Julia: doc how to make packages work with custom pkg dir.

[steverweber]

perhaps should add some info on dirname(@__FILE__) in:
http://docs.julialang.org/en/release-0.4/stdlib/pkg/#Base.Pkg.dir
so devs are more likely to make packages that work under a custom LOAD_PATH https://github.com/JuliaLang/julia/issues/2295

https://github.com/randyzwitch/NoveltyColors.jl/issues/5
https://github.com/timothyrenner/ColorBrewer.jl/issues/10

[vtjnash]

fwiw, there's also the convenience function Base.source_dir() that gives the same result

[steverweber]

didn't seem official in 2013
https://groups.google.com/forum/#!msg/julia-users/cgX6Gv2lP7U/mx6l7A2bLl4J

[helgee]

Since Base.source_dir() is basically the same thing as the dirname(@__FILE__) idiom but looks at lot nicer and less "magical" I would suggest to make it official and exported.

[stevengj]

See also the discussion in #8679 and #12120.

[simonster]

Base.source_dir() doesn't just look less magical than dirname(@__FILE__). It is actually less magical, and thus easier to misuse. If you call it from anywhere but top-level code, it is unlikely to do what you expect. See https://github.com/JuliaLang/julia/issues/4530#issuecomment-26360609 where I convinced @StefanKarpinski to implement @__FILE__ instead of exporting Base.source_path(). (If people want @__DIR__, that's fine with me, though.)

[helgee]

@simonster point taken.

Is there a case where one cannot use dirname(@__FILE__) and must use Pkg.dir(name) instead? If not the latter should be deprecated and if yes the difference should be documented.

[simonster]

If a package wants to access a different package's directory, then dirname(@__FILE__) will not work, but Base.find_in_path(name) might be a better solution than Pkg.dir(name).

[tkelman]

Or have the package that needs its location used elsewhere define a module-level constant with the value of dirname(@__FILE__).

[helgee]

Accessing another package's files without the paths of those being part of the contract (the API) seems like asking for trouble.

[vtjnash]

dup of https://github.com/JuliaLang/julia/issues/12120