From: David Herrmann <dh.herrmann@gmail.com>
Date: Fri, 12 Dec 2014 08:43:54 +0000 (+0100)
Subject: hwdb: fix dangling 'else' ambuguity
X-Git-Tag: v219~1043
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=commitdiff_plain;h=bff686e2a981ccd0888cdf1981977d24320f1770;hp=0b9315719154fa7ea1a075e1b3785713f5acc3a1

hwdb: fix dangling 'else' ambuguity

Imagine the following use of hwdb:

    if (condition_A)
        SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value)
            operation_A(key, value);
    else
        log_error("...");

This should work just fine, but but definitely does not what you would
expect. Due to how SD_HWDB_FOREACH_PROPERTY is defined, the dangling
'else' is linked to the hidden 'if' statement in the macro instead of the
outer 'if (condition_A)'. This is unexpected and really annoying to debug.

Fix this by never leaving un-finished if-statements in
SD_HWDB_FOREACH_PROPERTY(). We simply inverse the if() statement and
explicitly add an 'else'-branch. This way, the statement is closed and all
ambuguities are resolved.
---

diff --git a/src/systemd/sd-hwdb.h b/src/systemd/sd-hwdb.h
index f41555df7..3c44b981d 100644
--- a/src/systemd/sd-hwdb.h
+++ b/src/systemd/sd-hwdb.h
@@ -39,8 +39,9 @@ int sd_hwdb_get(sd_hwdb *hwdb, const char *modalias, const char *key, const char
 int sd_hwdb_seek(sd_hwdb *hwdb, const char *modalias);
 int sd_hwdb_enumerate(sd_hwdb *hwdb, const char **key, const char **value);
 
+/* the inverse condition avoids ambiguity of danling 'else' after the macro */
 #define SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value)            \
-        if (sd_hwdb_seek(hwdb, modalias) >= 0)                          \
-                while (sd_hwdb_enumerate(hwdb, &(key), &(value)) > 0)
+        if (sd_hwdb_seek(hwdb, modalias) < 0) { }                       \
+        else while (sd_hwdb_enumerate(hwdb, &(key), &(value)) > 0)
 
 #endif