Getting compilation warning during precompile

[djsegal]

I use the following line of code in one of my packages:

const atm_conversion =
  uconvert(u"atm", 1e20u"keV/m^3") / 1u"atm"

However, this gives the following warnings on the initial compile:

WARNING: eval from module Unitful to FusionSystems:
Expr(:call, :^, Unitful.FreeUnits{(Unitful.Unit{:Meter, Unitful.Dimensions{(Unitful.Dimension{:Length}(power=Base.Rational{Int64}(num=1, den=1)),)}}(tens=0, power=Base.Rational{Int64}(num=1, den=1)),), Unitful.Dimensions{(Unitful.Dimension{:Length}(power=Base.Rational{Int64}(num=1, den=1)),)}}(), 3)::Any
  ** incremental compilation may be broken for this module **

WARNING: eval from module Unitful to FusionSystems:
Expr(:call, :/, Unitful.FreeUnits{(Unitful.Unit{:eV, Unitful.Dimensions{(Unitful.Dimension{:Length}(power=Base.Rational{Int64}(num=2, den=1)), Unitful.Dimension{:Mass}(power=Base.Rational{Int64}(num=1, den=1)), Unitful.Dimension{:Time}(power=Base.Rational{Int64}(num=-2, den=1)))}}(tens=3, power=Base.Rational{Int64}(num=1, den=1)),), Unitful.Dimensions{(Unitful.Dimension{:Length}(power=Base.Rational{Int64}(num=2, den=1)), Unitful.Dimension{:Mass}(power=Base.Rational{Int64}(num=1, den=1)), Unitful.Dimension{:Time}(power=Base.Rational{Int64}(num=-2, den=1)))}}(), Unitful.FreeUnits{(Unitful.Unit{:Meter, Unitful.Dimensions{(Unitful.Dimension{:Length}(power=Base.Rational{Int64}(num=1, den=1)),)}}(tens=0, power=Base.Rational{Int64}(num=3, den=1)),), Unitful.Dimensions{(Unitful.Dimension{:Length}(power=Base.Rational{Int64}(num=3, den=1)),)}}())::Any
  ** incremental compilation may be broken for this module **

How do I prevent it?

[ajkeller34]

The issue is that @u_str is dynamic and looks through registered modules to see what unit symbols are available at the time the macro is expanded. As a result, @u_str doesn't play well with precompilation. It is more explicit if slightly more annoying to write Unitful.atm instead of u"atm", which indicates that you want Unitful's definition of atm even if you've registered some other modules that may define their own atm. I've verified that this will compile:

const atm_conversion =
  uconvert(Unitful.atm, 1e20*Unitful.keV/Unitful.m^3) / (Unitful.atm)

const wb_conversion =
  uconvert(Unitful.Wb, Unitful.µ0 * 1*Unitful.MA*Unitful.m) / Unitful.Wb

This point could use some better documentation if you're up for a PR.

[rafaqz]

I just started getting these now that 0.7 does automatic precompilation. I have some files with a few hundred unit declarations, each with 1-4 units. Adding hundreds of Unitful. isn't a great solution to this problem!

How about a second string macro that is Unitful specific and precompilation friendly?

U"m*s^-1"

Otherwise it's using Unitful: m, s, mol, mmol, kg, g ...

[pjabardo]

I will take a look tonight or tomorrow