glib: Various minor scan-build fixes

These squash various warnings from `scan-build`. None of them are
legitimate bugs, but some of them do improve code readability a bit.
Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #1767

gio/gcredentials.c

@@ -542,13 +542,12 @@ g_credentials_set_unix_user (GCredentials    *credentials,
                              uid_t            uid,
                              GError         **error)
 {
-  gboolean ret;
+  gboolean ret = FALSE;
 
   g_return_val_if_fail (G_IS_CREDENTIALS (credentials), FALSE);
   g_return_val_if_fail (uid != -1, FALSE);
   g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
 
-  ret = FALSE;
 #if G_CREDENTIALS_USE_LINUX_UCRED
   credentials->native.uid = uid;
   ret = TRUE;

glib/gchecksum.c

@@ -1344,6 +1344,7 @@ sha512_sum_close (Sha512sum *sha512)
   memset (pad + pad_len, 0x00, zeros / 8);
   pad_len += zeros / 8;
   zeros = zeros % 8;
+  (void) zeros;  /* don’t care about the dead store */
 
   /* put message bit length at the end of padding */
   PUT_UINT64 (sha512->data_len[1], pad, pad_len);

glib/gkeyfile.c

@@ -3317,6 +3317,7 @@ g_key_file_set_key_comment (GKeyFile     *key_file,
   pair->value = g_key_file_parse_comment_as_value (key_file, comment);
   
   key_node = g_list_insert (key_node, pair, 1);
+  (void) key_node;
 
   return TRUE;
 }

glib/gmain.c

@@ -1040,6 +1040,7 @@ find_source_list_for_priority (GMainContext *context,
        * context->source_lists without having to walk the list again.
        */
       last = g_list_append (last, source_list);
+      (void) last;
     }
   return source_list;
 }

glib/gmarkup.c

@@ -2917,7 +2917,6 @@ g_markup_collect_attributes (const gchar         *element_name,
 failure:
   /* replay the above to free allocations */
   type = first_type;
-  attr = first_attr;
 
   va_start (ap, first_attr);
   while (type != G_MARKUP_COLLECT_INVALID)
@@ -2952,7 +2951,10 @@ failure:
 
       type = va_arg (ap, GMarkupCollectType);
       if (type != G_MARKUP_COLLECT_INVALID)
-        attr = va_arg (ap, const char *);
+        {
+          attr = va_arg (ap, const char *);
+          (void) attr;
+        }
     }
   va_end (ap);
 

glib/gmessages.c

@@ -1313,7 +1313,7 @@ g_logv (const gchar   *log_domain,
     {
       GLogLevelFlags test_level;
 
-      test_level = 1 << i;
+      test_level = 1L << i;
       if (log_level & test_level)
 	{
 	  GLogDomain *domain;

glib/grand.c

@@ -502,7 +502,7 @@ g_rand_int_range (GRand  *rand,
                   gint32  end)
 {
   guint32 dist = end - begin;
-  guint32 random;
+  guint32 random = 0;
 
   g_return_val_if_fail (rand != NULL, begin);
   g_return_val_if_fail (end > begin, begin);
@@ -563,7 +563,6 @@ g_rand_int_range (GRand  *rand,
 	}
       break;
     default:
-      random = 0;		/* Quiet GCC */
       g_assert_not_reached ();
     }      
  

glib/gspawn.c

@@ -435,8 +435,6 @@ g_spawn_sync (const gchar          *working_directory,
          (outpipe >= 0 ||
           errpipe >= 0))
     {
-      ret = 0;
-          
       FD_ZERO (&fds);
       if (outpipe >= 0)
         FD_SET (outpipe, &fds);

glib/gtestutils.c

@@ -3694,6 +3694,9 @@ g_test_trap_assertions (const char     *domain,
       g_assertion_message (domain, file, line, func, msg);
       g_free (msg);
     }
+
+  (void) logged_child_output;  /* shut up scan-build about the final unread assignment */
+
   g_free (process_id);
 }
 

glib/gunidecomp.c

@@ -443,6 +443,7 @@ _g_utf8_normalize_wc (const gchar    *str,
     {
       g_unicode_canonical_ordering (wc_buffer + last_start, n_wc - last_start);
       last_start = n_wc;
+      (void) last_start;
     }
 	  
   wc_buffer[n_wc] = 0;

glib/gvariant-parser.c

@@ -2527,6 +2527,8 @@ g_variant_new_parsed_va (const gchar *format,
   if (*stream.stream)
     g_error ("g_variant_new_parsed: trailing text after value");
 
+  g_clear_error (&error);
+
   return result;
 }
 

glib/tests/bookmarkfile.c

@@ -175,6 +175,7 @@ test_misc (void)
                                         &error);
   g_assert_error (error, G_BOOKMARK_FILE_ERROR, G_BOOKMARK_FILE_ERROR_INVALID_VALUE);
   g_clear_error (&error);
+  g_assert_false (res);
 
   g_bookmark_file_set_mime_type (bookmark, 
                                  "file:///tmp/schedule1.ps",