MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0014052CMakeCMakepublic2013-03-31 11:572016-06-10 14:31
Reporteralecool 
Assigned ToKitware Robot 
PrioritynormalSeveritymajorReproducibilityalways
StatusclosedResolutionmoved 
PlatformPCOSWindowsOS Version7 64 bit
Product VersionCMake 2.8.10.2 
Target VersionFixed in Version 
Summary0014052: System-specific variables are undefined before using project() command
DescriptionUsing a trivial CMakeLists.txt, the MSVC variable is NOT defined when I add a project() command. The bug is reproduced with both generators "Visual Studio 10" and "Visual Studio 11" as well as the Win64 versions. Likewise, the MSYS variable is undefined when using the "MSYS Makefiles" generator. These are the only build toolsets that I cared to install on my system.
Steps To Reproduce### Using the following CMakeLists.txt
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)

message( INFO ${CMAKE_GENERATOR} )
if(WIN32)
    message(INFO Win32)
    if(MSVC)
      message(INFO MSVC)
    else()
        message(INFO not MSVC)
    endif()

    if(MSVC_IDE)
      message(INFO MSVC_IDE)
    else()
        message(INFO not MSVC_IDE)
    endif()
    
    if(MSYS)
      message(INFO MSYS)
    else()
        message(INFO not MSYS)
    endif()
else()
    message(INFO not Win32)
endif()

#Project configuration
project (test)

message( INFO ${CMAKE_GENERATOR} )
if(WIN32)
    message(INFO Win32)
    if(MSVC)
      message(INFO MSVC)
    else()
        message(INFO not MSVC)
    endif()

    if(MSVC_IDE)
      message(INFO MSVC_IDE)
    else()
        message(INFO not MSVC_IDE)
    endif()
    
    if(MSYS)
      message(INFO MSYS)
    else()
        message(INFO not MSYS)
    endif()
else()
    message(INFO not Win32)
endif()


I get the following output:
>cmake -G"Visual Studio 11" ..
INFOVisual Studio 11
INFOWin32
INFOnotMSVC
INFOnotMSVC_IDE
INFOnotMSYS
-- The C compiler identification is MSVC 17.0.51106.1
-- The CXX compiler identification is MSVC 17.0.51106.1
-- Check for working C compiler using: Visual Studio 11
-- Check for working C compiler using: Visual Studio 11 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler using: Visual Studio 11
-- Check for working CXX compiler using: Visual Studio 11 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
INFOVisual Studio 11
INFOWin32
INFOMSVC
INFOMSVC_IDE
INFOnotMSYS
-- Configuring done
-- Generating done
-- Build files have been written to: E:/dev/cpp/test/TestCMake/VC11_x86

### Removing the project command as follows:
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)

message( INFO ${CMAKE_GENERATOR} )
if(WIN32)
    message(INFO Win32)
    if(MSVC)
      message(INFO MSVC)
    else()
        message(INFO not MSVC)
    endif()

    if(MSVC_IDE)
      message(INFO MSVC_IDE)
    else()
        message(INFO not MSVC_IDE)
    endif()
    
    if(MSYS)
      message(INFO MSYS)
    else()
        message(INFO not MSYS)
    endif()
else()
    message(INFO not Win32)
endif()

#Project configuration
# project (test)

message( INFO ${CMAKE_GENERATOR} )
if(WIN32)
    message(INFO Win32)
    if(MSVC)
      message(INFO MSVC)
    else()
        message(INFO not MSVC)
    endif()

    if(MSVC_IDE)
      message(INFO MSVC_IDE)
    else()
        message(INFO not MSVC_IDE)
    endif()
    
    if(MSYS)
      message(INFO MSYS)
    else()
        message(INFO not MSYS)
    endif()
else()
    message(INFO not Win32)
endif()

I get the following output, which was expected with the previous CMakeLists.txt
>cmake -G"Visual Studio 11" ..
-- The C compiler identification is MSVC 17.0.51106.1
-- The CXX compiler identification is MSVC 17.0.51106.1
-- Check for working C compiler using: Visual Studio 11
-- Check for working C compiler using: Visual Studio 11 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler using: Visual Studio 11
-- Check for working CXX compiler using: Visual Studio 11 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
INFOVisual Studio 11
INFOWin32
INFOMSVC
INFOMSVC_IDE
INFOnotMSYS
INFOVisual Studio 11
INFOWin32
INFOMSVC
INFOMSVC_IDE
INFOnotMSYS
-- Configuring done
-- Generating done
-- Build files have been written to: E:/dev/cpp/test/TestCMake/VC11_x86
Additional InformationWe observe that depending on the presence and the position of the project() command, the behavior of code dependent on the definition of system-specific variables can change a great deal. I couldn't find any documentation whether this is known and specified behavior, and it seems a bit counter-intuitive that a command documented as "Setting a name for the entire project" would influence the behavior of a cmake script that much.
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Issue History
Date ModifiedUsernameFieldChange
2013-03-31 11:57alecoolNew Issue
2013-03-31 14:29Eric NOULARDNote Added: 0032732
2013-03-31 17:06alecoolNote Added: 0032733
2013-04-01 08:04Brad KingNote Added: 0032734
2016-06-10 14:28Kitware RobotNote Added: 0042258
2016-06-10 14:28Kitware RobotStatusnew => resolved
2016-06-10 14:28Kitware RobotResolutionopen => moved
2016-06-10 14:28Kitware RobotAssigned To => Kitware Robot
2016-06-10 14:31Kitware RobotStatusresolved => closed

Notes
(0032732)
Eric NOULARD   
2013-03-31 14:29   
AIFAIK this is not a bug, this is the way it works in CMake for ages.

Setting MSVC before

project(Blah C)

does not seem possible because (cmake --help-variable MSVC)
  MSVC
       True when using Microsoft Visual C

and no C compiler is searched by CMake before the C language is enabled:

1) by project(Blah C) or project(Blah) (which enables C and CXX by default)
2) by enable enable_language(C)

I shall add that "asking" for a generator on the command line/GUI
does not make it available so that MVSC will be set as soon as
C - language is enabled AND some MS C compiler is found.
I mean you may ask for "Visual Studio 11" but CMake may not
be able to find the corresponding compiler.

Then regarding your test. you should always try from a pristine
build directory, I think (but I may be wrong)
that in your case you did not delete
the cache and/or use a pristine build dir so that the value
of MSVC may be cached from the previous run.
(0032733)
alecool   
2013-03-31 17:06   
I did clean my cache between every try at running the project generation.
I felt that "it's the way it works" would be the answer i'd get.

Anyway, it seems that when not having a project() command (nor enable_language()), the language is determined before everything : in the second try of the bug report, when no project() is used, the two test sequences are displayed consecutively, both after compiler identification ; whereas in the first try (using project()), I get the first test sequence, then the identification of the compiler, then the second test sequence.

In my case (where I found out about this behavior), I tried to detect boost using find_package, which would fail when the find_package command is called before the project command. Having such strong behavior implications on a command that "sets the name of the project" is a bit counter-intuitive.

I wonder why cmake would be able to detect the presence of the compiler first-off when there is no project() command, and would need to wait to proceed that command when it is used in the script.
(0032734)
Brad King   
2013-04-01 08:04   
Re 0014052:0032733: A project() command is required (exactly to detect system/compiler info) so if there isn't one CMake inserts one implicitly on line 0 of the top-level CMakeLists.txt file.
(0042258)
Kitware Robot   
2016-06-10 14:28   
Resolving issue as `moved`.

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