wt-status: fix possible use of uninitialized variable

In wt_status_print_change_data, we accept a change_type flag
that is meant to be either WT_STATUS_UPDATED or
WT_STATUS_CHANGED.  We then switch() on this value to set
the local variable "status" for each case, but do not
provide a fallback "default" label to the switch statement.

As a result, the compiler realizes that "status" might be
unset, and complains with a warning. To silence this
warning, we use the "int status = status" trick.  This is
correct with the current code, as all callers provide one of
the two expected change_type flags. However, it's also a
maintenance trap, as there is nothing to prevent future
callers from passing another flag, nor to document this
assumption.

Instead of using the "x = x" hack, let's handle the default
case in the switch() statement with a die("BUG"). That tells
the compiler and any readers of the code exactly what the
function's input assumptions are.

We could also convert the flag to an enum, which would
provide a compile-time check on the function input. However,
since these flags are part of a larger enum, that would make
the code unnecessarily complex (we would have to make a new
enum with just the two flags, and then convert it to the old
enum for passing to sub-functions).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/wt-status.c b/wt-status.c
index ef405d03d928c34fe90e27b188bb7a942e3f834c..75558177860d14120636859e2dcc29b48b72a721 100644 (file)
--- a/wt-status.c
+++ b/wt-status.c
@@ -264,7 +264,7 @@ static void wt_status_print_change_data(struct wt_status *s,
 {
        struct wt_status_change_data *d = it->util;
        const char *c = color(change_type, s);
-       int status = status;
+       int status;
        char *one_name;
        char *two_name;
        const char *one, *two;
@@ -292,6 +292,9 @@ static void wt_status_print_change_data(struct wt_status *s,
                }
                status = d->worktree_status;
                break;
+       default:
+               die("BUG: unhandled change_type %d in wt_status_print_change_data",
+                   change_type);
        }
 
        one = quote_path(one_name, -1, &onebuf, s->prefix);