Compiling Crystal code in postinstall

[ysbaddaden]

The postinstall script was added to allow the compilation of external C libraries when a Shard is installed as a dependency. But, it may be used to build Crystal binaries that the library (or the project that installed the dependency) could leverage. This may happen more often when #95 is implemented.

The issue is for transitive dependencies, that is when a dependency requires other dependencies to build the executables: they must be 1. installed and 2. accessible.

Shards currently installs dependencies in no specific order —they're actually installed in the order they are found— and immediately runs the postinstall script. It's thus likely that the dependencies of a dependency won't be available when a Shard tries to build Crystal code. Furthermore, dependencies are installed inside a single lib folder, thus even though they are accessible when building the main project, they aren't made accessible when building inside the dependency (i.e. there is no lib folder inside the dependency).

Possible solutions to the availability of transitive dependencies:

• install all shards and postpone the postinstall script (and executables installation) until they are all installed (basic, can fail if a shard requires a dependency binary);
• sort dependencies, install them in a manner that when installing a library, it's dependencies have already been installed (complex, beware of recursive dependencies).

Possible solution to the accessibility of transitive dependencies:

• manipulate the CRYSTAL_PATH environment variable when running the postinstall script, so it includes the main project's lib folder.

[Sija]

install all shards and postpone the postinstall script (and executables installation) until they are all installed;

That sounds like a sensible interim solution. Especially useful now, when #126 is merged.