[Scons-users] Previous build information lost with ProtoBuilder/Gch interaction

[Dirk Bächle]

Hi Carl,

On 04.08.2015 04:36, Carl Cerecke wrote:
> I have two Sconscript files, both building a single static library,
> and both called from the same SConstruct (they are the only two
> Sconscript files called).
>
> [...]
>
> Building from scratch works fine.
>
> Problem: Rebuilding (after no changes) builds everything again and
> [...]
>
> What is utterly confusing is that, whether or not libGch finds
> previous build information or not, depends on whether an unrelated
> dependency exists in a *separate* Sconscript file that should be
> completely independent!
>
> Both Sconscript files use a clone of the environment they imported
> from the parent SConstruct, so they should be independent.
>
just to make a few things clear. The Nodes of the different environments are treated separately, regarding how they are 
created...meaning: the single Actions of the Builder are executed in the Environments as you've specified them.
However, the dependency tracking between the single targets (like Programs, Libraries,...) and back to their sources, always 
operates on the full VFS (virtual filesystem). With VFS I don't mean the dependency tree (DAG) that SCons implicitly creates during 
the build phase. It's a tree structure where SCons keeps track of which Nodes (Targets/Sources/Generated headers/...) exist, or 
should come into existence later during the actual build. This "file tree" is fed from the info (basically stemming from the 
Emitters of the single Builders, "what goes in, and what goes out?") in *all* your SConstructs/SConscripts that are read in.

And this is done so by design. Because we *want* to automatically detect a dependency between a library "libfoo" and a main program 
"bar", even if both are created in different Environments. So, the behaviour that you see is, more or less, expected...

In addition to what William said, I'd also like to have a closer look at some of your example code before making any further claims 
and statements about what could possibly go wrong.

Best regards,

Dirk