partial parsing (sound)

[florianschanda]

Use-case:

• provide include directories with new switch (e.g. -I)
• provide set of files we're interested in
• want to parse all files that we need to generate all possible messages relating to these files

• move preamble parsing from check and trlc files to the register step (like we do for rsl files)
• discover all files in include dirs
• build package dependency graph in source manager
• parse the transitive closure of the files or dirs we need (effectively equivalent to manually specifying only the necessary files)