Improve capture completions in capture context

[zachallaun]

Completions in a capture context can be improved in a number of ways. In the following examples, consider that you have a function/1 and function/2 in scope.

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Improve labels

If we're in a capture context, it would be nice if completions started with & to indicate that it is being considered in the completion responses.

&fun|

# desired completions:
# &function(arg1)
# &function/1
# &function(arg1, arg2)
# &function/2

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Using additional &fun/arity context

When /arity is present, it should be used to improve completions.

&fun|/2

# current completions:
# function(arg1)
# function/1
# function(arg1, arg2)
# function/2

# desired completions:
# &function/2
# &function(arg1, arg2)
# &function/1
# &function(arg1)

Additionally:

• Selecting function/2 inserts an additional /2, resulting in &function/2/2. It should emit a text edit resulting in &function/2. The same issue exists with function/1, which currently results in &function/1/2.
• Selecting function(arg1, arg2) results in &function(arg1, arg2)/2. It should remove the /2.

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Using additional &fun(arg) context

When (arg, ...) is present, it should be used to improve completions.

&fun|/(&1,  arg)

# current completions:
# function(arg1)
# function/1
# function(arg1, arg2)
# function/2

# desired completions:
# &function(arg1, arg2)
# &function/2
# &function(arg1)
# &function/1

Additionally:

• Selecting &function(arg1, arg2) inserts additional args, resulting in &function(arg1, arg2)(&1, arg). It should emit a text edit resulting in &function(arg1, arg2).

[zachallaun]

Regarding sorting: Currently function/2 and function(arg1, arg2) return the same sort text.

[zachallaun]

Regarding prefixing labels with &: maybe this shouldn't be done, as it confuses things somewhat for qualified captures:

&Enum.reduce_w|

# completions:
# reduce_while/3
# reduce_while(enumerable, acc fun)

It might be confusing for the completions to include &, e.g. &reduce_while/3, since what we're really completing is &Enum.reduce_while/3.

[zachallaun]

Some work-in-progress code can be found here: https://github.com/lexical-lsp/lexical/tree/za-capture-completions