[SOLVED] CMake unable to handle conjunction in if

Issue

I have the following minimal non-working example as CMakeLists.txt:

project(MinimalWorkingExample)

if(NOT WIN32 AND WIN32)
    message("If branch!!")
else()
    message("Else branch!!")
endif()
if(${ENABLE_COVERAGE})
    message("If branch 2!!")
else()
    message("Else branch 2!!")
endif()
if(${ENABLE_COVERAGE} AND ${ENABLE_COVERAGE})
    message("If branch 3!!")
else()
    message("Else branch 3!!")
endif()
if(NOT WIN32 AND NOT WIN32)
    message("If branch 4!!")
else()
    message("Else branch 4!!")
endif()
if(NOT WIN32)
    if(${ENABLE_COVERAGE})
        message("If-If branch!!")
    else()
        message("If-Else branch!!")
    endif()
else()
    if(${ENABLE_COVERAGE})
        message("Else-If branch!!")
    else()
        message("Else-Else branch!!")
    endif()
endif()
if(NOT WIN32 AND ${ENABLE_COVERAGE})
    message("Last branch")
endif()

using this with CMake 3.24.2 under windows produces the following output (besides the usual compiler identification etc., which has no warning or error in it):

Else branch!!
Else branch 2!!
Else branch 3!!
Else branch 4!!
Else-Else branch!!
CMake Error at CMakeLists.txt:36 (if):
  if given arguments:

    "NOT" "WIN32" "AND"

  Unknown arguments specified

How come that I'm not allowed to have a conjunction of a variable like ENABLE_COVERAGE and a predefined symbol like WIN32?

Solution

This is explained in CMake documentation https://cmake.org/cmake/help/latest/command/if.html#variable-expansion .

The following line with empty ENABLE_COVERAGE:

if(NOT WIN32 AND ${ENABLE_COVERAGE})

Expands to:

if(NOT WIN32 AND)

which is invalid.

As a rule of thumb, you should never use ${...} inside if. Remember to check your scripts with cmake-lint.

How come that I'm not allowed to have a conjunction of a variable like ENABLE_COVERAGE and a predefined symbol like WIN32?

You are, you want:

 if(NOT WIN32 AND ENABLE_COVERAGE)

Or potentially:

 if(NOT WIN32 AND "${ENABLE_COVERAGE}")

Depending on how you want to handle https://cmake.org/cmake/help/latest/command/if.html#basic-expressions .

Answered By - KamilCuk

Answer Checked By - Marilyn (WPSolving Volunteer)