Hi there
Given we have the formatter now I would be tempted to avoid editing strings
and instead update the AST of the file, render that to a string, format it
and write it back to the file. Would be more reliable.
Cheers,
Louis
On Mon, 26 Feb 2018, 12:11 Serge Smetana, wrote:
> Hi,
>
> I would like Elixir AST nodes to include begin and end parse character
> offsets.
> This would make it easier to write refactoring tools that modify parts of
> Elixir source files.
>
> Usecase:
>
> We have a library https://github.com/assert-value/assert_value_elixir
> that is
> able to create and update expected values in tests. For example, given the
> following:
>
> assert_value 2 + 2 == 2 + 3
>
> our code will find the location of `2 + 3` and replace it with `4`:
>
> assert_value 2 + 2 == 4
>
> Today determining the location of `2 + 3` in the source file is
> difficult. For
> now, we use a custom-made parser which processes code char by char until
> it gets
> value matching AST:
>
> https://github.com/assert-value/assert_value_elixir/blob/master/lib/assert_value/parser.ex
> But if we had the parse offsets it would be much easier.
>
> Proposed interface:
>
> Probably need two sets of offsets, exclusive and inclusive of children.
> For
> each probably best to store beginning offset and length. Will need
> reasonable
> handling for parentheses and other tokens that do not make it into AST.
>
> Existing implementation:
>
> Elixir AST nodes do have useful info on this already. We use the "line:"
> which
> is very helpful. We don't use "column:", it did not seem useful given our
> implementation. We may be missing something obvious here.
>
> Details:
>
> In Elixir 1.6 compiled code AST has only function line number in meta. Even
> "columns: true" in Code.string_to_quoted gives only function starting
> column
> without information about arguments.
>
> Consider the following code:
>
> Code.string_to_quoted!("(41.00 == 42.)", columns: true)
> #=> {:==, [line: 1, column: 8], [41.0, 42.0]}
>
> From the AST you don't know where to find 41.00 and 42. in a code.
> Column information does not help. AST values of 41.0 and 42.0 don't have
> information about how original values were formatted.
>
> Thanks,
> Serge
>
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