warning cleanup: suspicious switch fallthrough cases.

This is the seventh round of an effort to enable GCC's -Wextra
option. Warnings about switch fallthrough situations are
addressed. GCC now has a diagnostic for this that is enabled
by -Wextra in such a way that if a fallthrough comment is
present, the diagnostic is suppressed. In much of the code,
we have such a comment. It's missing in a few places, or
misplaced. There are also some real bugs.

* hash.c (hash_buf): Add fallthrough comments to intentional
fallthrough cases.
(hash_hash_op): bugfix: add break statement. The 32 and 64
bit cases are independent (at compile time).

* lib.c (cdr, nullify, list_collect, empty): Add fallthrough
comment.
(int_str): Add missing break. This has not caused a
bug though because setting the octzero flag in the zerox
case is harmless to the logic which follows.

* linenoise.c (edit): Move misplaced fallthrough.

* sysif.c (fcntl_wrap): Bugfix: add missing break, without
which errno is tampered to hold EINVAL, in spite of a
successful F_SETLK, F_SETLKW or F_GETLK operation.

* unwind.h (jmp_restore): Declare noreturn, so that GCC
does not issue a false positive warning about a fallthrough
in uw_unwind_to_exit_point.

* utf8.c (utf8_from_buf, utf8_decode): Move a fallthrough
comment outside of preprocessing, so it is properly processed
by GCC's diagnostic.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib.c b/lib.c
index c61cf60d..6fae0008 100644
--- a/lib.c
+++ b/lib.c
@@ -601,6 +601,7 @@ val cdr(val cons)
           return funcall2(lambda_meth, cons, rcons(one, t));
       }
     }
+    /* fallthrough */
   default:
     type_mismatch(lit("cdr: ~s is not a cons"), cons, nao);
   }
@@ -1061,6 +1062,7 @@ val nullify(val seq)
       if (nullify_meth)
         return funcall1(nullify_meth, seq);
     }
+    /* fallthrough */
   default:
     return seq;
   }
@@ -1107,6 +1109,7 @@ again:
       replace_obj(tailobj, items, t, t);
       return ptail;
     }
+    /* fallthrough */
   default:
     uw_throwf(error_s, lit("cannot append ~s"), deref(ptail), nao);
   }
@@ -4568,8 +4571,10 @@ val int_str(val str, val base)
     case 'x': case 'X':
       zerox = 1;
       wcs += 2;
+      break;
     default:
       octzero = 1;
+      break;
     }
     break;
   }
@@ -10415,6 +10420,7 @@ val empty(val seq)
         return eq(funcall1(length_meth, seq), zero);
       return if3(nullify_meth && funcall1(nullify_meth, seq), nil, seq);
     }
+    /* fallthrough */
   default:
     type_mismatch(lit("empty: ~s is not a sequence"), seq, nao);
   }