[PATCH] c-family: add name_hint/deferred_diagnostic (v3)

[David Malcolm <dmalcolm at redhat dot com>]

Jeff: You previously had concerns about the refcounting used in v1
of this patch; this avoids that in favor of using gnu::unique_ptr.
Joseph already approved the C frontend parts of v2 of this
patch.  

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
OK for trunk?

Changed in v3:
- We can't directly include "unique-ptr.h" due to the fix for
  PR bootstrap/82610; see:
    https://gcc.gnu.org/ml/gcc-patches/2017-10/msg01289.html
  The fix is to define INCLUDE_UNIQUE_PTR before including system.h.
  This version of the patch moves the usage of gnu::unique_ptr from
  c-common.h to a new name-hint.h header, to avoid having to define
  INCLUDE_UNIQUE_PTR everywhere that uses c-common.h.
- Updated for *_at_rich_loc renaming

Changed in v2:
- dropped refcounting in favor of using gnu::unique_ptr.  One
  wart with this is that the handling of suppressed diagnostics
  has to happen in every deferred_diagnostic subclass, rather
  than in the name_hint class.  It would be possible to fix this
  by introducing another dynamically-allocated object to manage
  this concern, but adding another dynamic allocation seemed like
  overkill.

Blurb from v1:

In various places we use lookup_name_fuzzy to provide a hint,
and can report messages of the form:
  error: unknown foo named 'bar'
or:
  error: unknown foo named 'bar'; did you mean 'SUGGESTION?

This patch provides a way for lookup_name_fuzzy to provide
both the suggestion above, and (optionally) additional hints
that can be printed e.g.

  note: did you forget to include <SOME_HEADER.h>?

This patch provides the mechanism and ports existing users
of lookup_name_fuzzy to the new return type.
There are no uses of such hints in this patch, but followup
patches provide various front-end specific uses of this.

gcc/c-family/ChangeLog:
	* c-common.h (enum lookup_name_fuzzy_kind): Move to name-hint.h.
	(lookup_name_fuzzy): Likewise.  Convert return type from
	const char * to name_hint.  Add location_t param.
	* name-hint.h: New header.

gcc/c/ChangeLog:
	* c-decl.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(implicit_decl_warning): Convert "hint" from
	const char * to name_hint.  Pass location to
	lookup_name_fuzzy.  Suppress any deferred diagnostic if the
	warning was not printed.
	(undeclared_variable): Likewise for "guessed_id".
	(lookup_name_fuzzy): Convert return type from const char *
	to name_hint.  Add location_t param.
	* c-parser.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(c_parser_declaration_or_fndef): Convert "hint" from
	const char * to name_hint.  Pass location to lookup_name_fuzzy.
	(c_parser_parameter_declaration): Likewise.

gcc/cp/ChangeLog:
	* name-lookup.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(suggest_alternatives_for): Convert "fuzzy_name" from const char *
	to name_hint, and rename to "hint".  Pass location to
	lookup_name_fuzzy.
	(lookup_name_fuzzy): Convert return type from const char *
	to name_hint.  Add location_t param.
	* parser.c: Define INCLUDE_UNIQUE_PTR before including system.h.
	Include "c-family/name-hint.h"
	(cp_parser_diagnose_invalid_type_name): Convert
	"suggestion" from const char * to name_hint, and rename to "hint".
	Pass location to lookup_name_fuzzy.
---
 gcc/c-family/c-common.h  |  12 -----
 gcc/c-family/name-hint.h | 121 +++++++++++++++++++++++++++++++++++++++++++++++
 gcc/c/c-decl.c           |  37 ++++++++-------
 gcc/c/c-parser.c         |  18 ++++---
 gcc/cp/name-lookup.c     |  15 +++---
 gcc/cp/parser.c          |  12 +++--
 6 files changed, 169 insertions(+), 46 deletions(-)
 create mode 100644 gcc/c-family/name-hint.h

diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 7e1877e..0f84de9 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -990,18 +990,6 @@ extern tree lookup_label (tree);
 extern tree lookup_name (tree);
 extern bool lvalue_p (const_tree);
 
-enum lookup_name_fuzzy_kind {
-  /* Names of types.  */
-  FUZZY_LOOKUP_TYPENAME,
-
-  /* Names of function decls.  */
-  FUZZY_LOOKUP_FUNCTION_NAME,
-
-  /* Any name.  */
-  FUZZY_LOOKUP_NAME
-};
-extern const char *lookup_name_fuzzy (tree, enum lookup_name_fuzzy_kind);
-
 extern bool vector_targets_convertible_p (const_tree t1, const_tree t2);
 extern bool vector_types_convertible_p (const_tree t1, const_tree t2, bool emit_lax_note);
 extern tree c_build_vec_perm_expr (location_t, tree, tree, tree, bool = true);
diff --git a/gcc/c-family/name-hint.h b/gcc/c-family/name-hint.h
new file mode 100644
index 0000000..9f342c8
--- /dev/null
+++ b/gcc/c-family/name-hint.h
@@ -0,0 +1,121 @@
+/* Support for offering suggestions for handling unrecognized names.
+   Copyright (C) 2016-2017 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_NAME_HINT_H
+#define GCC_NAME_HINT_H
+
+/* This header uses gnu::unique_ptr, but unique-ptr.h can't be directly
+   included due to issues with macros.  Hence it must be included from
+   system.h by defining INCLUDE_UNIQUE_PTR in any source file using it.  */
+
+#ifndef GNU_UNIQUE_PTR_H
+# error "You must define INCLUDE_UNIQUE_PTR before including system.h to use name-hint.h"
+#endif
+
+enum lookup_name_fuzzy_kind {
+  /* Names of types.  */
+  FUZZY_LOOKUP_TYPENAME,
+
+  /* Names of function decls.  */
+  FUZZY_LOOKUP_FUNCTION_NAME,
+
+  /* Any name.  */
+  FUZZY_LOOKUP_NAME
+};
+
+/* A deferred_diagnostic is a wrapper around optional extra diagnostics
+   that we may want to bundle into a name_hint.
+
+   The diagnostic is emitted by the subclass destructor, which should
+   check that is_suppressed_p () is not true.  */
+
+class deferred_diagnostic
+{
+ public:
+  virtual ~deferred_diagnostic () {}
+
+  location_t get_location () const { return m_loc; }
+
+  /* Call this if the corresponding warning was not emitted,
+     in which case we should also not emit the deferred_diagnostic.  */
+  void suppress ()
+  {
+    m_suppress = true;
+  }
+
+  bool is_suppressed_p () const { return m_suppress; }
+
+ protected:
+  deferred_diagnostic (location_t loc)
+  : m_loc (loc), m_suppress (false) {}
+
+ private:
+  location_t m_loc;
+  bool m_suppress;
+};
+
+/* A name_hint is an optional string suggestion, along with an
+   optional deferred_diagnostic.
+   For example:
+
+       error: unknown foo named 'bar'
+
+   if the SUGGESTION is "baz", then one might print:
+
+       error: unknown foo named 'bar'; did you mean 'baz'?
+
+   and the deferred_diagnostic allows for additional (optional)
+   diagnostics e.g.:
+
+       note: did you check behind the couch?
+
+   The deferred_diagnostic is emitted by its destructor, when the
+   name_hint goes out of scope.  */
+
+class name_hint
+{
+public:
+  name_hint () : m_suggestion (NULL), m_deferred () {}
+
+  name_hint (const char *suggestion, deferred_diagnostic *deferred)
+  : m_suggestion (suggestion), m_deferred (deferred)
+  {
+  }
+
+  const char *suggestion () const { return m_suggestion; }
+  operator bool () const { return m_suggestion != NULL; }
+
+  /* Call this on a name_hint if the corresponding warning was not emitted,
+     in which case we should also not emit the deferred_diagnostic.  */
+
+  void suppress ()
+  {
+    if (m_deferred)
+      m_deferred->suppress ();
+  }
+
+private:
+  const char *m_suggestion;
+  gnu::unique_ptr<deferred_diagnostic> m_deferred;
+};
+
+extern name_hint lookup_name_fuzzy (tree, enum lookup_name_fuzzy_kind,
+				    location_t);
+
+#endif /* ! GCC_NAME_HINT_H */
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index d95a2b6..7726476 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -25,6 +25,7 @@ along with GCC; see the file COPYING3.  If not see
    line numbers.  For example, the CONST_DECLs for enum values.  */
 
 #include "config.h"
+#define INCLUDE_UNIQUE_PTR
 #include "system.h"
 #include "coretypes.h"
 #include "target.h"
@@ -54,6 +55,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "spellcheck-tree.h"
 #include "gcc-rich-location.h"
 #include "asan.h"
+#include "c-family/name-hint.h"
 
 /* In grokdeclarator, distinguish syntactic contexts of declarators.  */
 enum decl_context
@@ -3109,20 +3111,20 @@ implicit_decl_warning (location_t loc, tree id, tree olddecl)
     return;
 
   bool warned;
-  const char *hint = NULL;
+  name_hint hint;
   if (!olddecl)
-    hint = lookup_name_fuzzy (id, FUZZY_LOOKUP_FUNCTION_NAME);
+    hint = lookup_name_fuzzy (id, FUZZY_LOOKUP_FUNCTION_NAME, loc);
 
   if (flag_isoc99)
     {
       if (hint)
 	{
 	  gcc_rich_location richloc (loc);
-	  richloc.add_fixit_replace (hint);
+	  richloc.add_fixit_replace (hint.suggestion ());
 	  warned = pedwarn (&richloc, OPT_Wimplicit_function_declaration,
 			    "implicit declaration of function %qE;"
 			    " did you mean %qs?",
-			    id, hint);
+			    id, hint.suggestion ());
 	}
       else
 	warned = pedwarn (loc, OPT_Wimplicit_function_declaration,
@@ -3131,11 +3133,11 @@ implicit_decl_warning (location_t loc, tree id, tree olddecl)
   else if (hint)
     {
       gcc_rich_location richloc (loc);
-      richloc.add_fixit_replace (hint);
+      richloc.add_fixit_replace (hint.suggestion ());
       warned = warning_at
 	(&richloc, OPT_Wimplicit_function_declaration,
 	 G_("implicit declaration of function %qE; did you mean %qs?"),
-	 id, hint);
+	 id, hint.suggestion ());
     }
   else
     warned = warning_at (loc, OPT_Wimplicit_function_declaration,
@@ -3143,6 +3145,9 @@ implicit_decl_warning (location_t loc, tree id, tree olddecl)
 
   if (olddecl && warned)
     locate_old_decl (olddecl);
+
+  if (!warned)
+    hint.suppress ();
 }
 
 /* This function represents mapping of a function code FCODE
@@ -3466,15 +3471,15 @@ undeclared_variable (location_t loc, tree id)
 
   if (current_function_decl == NULL_TREE)
     {
-      const char *guessed_id = lookup_name_fuzzy (id, FUZZY_LOOKUP_NAME);
+      name_hint guessed_id = lookup_name_fuzzy (id, FUZZY_LOOKUP_NAME, loc);
       if (guessed_id)
 	{
 	  gcc_rich_location richloc (loc);
-	  richloc.add_fixit_replace (guessed_id);
+	  richloc.add_fixit_replace (guessed_id.suggestion ());
 	  error_at (&richloc,
 		    "%qE undeclared here (not in a function);"
 		    " did you mean %qs?",
-		    id, guessed_id);
+		    id, guessed_id.suggestion ());
 	}
       else
 	error_at (loc, "%qE undeclared here (not in a function)", id);
@@ -3484,15 +3489,15 @@ undeclared_variable (location_t loc, tree id)
     {
       if (!objc_diagnose_private_ivar (id))
 	{
-	  const char *guessed_id = lookup_name_fuzzy (id, FUZZY_LOOKUP_NAME);
+	  name_hint guessed_id = lookup_name_fuzzy (id, FUZZY_LOOKUP_NAME, loc);
 	  if (guessed_id)
 	    {
 	      gcc_rich_location richloc (loc);
-	      richloc.add_fixit_replace (guessed_id);
+	      richloc.add_fixit_replace (guessed_id.suggestion ());
 	      error_at (&richloc,
 			"%qE undeclared (first use in this function);"
 			" did you mean %qs?",
-			id, guessed_id);
+			id, guessed_id.suggestion ());
 	    }
 	  else
 	    error_at (loc, "%qE undeclared (first use in this function)", id);
@@ -4003,8 +4008,8 @@ lookup_name_in_scope (tree name, struct c_scope *scope)
    It also looks for start_typename keywords, to detect "singed" vs "signed"
    typos.  */
 
-const char *
-lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
+name_hint
+lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind, location_t)
 {
   gcc_assert (TREE_CODE (name) == IDENTIFIER_NODE);
 
@@ -4094,9 +4099,9 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
 
   tree best = bm.get_best_meaningful_candidate ();
   if (best)
-    return IDENTIFIER_POINTER (best);
+    return name_hint (IDENTIFIER_POINTER (best), NULL);
   else
-    return NULL;
+    return name_hint (NULL, NULL);
 }
 
 
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 7bca5f1..dae8297 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -36,6 +36,7 @@ along with GCC; see the file COPYING3.  If not see
    location rather than implicitly using input_location.  */
 
 #include "config.h"
+#define INCLUDE_UNIQUE_PTR
 #include "system.h"
 #include "coretypes.h"
 #include "target.h"
@@ -65,6 +66,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "read-rtl-function.h"
 #include "run-rtl-passes.h"
 #include "intl.h"
+#include "c-family/name-hint.h"
 
 /* We need to walk over decls with incomplete struct/union/enum types
    after parsing the whole translation unit.
@@ -1808,13 +1810,14 @@ c_parser_declaration_or_fndef (c_parser *parser, bool fndef_ok,
 	}
       else
 	{
-	  const char *hint = lookup_name_fuzzy (name, FUZZY_LOOKUP_TYPENAME);
+	  name_hint hint = lookup_name_fuzzy (name, FUZZY_LOOKUP_TYPENAME,
+					      here);
 	  if (hint)
 	    {
-	      richloc.add_fixit_replace (hint);
+	      richloc.add_fixit_replace (hint.suggestion ());
 	      error_at (&richloc,
 			"unknown type name %qE; did you mean %qs?",
-			name, hint);
+			name, hint.suggestion ());
 	    }
 	  else
 	    error_at (here, "unknown type name %qE", name);
@@ -4066,15 +4069,16 @@ c_parser_parameter_declaration (c_parser *parser, tree attrs)
       c_parser_set_source_position_from_token (token);
       if (c_parser_next_tokens_start_typename (parser, cla_prefer_type))
 	{
-	  const char *hint = lookup_name_fuzzy (token->value,
-						FUZZY_LOOKUP_TYPENAME);
+	  name_hint hint = lookup_name_fuzzy (token->value,
+					      FUZZY_LOOKUP_TYPENAME,
+					      token->location);
 	  if (hint)
 	    {
 	      gcc_rich_location richloc (token->location);
-	      richloc.add_fixit_replace (hint);
+	      richloc.add_fixit_replace (hint.suggestion ());
 	      error_at (&richloc,
 			"unknown type name %qE; did you mean %qs?",
-			token->value, hint);
+			token->value, hint.suggestion ());
 	    }
 	  else
 	    error_at (token->location, "unknown type name %qE", token->value);
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index b4976d8..8c7fb97 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -19,6 +19,7 @@ along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
 #include "config.h"
+#define INCLUDE_UNIQUE_PTR
 #include "system.h"
 #include "coretypes.h"
 #include "cp-tree.h"
@@ -32,6 +33,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gcc-rich-location.h"
 #include "spellcheck-tree.h"
 #include "parser.h"
+#include "c-family/name-hint.h"
 
 static cxx_binding *cxx_binding_make (tree value, tree type);
 static cp_binding_level *innermost_nonclass_level (void);
@@ -5371,13 +5373,14 @@ suggest_alternatives_for (location_t location, tree name,
     }
   else if (!suggest_misspellings)
     ;
-  else if (const char *fuzzy = lookup_name_fuzzy (name, FUZZY_LOOKUP_NAME))
+  else if (name_hint hint = lookup_name_fuzzy (name, FUZZY_LOOKUP_NAME,
+					       location))
     {
       /* Show a spelling correction.  */
       gcc_rich_location richloc (location);
 
-      richloc.add_fixit_replace (fuzzy);
-      inform (&richloc, "suggested alternative: %qs", fuzzy);
+      richloc.add_fixit_replace (hint.suggestion ());
+      inform (&richloc, "suggested alternative: %qs", hint.suggestion ());
     }
 }
 
@@ -5628,8 +5631,8 @@ consider_binding_level (tree name, best_match <tree, const char *> &bm,
    macro names, returning the best match as a const char *, or NULL if
    no reasonable match is found.  */
 
-const char *
-lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
+name_hint
+lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind, location_t)
 {
   gcc_assert (TREE_CODE (name) == IDENTIFIER_NODE);
 
@@ -5683,7 +5686,7 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
       bm.consider (IDENTIFIER_POINTER (resword_identifier));
     }
 
-  return bm.get_best_meaningful_candidate ();
+  return name_hint (bm.get_best_meaningful_candidate (), NULL);
 }
 
 /* Subroutine of outer_binding.
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 77b9637..8775eeb 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -19,6 +19,7 @@ along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
 #include "config.h"
+#define INCLUDE_UNIQUE_PTR
 #include "system.h"
 #include "coretypes.h"
 #include "cp-tree.h"
@@ -43,6 +44,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cp-cilkplus.h"
 #include "gcc-rich-location.h"
 #include "tree-iterator.h"
+#include "c-family/name-hint.h"
 
 
 /* The lexer.  */
@@ -3287,16 +3289,16 @@ cp_parser_diagnose_invalid_type_name (cp_parser *parser, tree id,
   else if (!parser->scope)
     {
       /* Issue an error message.  */
-      const char *suggestion = NULL;
+      name_hint hint;
       if (TREE_CODE (id) == IDENTIFIER_NODE)
-        suggestion = lookup_name_fuzzy (id, FUZZY_LOOKUP_TYPENAME);
-      if (suggestion)
+	hint = lookup_name_fuzzy (id, FUZZY_LOOKUP_TYPENAME, location);
+      if (hint)
 	{
 	  gcc_rich_location richloc (location);
-	  richloc.add_fixit_replace (suggestion);
+	  richloc.add_fixit_replace (hint.suggestion ());
 	  error_at (&richloc,
 		    "%qE does not name a type; did you mean %qs?",
-		    id, suggestion);
+		    id, hint.suggestion ());
 	}
       else
 	error_at (location, "%qE does not name a type", id);
-- 
1.8.5.3