared in this scope; did you mean 'JSON_OBJECT'?
is nonsensical.

This patch tweaks dump_scope to detect unscoped enums, and to use the
enclosing namespace for them, so that the CONST_DECL is dumped as
"json::JSON_OBJECT".

This changes the output for the above so that it refers to the
namespace, fixing the issue:

<source>:8:3: error: 'JSON_OBJECT' was not declared in this scope; did
   you mean 'json::JSON_OBJECT'?
    9 |   JSON_OBJECT;
      |   ^~~~~~~~~~~
      |   json::JSON_OBJECT
<source>3:10: note: 'json::JSON_OBJECT' declared here
    3 |   enum { JSON_OBJECT };
      |          ^~~~~~~~~~~

The patch also fixes scope-printing for values within scoped enums.
To exercise this, the patch extends the scanner for namespaces for
exact matches for a name, so that we also scan inside scoped
enums, to cover the case where someone doesn't supply the scope.

Hence with the patch given e.g.:

enum class vegetable { CARROT, TURNIP };

we're able to offer e.g.:

suggestions-scoped-enums.C:50:3: error: 'CARROT' was not declared in
  this scope; did you mean 'vegetable::CARROT'?
   50 |   CARROT;
      |   ^~~~~~
      |   vegetable::CARROT

and this exercises the code path above.  The patch updates dump_scope
for scoped enums so that we print the scope when printing the
value ("vegetable::CARROT"), rather than just the name of the value
("CARROT").

Finally, the patch adds spell-corrections within a scoped enum,
giving e.g.:

suggestions-scoped-enums.C:18:14: error: 'TURNUP' is not a member of
  'vegetable'; did you mean 'TURNIP'?
   18 |   vegetable::TURNUP;
      |              ^~~~~~
      |              TURNIP

gcc/cp/ChangeLog:
	PR c++/88121
	* cp-name-hint.h (suggest_alternative_in_scoped_enum): New decl.
	* error.c (dump_scope): Ensure that we print any scope for values
	of unscoped enums.  Print the scope of values of scoped enums.
	(qualified_name_lookup_error): Offer suggestions for failures
	within scoped enums by calling suggest_alternative_in_scoped_enum.
	* name-lookup.c (class namespace_hints): Update comment to mention
	scoped enums.
	(namespace_hints::namespace_hints): Call
	maybe_add_candidate_for_scoped_enum.
	(namespace_hints::maybe_add_candidate_for_scoped_enum): New member
	(suggest_alternatives_for): Update comment to mention scoped
	enums.
	(suggest_alternative_in_scoped_enum): New function.

gcc/testsuite/ChangeLog:
	PR c++/88121
	* g++.dg/lookup/suggestions-scoped-enums.C: New test.
	* g++.dg/lookup/suggestions-unscoped-enums.C: New test.

From-SVN: r266644

7 files changed, 310 insertions, 12 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index f7f2020..853e139 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,20 @@
+2018-11-29  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/88121
+	* cp-name-hint.h (suggest_alternative_in_scoped_enum): New decl.
+	* error.c (dump_scope): Ensure that we print any scope for values
+	of unscoped enums.  Print the scope of values of scoped enums.
+	(qualified_name_lookup_error): Offer suggestions for failures
+	within scoped enums by calling suggest_alternative_in_scoped_enum.
+	* name-lookup.c (class namespace_hints): Update comment to mention
+	scoped enums.
+	(namespace_hints::namespace_hints): Call
+	maybe_add_candidate_for_scoped_enum.
+	(namespace_hints::maybe_add_candidate_for_scoped_enum): New member
+	(suggest_alternatives_for): Update comment to mention scoped
+	enums.
+	(suggest_alternative_in_scoped_enum): New function.
+
 2018-11-28  Marek Polacek  <polacek@redhat.com>
 
 	Implement P1094R2, Nested inline namespaces.
diff --git a/gcc/cp/cp-name-hint.h b/gcc/cp/cp-name-hint.h
index 5d1cdc3..2f9da73 100644
--- a/gcc/cp/cp-name-hint.h
+++ b/gcc/cp/cp-name-hint.h
@@ -33,5 +33,6 @@ along with GCC; see the file COPYING3.  If not see
 extern name_hint suggest_alternatives_for (location_t, tree, bool);
 extern name_hint suggest_alternatives_in_other_namespaces (location_t, tree);
 extern name_hint suggest_alternative_in_explicit_scope (location_t, tree, tree);
+extern name_hint suggest_alternative_in_scoped_enum (tree, tree);
 
 #endif /* GCC_CP_NAME_HINT_H */
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 72b42bd..f9b0b99 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -182,6 +182,12 @@ dump_scope (cxx_pretty_printer *pp, tree scope, int flags)
   if (scope == NULL_TREE)
     return;
 
+  /* Enum values within an unscoped enum will be CONST_DECL with an
+     ENUMERAL_TYPE as their "scope".  Use CP_TYPE_CONTEXT of the
+     ENUMERAL_TYPE, so as to print any enclosing namespace.  */
+  if (UNSCOPED_ENUM_P (scope))
+    scope = CP_TYPE_CONTEXT (scope);
+
   if (TREE_CODE (scope) == NAMESPACE_DECL)
     {
       if (scope != global_namespace)
@@ -190,7 +196,8 @@ dump_scope (cxx_pretty_printer *pp, tree scope, int flags)
 	  pp_cxx_colon_colon (pp);
 	}
     }
-  else if (AGGREGATE_TYPE_P (scope))
+  else if (AGGREGATE_TYPE_P (scope)
+	   || SCOPED_ENUM_P (scope))
     {
       dump_type (pp, scope, f);
       pp_cxx_colon_colon (pp);
@@ -4261,7 +4268,21 @@ qualified_name_lookup_error (tree scope, tree name,
 	  print_candidates (decl);
 	}
       else
-	error_at (location, "%qD is not a member of %qT", name, scope);
+	{
+	  name_hint hint;
+	  if (SCOPED_ENUM_P (scope))
+	    hint = suggest_alternative_in_scoped_enum (name, scope);
+	  if (const char *suggestion = hint.suggestion ())
+	    {
+	      gcc_rich_location richloc (location);
+	      richloc.add_fixit_replace (suggestion);
+	      error_at (&richloc,
+			"%qD is not a member of %qT; did you mean %qs?",
+			name, scope, suggestion);
+	    }
+	  else
+	    error_at (location, "%qD is not a member of %qT", name, scope);
+	}
     }
   else if (scope != global_namespace)
     {
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index 239bb01..cadf380 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -5396,8 +5396,8 @@ class suggest_alternatives : public deferred_diagnostic
 };
 
 /* A class for encapsulating the result of a search across
-   multiple namespaces for an unrecognized name seen at a
-   given source location.  */
+   multiple namespaces (and scoped enums within them) for an
+   unrecognized name seen at a given source location.  */
 
 class namespace_hints
 {
@@ -5408,6 +5408,8 @@ class namespace_hints
   name_hint maybe_decorate_with_limit (name_hint);
 
  private:
+  void maybe_add_candidate_for_scoped_enum (tree scoped_enum, tree name);
+
   location_t m_loc;
   tree m_name;
   vec<tree> m_candidates;
@@ -5419,8 +5421,8 @@ class namespace_hints
   bool m_limited;
 };
 
-/* Constructor for namespace_hints.  Search namespaces, looking for a match
-   for unrecognized NAME seen at LOC.  */
+/* Constructor for namespace_hints.  Search namespaces and scoped enums,
+   looking for an exact match for unrecognized NAME seen at LOC.  */
 
 namespace_hints::namespace_hints (location_t loc, tree name)
 : m_loc(loc), m_name (name)
@@ -5451,10 +5453,22 @@ namespace_hints::namespace_hints (location_t loc, tree name)
 
 	  for (tree decl = NAMESPACE_LEVEL (ns)->names;
 	       decl; decl = TREE_CHAIN (decl))
-	    if (TREE_CODE (decl) == NAMESPACE_DECL
-		&& !DECL_NAMESPACE_ALIAS (decl)
-		&& !DECL_NAMESPACE_INLINE_P (decl))
-	      children.safe_push (decl);
+	    {
+	      if (TREE_CODE (decl) == NAMESPACE_DECL
+		  && !DECL_NAMESPACE_ALIAS (decl)
+		  && !DECL_NAMESPACE_INLINE_P (decl))
+		children.safe_push (decl);
+
+	      /* Look for exact matches for NAME within scoped enums.
+		 These aren't added to the worklist, and so don't count
+		 against the search limit.  */
+	      if (TREE_CODE (decl) == TYPE_DECL)
+		{
+		  tree type = TREE_TYPE (decl);
+		  if (SCOPED_ENUM_P (type))
+		    maybe_add_candidate_for_scoped_enum (type, name);
+		}
+	    }
 
 	  while (!m_limited && !children.is_empty ())
 	    {
@@ -5522,11 +5536,32 @@ namespace_hints::maybe_decorate_with_limit (name_hint hint)
     return hint;
 }
 
+/* Look inside SCOPED_ENUM for exact matches for NAME.
+   If one is found, add its CONST_DECL to m_candidates.  */
+
+void
+namespace_hints::maybe_add_candidate_for_scoped_enum (tree scoped_enum,
+						      tree name)
+{
+  gcc_assert (SCOPED_ENUM_P (scoped_enum));
+
+  for (tree iter = TYPE_VALUES (scoped_enum); iter; iter = TREE_CHAIN (iter))
+    {
+      tree id = TREE_PURPOSE (iter);
+      if (id == name)
+	{
+	  m_candidates.safe_push (TREE_VALUE (iter));
+	  return;
+	}
+    }
+}
+
 /* Generate a name_hint at LOCATION for NAME, an IDENTIFIER_NODE for which
    name lookup failed.
 
-   Search through all available namespaces and generate a suggestion and/or
-   a deferred diagnostic that lists possible candidate(s).
+   Search through all available namespaces and any scoped enums within them
+   and generate a suggestion and/or a deferred diagnostic that lists possible
+   candidate(s).
 
    If no exact matches are found, and SUGGEST_MISSPELLINGS is true, then also
    look for near-matches and suggest the best near-match, if there is one.
@@ -5910,6 +5945,23 @@ suggest_alternative_in_explicit_scope (location_t location, tree name,
   return name_hint ();
 }
 
+/* Given NAME, look within SCOPED_ENUM for possible spell-correction
+   candidates.  */
+
+name_hint
+suggest_alternative_in_scoped_enum (tree name, tree scoped_enum)
+{
+  gcc_assert (SCOPED_ENUM_P (scoped_enum));
+
+  best_match <tree, const char *> bm (name);
+  for (tree iter = TYPE_VALUES (scoped_enum); iter; iter = TREE_CHAIN (iter))
+    {
+      tree id = TREE_PURPOSE (iter);
+      bm.consider (IDENTIFIER_POINTER (id));
+    }
+  return name_hint (bm.get_best_meaningful_candidate (), NULL);
+}
+
 /* Look up NAME (an IDENTIFIER_NODE) in SCOPE (either a NAMESPACE_DECL
    or a class TYPE).
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4a10014..7c760da 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-11-29  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/88121
+	* g++.dg/lookup/suggestions-scoped-enums.C: New test.
+	* g++.dg/lookup/suggestions-unscoped-enums.C: New test.
+
 2018-11-29  Peter Bergner  <bergner@linux.ibm.com>
 
 	PR target/87496
diff --git a/gcc/testsuite/g++.dg/lookup/suggestions-scoped-enums.C b/gcc/testsuite/g++.dg/lookup/suggestions-scoped-enums.C
new file mode 100644
index 0000000..fa6e7cb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/suggestions-scoped-enums.C
@@ -0,0 +1,110 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-fdiagnostics-show-caret" }
+
+/* Verify that we offer suggestions for misspelled values
+   in scoped enums, and for values from scoped enums that
+   are missing their scope.
+   Verify that we emit fix-it hints for those cases for
+   which we have adequate location information.  */
+
+enum class vegetable { CARROT, TURNIP }; // { dg-line decl_of_vegetable }
+namespace pasta
+{
+  enum class shape { LASAGNA, LINGUINE, SPAGHETTI, TAGLIATELLE }; // { dg-line decl_of_shape }
+}
+
+void misspelled_value_in_scoped_enum ()
+{
+  vegetable::TURNUP; // { dg-error "'TURNUP' is not a member of 'vegetable'; did you mean 'TURNIP'" }
+  /* { dg-begin-multiline-output "" }
+   vegetable::TURNUP;
+              ^~~~~~
+              TURNIP
+     { dg-end-multiline-output "" } */
+}
+
+void misspelled_value_using_explicit_ns ()
+{
+  pasta::shape::SPOOGHETTI; // { dg-error "'SPOOGHETTI' is not a member of 'pasta::shape'; did you mean 'SPAGHETTI'" }
+  /* { dg-begin-multiline-output "" }
+   pasta::shape::SPOOGHETTI;
+                 ^~~~~~~~~~
+                 SPAGHETTI
+     { dg-end-multiline-output "" } */
+}
+
+namespace pasta {
+void misspelled_value_using_implicit_ns ()
+{
+  shape::SPOOGHETTI; // { dg-error "'SPOOGHETTI' is not a member of 'pasta::shape'; did you mean 'SPAGHETTI'" }
+  /* { dg-begin-multiline-output "" }
+   shape::SPOOGHETTI;
+          ^~~~~~~~~~
+          SPAGHETTI
+     { dg-end-multiline-output "" } */
+}
+} // namespace pasta
+
+void unqualified_enum_in_global_ns ()
+{
+  CARROT; // { dg-error "'CARROT' was not declared in this scope; did you mean 'vegetable::CARROT'" }
+  /* { dg-begin-multiline-output "" }
+   CARROT;
+   ^~~~~~
+   vegetable::CARROT
+     { dg-end-multiline-output "" } */
+  // { dg-message "'vegetable::CARROT' declared here" "" { target *-*-* } decl_of_vegetable }
+  /* { dg-begin-multiline-output "" }
+ enum class vegetable { CARROT, TURNIP };
+                        ^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+void unqualified_enum_in_ns ()
+{
+  LASAGNA; // { dg-error "'LASAGNA' was not declared in this scope; did you mean 'pasta::shape::LASAGNA'" }
+  /* { dg-begin-multiline-output "" }
+   LASAGNA;
+   ^~~~~~~
+   pasta::shape::LASAGNA
+     { dg-end-multiline-output "" } */
+  // { dg-message "'pasta::shape::LASAGNA' declared here" "" { target *-*-* } decl_of_shape }
+  /* { dg-begin-multiline-output "" }
+   enum class shape { LASAGNA, LINGUINE, SPAGHETTI, TAGLIATELLE };
+                      ^~~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+/* We can't guarantee location information here, so don't expect a
+   fix-it hint.  */
+
+void unqualified_enum_in_explicit_ns ()
+{
+  pasta::LINGUINE; // { dg-error "'LINGUINE' is not a member of 'pasta'; did you mean 'pasta::shape::LINGUINE'" }
+  /* { dg-begin-multiline-output "" }
+   pasta::LINGUINE;
+          ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "'pasta::shape::LINGUINE' declared here" "" { target *-*-* } decl_of_shape }
+  /* { dg-begin-multiline-output "" }
+   enum class shape { LASAGNA, LINGUINE, SPAGHETTI, TAGLIATELLE };
+                               ^~~~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+namespace pasta {
+void unqualified_enum_in_implicit_ns ()
+{
+  TAGLIATELLE; // { dg-error "'TAGLIATELLE' was not declared in this scope; did you mean 'pasta::shape::TAGLIATELLE'" }
+  /* { dg-begin-multiline-output "" }
+   TAGLIATELLE;
+   ^~~~~~~~~~~
+   pasta::shape::TAGLIATELLE
+     { dg-end-multiline-output "" } */
+  // { dg-message "'pasta::shape::TAGLIATELLE' declared here" "" { target *-*-* } decl_of_shape }
+  /* { dg-begin-multiline-output "" }
+   enum class shape { LASAGNA, LINGUINE, SPAGHETTI, TAGLIATELLE };
+                                                    ^~~~~~~~~~~
+     { dg-end-multiline-output "" } */
+}
+}
diff --git a/gcc/testsuite/g++.dg/lookup/suggestions-unscoped-enums.C b/gcc/testsuite/g++.dg/lookup/suggestions-unscoped-enums.C
new file mode 100644
index 0000000..0dcff88
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/suggestions-unscoped-enums.C
@@ -0,0 +1,91 @@
+// { dg-options "-fdiagnostics-show-caret" }
+
+enum { LASAGNA, SPAGHETTI };
+namespace outer_ns_a
+{
+  enum enum_in_outer_ns_a { STRAWBERRY, BANANA };
+  namespace inner_ns
+  {
+    enum enum_in_inner_ns { ELEPHANT, LION };
+  }
+}
+namespace outer_ns_b
+{
+  enum enum_in_outer_ns_b { NIGHT, DAY };
+}
+
+void misspelled_enum_in_global_ns ()
+{
+  SPOOGHETTI; // { dg-error "'SPOOGHETTI' was not declared in this scope; did you mean 'SPAGHETTI'" }
+  /* { dg-begin-multiline-output "" }
+   SPOOGHETTI;
+   ^~~~~~~~~~
+   SPAGHETTI
+     { dg-end-multiline-output "" } */
+}
+
+void unqualified_enum_in_outer_ns ()
+{
+  BANANA; // { dg-error "'BANANA' was not declared in this scope; did you mean 'outer_ns_a::BANANA'" }
+  /* { dg-begin-multiline-output "" }
+   BANANA;
+   ^~~~~~
+   outer_ns_a::BANANA
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+   enum enum_in_outer_ns_a { STRAWBERRY, BANANA };
+                                         ^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+namespace outer_ns_a
+{
+  void misspelled_unqualified_enum_in_outer_ns () {
+    BANANAS; // { dg-error "'BANANAS' was not declared in this scope; did you mean 'BANANA'" }
+  /* { dg-begin-multiline-output "" }
+     BANANAS;
+     ^~~~~~~
+     BANANA
+     { dg-end-multiline-output "" } */
+  }
+};
+
+void unqualified_enum_in_inner_ns ()
+{
+  ELEPHANT; // { dg-error "'ELEPHANT' was not declared in this scope; did you mean 'outer_ns_a::inner_ns::ELEPHANT'" }
+  /* { dg-begin-multiline-output "" }
+   ELEPHANT;
+   ^~~~~~~~
+   outer_ns_a::inner_ns::ELEPHANT
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+     enum enum_in_inner_ns { ELEPHANT, LION };
+                             ^~~~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+void partially_qualified_enum_in_inner_ns ()
+{
+  outer_ns_a::ELEPHANT; // { dg-error "'ELEPHANT' is not a member of 'outer_ns_a'; did you mean 'outer_ns_a::inner_ns::ELEPHANT'" }
+  /* { dg-begin-multiline-output "" }
+   outer_ns_a::ELEPHANT;
+               ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+     enum enum_in_inner_ns { ELEPHANT, LION };
+                             ^~~~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+void wrongly_qualified_enum ()
+{
+  outer_ns_a::NIGHT; // { dg-error "'NIGHT' is not a member of 'outer_ns_a'; did you mean 'outer_ns_b::NIGHT'" }
+  /* { dg-begin-multiline-output "" }
+   outer_ns_a::NIGHT;
+               ^~~~~
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+   enum enum_in_outer_ns_b { NIGHT, DAY };
+                             ^~~~~
+     { dg-end-multiline-output "" } */
+}