[Scons-users] Code not rebuilt when switching between two VisualStudio versions

[Mats Wichmann]

On 3/26/21 1:52 AM, Steve Hill (Wireless) via Scons-users wrote:
> Hi Bill,
> 
> The command line is unchanged. When you install the coverage tool, it 
> results in vcvarsall.bat adding the path to the coverage ‘bin’ directory 
> ahead of the one for MSVC:
> 
> PATH=*C:\Program Files (x86)\BullseyeCoverage\bin*;C:\Program Files 
> (x86)\Microsoft Visual Studio 
> 14.0\VC\Tools\MSVC\14.15.26726\bin\HostX64\x64;C:\Program Files 
> (x86)\Microsoft Visual Studio 14.0\Common7\IDE\VC\VCPackages;C:\Program 
> Files (x86)\...
> 
> That means that the cl.exe and link.exe that are invoked are the 
> coverage versions, which then do what they need to do before invoking 
> the real compiler or linker (presumably using the directories in the 
> PATH other than its own.) We have other tools (e.g. dynamic code 
> analysis) that work in the same way – it seems quite standard, under 
> Windows at least; this just happens to be the first tool where we have 
> encountered it.
> 
> Since it supports multiple versions of MSVS, it may call the compiler 
> for either MSVS 2017 or MSVS 2019 – but SCons has no way of knowing 
> that. I figure that I need to somehow tell SCons that this extra 
> dependency exists.
> 
> I’ve tried:
> 
> env.Depends(

One of the decision points as to whether to rebuild is whether the 
string which will be issued as the command to build a file (the 
builder's "action") has changed. The string is hashed, and that is 
compared with the action signature stored away from earlier builds.  The 
problem you're having here is that the action doesn't contain the actual 
compiler name/path, so SCons sees no difference.

There is  a way to add things to be considered as part of an action 
signature - namely you can include construction variables, whose values 
will be slurped up and included. It looks something like this (from the 
manpage):

a = Action(build_it, varlist=['XXX'])

The problem is you're not writing your own actions, you want this to 
happen for pre-defined actions attached to the SCons-provided builders 
you're using (I assume you're using the standard ones like Program, 
Object, etc.).  Changing an existing action is tricky.

You can read a bit more here:

https://scons.org/doc/production/HTML/scons-man.html#action_objects

Maybe someone else knows another route?

(I'm going to look at eventually adding something on this somewhere, 
either docs or scons-recipes, you're right that the concept of  a tool 
masquerading as another tool is relatively common - on Linux/UNIX ccache 
is one of those. This means SCons doesn't see the actual one, and might 
not detect changes).