Expression did not evaluate to a known generator expression
```
I’m not sure where the semicolon is coming from, but here’s the output for verification.
```cmake
message(STATUS "HDF5_VERSION = ${HDF5_VERSION}")
message(STATUS "hdf5-\${HDF5_VERSION} = hdf5-${HDF5_VERSION}")
message(STATUS "1.12.0 = 1.12.0")
```
```auto
-- HDF5_VERSION = 1.12.0
-- hdf5-${HDF5_VERSION} = hdf5-1.12.0
-- 1.12.0 = 1.12.0
```
Any advice? It was working yesterday, I swear.
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [April 14, 2023, 2:29am UTC](https://discourse.cmake.org/t/generator-expression-error/7906/2 "2023-04-14T02:29:22Z")
Modify your actual project to print the value of `HDF5_VERSION` immediately before you call `ExternalProject_Add()` and confirm it holds the value you expect. That may reveal something to explore. The error message printed by CMake doesn’t make a lot of sense with the semicolon in there right now.
---
### Author:  [@fenrir](https://discourse.cmake.org/u/fenrir)
#### Post date: [April 14, 2023, 6:39am UTC](https://discourse.cmake.org/t/generator-expression-error/7906/3 "2023-04-14T06:39:48Z")
Wild guess:
Do you use `LIST_SEPARATOR ":"` by any chance?
---
### Author:  [@KBentley57](https://discourse.cmake.org/u/KBentley57)
#### Post date: [April 14, 2023, 2:30pm UTC](https://discourse.cmake.org/t/generator-expression-error/7906/4 "2023-04-14T14:30:38Z")
Thanks Craig. I tried to keep it short, but I might as well post the whole file. Here’s what’s running right now. Those calls are immediately before the externalrproject\_add function.
```auto
################################################################################
#
# Kyle Bentley
# Torch Technologies
# kyle.bentley@torchtechnologies.com
# 2021/04/13
#
# This package installs hdf5, a file format used everywhere.
#
# https://www.hdfgroup.org/solutions/hdf5/
#
################################################################################
message(STATUS "HDF5_VERSION = ${HDF5_VERSION}")
message(STATUS "hdf5-\${HDF5_VERSION} = hdf5-${HDF5_VERSION}")
message(STATUS "1.12.0 = 1.12.0")
ExternalProject_Add(hdf5
URL ${SUPPORTPACKAGES_PACKAGE_DIR}/@canonical_name@
URL_MD5 @package_md5@
PREFIX ${CMAKE_CURRENT_BINARY_DIR}/hdf5
INSTALL_DIR ${CMAKE_INSTALL_PREFIX}
SOURCE_SUBDIR $<$:hdf5-${HDF5_VERSION}>
CMAKE_ARGS
-DCMAKE_MODULE_PATH=/Modules
-DCMAKE_PREFIX_PATH=
-DCMAKE_INSTALL_PREFIX=
-DCMAKE_INSTALL_LIBDIR=/lib
-DH5_DEFAULT_PLUGINDIR=/lib
-DHDF5_ENABLE_PARALLEL=ON
-DHDF5_BUILD_FORTRAN=OFF
-DONLY_SHARED_LIBS=ON
-DCMAKE_ANSI_CFLAGS=-fPIC
-DBUILD_TESTING=FALSE
-DHDF5_ENABLE_ASSERTS=TRUE
-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
-DHDF5_ENABLE_MAP_API=TRUE
-DHDF5_ENABLE_Z_LIB_SUPPORT=ON
-DHDF5_BUILD_CPP_LIB=FALSE
-DHDF5_ENABLE_OPTIMIZATION=TRUE
-DOPTIMIZE_CFLAGS=${COMMON_C_FLAGS}
-DDEFAULT_API_VERSION:STRING=v18
$<$:-DMPIEXEC_EXECUTABLE=/bin/mpiexec>
$<$:-DMPI_LIBRARY=/lib/libmpi.so>
$<$:-DMPI_HOME=>
$<$:-DMPI_ROOT=>
$<$:-DMPI_C_INCLUDE_DIRS=/include>
$<$:-DZLIB_ROOT=$>
LOG_CONFIGURE 1
LOG_BUILD 1
LOG_INSTALL 1
)
if(BUILD_LOCAL_MPI)
add_dependencies(hdf5 ${MPI_TARGET})
endif(BUILD_LOCAL_MPI)
if(BUILD_ZLIB)
add_dependencies(hdf5 zlib)
endif(BUILD_ZLIB)
```
The output of which gets to this point, described above.
```auto
-- HDF5_VERSION = 1.12.0
-- hdf5-${HDF5_VERSION} = hdf5-1.12.0
-- 1.12.0 = 1.12.0
-- Configuring done
CMake Error at /usr/share/cmake-3.23/Modules/ExternalProject.cmake:1995 (file):
Error evaluating generator expression:
$
Expression did not evaluate to a known generator expression
Call Stack (most recent call first):
/usr/share/cmake-3.23/Modules/ExternalProject.cmake:2286 (_ep_write_log_script)
/usr/share/cmake-3.23/Modules/ExternalProject.cmake:3229:EVAL:2 (ExternalProject_Add_Step)
/usr/share/cmake-3.23/Modules/ExternalProject.cmake:3229 (cmake_language)
/usr/share/cmake-3.23/Modules/ExternalProject.cmake:3643 (_ep_add_configure_command)
build/Modules/hdf5.cmake:21 (ExternalProject_Add)
cmakefiles/options/sp_templates.cmake:239 (include)
CMakeLists.txt:522 (include)
```
---
### Author:  [@KBentley57](https://discourse.cmake.org/u/KBentley57)
#### Post date: [April 14, 2023, 2:32pm UTC](https://discourse.cmake.org/t/generator-expression-error/7906/5 "2023-04-14T14:32:03Z")
Good thinking on the LIST\_SEPARATOR. I use it in other places, but nowhere around here. I just grepped the entire project and the only places I see it don’t use a colon.
---
### Author:  [@KBentley57](https://discourse.cmake.org/u/KBentley57)
#### Post date: [April 14, 2023, 3:18pm UTC](https://discourse.cmake.org/t/generator-expression-error/7906/6 "2023-04-14T15:18:25Z")
I compiled a 3.20.2 version of CMake that I keep around. The behavior is not exhibited in that version.
What’s your thoughts on that? I’m using debian 11, with the version from the repos. Is it worthy of a bug report?
```auto
bentleykw@bentleykw:~$ aptitude show cmake
Package: cmake
Version: 3.23.2-1
State: installed
Automatically installed: no
Multi-Arch: foreign
Priority: optional
Section: devel
Maintainer: Debian CMake Team
Architecture: amd64
Uncompressed Size: 27.9 M
Depends: libarchive13 (>= 3.3.3), libc6 (>= 2.33), libcurl4 (>= 7.16.2),
libexpat1 (>= 2.0.1), libgcc-s1 (>= 3.0), libjsoncpp25 (>= 1.9.5),
librhash0 (>= 1.2.6), libstdc++6 (>= 12), libuv1 (>= 1.38.0), zlib1g
(>= 1:1.1.4), cmake-data (= 3.23.2-1), procps
Recommends: gcc, make
Suggests: cmake-doc, ninja-build, cmake-format
Conflicts: cmake:i386
Provides: cmake:i386 (= 3.23.2-1)
Provided by: cmake:i386 (3.18.4-2+deb11u1)
```
Thanks,
Kyle
---
### Author:  [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [April 19, 2023, 5:05am UTC](https://discourse.cmake.org/t/generator-expression-error/7906/7 "2023-04-19T05:05:09Z")
Please put together a minimal, complete example that reproduces the problem. Make it as simple as possible so that someone can easily replicate it. If you can do that, then open a bug report and attach that minimal example.