Import a build.zig file as a build step

[AndreaOrru]

Kinda like this:
https://github.com/zig-lang/zig/blob/master/test/build_examples.zig

But included in the standard build system.

[andrewrk]

Why does it need to be a separate build file? In the example you linked, we're testing the zig build system itself which is the reason for running zig build in a subprocess.

In your case, can you not import the file and pass it the Builder reference?

[andrewrk]

Related: #353

[AndreaOrru]

No. For example, the paths are going to be inconsistent: relative to the root of the project when building the module from the main build.zig, and to the module directory when building it by itself.

You should be able to cd into the module directory and build it independently from the rest of the project.

[AndreaOrru]

Related issue: if two executables are part of the same build, and you call .setBuildMode(b.standardReleaseOptions()) on both, you get this error:

Option 'release-safe' declared twice.

[andrewrk]

The standardReleaseOptions issue is resolved.

[andrewrk]

Related to #353 and #943