Spelling suggestions for misspelled preprocessor directives

This patch allows the preprocessor to offer suggestions for misspelled
directives, taking us from e.g.:

test.c:5:2: error: invalid preprocessing directive #endfi
 #endfi
  ^~~~~

to:

test.c:5:2: error: invalid preprocessing directive #endfi; did you mean #endif?
 #endfi
  ^~~~~
  endif

gcc/c-family/ChangeLog:
	* c-common.c: Include "spellcheck.h".
	(cb_get_suggestion): New function.
	* c-common.h (cb_get_suggestion): New decl.
	* c-lex.c (init_c_lex): Initialize cb->get_suggestion to
	cb_get_suggestion.

gcc/testsuite/ChangeLog:
	* gcc.dg/cpp/misspelled-directive-1.c: New testcase.
	* gcc.dg/cpp/misspelled-directive-2.c: New testcase.

libcpp/ChangeLog:
	* directives.c (directive_names): New array.
	(_cpp_handle_directive): Offer spelling suggestions for misspelled
	directives.
	* errors.c (cpp_diagnostic_at_richloc): New function.
	(cpp_error_at_richloc): New function.
	* include/cpplib.h (struct cpp_callbacks): Add field
	"get_suggestion".
	(cpp_error_at_richloc): New decl.

From-SVN: r239585

7 files changed, 69 insertions, 0 deletions

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index cc82370..1ed5268 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,11 @@
+2016-08-18  David Malcolm  <dmalcolm@redhat.com>
+
+	* c-common.c: Include "spellcheck.h".
+	(cb_get_suggestion): New function.
+	* c-common.h (cb_get_suggestion): New decl.
+	* c-lex.c (init_c_lex): Initialize cb->get_suggestion to
+	cb_get_suggestion.
+
 2016-08-18  Marek Polacek  <polacek@redhat.com>
 
 	PR c/71514
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 22e3844..9082883 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -46,6 +46,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "opts.h"
 #include "gimplify.h"
 #include "substring-locations.h"
+#include "spellcheck.h"
 
 cpp_reader *parse_in;		/* Declared in c-pragma.h.  */
 
@@ -12948,6 +12949,22 @@ cb_get_source_date_epoch (cpp_reader *pfile ATTRIBUTE_UNUSED)
   return (time_t) epoch;
 }
 
+/* Callback for libcpp for offering spelling suggestions for misspelled
+   directives.  GOAL is an unrecognized string; CANDIDATES is a
+   NULL-terminated array of candidate strings.  Return the closest
+   match to GOAL within CANDIDATES, or NULL if none are good
+   suggestions.  */
+
+const char *
+cb_get_suggestion (cpp_reader *, const char *goal,
+		   const char *const *candidates)
+{
+  best_match<const char *, const char *> bm (goal);
+  while (*candidates)
+    bm.consider (*candidates++);
+  return bm.get_best_meaningful_candidate ();
+}
+
 /* Check and possibly warn if two declarations have contradictory
    attributes, such as always_inline vs. noinline.  */
 
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 4673123..31320bf 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1110,6 +1110,11 @@ extern time_t cb_get_source_date_epoch (cpp_reader *pfile);
    __TIME__ can store.  */
 #define MAX_SOURCE_DATE_EPOCH HOST_WIDE_INT_C (253402300799)
 
+/* Callback for libcpp for offering spelling suggestions for misspelled
+   directives.  */
+extern const char *cb_get_suggestion (cpp_reader *, const char *,
+				      const char *const *);
+
 extern GTY(()) string_concat_db *g_string_concat_db;
 
 /* libcpp can calculate location information about a range of characters
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index 4c7e385..c904ee6 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -81,6 +81,7 @@ init_c_lex (void)
   cb->read_pch = c_common_read_pch;
   cb->has_attribute = c_common_has_attribute;
   cb->get_source_date_epoch = cb_get_source_date_epoch;
+  cb->get_suggestion = cb_get_suggestion;
 
   /* Set the debug callbacks if we can use them.  */
   if ((debug_info_level == DINFO_LEVEL_VERBOSE
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index e37bff4..21e9770 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2016-08-18  David Malcolm  <dmalcolm@redhat.com>
+
+	* gcc.dg/cpp/misspelled-directive-1.c: New testcase.
+	* gcc.dg/cpp/misspelled-directive-2.c: New testcase.
+
 2016-08-18  Marek Polacek  <polacek@redhat.com>
 
 	PR c/71514
diff --git a/gcc/testsuite/gcc.dg/cpp/misspelled-directive-1.c b/gcc/testsuite/gcc.dg/cpp/misspelled-directive-1.c
new file mode 100644
index 0000000..f79670a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/misspelled-directive-1.c
@@ -0,0 +1,12 @@
+#ifndef SOME_GUARD /* { dg-error "unterminated" } */
+
+#if 1
+/* Typo here: "endfi" should have been "endif".  */
+#endfi /* { dg-error "invalid preprocessing directive #endfi; did you mean #endif?" } */
+
+int make_non_empty;
+
+/* Another transposition typo:  */
+#deifne FOO /* { dg-error "invalid preprocessing directive #deifne; did you mean #define?" } */ 
+
+#endif /* #ifndef SOME_GUARD */
diff --git a/gcc/testsuite/gcc.dg/cpp/misspelled-directive-2.c b/gcc/testsuite/gcc.dg/cpp/misspelled-directive-2.c
new file mode 100644
index 0000000..7ec5dee
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/misspelled-directive-2.c
@@ -0,0 +1,21 @@
+/* { dg-options "-fdiagnostics-show-caret" } */
+
+#endfi /* { dg-error "invalid preprocessing directive #endfi; did you mean #endif?" } */
+
+/* Verify that we offer fix-it hints.  */
+/* { dg-begin-multiline-output "" }
+ #endfi
+  ^~~~~
+  endif
+  { dg-end-multiline-output "" } */
+
+/* Test coverage for the case of an unrecognized directive where no suggestion
+   is offered.  */
+
+#this_does_not_match_anything /* { dg-error "invalid preprocessing directive #this_does_not_match_anything" } */
+/* { dg-begin-multiline-output "" }
+ #this_does_not_match_anything
+  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  { dg-end-multiline-output "" } */
+
+int make_non_empty;