Add legacy macro option

CMakeLists.txt

@@ -547,6 +547,11 @@ else()
   set(NETCDF_ENABLE_HDF4 OFF)
 endif()
 
+# Option legacy  macros 
+# Do we want to enable unsafe macros, e.g. _FillValue in addition to NC_FillValue.
+# See https://github.com/Unidata/netcdf-c/issues/3029
+option(NETCDF_ENABLE_LEGACY_MACROS "Enable legacy macros for backwards compatibility. Use with Caution." ON)
+
 # Option Logging, only valid for netcdf4 dispatchers.
 option(NETCDF_ENABLE_LOGGING "Enable Logging." OFF)
 if(NOT NETCDF_ENABLE_NETCDF4)
@@ -662,14 +667,18 @@ if(ENABLE_PLUGIN_INSTALL)
         set(NETCDF_PLUGIN_INSTALL_DIR "$ENV{HDF5_PLUGIN_PATH}")
       else()
         if(ISMSVC OR ISMINGW)
-	  set(NETCDF_PLUGIN_INSTALL_DIR "$ENV{ALLUSERSPROFILE}\\hdf5\\lib\\plugin")
-	else()
-	  set(NETCDF_PLUGIN_INSTALL_DIR "/usr/local/hdf5/lib/plugin")
-	endif()
-      endif()
-        message(STATUS "Defaulting to -DPLUGIN_INSTALL_DIR=${NETCDF_PLUGIN_INSTALL_DIR}")
+	        set(NETCDF_PLUGIN_INSTALL_DIR "$ENV{ALLUSERSPROFILE}\\hdf5\\lib\\plugin")
+	      else()
+          if(NOT DEFINED CMAKE_INSTALL_PREFIX)
+            set(NETCDF_PLUGIN_INSTALL_DIR "/usr/local/hdf5/lib/plugin")
+          else()
+            set(NETCDF_PLUGIN_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/hdf5/lib/plugin")
+          endif(NOT DEFINED CMAKE_INSTALL_PREFIX)
+        endif(ISMSVC OR ISMINGW)
+      endif(DEFINED ENV{HDF5_PLUGIN_PATH})
+      message(STATUS "Defaulting to -DPLUGIN_INSTALL_DIR=${NETCDF_PLUGIN_INSTALL_DIR}")
     endif()
-endif()
+endif(ENABLE_PLUGIN_INSTALL)
 
 if(ENABLE_PLUGIN_INSTALL)
   # Use the lowest priority dir in the path
@@ -1694,6 +1703,7 @@ is_enabled(NETCDF_ENABLE_PARALLEL4 HAS_PARALLEL4)
 is_enabled(NETCDF_ENABLE_DAP HAS_DAP)
 is_enabled(NETCDF_ENABLE_DAP2 HAS_DAP2)
 is_enabled(NETCDF_ENABLE_DAP4 HAS_DAP4)
+is_enabled(NETCDF_ENABLE_LEGACY_MACROS HAS_LEGACY_MACROS)
 is_enabled(NETCDF_ENABLE_BYTERANGE HAS_BYTERANGE)
 is_enabled(NETCDF_ENABLE_DISKLESS HAS_DISKLESS)
 is_enabled(USE_MMAP HAS_MMAP)

RELEASE_NOTES.md

@@ -9,12 +9,14 @@ This file contains a high-level description of this package's evolution. Release
 
 ## Known Issue
 
-* Parallel operation using `mpich 4.2.0` (the default on `Ubuntu 24.04`) results in 'unexpected results' when running `nc_test4/run_par_test.sh`.  This can be fixed by removing `mpich` and associated libraries and development packages and installing `mpich 4.2.2` by hand, or by using `openmpi` provided via `apt`.
+> Parallel operation using `mpich 4.2.0` (the default on `Ubuntu 24.04`) results in 'unexpected results' when running `nc_test4/run_par_test.sh`.  This can be fixed by removing `mpich` and associated libraries and development packages and installing `mpich 4.2.2` by hand, or by using `openmpi` provided via `apt`.
 
 ## Release Notes
 
 ### Release Candidate 2 - TBD
 
+> Note: To avoid a conflict between `_FillValue` and `libc++18`, we have introduced a new option, `--enable-legacy-macros` for autotools and `NETCDF_ENABLE_LEGACY_MACROS` for cmake.  These are turned on by default currently but will be turned off eventually.  Developers are encouraged to move away from the `FillValue` macro and replace it with the new `NC_FillValue` macro.  See [Github #2858](https://github.com/Unidata/netcdf-c/issues/2858) for more information. 
+
 * Provide better documentation for the .rc file mechanism and API. See [Github #2956](https://github.com/Unidata/netcdf-c/pull/2956) for more information.
 * Convert NCZarr V2 to store all netcdf-4 specific info as attributes. This improves interoperability with other Zarr implementations by no longer using non-standard keys. The price to be paid is that lazy attribute reading cannot be supported. See [Github #2836](https://github.com/Unidata/netcdf-c/pull/2936) for more information.
 * Cleanup the option code for NETCDF_ENABLE_SET_LOG_LEVEL\[_FUNC\] See [Github #2931](https://github.com/Unidata/netcdf-c/pull/2931) for more information.

config.h.cmake.in

@@ -496,6 +496,9 @@ with zip */
 /* Idspatch table version */
 #cmakedefine NC_DISPATCH_VERSION ${NC_DISPATCH_VERSION}
 
+/* Enable Legacy, potential-conflict Macro _FillValue */
+#cmakedefine NETCDF_ENABLE_LEGACY_MACROS
+
 /* no IEEE float on this platform */
 #cmakedefine NO_IEEE_FLOAT 1
 

configure.ac

@@ -462,6 +462,19 @@ else
    enable_set_log_level=no
 fi
 
+# Do we want to enable unsafe macros, e.g. _FillValue in addition to NC_FillValue.
+# See https://github.com/Unidata/netcdf-c/issues/3029
+AC_MSG_CHECKING([whether to allow legacy macros])
+AC_ARG_ENABLE([legacy-macros],
+               [AS_HELP_STRING([--disable-legacy-macros],
+                              [enable legacy macros for backwards compatibility purposes. Use with caution.\
+                              This can lead to unexpected consequences/behavior.])])
+test "x$enable_legacy_macros" = xno || enable_legacy_macros=yes
+AC_MSG_RESULT($enable_legacy_macros)
+if test "x$enable_legacy_macros" = xyes; then
+   AC_DEFINE([NETCDF_ENABLE_LEGACY_MACROS], 1, [If true, enable legacy macros in netcdf.h])
+fi
+
 # Does the user want to allow reading of remote data via range headers?
 AC_MSG_CHECKING([whether byte range support is enabled])
 AC_ARG_ENABLE([byterange],
@@ -1932,6 +1945,7 @@ AM_CONDITIONAL(USE_DAP, [test "x$enable_dap" = xyes]) # Alias
 # Provide protocol specific flags
 AM_CONDITIONAL(NETCDF_ENABLE_DAP, [test "x$enable_dap" = xyes])
 AM_CONDITIONAL(NETCDF_ENABLE_DAP4, [test "x$enable_dap4" = xyes])
+AM_CONDITIONAL(NETCDF_ENABLE_LEGACY_MACROS, [test "x$netcdf_enable_legacy_macros" = xyes])
 AM_CONDITIONAL(USE_STRICT_NULL_BYTE_HEADER_PADDING, [test x$enable_strict_null_byte_header_padding = xyes])
 AM_CONDITIONAL(NETCDF_ENABLE_CDF5, [test "x$enable_cdf5" = xyes])
 AM_CONDITIONAL(NETCDF_ENABLE_DAP_REMOTE_TESTS, [test "x$enable_dap_remote_tests" = xyes])
@@ -2050,6 +2064,7 @@ AC_SUBST(NC_LIBS,[$NC_LIBS])
 AC_SUBST(HAS_DAP,[$enable_dap])
 AC_SUBST(HAS_DAP2,[$enable_dap])
 AC_SUBST(HAS_DAP4,[$enable_dap4])
+AC_SUBST(HAS_LEGACY_MACROS,[$enable_legacy_macros])
 AC_SUBST(HAS_NC2,[$nc_build_v2])
 AC_SUBST(HAS_CDF5,[$enable_cdf5])
 AC_SUBST(HAS_HDF4,[$enable_hdf4])
@@ -2156,8 +2171,13 @@ elif test "x$with_plugin_dir" = xyes ; then # --with-plugin-dir, no argument
         if test "x$ISMSVC" = xyes || test "x$ISMINGW" = xyes; then
 	    PLUGIN_PATH="${ALLUSERSPROFILE}\\hdfd5\\lib\\plugin"
 	else
-	    PLUGIN_PATH="/usr/local/hdf5/lib/plugin"
-	fi
+      if test "x${prefix}" = xNONE ; then
+   	    PLUGIN_PATH="/usr/local/hdf5/lib/plugin"
+      else 
+         PLUGIN_PATH="${prefix}/hdf5/lib/plugin"
+      fi
+
+   fi
     fi
     # Use the lowest priority dir in the path
     if test "x$ISMSVC" = xyes || test "x$ISMINGW" = xyes; then

include/netcdf.h

@@ -109,7 +109,15 @@ extern "C" {
  * different value than the above defaults, create an attribute with
  * the same type as the variable and this reserved name. The value you
  * give the attribute will be used as the fill value for that
- * variable. */
+ * variable. 
+ * Refactored to NC_FillValue in support of 
+ * https://github.com/Unidata/netcdf-c/issues/2858, and parameterized
+ * behind an unsafe macros option as part of 
+ * https://github.com/Unidata/netcdf-c/issues/3029
+ */
+#ifdef NETCDF_ENABLE_LEGACY_MACROS
+#define _FillValue      "_FillValue"
+#endif
 #define NC_FillValue      "_FillValue"
 #define NC_FILL         0       /**< Argument to nc_set_fill() to clear NC_NOFILL */
 #define NC_NOFILL       0x100   /**< Argument to nc_set_fill() to turn off filling of data. */

libnetcdf.settings.in

@@ -24,6 +24,7 @@ Shared Library:		@enable_shared@
 Static Library:		@enable_static@
 Extra libraries:	@LIBS@
 XML Parser:             @XMLPARSER@
+Legacy Macros:          @HAS_LEGACY_MACROS@
 
 # Features
 --------

plugins/Makefile.am

@@ -14,7 +14,7 @@ AM_LDFLAGS += -module -avoid-version -shared -export-dynamic $(NOUNDEFINED)
 # Create an alternate directory if not installing.
 ALTPLUGINDIR = ${abs_top_builddir}/plugins/plugindir
 
-RPATH = -rpath $(abs_builddir)/.libs
+RPATH = -rpath $(abs_top_builddir)/.libs
 
 # This is where the plugins are to be installed
 if ENABLE_PLUGIN_DIR