[PATCH 02/02] C FE: add fix-it hint for . vs ->

[David Malcolm <dmalcolm at redhat dot com>]

This is the most trivial example of a real fix-it example I could think
of: if the user writes
	ptr.field
rather than ptr->field.

gcc/c/ChangeLog:
	* c-typeck.c (build_component_ref): Special-case POINTER_TYPE when
	generating a "not a structure of union"  error message, and
	suggest a "->" rather than a ".", providing a fix-it hint.

gcc/testsuite/ChangeLog:
	* gcc.dg/fixits.c: New file.
---
 gcc/c/c-typeck.c              | 15 +++++++++++++++
 gcc/testsuite/gcc.dg/fixits.c | 14 ++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/fixits.c

diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index c2e16c6..6fe1ca8 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -2336,6 +2336,21 @@ build_component_ref (location_t loc, tree datum, tree component)
 
       return ref;
     }
+  else if (code == POINTER_TYPE && !c_dialect_objc ())
+    {
+      /* Special-case the error message for "ptr.field" for the case
+	 where the user has confused "." vs "->".
+	 We don't do it for Objective-C, since Objective-C 2.0 dot-syntax
+	 allows "." for ptrs; we could be handling a failed attempt
+	 to access a property.  */
+      rich_location richloc (line_table, loc);
+      /* "loc" should be the "." token.  */
+      richloc.add_fixit_replace (source_range::from_location (loc), "->");
+      error_at_rich_loc (&richloc,
+			 "%qE is a pointer; did you mean to use %<->%>?",
+			 datum);
+      return error_mark_node;
+    }
   else if (code != ERROR_MARK)
     error_at (loc,
 	      "request for member %qE in something not a structure or union",
diff --git a/gcc/testsuite/gcc.dg/fixits.c b/gcc/testsuite/gcc.dg/fixits.c
new file mode 100644
index 0000000..3b8c8a8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fixits.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-fdiagnostics-show-caret" } */
+
+struct foo { int x; };
+
+int test (struct foo *ptr)
+{
+  return ptr.x; /* { dg-error "'ptr' is a pointer; did you mean to use '->'?" } */
+/* { dg-begin-multiline-output "" }
+   return ptr.x;
+             ^
+             ->
+   { dg-end-multiline-output "" } */
+}
-- 
1.8.5.3