maint: add assertions to placate static analysis tools

A static analysis tool (http://labs.oracle.com/projects/parfait/)
produced some false positive diagnostics.  Add assertions to help
it understand that the code is correct.
* src/stty.c: Include <assert.h>.
(display_changed): Add an assertion to placate parfait.
(display_all): Likewise.
* src/sort.c: Include <assert.h>.
(main): Add an assertion to placate parfait.
* src/fmt.c: Include <assert.h>.
(get_paragraph): Add an assertion to placate parfait.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/fmt.c b/src/fmt.c
index 308b64555..3da198e16 100644
--- a/src/fmt.c
+++ b/src/fmt.c
@@ -20,6 +20,7 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <getopt.h>
+#include <assert.h>
 
 /* Redefine.  Otherwise, systems (Unicos for one) with headers that define
    it to be a type get syntax errors for the variable declaration below.  */
@@ -610,6 +611,11 @@ get_paragraph (FILE *f)
       while (same_para (c) && in_column == other_indent)
         c = get_line (f, c);
     }
+
+  /* Tell static analysis tools that using word_limit[-1] is ok.
+     word_limit is guaranteed to have been incremented by get_line.  */
+  assert (word < word_limit);
+
   (word_limit - 1)->period = (word_limit - 1)->final = true;
   next_char = c;
   return true;