d1ac752de6
This is a big commit, but it breaks into two conceptual pieces. The first is to "parse without copying". We replace a stream of an owned collection of edn::ValueAndSpan and instead have a stream of a borrowed collection of &edn::ValueAndSpan references. (Generally, this is represented as an iterator over a slice, but it can be over other things too.) Cloning such iterators is constant time, which improves on cloning an owned collection of edn::ValueAndSpan, which is linear time in the length of the collection and additional time depending on the complexity of the EDN values. The second conceptual piece is to parse keyword maps using a special parser and a macro to build the parser implementations. Before, we created a new edn::ValueAndSpan::Map to represent a keyword map in vector form; since we're working with &edn::ValueAndSpan references now, we can't create an &edn::ValueAndSpan reference with an appropriate lifetime. Therefore we generalize the concept of iteration slightly and turn keyword maps in map form into linear iterators by flattening the value maps. This is a potentially obscuring transformation, so we have to take care to protect against some failure cases. (See the comments and the tests in the code.) After these changes, parsing using `combine` is linear time (and reasonably fast).
137 lines
5 KiB
Rust
137 lines
5 KiB
Rust
// Copyright 2016 Mozilla
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
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// this file except in compliance with the License. You may obtain a copy of the
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// License at http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing, software distributed
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// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
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// CONDITIONS OF ANY KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations under the License.
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// use combine::{
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// ParseResult,
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// };
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// use combine::combinator::{
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// Expected,
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// FnParser,
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// };
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use combine::{
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ParseResult,
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};
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// use combine::primitives; // To not shadow Error.
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// use combine::primitives::{
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// Consumed,
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// FastResult,
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// };
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use combine::combinator::{
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Expected,
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FnParser,
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};
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/// A type definition for a function parser that either parses an `O` from an input stream of type
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/// `I`, or fails with an "expected" failure.
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/// See <https://docs.rs/combine/2.2.1/combine/trait.Parser.html#method.expected> for more
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/// illumination.
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/// Nothing about this is specific to the result type of the parser.
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pub type ResultParser<O, I> = Expected<FnParser<I, fn(I) -> ParseResult<O, I>>>;
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pub struct KeywordMapParser<T>(pub T);
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/// `satisfy_unwrap!` makes it a little easier to implement a `satisfy_map`
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/// body that matches a particular `Value` enum case, otherwise returning `None`.
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#[macro_export]
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macro_rules! satisfy_unwrap {
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( $cas: path, $var: ident, $body: block ) => {
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satisfy_map(|x: edn::Value| if let $cas($var) = x $body else { None })
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}
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}
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/// Generate a `satisfy_map` expression that matches a `PlainSymbol`
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/// value with the given name.
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///
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/// We do this rather than using `combine::token` so that we don't
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/// need to allocate a new `String` inside a `PlainSymbol` inside a `Value`
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/// just to match input.
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#[macro_export]
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macro_rules! matches_plain_symbol {
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($name: expr, $input: ident) => {
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satisfy_map(|x: edn::Value| {
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if let edn::Value::PlainSymbol(ref s) = x {
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if s.0.as_str() == $name {
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return Some(());
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}
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}
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return None;
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}).parse_stream($input)
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}
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}
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#[macro_export]
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macro_rules! def_parser {
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( $parser: ident, $name: ident, $result_type: ty, $body: block ) => {
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impl<'p> $parser<'p> {
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fn $name<'a>() -> ResultParser<$result_type, $crate::value_and_span::Stream<'a>> {
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fn inner<'a>(input: $crate::value_and_span::Stream<'a>) -> ParseResult<$result_type, $crate::value_and_span::Stream<'a>> {
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$body.parse_lazy(input).into()
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}
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parser(inner as fn($crate::value_and_span::Stream<'a>) -> ParseResult<$result_type, $crate::value_and_span::Stream<'a>>).expected(stringify!($name))
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}
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}
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}
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}
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/// `assert_parses_to!` simplifies some of the boilerplate around running a
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/// parser function against input and expecting a certain result.
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#[macro_export]
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macro_rules! assert_parses_to {
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( $parser: expr, $input: expr, $expected: expr ) => {{
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let input = $input.with_spans();
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let par = $parser();
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let stream = input.atom_stream();
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let result = par.skip(eof()).parse(stream).map(|x| x.0);
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assert_eq!(result, Ok($expected));
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}}
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}
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/// `assert_edn_parses_to!` simplifies some of the boilerplate around running a parser function
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/// against string input and expecting a certain result.
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#[macro_export]
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macro_rules! assert_edn_parses_to {
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( $parser: expr, $input: expr, $expected: expr ) => {{
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let input = edn::parse::value($input).expect("to be able to parse input as EDN");
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let par = $parser();
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let stream = input.atom_stream();
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let result = par.skip(eof()).parse(stream).map(|x| x.0);
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assert_eq!(result, Ok($expected));
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}}
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}
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/// `assert_parse_failure_contains!` simplifies running a parser function against string input and
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/// expecting a certain failure. This is working around the complexity of pattern matching parse
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/// errors that contain spans.
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#[macro_export]
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macro_rules! assert_parse_failure_contains {
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( $parser: expr, $input: expr, $expected: expr ) => {{
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let input = edn::parse::value($input).expect("to be able to parse input as EDN");
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let par = $parser();
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let stream = input.atom_stream();
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let result = par.skip(eof()).parse(stream).map(|x| x.0).map_err(|e| -> ::ValueParseError { e.into() });
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assert!(format!("{:?}", result).contains($expected), "Expected {:?} to contain {:?}", result, $expected);
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}}
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}
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#[macro_export]
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macro_rules! keyword_map_of {
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($(($keyword:expr, $value:expr)),+) => {{
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let mut seen = std::collections::BTreeSet::default();
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$(
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if !seen.insert($keyword) {
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panic!("keyword map has repeated key: {}", stringify!($keyword));
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}
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)+
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KeywordMapParser(($(($keyword, $value)),+))
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}}
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}
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