Read sources in rule?

[Magnus Andersson]

Hi,

Is it possible to read source files (that is, the files in parameter 'srcs') and use their contents in a Starlark rule?

We are writing rules for a proprietary DSL. Some information about dependencies are defined in the source files, and we wonder if will need to duplicate this information in our rules.

Thanks,

Magnus

[Paul Johnston]

To my knowledge, not in a *build rule*.  However, a *repository rule* can do arbitrary things that could include reading source files and generating starlark, which could then be consumed by build rules.

[Austin Schuh]

Magnus,

rules_go solves this problem with gazelle if you are looking for prior art.

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[Jay Conrod]

To expand on this, gazelle is an extensible build file generating tool. It has built-in support for Go and proto, and it can be extended to generate rules for other languages.

In the rule implementation though, there's no way to access contents of source files. Only actions declared by rules may access files.

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