[cmake-developers] [CMake 0015885]: Ninja always relinks libraries that doesn't export any symbols (on Windows)

[Mantis Bug Tracker]

The following issue has been SUBMITTED. 
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https://cmake.org/Bug/view.php?id=15885 
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Reported By:                Pavel Solodovnikov
Assigned To:                
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Project:                    CMake
Issue ID:                   15885
Category:                   CMake
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
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Date Submitted:             2015-12-16 05:22 EST
Last Modified:              2015-12-16 05:22 EST
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Summary:                    Ninja always relinks libraries that doesn't export
any symbols (on Windows)
Description: 
Consider the following test case:

CMakeLists.txt:

cmake_minimum_required(VERSION 2.8)
project(foo CXX)
add_library(foo SHARED test.cpp)

test.cpp:

void foo()
{}


With such setup when I run cmake (cmake -G Ninja) and execute several
consecutive builds, each time ninja relinks "foo" library.

If test.cpp instead contains exported symbol, for example:

__declspec( dllexport ) void foo(){}

ninja works as expected, reporting for the second build "ninja: no work to do".


The cause of the problem is that cmake generates link rule for "foo.dll" in such
a way that it depends on "foo.lib" file existence:

build foo.dll foo.lib: CXX_SHARED_LIBRARY_LINKER__foo
CMakeFiles\foo.dir\test.cpp.obj

If a library has no exported symbols, MSVC doesn't produce a ".lib" file for it
during a build. Because of that ninja assumes it needs to relink again to
produce import library for "foo.dll".

Steps to Reproduce: 
1) extract attached archive with test files (CMakeLists.txt and test.cpp).
2) run "cmake -G Ninja"
3) ninja (builds and links library)
4) ninja (should report "no work to do" but relinks the library again)

Additional Information: 
It's a windows-specific case (more specifically Windows + MSVC, I assume, at
least not tested with MinGW toolchain), does not occur on linux since there is
no such thing as "import library" for shared libraries.
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Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2015-12-16 05:22 Pavel SolodovnikovNew Issue                                    
2015-12-16 05:22 Pavel SolodovnikovFile Added: cmake_relink_test.zip            
       
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