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Improve error recovery in delimited groups when can't parse anything inside (#601)
Simpler variant of #594. While writing an issue for the potential null parse recovery, it just hit me that we might not need to support that generally but rather just limiting that to the delimited group would give us enough bang for the buck. TerminatedBy null parse recovery can be a bit too greedy, i.e. we might recover some unexpected item definition just because... we recovered at the final terminator. However, the delimited group is a reasonable boundary since it's simple (2-3 kinds of general delimiters versus different kinds of potentially versioned terminated statements) and the opening delimiter must always match the closing one, so it produces more reliable and self-contained recovered phrases, hence attempting to recover from a null parse in a delimited group makes more sense.
1 parent 1a258c4 commit cbd2a79

12 files changed

Lines changed: 336 additions & 72 deletions

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‎.changeset/nervous-elephants-change.md‎

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@@ -0,0 +1,5 @@
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---
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"@nomicfoundation/slang": patch
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---
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Attempt parser error recovery between bracket delimiters

‎crates/codegen/parser/generator/src/parser_definition.rs‎

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@@ -187,6 +187,7 @@ impl ParserDefinitionNodeExtensions for ParserDefinitionNode {
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|input| Lexer::leading_trivia(self, input),
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TokenKind::#close_token,
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Self::#delimiters(),
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RecoverFromNoMatch::Yes,
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)
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)?;
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},
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|input| Lexer::leading_trivia(self, input),
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TokenKind::#terminator_token_kind,
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Self::#delimiters(),
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RecoverFromNoMatch::No,
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)
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)?;
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},

‎crates/codegen/parser/runtime/src/support/recovery.rs‎

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@@ -7,6 +7,18 @@ use crate::text_index::{TextRange, TextRangeExtensions as _};
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use super::parser_result::SkippedUntil;
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use super::ParserContext;
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/// An explicit parameter for the [`ParserResult::recover_until_with_nested_delims`] method.
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pub enum RecoverFromNoMatch {
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Yes,
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No,
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}
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impl RecoverFromNoMatch {
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pub fn as_bool(&self) -> bool {
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matches!(self, RecoverFromNoMatch::Yes)
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}
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}
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fn opt_parse(
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input: &mut ParserContext,
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parse: impl Fn(&mut ParserContext) -> ParserResult,
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leading_trivia: impl Fn(&mut ParserContext) -> ParserResult,
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expected: TokenKind,
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delims: &[(TokenKind, TokenKind)],
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recover_from_no_match: RecoverFromNoMatch,
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) -> ParserResult {
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let before_recovery = input.position();
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token
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};
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let (mut nodes, mut expected_tokens, is_incomplete) = match self {
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ParserResult::IncompleteMatch(result) => (result.nodes, result.expected_tokens, true),
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enum ParseResultKind {
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Match,
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Incomplete,
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NoMatch,
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}
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let (mut nodes, mut expected_tokens, result_kind) = match self {
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ParserResult::IncompleteMatch(result) => (
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result.nodes,
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result.expected_tokens,
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ParseResultKind::Incomplete,
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),
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ParserResult::Match(result) if peek_token_after_trivia() != Some(expected) => {
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(result.nodes, result.expected_tokens, false)
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(result.nodes, result.expected_tokens, ParseResultKind::Match)
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}
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ParserResult::NoMatch(result) if recover_from_no_match.as_bool() => {
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(vec![], result.expected_tokens, ParseResultKind::NoMatch)
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}
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// No need to recover, so just return as-is.
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_ => return self,
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match skip_until_with_nested_delims(input, next_token, expected, delims) {
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Some((found, skipped_range)) => {
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nodes.extend(leading_trivia);
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if !is_incomplete {
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if matches!(result_kind, ParseResultKind::Match) {
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expected_tokens.push(expected);
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}
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None => {
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input.set_position(before_recovery);
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if is_incomplete {
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return ParserResult::incomplete_match(nodes, expected_tokens);
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} else {
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return ParserResult::r#match(nodes, expected_tokens);
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}
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return match result_kind {
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ParseResultKind::Match => ParserResult::r#match(nodes, expected_tokens),
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ParseResultKind::Incomplete => {
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ParserResult::incomplete_match(nodes, expected_tokens)
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}
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ParseResultKind::NoMatch => ParserResult::no_match(expected_tokens),
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};
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}
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}
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}

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