Deprecate ImmutableArrays and FixedSizeArrays compatibility interfaces

[c42f]

As briefly mentioned in #503

At this stage, people should use the StaticArrays APIs directly. If there's anything useful left in StaticArrays.FixedSizeArrays we should fold it into the main API, or move it to other packages where it fits more neatly.

CC @andyferris @SimonDanisch

[edit] Closes #459

[SimonDanisch]

I'm not against this, but we'll need to make extra sure that the transition is smooth.
Almost all my packages rely on this, so messing this up would take out quite a lot of packages^^

[mschauer]

Data point: I have no dependency on that code since a long time.

[timholy]

Deprecating those will help a lot with #18. And I'm not sure it's even being used as is; https://github.com/JuliaGeometry/GeometryTypes.jl/blob/65f4f2a65f353968aa0eaf9ee18a1a23352290c3/src/types.jl#L47 suggests GeometryTypes is creating its own Vec rather than using the one in StaticArrays.FixedSizeArrays.

[timholy]

Deprecating those will help a lot with #18. And I'm not sure it's even being used as is; https://github.com/JuliaGeometry/GeometryTypes.jl/blob/65f4f2a65f353968aa0eaf9ee18a1a23352290c3/src/types.jl#L47 suggests GeometryTypes is creating its own Vec rather than using the one in StaticArrays.FixedSizeArrays.

[c42f]

@SimonDanisch yes I don't want to leave you scrambling! Do your packages depend on it via GeometryTypes? Perhaps we could move @fixed_vector to there?

[andyferris]

IIRC there was a GeometryTypes PR to move the functionality there?

[c42f]

Ah yes: JuliaGeometry/GeometryTypes.jl#153. Good timing (thanks @aaronang).

See also JuliaGeometry/GeometryTypes.jl#132 and #459 which I didn't see before making this PR :)

[mkborregaard]

This broke Plots.

[KristofferC]

Minor releases are typically breaking.

[mkborregaard]

Thanks for the info I guess? :-)

[mkborregaard]

Also, this JuliaLang/METADATA.jl#19050 (comment)

[c42f]

Sorry for the breakage, the intention was to provide a proper deprecation warning, and indeed this does so on the surface:

julia> using StaticArrays.FixedSizeArrays
WARNING: StaticArrays.FixedSizeArrays is deprecatedStaticArrays.FixedSizeArrays is deprecated. Use StaticArrays directly.
 in module StaticArrays

julia> Vec(1,2,3)
3-element Vec{3,Int64}:
 1
 2
 3

(botched warning notwithstanding)

So now we need to figure out why it broke it, and quickly release a patch update.

[fredrikekre]

I am working on a patch. The problem is that before this worked:

using StaticArrays.FixedSizeArrays
FixedSizeArrays.Vec

since the using call brought in FixedSizeArrays, but after this PR that does not happen.

[c42f]

Oh I see.