CPack: Restore support for 0-valued version components

In commit v3.12.0-rc1~136^2 (CPack: Use project version as default for
`CPACK_PACKAGE_VERSION`, 2018-04-29) we did not account for the value of
`CMAKE_PROJECT_VERSION_{MAJOR,MINOR,PATCH}` having `0`.  Fix the logic
to distinguish between unprovided version components and `0` components.

While at it, add a test case covering the behavior described in the
documentation by the original commit.  The number of version components
in the package name should match those provided to the `project()`
command `VERSION` option.

Fixes: #18199

Modules/CPack.cmake

@@ -403,28 +403,31 @@ endfunction()
 
 # Set the package name
 _cpack_set_default(CPACK_PACKAGE_NAME "${CMAKE_PROJECT_NAME}")
-if(CMAKE_PROJECT_VERSION_MAJOR)
+
+# Set the package version
+if(CMAKE_PROJECT_VERSION_MAJOR GREATER_EQUAL 0)
   _cpack_set_default(CPACK_PACKAGE_VERSION_MAJOR "${CMAKE_PROJECT_VERSION_MAJOR}")
-  if(CMAKE_PROJECT_VERSION_MINOR)
+  if(CMAKE_PROJECT_VERSION_MINOR GREATER_EQUAL 0)
     _cpack_set_default(CPACK_PACKAGE_VERSION_MINOR "${CMAKE_PROJECT_VERSION_MINOR}")
-    if(CMAKE_PROJECT_VERSION_PATCH)
+    if(CMAKE_PROJECT_VERSION_PATCH GREATER_EQUAL 0)
       _cpack_set_default(CPACK_PACKAGE_VERSION_PATCH "${CMAKE_PROJECT_VERSION_PATCH}")
-      _cpack_set_default(CPACK_PACKAGE_VERSION
-        "${CPACK_PACKAGE_VERSION_MAJOR}.${CPACK_PACKAGE_VERSION_MINOR}.${CPACK_PACKAGE_VERSION_PATCH}")
-    else()
-      _cpack_set_default(CPACK_PACKAGE_VERSION
-      "${CPACK_PACKAGE_VERSION_MAJOR}.${CPACK_PACKAGE_VERSION_MINOR}")
     endif()
-  else()
-    _cpack_set_default(CPACK_PACKAGE_VERSION "${CPACK_PACKAGE_VERSION_MAJOR}")
   endif()
 else()
   _cpack_set_default(CPACK_PACKAGE_VERSION_MAJOR "0")
   _cpack_set_default(CPACK_PACKAGE_VERSION_MINOR "1")
   _cpack_set_default(CPACK_PACKAGE_VERSION_PATCH "1")
-  _cpack_set_default(CPACK_PACKAGE_VERSION
-    "${CPACK_PACKAGE_VERSION_MAJOR}.${CPACK_PACKAGE_VERSION_MINOR}.${CPACK_PACKAGE_VERSION_PATCH}")
 endif()
+if(NOT DEFINED CPACK_PACKAGE_VERSION)
+  set(CPACK_PACKAGE_VERSION "${CPACK_PACKAGE_VERSION_MAJOR}")
+  if(CPACK_PACKAGE_VERSION_MINOR GREATER_EQUAL 0)
+    string(APPEND CPACK_PACKAGE_VERSION ".${CPACK_PACKAGE_VERSION_MINOR}")
+    if(CPACK_PACKAGE_VERSION_PATCH GREATER_EQUAL 0)
+      string(APPEND CPACK_PACKAGE_VERSION ".${CPACK_PACKAGE_VERSION_PATCH}")
+    endif()
+  endif()
+endif()
+
 _cpack_set_default(CPACK_PACKAGE_VENDOR "Humanity")
 if(CMAKE_PROJECT_DESCRIPTION)
   _cpack_set_default(CPACK_PACKAGE_DESCRIPTION_SUMMARY

Tests/RunCMake/CPackConfig/RunCMakeTest.cmake

@@ -4,3 +4,6 @@ run_cmake(Simple)
 run_cmake(Default)
 run_cmake(Special)
 run_cmake(Verbatim)
+run_cmake(Version1)
+run_cmake(Version2)
+run_cmake(Version3)

Tests/RunCMake/CPackConfig/Version1-check.cmake

@@ -0,0 +1,6 @@
+include(${RunCMake_SOURCE_DIR}/check.cmake)
+
+test_variable(CPACK_PACKAGE_VERSION "0")
+test_variable(CPACK_PACKAGE_VERSION_MAJOR "0")
+test_variable(CPACK_PACKAGE_VERSION_MINOR "")
+test_variable(CPACK_PACKAGE_VERSION_PATCH "")

Tests/RunCMake/CPackConfig/Version1.cmake

@@ -0,0 +1 @@
+project(Version LANGUAGES NONE VERSION 0)

Tests/RunCMake/CPackConfig/Version2-check.cmake

@@ -0,0 +1,6 @@
+include(${RunCMake_SOURCE_DIR}/check.cmake)
+
+test_variable(CPACK_PACKAGE_VERSION "1.0")
+test_variable(CPACK_PACKAGE_VERSION_MAJOR "1")
+test_variable(CPACK_PACKAGE_VERSION_MINOR "0")
+test_variable(CPACK_PACKAGE_VERSION_PATCH "")

Tests/RunCMake/CPackConfig/Version2.cmake

@@ -0,0 +1 @@
+project(Version LANGUAGES NONE VERSION 1.0)

Tests/RunCMake/CPackConfig/Version3-check.cmake

@@ -0,0 +1,6 @@
+include(${RunCMake_SOURCE_DIR}/check.cmake)
+
+test_variable(CPACK_PACKAGE_VERSION "1.1.0")
+test_variable(CPACK_PACKAGE_VERSION_MAJOR "1")
+test_variable(CPACK_PACKAGE_VERSION_MINOR "1")
+test_variable(CPACK_PACKAGE_VERSION_PATCH "0")

Tests/RunCMake/CPackConfig/Version3.cmake

@@ -0,0 +1 @@
+project(Version LANGUAGES NONE VERSION 1.1.0)