style: avoid using unintialized variables

CMakeLists.txt

@@ -73,6 +73,8 @@ if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
     set(CMAKE_CXX_EXTENSIONS OFF)
     set(CMAKE_CXX_STANDARD_REQUIRED ON)
   endif()
+
+  set(pybind11_system "")
 else()
   set(PYBIND11_MASTER_PROJECT OFF)
   set(pybind11_system SYSTEM)

tests/CMakeLists.txt

@@ -24,7 +24,7 @@ include(CMakeParseArguments)
 # Usage:
 #   pybind11_filter_tests(LISTNAME file1.cpp file2.cpp ... MESSAGE "")
 #
-macro(PYBIND11_FILTER_TESTS LISTNAME)
+macro(pybind11_filter_tests LISTNAME)
   cmake_parse_arguments(ARG "" "MESSAGE" "" ${ARGN})
   set(PYBIND11_FILTER_TESTS_FOUND OFF)
   foreach(filename IN LISTS ARG_UNPARSED_ARGUMENTS)
@@ -39,6 +39,14 @@ macro(PYBIND11_FILTER_TESTS LISTNAME)
   endif()
 endmacro()
 
+macro(possibly_uninitialized)
+  foreach(VARNAME ${ARGN})
+    if(NOT DEFINED "${VARNAME}")
+      set("${VARNAME}" "")
+    endif()
+  endforeach()
+endmacro()
+
 # New Python support
 if(DEFINED Python_EXECUTABLE)
   set(PYTHON_EXECUTABLE "${Python_EXECUTABLE}")
@@ -67,7 +75,7 @@ if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
   find_package(pybind11 REQUIRED CONFIG)
 endif()
 
-if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+if(NOT CMAKE_BUILD_TYPE AND NOT DEFINED CMAKE_CONFIGURATION_TYPES)
   message(STATUS "Setting tests build type to MinSizeRel as none was specified")
   set(CMAKE_BUILD_TYPE
       MinSizeRel
@@ -345,11 +353,14 @@ foreach(target ${test_targets})
   if(NOT CMAKE_LIBRARY_OUTPUT_DIRECTORY)
     set_target_properties(${target} PROPERTIES LIBRARY_OUTPUT_DIRECTORY
                                                "${CMAKE_CURRENT_BINARY_DIR}")
-    foreach(config ${CMAKE_CONFIGURATION_TYPES})
-      string(TOUPPER ${config} config)
-      set_target_properties(${target} PROPERTIES LIBRARY_OUTPUT_DIRECTORY_${config}
-                                                 "${CMAKE_CURRENT_BINARY_DIR}")
-    endforeach()
+
+    if(DEFINED CMAKE_CONFIGURATION_TYPES)
+      foreach(config ${CMAKE_CONFIGURATION_TYPES})
+        string(TOUPPER ${config} config)
+        set_target_properties(${target} PROPERTIES LIBRARY_OUTPUT_DIRECTORY_${config}
+                                                   "${CMAKE_CURRENT_BINARY_DIR}")
+      endforeach()
+    endif()
   endif()
 endforeach()
 

tests/test_cmake_build/CMakeLists.txt

@@ -55,6 +55,8 @@ function(pybind11_add_build_test name)
   add_dependencies(test_cmake_build test_build_${name})
 endfunction()
 
+possibly_uninitialized(PYTHON_MODULE_EXTENSION Python_INTERPRETER_ID)
+
 pybind11_add_build_test(subdirectory_function)
 pybind11_add_build_test(subdirectory_target)
 if("${PYTHON_MODULE_EXTENSION}" MATCHES "pypy" OR "${Python_INTERPRETER_ID}" STREQUAL "PyPy")

tests/test_embed/CMakeLists.txt

@@ -1,4 +1,7 @@
+possibly_uninitialized(PYTHON_MODULE_EXTENSION Python_INTERPRETER_ID)
+
 if("${PYTHON_MODULE_EXTENSION}" MATCHES "pypy" OR "${Python_INTERPRETER_ID}" STREQUAL "PyPy")
+  message(STATUS "Skipping embed test on PyPy")
   add_custom_target(cpptest) # Dummy target on PyPy. Embedding is not supported.
   set(_suppress_unused_variable_warning "${DOWNLOAD_CATCH}")
   return()

tools/FindEigen3.cmake

@@ -64,6 +64,9 @@ if(EIGEN3_INCLUDE_DIR)
   set(EIGEN3_FOUND ${EIGEN3_VERSION_OK})
 
 else(EIGEN3_INCLUDE_DIR)
+  if(NOT DEFINED KDE4_INCLUDE_DIR)
+    set(KDE4_INCLUDE_DIR "")
+  endif()
 
   find_path(
     EIGEN3_INCLUDE_DIR

tools/FindPythonLibsNew.cmake

@@ -57,6 +57,8 @@ endif()
 
 if(PythonLibsNew_FIND_QUIETLY)
   set(_pythonlibs_quiet QUIET)
+else()
+  set(_pythonlibs_quiet "")
 endif()
 
 if(PythonLibsNew_FIND_REQUIRED)

tools/pybind11NewTools.cmake

@@ -12,6 +12,8 @@ get_property(
 
 if(pybind11_FIND_QUIETLY)
   set(_pybind11_quiet QUIET)
+else()
+  set(_pybind11_quiet "")
 endif()
 
 if(CMAKE_VERSION VERSION_LESS 3.12)

tools/pybind11Tools.cmake

@@ -10,6 +10,8 @@ include(CMakeParseArguments)
 
 if(pybind11_FIND_QUIETLY)
   set(_pybind11_quiet QUIET)
+else()
+  set(_pybind11_quiet "")
 endif()
 
 # If this is the first run, PYTHON_VERSION can stand in for PYBIND11_PYTHON_VERSION
@@ -22,11 +24,16 @@ if(NOT DEFINED PYBIND11_PYTHON_VERSION AND DEFINED PYTHON_VERSION)
       CACHE STRING "Python version to use for compiling modules")
   unset(PYTHON_VERSION)
   unset(PYTHON_VERSION CACHE)
-else()
-  # If this is set as a normal variable, promote it, otherwise, make an empty cache variable.
+elseif(DEFINED PYBIND11_PYTHON_VERSION)
+  # If this is set as a normal variable, promote it
   set(PYBIND11_PYTHON_VERSION
       "${PYBIND11_PYTHON_VERSION}"
       CACHE STRING "Python version to use for compiling modules")
+else()
+  # Make an empty cache variable.
+  set(PYBIND11_PYTHON_VERSION
+      ""
+      CACHE STRING "Python version to use for compiling modules")
 endif()
 
 # A user can set versions manually too