[PATCH] Fix spelling suggestions for reserved words (PR c++/80177)

[David Malcolm <dmalcolm at redhat dot com>]

As noted in the PR, the C++ frontend currently offers a poor
suggestion for this misspelling:

a.C: In function ‘void f()’:
a.C:3:3: error: ‘static_assertion’ was not declared in this scope
   static_assertion (1 == 0, "1 == 0");
   ^~~~~~~~~~~~~~~~
a.C:3:3: note: suggested alternative: ‘__cpp_static_assert’
   static_assertion (1 == 0, "1 == 0");
   ^~~~~~~~~~~~~~~~
   __cpp_static_assert

when it ought to offer "static_assert" as a suggestion instead.

The root causes are two issues within lookup_name_fuzzy
(called here with FUZZY_LOOKUP_NAME):

(a) If it finds a good enough match in the preprocessor it will
    return the best match *before* considering reserved words,
    rather than picking the closest match overall.

    The fix is to have merge all the results into one best_match
    instance, and pick the overall winner.  However, given that
    some candidates are identifiers (trees), and others are cpp
    macros, the best_match instance's candidate type needs to
    be converted from tree to const char *.  This has some minor
    knock-on effects within name-lookup.c.  Sadly it means some
    extra calls to strlen (one per candidate), but this will be
    purely when error-handling.

(b) It rejects "static_assert" here:

      4998    if (!cp_keyword_starts_decl_specifier_p (resword->rid))
      4999      continue;

    as "static_assert" doesn't start a decl specifier.

    The fix is to only apply this rejection criterion if we're looking
    for typenames, rather than for names in general.

This patch addresses both issues and adds test coverage.

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu.
Adds 7 PASS and 1 UNSUPPORTED (for -std=c++98) to g++.sum

OK for next stage 1?

gcc/cp/ChangeLog:
	PR c++/80177
	* name-lookup.c (suggest_alternative_in_explicit_scope): Convert
	candidate type of bm from tree to const char *.
	(consider_binding_level): Likewise.
	(lookup_name_fuzzy): Likewise, using this to merge the best
	result from the preprocessor into bm, rather than immediately
	returning, so that better matches from reserved words can "win".
	Guard the rejection of keywords that don't start decl-specifiers
	so it only happens for FUZZY_LOOKUP_TYPENAME.

gcc/testsuite/ChangeLog:
	PR c++/80177
	* g++.dg/spellcheck-pr80177.C: New test case.
---
 gcc/cp/name-lookup.c                      | 37 +++++++++++++------------------
 gcc/testsuite/g++.dg/spellcheck-pr80177.C |  7 ++++++
 2 files changed, 23 insertions(+), 21 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/spellcheck-pr80177.C

diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index 994f7f0..16ec0a1 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -48,7 +48,8 @@ static bool lookup_using_namespace (tree, struct scope_binding *, tree,
 				    tree, int);
 static bool qualified_lookup_using_namespace (tree, tree,
 					      struct scope_binding *, int);
-static void consider_binding_level (tree name, best_match <tree, tree> &bm,
+static void consider_binding_level (tree name,
+				    best_match <tree, const char *> &bm,
 				    cp_binding_level *lvl,
 				    bool look_within_fields,
 				    enum lookup_name_fuzzy_kind kind);
@@ -4550,14 +4551,13 @@ suggest_alternative_in_explicit_scope (location_t location, tree name,
 
   cp_binding_level *level = NAMESPACE_LEVEL (scope);
 
-  best_match <tree, tree> bm (name);
+  best_match <tree, const char *> bm (name);
   consider_binding_level (name, bm, level, false, FUZZY_LOOKUP_NAME);
 
   /* See if we have a good suggesion for the user.  */
-  tree best_id = bm.get_best_meaningful_candidate ();
-  if (best_id)
+  const char *fuzzy_name = bm.get_best_meaningful_candidate ();
+  if (fuzzy_name)
     {
-      const char *fuzzy_name = IDENTIFIER_POINTER (best_id);
       gcc_rich_location richloc (location);
       richloc.add_fixit_replace (fuzzy_name);
       inform_at_rich_loc (&richloc, "suggested alternative: %qs",
@@ -4797,7 +4797,7 @@ qualified_lookup_using_namespace (tree name, tree scope,
    Traverse binding level LVL, looking for good name matches for NAME
    (and BM).  */
 static void
-consider_binding_level (tree name, best_match <tree, tree> &bm,
+consider_binding_level (tree name, best_match <tree, const char *> &bm,
 			cp_binding_level *lvl, bool look_within_fields,
 			enum lookup_name_fuzzy_kind kind)
 {
@@ -4809,7 +4809,7 @@ consider_binding_level (tree name, best_match <tree, tree> &bm,
 	tree best_matching_field
 	  = lookup_member_fuzzy (type, name, want_type_p);
 	if (best_matching_field)
-	  bm.consider (best_matching_field);
+	  bm.consider (IDENTIFIER_POINTER (best_matching_field));
       }
 
   for (tree t = lvl->names; t; t = TREE_CHAIN (t))
@@ -4838,7 +4838,7 @@ consider_binding_level (tree name, best_match <tree, tree> &bm,
       if (tree name = DECL_NAME (d))
 	/* Ignore internal names with spaces in them.  */
 	if (!strchr (IDENTIFIER_POINTER (name), ' '))
-	  bm.consider (DECL_NAME (d));
+	  bm.consider (IDENTIFIER_POINTER (name));
     }
 }
 
@@ -4851,7 +4851,7 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
 {
   gcc_assert (TREE_CODE (name) == IDENTIFIER_NODE);
 
-  best_match <tree, tree> bm (name);
+  best_match <tree, const char *> bm (name);
 
   cp_binding_level *lvl;
   for (lvl = scope_chain->class_bindings; lvl; lvl = lvl->level_chain)
@@ -4874,9 +4874,9 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
      the identifiers already checked.  */
   best_macro_match bmm (name, bm.get_best_distance (), parse_in);
   cpp_hashnode *best_macro = bmm.get_best_meaningful_candidate ();
-  /* If a macro is the closest so far to NAME, suggest it.  */
+  /* If a macro is the closest so far to NAME, consider it.  */
   if (best_macro)
-    return (const char *)best_macro->ident.str;
+    bm.consider ((const char *)best_macro->ident.str);
 
   /* Try the "starts_decl_specifier_p" keywords to detect
      "singed" vs "signed" typos.  */
@@ -4884,8 +4884,9 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
     {
       const c_common_resword *resword = &c_common_reswords[i];
 
-      if (!cp_keyword_starts_decl_specifier_p (resword->rid))
-	continue;
+      if (kind == FUZZY_LOOKUP_TYPENAME)
+	if (!cp_keyword_starts_decl_specifier_p (resword->rid))
+	  continue;
 
       tree resword_identifier = ridpointers [resword->rid];
       if (!resword_identifier)
@@ -4897,16 +4898,10 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind)
       if (!C_IS_RESERVED_WORD (resword_identifier))
 	continue;
 
-      bm.consider (resword_identifier);
+      bm.consider (IDENTIFIER_POINTER (resword_identifier));
     }
 
-  /* See if we have a good suggesion for the user.  */
-  tree best_id = bm.get_best_meaningful_candidate ();
-  if (best_id)
-    return IDENTIFIER_POINTER (best_id);
-
-  /* No meaningful suggestion available.  */
-  return NULL;
+  return bm.get_best_meaningful_candidate ();
 }
 
 /* Subroutine of outer_binding.
diff --git a/gcc/testsuite/g++.dg/spellcheck-pr80177.C b/gcc/testsuite/g++.dg/spellcheck-pr80177.C
new file mode 100644
index 0000000..2ff24e8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/spellcheck-pr80177.C
@@ -0,0 +1,7 @@
+// { dg-do compile { target c++11 } }
+
+void pr80177 ()
+{
+  static_assertion (1 == 0, "1 == 0"); // { dg-error "3: 'static_assertion' was not declared in this scope" }
+  // { dg-message "3: suggested alternative: 'static_assert'" "" { target *-*-* } .-1 }
+}
-- 
1.8.5.3