Fix error building without CMAKE_BUILD_TYPE being set

[ideasman42]

This resolves the error building without a CMAKE_BUILD_TYPE.

CMake Error at CMakeLists.txt:36 (string):                                                                                                                                                          
  string no output variable specified

Describe your PR, what does it fix/add?

Resolve a build error with CMake.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

Is it ready for merging, or does it need work?

It's ready.

[q234rty]

It would be better to also fix other valid CMAKE_BUILD_TYPE s as well, i.e. translate None to meson empty, RelWithDebInfo to meson debugoptimized, MinSizeRel to meson minsize .

[vaxerski]

true that. Also, why is it _INIT?

[ideasman42]

true that. Also, why is it _INIT?

This is used to set the initial build type, setting CMAKE_BUILD_TYPE would override the build type set that was already set, preventing other kinds of builds, "Debug" "RelWithDebInfo"... etc.

Strangely CMAKE_BUILD_TYPE_INIT is undocumented, but it is used. See:

• https://gitlab.kitware.com/cmake/cmake/-/blob/ee5f31ba727e392e1ebc9f5be54c74ac1868d029/Modules/CMakeInitializeConfigs.cmake#L22

• https://stackoverflow.com/questions/46820155/should-i-cache-cmake-build-type/46835792#46835792

---

If you wanted to avoid relying on an undocumented variable you could always do something like this:

if(NOT CMAKE_BUILD_TYPE)
  set(CMAKE_BUILD_TYPE "Release" CACHE STRING)
endif()

---

An alternative solution could be to support an empty CMAKE_BUILD_TYPE since CMake it's self allows this, e.g.

if(CMAKE_BUILD_TYPE)
    string(TOLOWER ${CMAKE_BUILD_TYPE} BUILDTYPE_LOWER)
else()
    set(BUILDTYPE_LOWER "release")
endif()

[vaxerski]

latter seems more reasonable (supporting empty)

[ideasman42]

Updated to convert the CMake build type to meson build types (with support for empty build type).

[q234rty]

cmake None i.e. meson's empty seems to be missing

[vaxerski]

lgtm, thanks!