Feature request: function to precompile all projects

[cserteGT3]

I'm thinking on this feature for a long time: it would be nice, if one could precompile all projects with one function call. It would be useful for example when a new julia version comes out and you want to precompile all projects. It doesn't save time, but saves you from "surprise" precompilation when you play with an older project and forget, that it wasn't used with the new julia version.

I'm planning to work on it and submit a PR, but wanted first to gather opinions on the idea.

[roflmaostc]

As discussed on Discourse:

using TOML
using Dates
using Pkg

"""
    precompile_envs(fname=".julia/logs/manifest_usage.toml"; 
                    time_diff=Dates.CompoundPeriod(Dates.Day(30)))

Precompile the environments listed in the TOML file `fname` if the last time they were used is greater than `time_diff`.
`fname` is the path to the TOML file that contains the information about the last time an environment on your machine was used.
As default `time_diff` is set to 30 days. 

So this script precompiles the environments that were used in the last 30 days. 
This is especially useful to save time after updating Julia.

"""
function precompile_envs(fname=".julia/logs/manifest_usage.toml"; time_diff=Dates.CompoundPeriod(Dates.Day(30)))
    # Load the project file
    toml = TOML.parsefile(fname)
    now = Dates.now()

    # Loop over the keys in the TOML file
    for key in keys(toml)

        for minor in 1:(Int(VERSION.minor)-1)
            if occursin("/v1.$(minor)/", key)
                continue
            end
        end
        time = toml[key][1]["time"]

        try
            # if time difference greater than time_diff, precompile
            if now - time < time_diff
                # Precompile the project if possible and catch errors
                try
                    @info "Precompiling $key"
                    Pkg.activate(dirname(key))
                    Pkg.precompile()
                catch e
                end
                # deactivate the project
                Pkg.activate()
            end
        catch e
            if isa(e, InterruptException)
                @info "Interrupted"
                return
            else
                rethrow(e)
            end
        end
    end
end

[roflmaostc]

Now registered as a small package

https://github.com/roflmaostc/PrecompileAfterUpdate.jl

[IanButterworth]

Something you'll want to factor in is that julia only keeps a certain number of cache files around for each package. So if you're precompiling all envs at once, you might be evicting work you just did.

So you might want to tell the user to increase https://docs.julialang.org/en/v1/manual/environment-variables/#env-max-num-precompile-files in conjunction with using that tool.