build: remove x-prefix comparisons

Very old shells suffered from bugs which meant that prefixing variables
with an "x" to ensure that the lefthand side of a comparison always
started with an alphanumeric character was needed. Modern shells don't
suffer from this issue (i.e Bash was fixed in 1996).

In any case, we've already got unprefixed checks used in our codebase,
i.e https://github.com/bitcoin/bitcoin/blob/master/configure.ac#L292,
and have dependencies (in depends) that also use unprefixed comparisons.

I think it's time that we can consolidate on not using the x-prefix
workaround. At best it's mostly just confusing.

More info:
https://github.com/koalaman/shellcheck/wiki/SC2268
https://www.vidarholen.net/contents/blog/?p=1035

Author: fanquake

build-aux/m4/bitcoin_find_bdb48.m4

@@ -6,9 +6,9 @@ AC_DEFUN([BITCOIN_FIND_BDB48],[
   AC_ARG_VAR([BDB_CFLAGS], [C compiler flags for BerkeleyDB, bypasses autodetection])
   AC_ARG_VAR([BDB_LIBS], [Linker flags for BerkeleyDB, bypasses autodetection])
 
-  if test "x$use_bdb" = "xno"; then
+  if test "$use_bdb" = "no"; then
     use_bdb=no
-  elif test "x$BDB_CFLAGS" = "x"; then
+  elif test "$BDB_CFLAGS" = ""; then
     AC_MSG_CHECKING([for Berkeley DB C++ headers])
     BDB_CPPFLAGS=
     bdbpath=X
@@ -28,7 +28,7 @@ AC_DEFUN([BITCOIN_FIND_BDB48],[
           #error "failed to find bdb 4.8+"
         #endif
       ]])],[
-        if test "x$bdbpath" = "xX"; then
+        if test "$bdbpath" = "X"; then
           bdbpath="${searchpath}"
         fi
       ],[
@@ -45,13 +45,13 @@ AC_DEFUN([BITCOIN_FIND_BDB48],[
         break
       ],[])
     done
-    if test "x$bdbpath" = "xX"; then
+    if test "$bdbpath" = "X"; then
       use_bdb=no
       AC_MSG_RESULT([no])
       AC_MSG_WARN([libdb_cxx headers missing])
       AC_MSG_WARN(AC_PACKAGE_NAME[ requires this library for BDB (legacy) wallet support])
       AC_MSG_WARN([Passing --without-bdb will suppress this warning])
-    elif test "x$bdb48path" = "xX"; then
+    elif test "$bdb48path" = "X"; then
       BITCOIN_SUBDIR_TO_INCLUDE(BDB_CPPFLAGS,[${bdbpath}],db_cxx)
       AC_ARG_WITH([incompatible-bdb],[AS_HELP_STRING([--with-incompatible-bdb], [allow using a bdb version other than 4.8])],[
         AC_MSG_WARN([Found Berkeley DB other than 4.8])
@@ -74,23 +74,23 @@ AC_DEFUN([BITCOIN_FIND_BDB48],[
   fi
   AC_SUBST(BDB_CPPFLAGS)
 
-  if test "x$use_bdb" = "xno"; then
+  if test "$use_bdb" = "no"; then
     use_bdb=no
-  elif test "x$BDB_LIBS" = "x"; then
+  elif test "$BDB_LIBS" = ""; then
     # TODO: Ideally this could find the library version and make sure it matches the headers being used
     for searchlib in db_cxx-4.8 db_cxx db4_cxx; do
       AC_CHECK_LIB([$searchlib],[main],[
         BDB_LIBS="-l${searchlib}"
         break
       ])
     done
-    if test "x$BDB_LIBS" = "x"; then
+    if test "$BDB_LIBS" = ""; then
         AC_MSG_WARN([libdb_cxx headers missing])
         AC_MSG_WARN(AC_PACKAGE_NAME[ requires this library for BDB (legacy) wallet support])
         AC_MSG_WARN([Passing --without-bdb will suppress this warning])
     fi
   fi
-  if test "x$use_bdb" != "xno"; then
+  if test "$use_bdb" != "no"; then
     AC_SUBST(BDB_LIBS)
     AC_DEFINE([USE_BDB], [1], [Define if BDB support should be compiled in])
     use_bdb=yes

build-aux/m4/bitcoin_qt.m4

@@ -5,8 +5,8 @@ dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
 dnl Helper for cases where a qt dependency is not met.
 dnl Output: If qt version is auto, set bitcoin_enable_qt to false. Else, exit.
 AC_DEFUN([BITCOIN_QT_FAIL],[
-  if test "x$bitcoin_qt_want_version" = xauto && test "x$bitcoin_qt_force" != xyes; then
-    if test "x$bitcoin_enable_qt" != xno; then
+  if test "$bitcoin_qt_want_version" = "auto" && test "$bitcoin_qt_force" != "yes"; then
+    if test "$bitcoin_enable_qt" != "no"; then
       AC_MSG_WARN([$1; bitcoin-qt frontend will not be built])
     fi
     bitcoin_enable_qt=no
@@ -17,7 +17,7 @@ AC_DEFUN([BITCOIN_QT_FAIL],[
 ])
 
 AC_DEFUN([BITCOIN_QT_CHECK],[
-  if test "x$bitcoin_enable_qt" != xno && test "x$bitcoin_qt_want_version" != xno; then
+  if test "$bitcoin_enable_qt" != "no" && test "$bitcoin_qt_want_version" != "no"; then
     true
     $1
   else
@@ -35,12 +35,12 @@ dnl Inputs: $4: If "yes", don't fail if $2 is not found.
 dnl Output: $1 is set to the path of $2 if found. $2 are searched in order.
 AC_DEFUN([BITCOIN_QT_PATH_PROGS],[
   BITCOIN_QT_CHECK([
-    if test "x$3" != x; then
+    if test "$3" != ""; then
       AC_PATH_PROGS([$1], [$2], [], [$3])
     else
       AC_PATH_PROGS([$1], [$2])
     fi
-    if test "x$$1" = x && test "x$4" != xyes; then
+    if test "$$1" = "" && test "$4" != "yes"; then
       BITCOIN_QT_FAIL([$1 not found])
     fi
   ])
@@ -57,14 +57,14 @@ AC_DEFUN([BITCOIN_QT_INIT],[
     [build bitcoin-qt GUI (default=auto)])],
     [
      bitcoin_qt_want_version=$withval
-     if test "x$bitcoin_qt_want_version" = xyes; then
+     if test "$bitcoin_qt_want_version" = "yes"; then
        bitcoin_qt_force=yes
        bitcoin_qt_want_version=auto
      fi
     ],
     [bitcoin_qt_want_version=auto])
 
-  AS_IF([test "x$with_gui" = xqt5_debug],
+  AS_IF([test "$with_gui" = "qt5_debug"],
         [AS_CASE([$host],
                  [*darwin*], [qt_lib_suffix=_debug],
                  [qt_lib_suffix= ]); bitcoin_qt_want_version=qt5],
@@ -87,7 +87,7 @@ AC_DEFUN([BITCOIN_QT_INIT],[
   dnl Android doesn't support D-Bus and certainly doesn't use it for notifications
   case $host in
     *android*)
-      if test "x$use_dbus" != xyes; then
+      if test "$use_dbus" != "yes"; then
         use_dbus=no
       fi
     ;;
@@ -119,10 +119,10 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
   CPPFLAGS="$QT_INCLUDES $CPPFLAGS"
   CXXFLAGS="$PIC_FLAGS $CXXFLAGS"
   _BITCOIN_QT_IS_STATIC
-  if test "x$bitcoin_cv_static_qt" = xyes; then
+  if test "$bitcoin_cv_static_qt" = "yes"; then
     _BITCOIN_QT_CHECK_STATIC_LIBS
 
-    if test "x$qt_plugin_path" != x; then
+    if test "$qt_plugin_path" != ""; then
       if test -d "$qt_plugin_path/platforms"; then
         QT_LIBS="$QT_LIBS -L$qt_plugin_path/platforms"
       fi
@@ -138,29 +138,29 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     fi
 
     AC_DEFINE([QT_STATICPLUGIN], [1], [Define this symbol if qt plugins are static])
-    if test "x$TARGET_OS" != xandroid; then
+    if test "$TARGET_OS" != "android"; then
       _BITCOIN_QT_CHECK_STATIC_PLUGIN([QMinimalIntegrationPlugin], [-lqminimal])
       AC_DEFINE([QT_QPA_PLATFORM_MINIMAL], [1], [Define this symbol if the minimal qt platform exists])
     fi
-    if test "x$TARGET_OS" = xwindows; then
+    if test "$TARGET_OS" = "windows"; then
       dnl Linking against wtsapi32 is required. See #17749 and
       dnl https://bugreports.qt.io/browse/QTBUG-27097.
       AX_CHECK_LINK_FLAG([-lwtsapi32], [QT_LIBS="$QT_LIBS -lwtsapi32"], [AC_MSG_ERROR([could not link against -lwtsapi32])])
       _BITCOIN_QT_CHECK_STATIC_PLUGIN([QWindowsIntegrationPlugin], [-lqwindows])
       _BITCOIN_QT_CHECK_STATIC_PLUGIN([QWindowsVistaStylePlugin], [-lqwindowsvistastyle])
       AC_DEFINE([QT_QPA_PLATFORM_WINDOWS], [1], [Define this symbol if the qt platform is windows])
-    elif test "x$TARGET_OS" = xlinux; then
+    elif test "$TARGET_OS" = "linux"; then
       _BITCOIN_QT_CHECK_STATIC_PLUGIN([QXcbIntegrationPlugin], [-lqxcb])
       AC_DEFINE([QT_QPA_PLATFORM_XCB], [1], [Define this symbol if the qt platform is xcb])
-    elif test "x$TARGET_OS" = xdarwin; then
+    elif test "$TARGET_OS" = "darwin"; then
       AX_CHECK_LINK_FLAG([-framework Carbon], [QT_LIBS="$QT_LIBS -framework Carbon"], [AC_MSG_ERROR(could not link against Carbon framework)])
       AX_CHECK_LINK_FLAG([-framework IOSurface], [QT_LIBS="$QT_LIBS -framework IOSurface"], [AC_MSG_ERROR(could not link against IOSurface framework)])
       AX_CHECK_LINK_FLAG([-framework Metal], [QT_LIBS="$QT_LIBS -framework Metal"], [AC_MSG_ERROR(could not link against Metal framework)])
       AX_CHECK_LINK_FLAG([-framework QuartzCore], [QT_LIBS="$QT_LIBS -framework QuartzCore"], [AC_MSG_ERROR(could not link against QuartzCore framework)])
       _BITCOIN_QT_CHECK_STATIC_PLUGIN([QCocoaIntegrationPlugin], [-lqcocoa])
       _BITCOIN_QT_CHECK_STATIC_PLUGIN([QMacStylePlugin], [-lqmacstyle])
       AC_DEFINE([QT_QPA_PLATFORM_COCOA], [1], [Define this symbol if the qt platform is cocoa])
-    elif test "x$TARGET_OS" = xandroid; then
+    elif test "$TARGET_OS" = "android"; then
       QT_LIBS="-Wl,--export-dynamic,--undefined=JNI_OnLoad -lplugins_platforms_qtforandroid_$ANDROID_ARCH -ljnigraphics -landroid -lqtfreetype_$ANDROID_ARCH $QT_LIBS"
       AC_DEFINE([QT_QPA_PLATFORM_ANDROID], [1], [Define this symbol if the qt platform is android])
     fi
@@ -169,11 +169,11 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
   CXXFLAGS=$TEMP_CXXFLAGS
   ])
 
-  if test "x$qt_bin_path" = x; then
+  if test "$qt_bin_path" = ""; then
     qt_bin_path="`$PKG_CONFIG --variable=host_bins ${qt_lib_prefix}Core 2>/dev/null`"
   fi
 
-  if test "x$use_hardening" != xno; then
+  if test "$use_hardening" != "no"; then
     BITCOIN_QT_CHECK([
     AC_MSG_CHECKING([whether -fPIE can be used with this Qt config])
     TEMP_CPPFLAGS=$CPPFLAGS
@@ -248,26 +248,26 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
   BITCOIN_QT_CHECK([
     bitcoin_enable_qt=yes
     bitcoin_enable_qt_test=yes
-    if test "x$have_qt_test" = xno; then
+    if test "$have_qt_test" = "no"; then
       bitcoin_enable_qt_test=no
     fi
     bitcoin_enable_qt_dbus=no
-    if test "x$use_dbus" != xno && test "x$have_qt_dbus" = xyes; then
+    if test "$use_dbus" != "no" && test "$have_qt_dbus" = "yes"; then
       bitcoin_enable_qt_dbus=yes
     fi
-    if test "x$use_dbus" = xyes && test "x$have_qt_dbus" = xno; then
+    if test "$use_dbus" = "yes" && test "$have_qt_dbus" = "no"; then
       AC_MSG_ERROR([libQtDBus not found. Install libQtDBus or remove --with-qtdbus.])
     fi
-    if test "x$LUPDATE" = x; then
+    if test "$LUPDATE" = ""; then
       AC_MSG_WARN([lupdate tool is required to update Qt translations.])
     fi
-    if test "x$LCONVERT" = x; then
+    if test "$LCONVERT" = ""; then
       AC_MSG_WARN([lconvert tool is required to update Qt translations.])
     fi
   ],[
     bitcoin_enable_qt=no
   ])
-  if test x$bitcoin_enable_qt = xyes; then
+  if test $bitcoin_enable_qt = "yes"; then
     AC_MSG_RESULT([$bitcoin_enable_qt ($qt_lib_prefix)])
   else
     AC_MSG_RESULT([$bitcoin_enable_qt])
@@ -348,18 +348,18 @@ AC_DEFUN([_BITCOIN_QT_CHECK_STATIC_LIBS], [
   PKG_CHECK_MODULES([QT_FB], [${qt_lib_prefix}FbSupport${qt_lib_suffix}], [QT_LIBS="$QT_FB_LIBS $QT_LIBS"])
   PKG_CHECK_MODULES([QT_FONTDATABASE], [${qt_lib_prefix}FontDatabaseSupport${qt_lib_suffix}], [QT_LIBS="$QT_FONTDATABASE_LIBS $QT_LIBS"])
   PKG_CHECK_MODULES([QT_THEME], [${qt_lib_prefix}ThemeSupport${qt_lib_suffix}], [QT_LIBS="$QT_THEME_LIBS $QT_LIBS"])
-  if test "x$TARGET_OS" = xlinux; then
+  if test "$TARGET_OS" = "linux"; then
     PKG_CHECK_MODULES([QT_INPUT], [${qt_lib_prefix}InputSupport], [QT_LIBS="$QT_INPUT_LIBS $QT_LIBS"])
     PKG_CHECK_MODULES([QT_SERVICE], [${qt_lib_prefix}ServiceSupport], [QT_LIBS="$QT_SERVICE_LIBS $QT_LIBS"])
     PKG_CHECK_MODULES([QT_XCBQPA], [${qt_lib_prefix}XcbQpa], [QT_LIBS="$QT_XCBQPA_LIBS $QT_LIBS"])
     PKG_CHECK_MODULES([QT_XKBCOMMON], [${qt_lib_prefix}XkbCommonSupport], [QT_LIBS="$QT_XKBCOMMON_LIBS $QT_LIBS"])
-  elif test "x$TARGET_OS" = xdarwin; then
+  elif test "$TARGET_OS" = "darwin"; then
     PKG_CHECK_MODULES([QT_CLIPBOARD], [${qt_lib_prefix}ClipboardSupport${qt_lib_suffix}], [QT_LIBS="$QT_CLIPBOARD_LIBS $QT_LIBS"])
     PKG_CHECK_MODULES([QT_GRAPHICS], [${qt_lib_prefix}GraphicsSupport${qt_lib_suffix}], [QT_LIBS="$QT_GRAPHICS_LIBS $QT_LIBS"])
     PKG_CHECK_MODULES([QT_SERVICE], [${qt_lib_prefix}ServiceSupport${qt_lib_suffix}], [QT_LIBS="$QT_SERVICE_LIBS $QT_LIBS"])
-  elif test "x$TARGET_OS" = xwindows; then
+  elif test "$TARGET_OS" = "windows"; then
     PKG_CHECK_MODULES([QT_WINDOWSUIAUTOMATION], [${qt_lib_prefix}WindowsUIAutomationSupport${qt_lib_suffix}], [QT_LIBS="$QT_WINDOWSUIAUTOMATION_LIBS $QT_LIBS"])
-  elif test "x$TARGET_OS" = xandroid; then
+  elif test "$TARGET_OS" = "android"; then
     PKG_CHECK_MODULES([QT_EGL], [${qt_lib_prefix}EglSupport${qt_lib_suffix}], [QT_LIBS="$QT_EGL_LIBS $QT_LIBS"])
     PKG_CHECK_MODULES([QT_SERVICE], [${qt_lib_prefix}ServiceSupport${qt_lib_suffix}], [QT_LIBS="$QT_SERVICE_LIBS $QT_LIBS"])
   fi
@@ -392,7 +392,7 @@ AC_DEFUN([_BITCOIN_QT_FIND_LIBS],[
 
   BITCOIN_QT_CHECK([
     PKG_CHECK_MODULES([QT_TEST], [${qt_lib_prefix}Test${qt_lib_suffix} $qt_version], [QT_TEST_INCLUDES="$QT_TEST_CFLAGS"; have_qt_test=yes], [have_qt_test=no])
-    if test "x$use_dbus" != xno; then
+    if test "$use_dbus" != "no"; then
       PKG_CHECK_MODULES([QT_DBUS], [${qt_lib_prefix}DBus $qt_version], [QT_DBUS_INCLUDES="$QT_DBUS_CFLAGS"; have_qt_dbus=yes], [have_qt_dbus=no])
     fi
   ])

build-aux/m4/bitcoin_subdir_to_include.m4

@@ -5,13 +5,13 @@ dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
 dnl BITCOIN_SUBDIR_TO_INCLUDE([CPPFLAGS-VARIABLE-NAME],[SUBDIRECTORY-NAME],[HEADER-FILE])
 dnl SUBDIRECTORY-NAME must end with a path separator
 AC_DEFUN([BITCOIN_SUBDIR_TO_INCLUDE],[
-  if test "x$2" = "x"; then
+  if test "$2" = ""; then
     AC_MSG_RESULT([default])
   else
     echo "#include <$2$3.h>" >conftest.cpp
     newinclpath=`${CXXCPP} ${CPPFLAGS} -M conftest.cpp 2>/dev/null | [ tr -d '\\n\\r\\\\' | sed -e 's/^.*[[:space:]:]\(\/[^[:space:]]*\)]$3[\.h[[:space:]].*$/\1/' -e t -e d`]
     AC_MSG_RESULT([${newinclpath}])
-    if test "x${newinclpath}" != "x"; then
+    if test "${newinclpath}" != ""; then
       eval "$1=\"\$$1\"' -I${newinclpath}'"
     fi
   fi