Refactors peg module into a directory. (#34)

Moves the Pest derived parser into the `gen` submodule to make it easier
to ignore for code coverage.  Exports the derived parser to the `peg` module.

Moves the PartiQL grammar file into the `peg` module sub-directory.

Adds codecov ignore for `peg::gen` which only contains the generated
Pest parser.

Fixes #29.

Author: almann

.github/codecov.yml

@@ -12,4 +12,4 @@ coverage:
 ignore:
   # Ignore the Pest generated code until we have a better way to test
   # and target coverage for it
-  - "partiql-parser/src/peg.rs"
+  - "partiql-parser/src/peg/gen.rs"

partiql-parser/src/peg/gen.rs

@@ -0,0 +1,7 @@
+// Copyright Amazon.com, Inc. or its affiliates.
+
+use pest_derive::Parser;
+
+#[derive(Parser)]
+#[grammar = "peg/partiql.pest"]
+pub(crate) struct PartiQLParser;

partiql-parser/src/peg.rs renamed to partiql-parser/src/peg/mod.rs

@@ -3,15 +3,15 @@
 //! Contains the [Pest](https://pest.rs) defined parser for PartiQL and a wrapper APIs that
 //! can be exported for users to consume.
 
+mod gen;
+
 use crate::prelude::*;
 use crate::result::{illegal_state, syntax_error};
 use pest::iterators::{Pair, Pairs};
 use pest::{Parser, RuleType};
-use pest_derive::Parser;
 
-#[derive(Parser)]
-#[grammar = "partiql.pest"]
-pub(crate) struct PartiQLParser;
+pub(crate) use gen::PartiQLParser;
+pub(crate) use gen::Rule;
 
 /// Extension methods for working with [`Pairs`].
 pub(crate) trait PairsExt<'val, R: RuleType> {