How to use VSCode and REPL to write and test a package?

Tooling VS Code
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6

Well I got three entirely opposed answers again. Is there not a built-in way that just works? How are new users supposed to take the advice to put all their code in functions and packages if everything breaks when they do? Sorry if I sound ungrateful, but I am really frustrated with this process. Given that reproducible environments and interactive development are two of the most touted features of Julia, I am surprised by how difficult it is to get them to work. Let me ask more direct questions with full examples.

MyPackage.jl 
module MyPackage

using LinearAlgebra: norm

include("myfile.jl")

end
myfile.jl 
export f

function f(x)
    function f_sub(y)
        norm(y)
    end
    2 * f_sub(x)
end

Package Dependencies

That doesn’t sound safe. I can use packages in the REPL that aren’t in my Package/Environment? This is why I am nervous that I am testing/exploring things that will not work in production.

julia> using MyPackage

(MyPackage) pkg> status
     Project MyPackage v0.1.0
      Status `C:\Users\nboyer.AIP\.julia\dev\MyPackage\Project.toml`
  [37e2e46d] LinearAlgebra

julia> using DataFrames

(MyPackage) pkg> status
     Project MyPackage v0.1.0
      Status `C:\Users\nboyer.AIP\.julia\dev\MyPackage\Project.toml`
  [37e2e46d] LinearAlgebra

julia> df = DataFrame(x=[3,4]) # Typed
2×1 DataFrame
 Row │ x     
     │ Int64
─────┼───────
   1 │     3
   2 │     4

julia> df = DataFrame(x=[3,4]) # Ctrl + Enter
ERROR: UndefVarError: DataFrame not defined

The last line errors if I run it from file, which is the behavior I would want, but once again the REPL behaves differently if I type code vs if I Ctrl+Enter it. Seems like I should avoid typing anything except using MyPackage in the REPL.

Ensuring that I only using MyPackage fixes the ambiguity above, but then it makes interactive development impossible.

Interactive Development

julia> using MyPackage

julia> y = [3, 4]
2-element Vector{Int64}:
 3
 4

julia>         norm(y) # Ctrl+Enter
ERROR: UndefVarError: norm not defined
Stacktrace:
 [1] top-level scope
   @ REPL[3]:1

julia> norm(y) # Typed
ERROR: UndefVarError: norm not defined
Stacktrace:
 [1] top-level scope
   @ REPL[4]:1

julia> using LinearAlgebra: norm

julia> norm(y)
5.0

Because of the previous point, I think the LinearAlgebra version used here could be different from the version locked in MyPackage. I don’t know how to reconcile these first two categories. I need safety and usability.

(I have also had the opposite behavior occur where I get an error from y not being defined rather than from norm, but I can’t seem to reproduce that right now.)

Sub-Functions

julia> using MyPackage

julia> f([3,4])
10.0

julia> MyPackage.f_sub([3,4])
ERROR: UndefVarError: f_sub not defined

I could of course move my sub-function outside and before the main function, but that seems weird if the sub-function only makes sense in the context of the main function. Is there a way to test these interactively or should I really eliminate all function nesting? I could use the debugger every time I need to test sub-functions, but that is slow and comes with its own set of problems.

Debugging

I figured out while writing this question that I should be debugging from a file in the test directory rather than from the src files, which explains why my debugger wasn’t doing anything. I am still confused about how to keep the test dependencies loaded and in sync with the package dependencies though.

Testing

I don’t follow what you mean by global environment. Do you mean MyPackage, test, or 1.7?

Is TestEnv.activate() different than `Pkg.activate(“test”)?

Is the typical workflow to tinker and debug from a test/manual_testing.jl file and then to formalize that code into test/runtests.jl once it is working then?

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