Make vcpkg.targets more defensive w.r.t. the naming of build configurations

[FrankHeimes]

I'm using Visual Studio 2017 with the vcpkg integration to build my projects.
The vcpkg/scripts/buildsystems/msbuild/vcpkg.targets file is of version #3504, 8. Aug. 2018.

Besides the well known build configurations Debug and Release, I also use other names that prefix or suffix additional words, like Test Debug or Debug CLR. In my project settings, I examine the configuraion name to automatically adjust certain project settings.

The problem with vcpkg is that the condition $(VcpkgConfiguration.StartsWith('Debug')) does match some cases, but not all. Also, creating the property $(VcpkgNormalizedConfiguration) as string and examining it later just to add a sub directory is more verbose than necessary.

I'd like to propose the following:

• Create a property $(VcpkgConfigSubdir) that is 'debug\' if the configuration contains 'Debug' (case-insensitive) and is empty in all other cases.
• Remove lot's of redundant code by inserting $(VcpkgConfigSubdir) into the strings.
• Remove the error message "Vcpkg is unable to link because we cannot decide between Release and Debug libraries." because $(VcpkgConfigSubdir) will always be defined and the test cannot fail anymore.

I have prepared a modified version of vcpkg.targets that works very well that I'd like to submit.

[Neumann-A]

As I was doing work on #4361 I also thought of changing this behavior but decided against it due to names like (Release_with_debug_symbols). Your current changes will link the debug libraries in this case which is wrong. The other question is if linking the release libraries in all other non debug named configurations is the right thing to do? (e.g. in cases like: Deb_Config) Having a hard error in these cases could be better than silently linking the release libraries.

In cases where the user defines configurations he should set $(VcpkgNormalizedConfiguration) to the appropriate vcpkg configuration via a project *.props file or via the Visual Studio GUI (see #4361)

[FrankHeimes]

... but decided against it due to names like (Release_with_debug_symbols).
... non debug named configurations ... (e.g. in cases like: Deb_Config)
In cases where the user defines configurations he should set $(VcpkgNormalizedConfiguration) ...

Good point. Having thought about this for a while, I think $(VcpkgNormalizedConfiguration) does have a right to exist. But it should be used consistently, i.e. it should replace all occurences of VcpkgConfiguration.StartsWith('...')

I'd still suggest using $(VcpkgConfigSubdir) as proposed to reduce the redundant code.
I updated my pull request appropriately.

[zufuliu]

I think at least StartsWith() can be replaced with Contains(). e.g:

VcpkgConfiguration.Contains('Debug')
VcpkgConfiguration.Contains('Release')

or

VcpkgConfiguration.ToLowerInvariant().Contains('debug')
VcpkgConfiguration.ToLowerInvariant().Contains('release')

[JackBoosY]

This issue hasn’t been updated in a year; if it is still an issue, please reopen this issue.