Refract

Refract lets you re-write Ruby at the AST level.

1. The Converter walks a concrete Prism syntax tree and produces an abstract Refract tree.
2. The MutationVisitor walks the Refract tree, allowing you to mutate existing nodes and insert new nodes.
3. Finally, the Formatter walks the Refract tree producing valid Ruby code.

What the round trip preserves

Converting and formatting preserves the meaning of the code, not its layout. Comments, heredocs, %w[] and other literal syntaxes, and optional parentheses are normalised.

When formatting a ProgramNode, the frozen_string_literal and encoding magic comments are re-emitted. shareable_constant_value is re-emitted around each statement containing a constant write it applies to. These are not re-emitted when formatting a smaller node, so formatted fragments take on the settings of the file they are evaluated in.

__LINE__ is formatted as the line number it had in the original source.

Not preserved:

• __END__ and the data after it, so DATA is not defined.
• The encoding of string literals containing raw non-ASCII bytes in an # encoding: ASCII-8BIT file, because Prism reports such files as UTF-8.

Run CORPUS=1 bundle exec qt test/corpus.test.rb to round trip every Ruby file in the standard library and installed gems.