BinaryProvider can install a library on Windows with Julia 0.7 but not with 0.6

[giordano]

I'm not sure this is a bug in this package, I opened a thread on discourse yesterday but got no reply. What I can't understand is why it works with Julia 0.7, but not with 0.6. Thus I suspect it might be a bug (or an error on my side that I can't see). In addition, I don't have a Windows box to play with, so it's a bit hard for me to track down the issue.

Below my issue report.

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I'm trying to switch a package to BinaryBuilder.jl. It works fine on most systems (at least, those that I can test with Travis), but I'm facing some difficulties with the Windows build: the library is successfully installed in Julia 0.7, but fails with Julia 0.6 with the following error:

LoadError: BinaryProvider.LibraryProduct(nothing, String["libwcs"], :libwcs, "Prefix(C:\\Users\\appveyor\\.julia\\v0.6\\WCS\\deps\\usr)") is not satisfied, cannot generate deps.jl!
while loading C:\Users\appveyor\.julia\v0.6\WCS\deps\build.jl, in expression starting on line 46

Here are some information:

• the script used to build the library: https://github.com/JuliaAstro/WCSLIBBuilder/blob/43b1ad73e51c45fb9975c0147c15ecef1011c815/build_tarballs.jl
• the tag where the built packages are stored: https://github.com/JuliaAstro/WCSLIBBuilder/releases/tag/v5.13a
• the build.jl script in the Julia wrapper: https://github.com/giordano/WCS.jl/blob/b570c9004682ff6fd71bb1f0728416091cf3f7ca/deps/build.jl
• AppVeyor: https://ci.appveyor.com/project/giordano/wcs-jl/build/1.0.6
  • Failure to install the library with Julia 0.6: https://ci.appveyor.com/project/giordano/wcs-jl/build/1.0.6/job/em7v7em5ug5rmnxq
  • Success with Julia 0.7: https://ci.appveyor.com/project/giordano/wcs-jl/build/1.0.6/job/4mavkajcido8kpbg

Has anyone a clue about why Julia 0.6 fails to install the library on Windows? Am I doing something wrong, maybe in the build script?