Не удается найти ошибку исходного файла при запуске CMake

Question

Ошибка с терминала:

ics45c@ics45c-2019fall : ~/projects/proj1 $ ./build app
-- Configuring done
CMake Error at CMakeLists.txt:49 (add_executable):
  Cannot find source file:

    /home/ics45c/projects/proj1/app/.#main.cpp

  Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp
  .hxx .in .txx


CMake Error: CMake can not determine linker language for target: a.out.gtest
CMake Error: Cannot determine link language for target "a.out.gtest".
CMake Error: CMake can not determine linker language for target: a.out.app
CMake Error: Cannot determine link language for target "a.out.app".
CMake Error: CMake can not determine linker language for target: a.out.exp
CMake Error: Cannot determine link language for target "a.out.exp".
-- Generating done
-- Build files have been written to: /home/ics45c/projects/proj1/out

Я проверил мой файловый менеджер и main.cpp и #main.cpp# находятся в местоположении /home/ics45c/projects/proj1/app

Также я не понимаю другихОшибки CMake после CMakeLists.txt также отсутствуют. Что это значит, что он не может определить язык компоновщика?

## Here is the CMakeLists.txt file ##

cmake_minimum_required(VERSION 3.10)

set(CMAKE_C_COMPILER clang)
set(CMAKE_CXX_COMPILER clang++)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

set(COMPILE_FLAGS "-stdlib=libc++ -Wall -pedantic-errors -Werror -g -fstandalone-debug")


project(a.out.app)

file(GLOB APP_SRC_FILES ${CMAKE_SOURCE_DIR}/app/*.cpp)

set(APP_SRC_FILES_EXCEPT_MAIN ${APP_SRC_FILES})
list(REMOVE_ITEM APP_SRC_FILES_EXCEPT_MAIN ${CMAKE_SOURCE_DIR}/app/main.cpp)

add_executable(${PROJECT_NAME} ${APP_SRC_FILES})
set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS ${COMPILE_FLAGS})
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_SOURCE_DIR}/app)
target_link_libraries(${PROJECT_NAME} pthread c++)

project(a.out.exp)

file(GLOB EXP_SRC_FILES ${CMAKE_SOURCE_DIR}/exp/*.cpp)

add_executable(${PROJECT_NAME} ${EXP_SRC_FILES} ${APP_SRC_FILES_EXCEPT_MAIN})
set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS ${COMPILE_FLAGS})
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_SOURCE_DIR}/app)
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_SOURCE_DIR}/exp)
target_link_libraries(${PROJECT_NAME} pthread c++)


project(a.out.gtest)

file(GLOB GTEST_SRC_FILES ${CMAKE_SOURCE_DIR}/gtest/*.cpp)

add_executable(${PROJECT_NAME} ${GTEST_SRC_FILES} ${APP_SRC_FILES_EXCEPT_MAIN})
set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS ${COMPILE_FLAGS})
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_SOURCE_DIR}/app)
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_SOURCE_DIR}/gtest)
target_link_libraries(${PROJECT_NAME} pthread c++ gtest gtest_main)

Строка 49 - это ошибка в соответствии с ошибкой CMake, но я понятия не имею, почему:

add_executable(${PROJECT_NAME} ${GTEST_SRC_FILES} ${APP_SRC_FILES_EXCEPT_MAIN})

Я просто ничего не понимаю, и это тоже мой первый пост в Stackoverflow.