[PATCH 4/4] C: add fixit hint to misspelled field names

[David Malcolm <dmalcolm at redhat dot com>]

Similar to the C++ case, but more involved as the location of the
pertinent token isn't readily available.  The patch adds it as a param
to build_component_ref.  All callers are updated to provide the info,
apart from objc_build_component_ref; fixing the latter would lead to
a cascade of other changes, so it's simplest to provide UNKNOWN_LOCATION
there and have build_component_ref fall back gracefully for this case
to the old behavior of showing a hint in the message, without a fixit
replacement in the source view.

This does slightly change the location of the error; before we had:

test.c:11:13: error: 'union u' has no member named 'colour'; did you mean 'color'?
   return ptr->colour;
             ^~

with the patch we have:

test.c:11:15: error: 'union u' has no member named 'colour'; did you mean 'color'?
   return ptr->colour;
               ^~~~~~
               color

I think the location change is an improvement.

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

OK for trunk?

gcc/c/ChangeLog:
	* c-parser.c (c_parser_postfix_expression): In __builtin_offsetof
	and structure element reference, capture the location of the
	element name token and pass it to build_component_ref.
	(c_parser_postfix_expression_after_primary): Likewise for
	structure element dereference.
	(c_parser_omp_variable_list): Likewise for
	OMP_CLAUSE_{_CACHE, MAP, FROM, TO},
	* c-tree.h (build_component_ref): Add location_t param.
	* c-typeck.c (build_component_ref): Add location_t param
	COMPONENT_LOC.  Use it, if available, when issuing hints about
	mispelled member names to provide a fixit replacement hint.

gcc/objc/ChangeLog:
	* objc-act.c (objc_build_component_ref): Update call
	to build_component_ref for added param, passing UNKNOWN_LOCATION.

gcc/testsuite/ChangeLog:
	* gcc.dg/spellcheck-fields-2.c: New test case.
---
 gcc/c/c-parser.c                           | 34 +++++++++++++++++++++---------
 gcc/c/c-tree.h                             |  2 +-
 gcc/c/c-typeck.c                           | 26 +++++++++++++++++++----
 gcc/objc/objc-act.c                        |  3 ++-
 gcc/testsuite/gcc.dg/spellcheck-fields-2.c | 19 +++++++++++++++++
 5 files changed, 68 insertions(+), 16 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/spellcheck-fields-2.c

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 36c44ab..19e6772 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -7707,8 +7707,9 @@ c_parser_postfix_expression (c_parser *parser)
 	       accept sub structure and sub array references.  */
 	    if (c_parser_next_token_is (parser, CPP_NAME))
 	      {
+		c_token *comp_tok = c_parser_peek_token (parser);
 		offsetof_ref = build_component_ref
-		  (loc, offsetof_ref, c_parser_peek_token (parser)->value);
+		  (loc, offsetof_ref, comp_tok->value, comp_tok->location);
 		c_parser_consume_token (parser);
 		while (c_parser_next_token_is (parser, CPP_DOT)
 		       || c_parser_next_token_is (parser,
@@ -7734,9 +7735,10 @@ c_parser_postfix_expression (c_parser *parser)
 			    c_parser_error (parser, "expected identifier");
 			    break;
 			  }
+			c_token *comp_tok = c_parser_peek_token (parser);
 			offsetof_ref = build_component_ref
-			  (loc, offsetof_ref,
-			   c_parser_peek_token (parser)->value);
+			  (loc, offsetof_ref, comp_tok->value,
+			   comp_tok->location);
 			c_parser_consume_token (parser);
 		      }
 		    else
@@ -8213,7 +8215,7 @@ c_parser_postfix_expression_after_primary (c_parser *parser,
 {
   struct c_expr orig_expr;
   tree ident, idx;
-  location_t sizeof_arg_loc[3];
+  location_t sizeof_arg_loc[3], comp_loc;
   tree sizeof_arg[3];
   unsigned int literal_zero_mask;
   unsigned int i;
@@ -8327,7 +8329,11 @@ c_parser_postfix_expression_after_primary (c_parser *parser,
 	  c_parser_consume_token (parser);
 	  expr = default_function_array_conversion (expr_loc, expr);
 	  if (c_parser_next_token_is (parser, CPP_NAME))
-	    ident = c_parser_peek_token (parser)->value;
+	    {
+	      c_token *comp_tok = c_parser_peek_token (parser);
+	      ident = comp_tok->value;
+	      comp_loc = comp_tok->location;
+	    }
 	  else
 	    {
 	      c_parser_error (parser, "expected identifier");
@@ -8339,7 +8345,8 @@ c_parser_postfix_expression_after_primary (c_parser *parser,
 	  start = expr.get_start ();
 	  finish = c_parser_peek_token (parser)->get_finish ();
 	  c_parser_consume_token (parser);
-	  expr.value = build_component_ref (op_loc, expr.value, ident);
+	  expr.value = build_component_ref (op_loc, expr.value, ident,
+					    comp_loc);
 	  set_c_expr_source_range (&expr, start, finish);
 	  expr.original_code = ERROR_MARK;
 	  if (TREE_CODE (expr.value) != COMPONENT_REF)
@@ -8359,7 +8366,11 @@ c_parser_postfix_expression_after_primary (c_parser *parser,
 	  c_parser_consume_token (parser);
 	  expr = convert_lvalue_to_rvalue (expr_loc, expr, true, false);
 	  if (c_parser_next_token_is (parser, CPP_NAME))
-	    ident = c_parser_peek_token (parser)->value;
+	    {
+	      c_token *comp_tok = c_parser_peek_token (parser);
+	      ident = comp_tok->value;
+	      comp_loc = comp_tok->location;
+	    }
 	  else
 	    {
 	      c_parser_error (parser, "expected identifier");
@@ -8375,7 +8386,7 @@ c_parser_postfix_expression_after_primary (c_parser *parser,
 					    build_indirect_ref (op_loc,
 								expr.value,
 								RO_ARROW),
-					    ident);
+					    ident, comp_loc);
 	  set_c_expr_source_range (&expr, start, finish);
 	  expr.original_code = ERROR_MARK;
 	  if (TREE_CODE (expr.value) != COMPONENT_REF)
@@ -10621,9 +10632,12 @@ c_parser_omp_variable_list (c_parser *parser,
 		      t = error_mark_node;
 		      break;
 		    }
-		  tree ident = c_parser_peek_token (parser)->value;
+
+		  c_token *comp_tok = c_parser_peek_token (parser);
+		  tree ident = comp_tok->value;
+		  location_t comp_loc = comp_tok->location;
 		  c_parser_consume_token (parser);
-		  t = build_component_ref (op_loc, t, ident);
+		  t = build_component_ref (op_loc, t, ident, comp_loc);
 		}
 	      /* FALLTHROUGH  */
 	    case OMP_CLAUSE_DEPEND:
diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
index 4633182..3201a71 100644
--- a/gcc/c/c-tree.h
+++ b/gcc/c/c-tree.h
@@ -604,7 +604,7 @@ extern struct c_expr convert_lvalue_to_rvalue (location_t, struct c_expr,
 					       bool, bool);
 extern void mark_exp_read (tree);
 extern tree composite_type (tree, tree);
-extern tree build_component_ref (location_t, tree, tree);
+extern tree build_component_ref (location_t, tree, tree, location_t);
 extern tree build_array_ref (location_t, tree, tree);
 extern tree build_external_ref (location_t, tree, int, tree *);
 extern void pop_maybe_used (bool);
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 58c2139..8aece1a 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -2309,10 +2309,12 @@ should_suggest_deref_p (tree datum_type)
 
 /* Make an expression to refer to the COMPONENT field of structure or
    union value DATUM.  COMPONENT is an IDENTIFIER_NODE.  LOC is the
-   location of the COMPONENT_REF.  */
+   location of the COMPONENT_REF.  COMPONENT_LOC is the location
+   of COMPONENT.  */
 
 tree
-build_component_ref (location_t loc, tree datum, tree component)
+build_component_ref (location_t loc, tree datum, tree component,
+		     location_t component_loc)
 {
   tree type = TREE_TYPE (datum);
   enum tree_code code = TREE_CODE (type);
@@ -2344,8 +2346,24 @@ build_component_ref (location_t loc, tree datum, tree component)
 	{
 	  tree guessed_id = lookup_field_fuzzy (type, component);
 	  if (guessed_id)
-	    error_at (loc, "%qT has no member named %qE; did you mean %qE?",
-		      type, component, guessed_id);
+	    {
+	      /* Attempt to provide a fixit replacement hint, if
+		 we have a valid range for the component.  */
+	      location_t reported_loc
+		= (component_loc != UNKNOWN_LOCATION) ? component_loc : loc;
+	      rich_location rich_loc (line_table, reported_loc);
+	      if (component_loc != UNKNOWN_LOCATION)
+		{
+		  source_range component_range =
+		    get_range_from_loc (line_table, component_loc);
+		  rich_loc.add_fixit_replace (component_range,
+					      IDENTIFIER_POINTER (guessed_id));
+		}
+	      error_at_rich_loc
+		(&rich_loc,
+		 "%qT has no member named %qE; did you mean %qE?",
+		 type, component, guessed_id);
+	    }
 	  else
 	    error_at (loc, "%qT has no member named %qE", type, component);
 	  return error_mark_node;
diff --git a/gcc/objc/objc-act.c b/gcc/objc/objc-act.c
index 4856457..44f01d2 100644
--- a/gcc/objc/objc-act.c
+++ b/gcc/objc/objc-act.c
@@ -2654,7 +2654,8 @@ objc_build_component_ref (tree datum, tree component)
   return finish_class_member_access_expr (datum, component, false,
                                           tf_warning_or_error);
 #else
-  return build_component_ref (input_location, datum, component);
+  return build_component_ref (input_location, datum, component,
+			      UNKNOWN_LOCATION);
 #endif
 }
 
diff --git a/gcc/testsuite/gcc.dg/spellcheck-fields-2.c b/gcc/testsuite/gcc.dg/spellcheck-fields-2.c
new file mode 100644
index 0000000..d6ebff1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/spellcheck-fields-2.c
@@ -0,0 +1,19 @@
+/* { dg-options "-fdiagnostics-show-caret" } */
+
+union u
+{
+  int color;
+  int shape;
+};
+
+int test (union u *ptr)
+{
+  return ptr->colour; /* { dg-error "did you mean .color.?" } */
+}
+
+/* Verify that we get an underline and a fixit hint.  */
+/* { dg-begin-multiline-output "" }
+   return ptr->colour;
+               ^~~~~~
+               color
+   { dg-end-multiline-output "" } */
-- 
1.8.5.3