syntax-check: drop useless useless-if-before-free

With most of new code using g_auto for cleanup, contributors
are used to most of the free fucntions handling NULL gracefully.

Also, despite finding some occurrences in current codebase:
  avoid_if_before_free
  ~/libvirt/src/ch/ch_monitor.c: if (mon->vm)
        virObjectUnref(mon->vm);
  ~/libvirt/src/util/virresctrl.c: if (a_type->masks[cache])
        virBitmapFree(a_type->masks[cache]);
the check passes succesfully, because the script's logic:

  Exit status:
    0   one or more matches
    1   no match
    2   an error

does not play nicely with xargs:

  xargs exits with the following status:
       0      if it succeeds
     123      if any invocation of the command exited with status 1-125

The list of functions is also out of date - e.g. qemuCapsFree has
been renamed since.

This also helps eliminate one more Perl script per our programming
languages strategy: https://libvirt.org/programming-languages.html

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

build-aux/syntax-check.mk

@@ -114,181 +114,6 @@ _test_script_regex = \<test-lib\.sh\>
 VC_LIST_ALWAYS_EXCLUDE_REGEX = \
   (^(docs/(news(-[0-9]*)?\.html\.in|.*\.patch))|\.(po|fig|gif|ico|png))$$
 
-# Functions like free() that are no-ops on NULL arguments.
-useless_free_options = \
-  --name=VBOX_UTF16_FREE \
-  --name=VBOX_UTF8_FREE \
-  --name=VBOX_COM_UNALLOC_MEM \
-  --name=VIR_FREE \
-  --name=qemuCapsFree \
-  --name=qemuMigrationCookieFree \
-  --name=qemuMigrationCookieGraphicsFree \
-  --name=sexpr_free \
-  --name=usbFreeDevice \
-  --name=virBandwidthDefFree \
-  --name=virBitmapFree \
-  --name=virCPUDefFree \
-  --name=virCapabilitiesFree \
-  --name=virCapabilitiesFreeGuest \
-  --name=virCapabilitiesFreeGuestDomain \
-  --name=virCapabilitiesFreeGuestFeature \
-  --name=virCapabilitiesFreeGuestMachine \
-  --name=virCapabilitiesFreeHostNUMACell \
-  --name=virCapabilitiesFreeMachines \
-  --name=virCgroupFree \
-  --name=virCommandFree \
-  --name=virConfFreeList \
-  --name=virConfFreeValue \
-  --name=virDomainActualNetDefFree \
-  --name=virDomainChrDefFree \
-  --name=virDomainControllerDefFree \
-  --name=virDomainDefFree \
-  --name=virDomainDeviceDefFree \
-  --name=virDomainDiskDefFree \
-  --name=virDomainEventCallbackListFree \
-  --name=virObjectEventQueueFree \
-  --name=virDomainFSDefFree \
-  --name=virDomainGraphicsDefFree \
-  --name=virDomainHostdevDefFree \
-  --name=virDomainInputDefFree \
-  --name=virDomainNetDefFree \
-  --name=virDomainObjFree \
-  --name=virDomainSmartcardDefFree \
-  --name=virDomainSnapshotObjFree \
-  --name=virDomainSoundDefFree \
-  --name=virDomainVideoDefFree \
-  --name=virDomainWatchdogDefFree \
-  --name=virFileDirectFdFree \
-  --name=virHashFree \
-  --name=virInterfaceDefFree \
-  --name=virInterfaceIpDefFree \
-  --name=virInterfaceObjFree \
-  --name=virInterfaceProtocolDefFree \
-  --name=virJSONValueFree \
-  --name=virLastErrFreeData \
-  --name=virNetMessageFree \
-  --name=virNWFilterDefFree \
-  --name=virNWFilterEntryFree \
-  --name=virNWFilterHashTableFree \
-  --name=virNWFilterIPAddrLearnReqFree \
-  --name=virNWFilterIncludeDefFree \
-  --name=virNWFilterObjFree \
-  --name=virNWFilterRuleDefFree \
-  --name=virNWFilterRuleInstFree \
-  --name=virNetworkDefFree \
-  --name=virNodeDeviceDefFree \
-  --name=virNodeDeviceObjFree \
-  --name=virObjectUnref \
-  --name=virObjectFreeCallback \
-  --name=virPCIDeviceFree \
-  --name=virSecretDefFree \
-  --name=virStorageEncryptionFree \
-  --name=virStorageEncryptionSecretFree \
-  --name=virStorageFileFreeMetadata \
-  --name=virStoragePoolDefFree \
-  --name=virStoragePoolObjFree \
-  --name=virStoragePoolSourceFree \
-  --name=virStorageVolDefFree \
-  --name=virThreadPoolFree \
-  --name=xmlBufferFree \
-  --name=xmlFree \
-  --name=xmlFreeDoc \
-  --name=xmlFreeNode \
-  --name=xmlXPathFreeContext \
-  --name=xmlXPathFreeObject
-
-# The following template was generated by this command:
-# make ID && aid free|grep '^vi'|sed 's/ .*//;s/^/#   /'
-# N virBufferFreeAndReset
-# y virCPUDefFree
-# y virCapabilitiesFree
-# y virCapabilitiesFreeGuest
-# y virCapabilitiesFreeGuestDomain
-# y virCapabilitiesFreeGuestFeature
-# y virCapabilitiesFreeGuestMachine
-# y virCapabilitiesFreeHostNUMACell
-# y virCapabilitiesFreeMachines
-# N virCapabilitiesFreeNUMAInfo FIXME
-# y virCgroupFree
-# N virConfFree               (diagnoses the "error")
-# y virConfFreeList
-# y virConfFreeValue
-# y virDomainChrDefFree
-# y virDomainControllerDefFree
-# y virDomainDefFree
-# y virDomainDeviceDefFree
-# y virDomainDiskDefFree
-# y virDomainEventCallbackListFree
-# y virDomainEventQueueFree
-# y virDomainFSDefFree
-# n virDomainFree
-# n virDomainFreeName (can't fix -- returns int)
-# y virDomainGraphicsDefFree
-# y virDomainHostdevDefFree
-# y virDomainInputDefFree
-# y virDomainNetDefFree
-# y virDomainObjFree
-# n virDomainSnapshotFree (returns int)
-# n virDomainSnapshotFreeName (returns int)
-# y virDomainSnapshotObjFree
-# y virDomainSoundDefFree
-# y virDomainVideoDefFree
-# y virDomainWatchdogDefFree
-# n virDrvNodeGetCellsFreeMemory (returns int)
-# n virDrvNodeGetFreeMemory (returns long long)
-# n virFree - dereferences param
-# n virFreeError
-# n virHashFree (takes 2 args)
-# y virInterfaceDefFree
-# n virInterfaceFree (returns int)
-# n virInterfaceFreeName
-# y virInterfaceIpDefFree
-# y virInterfaceObjFree
-# n virInterfaceObjListFree
-# y virInterfaceProtocolDefFree
-# y virJSONValueFree
-# y virLastErrFreeData
-# y virNWFilterDefFree
-# y virNWFilterEntryFree
-# n virNWFilterFree (returns int)
-# y virNWFilterHashTableFree
-# y virNWFilterIPAddrLearnReqFree
-# y virNWFilterIncludeDefFree
-# n virNWFilterFreeName (returns int)
-# y virNWFilterObjFree
-# n virNWFilterObjListFree FIXME
-# y virNWFilterRuleDefFree
-# n virNWFilterRuleFreeInstanceData (typedef)
-# y virNWFilterRuleInstFree
-# y virNetworkDefFree
-# n virNetworkFree (returns int)
-# n virNetworkFreeName (returns int)
-# n virNodeDevCapsDefFree FIXME
-# y virNodeDeviceDefFree
-# n virNodeDeviceFree (returns int)
-# y virNodeDeviceObjFree
-# n virNodeDeviceObjListFree FIXME
-# n virNodeGetCellsFreeMemory (returns int)
-# n virNodeGetFreeMemory (returns non-void)
-# y virSecretDefFree
-# n virSecretFree (returns non-void)
-# n virSecretFreeName (2 args)
-# n virSecurityLabelDefFree FIXME
-# n virStorageBackendDiskMakeFreeExtent (returns non-void)
-# y virStorageEncryptionFree
-# y virStorageEncryptionSecretFree
-# n virStorageFreeType (enum)
-# y virStoragePoolDefFree
-# n virStoragePoolFree (returns non-void)
-# n virStoragePoolFreeName (returns non-void)
-# y virStoragePoolObjFree
-# n virStoragePoolObjListFree FIXME
-# y virStoragePoolSourceFree
-# y virStorageVolDefFree
-# n virStorageVolFree (returns non-void)
-# n virStorageVolFreeName (returns non-void)
-# n virStreamFree
-
 # Avoid uses of write(2).  Either switch to streams (fwrite), or use
 # the safewrite wrapper.
 sc_avoid_write:
@@ -1250,17 +1075,6 @@ define _sc_search_regexp
    fi || :;
 endef
 
-sc_avoid_if_before_free:
-	@$(VC_LIST_EXCEPT)						\
-	  | $(GREP) -v useless-if-before-free				\
-	  | xargs							\
-	      $(top_srcdir)/build-aux/useless-if-before-free		\
-	      $(useless_free_options)					\
-	  && { printf '$(ME): found useless "if"'			\
-		      ' before "free" above\n' 1>&2;			\
-	       exit 1; }						\
-	  || :
-
 sc_cast_of_argument_to_free:
 	@prohibit='\<free *\( *\(' halt="don't cast free argument"	\
 	  $(_sc_search_regexp)
@@ -1777,7 +1591,7 @@ exclude_file_name_regexp--sc_prohibit_canonicalize_file_name = \
   ^(build-aux/syntax-check\.mk|tests/virfilemock\.c)$$
 
 exclude_file_name_regexp--sc_prohibit_raw_allocation = \
-  ^(docs/advanced-tests\.rst|src/util/viralloc\.[ch]|examples/.*|tests/(securityselinuxhelper|(vircgroup|nss)mock|commandhelper)\.c|tools/wireshark/src/packet-libvirt\.c|tools/nss/libvirt_nss(_leases|_macs)?\.c|build-aux/useless-if-before-free)$$
+  ^(docs/advanced-tests\.rst|src/util/viralloc\.[ch]|examples/.*|tests/(securityselinuxhelper|(vircgroup|nss)mock|commandhelper)\.c|tools/wireshark/src/packet-libvirt\.c|tools/nss/libvirt_nss(_leases|_macs)?\.c)$$
 
 exclude_file_name_regexp--sc_prohibit_readlink = \
   ^src/(util/virutil|lxc/lxc_container)\.c$$
@@ -1793,7 +1607,7 @@ exclude_file_name_regexp--sc_prohibit_xmlGetProp = ^src/util/virxml\.c$$
 
 exclude_file_name_regexp--sc_prohibit_xmlURI = ^src/util/viruri\.c$$
 
-exclude_file_name_regexp--sc_prohibit_return_as_function = \.py|build-aux/useless-if-before-free$$
+exclude_file_name_regexp--sc_prohibit_return_as_function = \.py$$
 
 exclude_file_name_regexp--sc_require_config_h = \
 	^(examples/|tools/virsh-edit\.c$$|tests/virmockstathelpers.c)

build-aux/useless-if-before-free

@@ -1,226 +0,0 @@
-#!/bin/sh
-#! -*-perl-*-
-
-# Detect instances of "if (p) free (p);".
-# Likewise "if (p != 0)", "if (0 != p)", or with NULL; and with braces.
-
-# Copyright (C) 2008-2019 Free Software Foundation, Inc.
-#
-# This program is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <https://www.gnu.org/licenses/>.
-#
-# Written by Jim Meyering
-
-# This is a prologue that allows to run a perl script as an executable
-# on systems that are compliant to a POSIX version before POSIX:2017.
-# On such systems, the usual invocation of an executable through execlp()
-# or execvp() fails with ENOEXEC if it is a script that does not start
-# with a #! line.  The script interpreter mentioned in the #! line has
-# to be /bin/sh, because on GuixSD systems that is the only program that
-# has a fixed file name.  The second line is essential for perl and is
-# also useful for editing this file in Emacs.  The next two lines below
-# are valid code in both sh and perl.  When executed by sh, they re-execute
-# the script through the perl program found in $PATH.  The '-x' option
-# is essential as well; without it, perl would re-execute the script
-# through /bin/sh.  When executed by  perl, the next two lines are a no-op.
-eval 'exec perl -wSx "$0" "$@"'
-     if 0;
-
-my $VERSION = '2018-03-07 03:47'; # UTC
-# The definition above must lie within the first 8 lines in order
-# for the Emacs time-stamp write hook (at end) to update it.
-# If you change this file with Emacs, please let the write hook
-# do its job.  Otherwise, update this string manually.
-
-use strict;
-use warnings;
-use Getopt::Long;
-
-(my $ME = $0) =~ s|.*/||;
-
-# use File::Coda; # https://meyering.net/code/Coda/
-END {
-  defined fileno STDOUT or return;
-  close STDOUT and return;
-  warn "$ME: failed to close standard output: $!\n";
-  $? ||= 1;
-}
-
-sub usage ($)
-{
-  my ($exit_code) = @_;
-  my $STREAM = ($exit_code == 0 ? *STDOUT : *STDERR);
-  if ($exit_code != 0)
-    {
-      print $STREAM "Try '$ME --help' for more information.\n";
-    }
-  else
-    {
-      print $STREAM <<EOF;
-Usage: $ME [OPTIONS] FILE...
-
-Detect any instance in FILE of a useless "if" test before a free call, e.g.,
-"if (p) free (p);".  Any such test may be safely removed without affecting
-the semantics of the C code in FILE.  Use --name=FOO --name=BAR to also
-detect free-like functions named FOO and BAR.
-
-OPTIONS:
-
-   --list       print only the name of each matching FILE (\\0-terminated)
-   --name=N     add name N to the list of \'free\'-like functions to detect;
-                  may be repeated
-
-   --help       display this help and exit
-   --version    output version information and exit
-
-Exit status:
-
-  0   one or more matches
-  1   no match
-  2   an error
-
-EXAMPLE:
-
-For example, this command prints all removable "if" tests before "free"
-and "kfree" calls in the linux kernel sources:
-
-    git ls-files -z |xargs -0 $ME --name=kfree
-
-EOF
-    }
-  exit $exit_code;
-}
-
-sub is_NULL ($)
-{
-  my ($expr) = @_;
-  return ($expr eq 'NULL' || $expr eq '0');
-}
-
-{
-  sub EXIT_MATCH {0}
-  sub EXIT_NO_MATCH {1}
-  sub EXIT_ERROR {2}
-  my $err = EXIT_NO_MATCH;
-
-  my $list;
-  my @name = qw(free);
-  GetOptions
-    (
-     help => sub { usage 0 },
-     version => sub { print "$ME version $VERSION\n"; exit },
-     list => \$list,
-     'name=s@' => \@name,
-    ) or usage 1;
-
-  # Make sure we have the right number of non-option arguments.
-  # Always tell the user why we fail.
-  @ARGV < 1
-    and (warn "$ME: missing FILE argument\n"), usage EXIT_ERROR;
-
-  my $or = join '|', @name;
-  my $regexp = qr/(?:$or)/;
-
-  # Set the input record separator.
-  # Note: this makes it impractical to print line numbers.
-  $/ = '"';
-
-  my $found_match = 0;
- FILE:
-  foreach my $file (@ARGV)
-    {
-      open FH, '<', $file
-        or (warn "$ME: can't open '$file' for reading: $!\n"),
-          $err = EXIT_ERROR, next;
-      while (defined (my $line = <FH>))
-        {
-          # Skip non-matching lines early to save time
-          $line =~ /\bif\b/
-            or next;
-          while ($line =~
-              /\b(if\s*\(\s*([^)]+?)(?:\s*!=\s*([^)]+?))?\s*\)
-              #  1          2                  3
-               (?:   \s*$regexp\s*\((?:\s*\([^)]+\))?\s*([^)]+)\)\s*;|
-                \s*\{\s*$regexp\s*\((?:\s*\([^)]+\))?\s*([^)]+)\)\s*;\s*\}))/sxg)
-            {
-              my $all = $1;
-              my ($lhs, $rhs) = ($2, $3);
-              my ($free_opnd, $braced_free_opnd) = ($4, $5);
-              my $non_NULL;
-              if (!defined $rhs) { $non_NULL = $lhs }
-              elsif (is_NULL $rhs) { $non_NULL = $lhs }
-              elsif (is_NULL $lhs) { $non_NULL = $rhs }
-              else { next }
-
-              # Compare the non-NULL part of the "if" expression and the
-              # free'd expression, without regard to white space.
-              $non_NULL =~ tr/ \t//d;
-              my $e2 = defined $free_opnd ? $free_opnd : $braced_free_opnd;
-              $e2 =~ tr/ \t//d;
-              if ($non_NULL eq $e2)
-                {
-                  $found_match = 1;
-                  $list
-                    and (print "$file\0"), next FILE;
-                  print "$file: $all\n";
-                }
-            }
-        }
-    }
-  continue
-    {
-      close FH;
-    }
-
-  $found_match && $err == EXIT_NO_MATCH
-    and $err = EXIT_MATCH;
-
-  exit $err;
-}
-
-my $foo = <<'EOF';
-# The above is to *find* them.
-# This adjusts them, removing the unnecessary "if (p)" part.
-
-# FIXME: do something like this as an option (doesn't do braces):
-free=xfree
-git grep -l -z "$free *(" \
-  | xargs -0 useless-if-before-free -l --name="$free" \
-  | xargs -0 perl -0x3b -pi -e \
-   's/\bif\s*\(\s*(\S+?)(?:\s*!=\s*(?:0|NULL))?\s*\)\s+('"$free"'\s*\((?:\s*\([^)]+\))?\s*\1\s*\)\s*;)/$2/s'
-
-# Use the following to remove redundant uses of kfree inside braces.
-# Note that -0777 puts perl in slurp-whole-file mode;
-# but we have plenty of memory, these days...
-free=kfree
-git grep -l -z "$free *(" \
-  | xargs -0 useless-if-before-free -l --name="$free" \
-  | xargs -0 perl -0777 -pi -e \
-     's/\bif\s*\(\s*(\S+?)(?:\s*!=\s*(?:0|NULL))?\s*\)\s*\{\s*('"$free"'\s*\((?:\s*\([^)]+\))?\s*\1\s*\);)\s*\}[^\n]*$/$2/gms'
-
-Be careful that the result of the above transformation is valid.
-If the matched string is followed by "else", then obviously, it won't be.
-
-When modifying files, refuse to process anything other than a regular file.
-EOF
-
-## Local Variables:
-## mode: perl
-## indent-tabs-mode: nil
-## eval: (add-hook 'before-save-hook 'time-stamp)
-## time-stamp-line-limit: 50
-## time-stamp-start: "my $VERSION = '"
-## time-stamp-format: "%:y-%02m-%02d %02H:%02M"
-## time-stamp-time-zone: "UTC0"
-## time-stamp-end: "'; # UTC"
-## End: