Only execute when names don't exist

[aplavin]

Related to #16, but not a duplicate.

I'm trying to finally transition from a custom startup.jl snippet to using BasicAutoloads. Struggling with how already-defined symbols are handled...

Non-defined symbols: in #16, you suggest writing like

["geomean", "harmmean", "mad", "quantile", "percentile", "weights"] => :(isdefined(Main, :quantile) || using StatsBase),

But that doesn't work the same as just putting using StatsBase:

# when I put [...] => :(using StatsBase)
julia> mad
 │ Package StatsBase not found, but a package named StatsBase is available from a registry. 
 │ Install package?
 │   (@v1.11) pkg> add StatsBase 

# when I put [...] => :(isdefined(Main, :quantile) || using StatsBase)
julia> mad
┌ Info: Failed to run `isdefined(Main, :quantile) || using StatsBase`
│   exception =
│    ArgumentError: Package StatsBase not found in current path.
└    - Run `import Pkg; Pkg.add("StatsBase")` to install the StatsBase package.
ERROR: UndefVarError: `mad` not defined in `Main`
Suggestion: check for spelling errors or missing imports.

Can BasicAutoloads check whether names exist and only run the RHS when they don't?

[LilithHafner]

#16 (comment) doesn't work for you because auto-install is implemented brittly:

BasicAutoloads.jl/src/BasicAutoloads.jl

Lines 72 to 81 in 352c26f

	expr.head in (:using, :import) || return
	for arg in expr.args
	arg isa Expr && arg.head == :. && length(arg.args) == 1 || continue
	mod = only(arg.args)
	mod isa Symbol && Base.identify_package(String(mod)) === nothing || continue
	isempty(REPL.install_packages_hooks) && isdefined(REPL, :load_pkg) && REPL.load_pkg()
	for f in REPL.install_packages_hooks
	Base.invokelatest(f, [mod]) && break
	end
	end

To my credit, the REPL's auto-install is just as brittle:

julia> true && using Distributions
ERROR: ArgumentError: Package Distributions not found in current path.
- Run `import Pkg; Pkg.add("Distributions")` to install the Distributions package.
Stacktrace:
 [1] macro expansion
   @ ./loading.jl:2296 [inlined]
 [2] macro expansion
   @ ./lock.jl:273 [inlined]
 [3] __require(into::Module, mod::Symbol)
   @ Base ./loading.jl:2271
 [4] #invoke_in_world#3
   @ ./essentials.jl:1089 [inlined]
 [5] invoke_in_world
   @ ./essentials.jl:1086 [inlined]
 [6] require(into::Module, mod::Symbol)
   @ Base ./loading.jl:2260
 [7] top-level scope
   @ REPL[1]:1

julia> using Distributions
 │ Package Distributions not found, but a package named Distributions is
 │ available from a registry. 
 │ Install package?
 │   (@v1.11) pkg> add Distributions 
 └ (y/n/o) [y]: 

A less brittle version (for either) could use a custom abstract interpreter or hack code loading at a deeper level.

I'm trying to keep this package as feature-free as possible so and very reluctant to add an option for only executing when names don't exist.

One option would be to make that the default behavior (i.e. only execute if the symbol is not defined in the REPL's active module)

[LilithHafner]

What's your usecase? i.e. why doesn't ["geomean", "harmmean", "mad", "quantile", "percentile", "weights"] => :(using StatsBase), work for you?

[aplavin]

What's your usecase? i.e. why doesn't ["geomean", "harmmean", "mad", "quantile", "percentile", "weights"] => :(using StatsBase), work for you?

Eg when several packages define a function with the same name, and typically I want to use PkgA (added to autoloads) but sometimes PkgB.
Or when a function is in scope cause it's reexported by another package, but BasicAutoloads still tries to import and install the registered package.
Or when a function with the same name is just defined in the REPL (this scenario also blocked by #21).

[LilithHafner]

Is there a specific example that you have encountered where a package was loaded that you didn't want loaded?