Extract variable/function

[sir4ur0n]

Kind of similar (or subset of) #85 : it would be reaaaaaaaaaaally good to be able to extract variable/function.

These features are amazingly useful in Java development and would be, too, in Haskell.

Ideas:

• For function extraction (i.e. extract in a top-level function): an option to add signature or not
• For variable extraction (i.e. extract in a value/function in the current scope): an option to switch between let...in... and ...where... syntaxes.

Note the option for function extraction would be useless if we had an option to add signature to an existing function.

Is such a thing possible?

[rikvdkleij]

Note the option for function extraction would be useless if we had an option to add signature to an existing function.

I do not understand this remark, there is an option to add type signature to function but it depends on -Wall

[rikvdkleij]

I think something is doable by selection an expression and extracting that to a function.

The biggest issue is that (what I already mentioned a couple of times in issues) is that the parser is not layout sensitive. So for example, a where clause is not identifiable. cc @ice1000

[rikvdkleij]

I do not understand this remark, there is an option to add type signature to function but it depends on -Wall

It is possible to make this a action which is always available when function has no type signature.

[sir4ur0n]

I do not understand this remark, there is an option to add type signature to function but it depends on -Wall

This is not enough. This also provides a quickfix for top-level bindings. It doesn't provide a way to add type info on bindings inside let or where bindings. It also doesn't provide the feature for packages with configuration -fno-warn-missing-signatures (which is common for test package).

foo :: Integer
foo =
  -- How do I add type information for a?
  let a = 42
   in a

{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
test_foo = testProperty "Foo" $ \a -> 
  -- How do I add type information for b?
  let b = SUT.myFunction a
   in b === 42

[rikvdkleij]

It doesn't provide a way to add type info on bindings inside let or where bindings.

That's not possible with the current parser.

[rikvdkleij]

So, I think it is possible to select an expression and extract that to a function.

See com.intellij.refactoring.actions.ExtractMethodAction and com.intellij.refactoring.extractMethod.ExtractMethodHandler

@Sir4ur0n Maybe you can implement this?

[sir4ur0n]

Thanks for the pointers, I'll try to take a look in the coming days. I hope the Intellij API for method/variable extraction is better documented than test creation/navigation one 😢

[ice1000]

I have to say with the current parser, extract method refactoring is almost impossible. I hope I'm wrong and I'm looking forward to see a nice implementation.

[rikvdkleij]

I hope the Intellij API for method/variable extraction is better documented than test creation/navigation one 😢

Sorry to say no, you have to look the code.

[rikvdkleij]

I have to say with the current parser, extract method refactoring is almost impossible.

I think it is only doable by selecting an expression.

[sir4ur0n]

It seems that part of the problem is: nothing is parsed as a PsiExpression by the parser. Everythin is just a PsiElement. ExtractMethodHandler expects the part being extracted to be a PsiExpression (which kind of makes sense). Any idea why the parser doesn't parse anything as a PsiExpression? Is it something that could be added/enhanced in the parser? No clue how the parsing bit works, sorry.

[ice1000]

PsiExpression is Java specific

[ice1000]

Is it something that could be added/enhanced in the parser? No clue how the parsing bit works, sorry.

There's HaskellExpression