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Reworked command parser #28

Merged
merged 1 commit into from
Oct 20, 2016
Merged

Reworked command parser #28

merged 1 commit into from
Oct 20, 2016

Commits on Oct 20, 2016

  1. Reworked command parser 

    Summary:

- Previously monolithic parsing logic split into a suite of composable
  parsers
- Relaxed grammar more closely follows typical command shell parsing
  behavior
- Introduces string interpolation support

Details:

This commit adds a new command parser which features a more relaxed
parsing grammar and support for string interpolation. This is achieved
by breaking out the lexing and parsing logic for major data types --
pipelines, names, args/options, variables, and interpolated strings --
into separate lexer/parser pairs which are combined to create the final
command parsing pipeline.

In the vast majority of cases the new parser produces identical AST
when compared against the existing parser. Aside from the new features
the only difference between the old and new parsers is their handling of
quoted strings. The old parser parsed them correctly but dropped the
strings when converting the AST to a string whereas the new parser
preserves quoting.

`Piper.Command.Parser` and `Piper.Command.ParserOptions` have been
changed to make the old and new parsers swappable. Setting the
`use_legacy_parser` field on `ParserOptions` to `true` will cause Piper
to parse command input with the old parser.

The command parser's test suite has been changed to cover new features
and ensure the legacy parser continues to work. First, the test modules
for variable binding, alias expansion, command lexing, and command
parsing were split into two "forks". The legacy fork captures these test
modules in their current state and runs them against the legacy
parser. These modules are prefixed with `Legacy`. The new fork, which
consists of the same test modules but retaining their non-legacy names,
have been extended to exercise the new parser.
    Kevin Smith committed Oct 20, 2016
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