Fix prerelease version matching to be more consistent with the find_package arguments.

cmake/examples.cmake

@@ -11,6 +11,7 @@ include(ExternalProject)
 
 # Internal utility function: Create a custom target representing a build of examples with custom options.
 function(add_examples_build NAME)
+
   ExternalProject_Add(${NAME}
     PREFIX ${NAME}
     SOURCE_DIR "${examples_dir}"

cmake/protobuf-config-version.cmake.in

@@ -1,28 +1,35 @@
 set(PACKAGE_VERSION "@protobuf_VERSION@")
+set(${PACKAGE_FIND_NAME}_VERSION_PRERELEASE "@protobuf_VERSION_PRERELEASE@" PARENT_SCOPE)
+
+# Prerelease versions cannot be passed in directly via the find_package command,
+# so we allow users to specify it in a variable
+if(NOT DEFINED "${${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE}")
+  set("${${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE}" "")
+else()
+  set(PACKAGE_FIND_VERSION ${PACKAGE_FIND_VERSION}-${${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE})
+endif()
+set(PACKAGE_FIND_VERSION_PRERELEASE "${${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE}")
 
+# VERSION_EQUAL ignores the prerelease strings, so we use STREQUAL.
 if(PACKAGE_FIND_VERSION STREQUAL PACKAGE_VERSION)
   set(PACKAGE_VERSION_EXACT TRUE)
 endif()
 
 set(PACKAGE_VERSION_COMPATIBLE TRUE) #Assume true until shown otherwise
 
-# Handle prerelease versions
-set(PACKAGE_FIND_VERSION_PRERELEASE "${${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE}")
-if(NOT "@protobuf_VERSION_PRERELEASE@" STREQUAL "")
-  if(NOT ${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE)
+if(NOT PACKAGE_FIND_VERSION_MAJOR EQUAL "@protobuf_VERSION_MAJOR@")
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+elseif(PACKAGE_FIND_VERSION VERSION_GREATER PACKAGE_VERSION)
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+elseif(PACKAGE_FIND_VERSION VERSION_EQUAL PACKAGE_VERSION)
+  # Do not match prerelease versions to non-prerelease version requests.
+  if(NOT "@protobuf_VERSION_PRERELEASE@" STREQUAL "" AND PACKAGE_FIND_VERSION_PRERELEASE STREQUAL "")
+    message(AUTHOR_WARNING "To use this prerelease version of ${PACKAGE_FIND_NAME}, set ${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE to '@protobuf_VERSION_PRERELEASE@' or greater.")
     set(PACKAGE_VERSION_COMPATIBLE FALSE)
-    message(AUTHOR_WARNING "To use this prerelease version of ${PACKAGE_FIND_NAME}, set ${PACKAGE_FIND_NAME}_FIND_VERSION_PRERELEASE to '@protobuf_VERSION_PRERELEASE@'.")
   endif()
 
-  if(NOT "${PACKAGE_FIND_VERSION}-${PACKAGE_FIND_VERSION_PRERELEASE}" STREQUAL "${PACKAGE_VERSION}")
-    set(PACKAGE_VERSION_COMPATIBLE FALSE)
-  else()
-    set(PACKAGE_VERSION_EXACT TRUE)
-  endif()
-else()
-  if(NOT PACKAGE_FIND_VERSION_MAJOR EQUAL "@protobuf_VERSION_MAJOR@")
-    set(PACKAGE_VERSION_COMPATIBLE FALSE)
-  elseif(PACKAGE_FIND_VERSION VERSION_GREATER PACKAGE_VERSION)
+  # Not robustly SemVer compliant, but protobuf never uses '.' separated prerelease identifiers.
+  if(PACKAGE_FIND_VERSION_PRERELEASE STRGREATER "@protobuf_VERSION_PRERELEASE@")
     set(PACKAGE_VERSION_COMPATIBLE FALSE)
   endif()
 endif()
@@ -39,4 +46,3 @@ if(NOT CMAKE_SIZEOF_VOID_P STREQUAL "@CMAKE_SIZEOF_VOID_P@")
   set(PACKAGE_VERSION_UNSUITABLE TRUE)
 endif()
 
-set(${PACKAGE_FIND_NAME}_VERSION_PRERELEASE "@protobuf_VERSION_PRERELEASE@" PARENT_SCOPE)