Fix the scope to look-up the constant as the receiver type of the macro

[makenowjust]

Fixed #5343. It is another solution than #5349. I believe this PR is better than #5349.

Currently the constant in expansion inside macro is resolved by caller-scope, for example:

class Foo
  macro foo
    {{Baz}}
  end
end

class Bar
  class Baz
  end

  def self.foo
    Foo.foo
  end
end

p Bar.foo # => Bar::Baz

It is unexpected because the constant inside method is of course resolved by the receiver type of the method. And so, the second example in #5343 is caused.

This PR fixed scope to look-up the constant as the receiver type of the macro.

[RX14]

@makenowjust say in that example the macro did want to access Baz, how would that be done?

[makenowjust]

@RX14 Using Bar::Baz is the right way.

[makenowjust]

It does not make a sense that this example works only if Foo.foo is called from the scope having Bar.

class Foo
  macro foo
    {{Baz}}
  end

  class Baz
  end
end

class Bar
  class Baz
  end

  def self.foo
    Foo.foo
  end
end

class FooBar
  def self.foo
    Foo.foo
  end
end

p Bar.foo # => Bar::Baz
p FooBar.foo # compilation error: undefined constant 'Baz'

Isn't it?

[RX14]

@makenowjust but now you have to pass in the outer scope somehow? Macros can reference local variables and local methods, why not local types too.

[makenowjust]

This example works. What is problem?

class Foo
  macro foo(x)
    {{x}}
  end

  macro bar
    Baz
  end
end

class Bar
  class Baz
  end

  def self.foo
    Foo.foo Baz
  end

  def self.bar
    Foo.bar
  end
end

p Bar.foo # => Bar::Baz
p Bar.bar # => Bar::Baz

This PR fixes the semantic in only macro expansion inside macro.

[RX14]

@makenowjust ah yes never mind me I was just confused.

[bew]

I think what @RX14 fears is that we may not be able to access a 'local' type from the macro system, as {% SomeType %}

module IncludeMe
  macro included
    STORAGE = [] of _ # Create a 'local' Type in the caller's (includer) scope
  end

  macro add(node)
    {% STORAGE << node %} # Access a 'local' type in the caller's scope, from the macro system
  end
end

class Foo
  include IncludeMe

  # Add some stuff from macros to a 'local' type
  add a + b
  add :bla
end

But it seems to still work, so 👍

[bew]

Can this go forward?

[asterite]

This fix is correct 👍

[RX14]

needs a rebase, sorry for the delay merging

[makenowjust]

I merged master into this on GitHub Web UI. Please do squash merge.

[sdogruyol]

Thanks a lot @makenowjust 🙏