jj_lib/

fileset_parser.rs

// Copyright 2024 The Jujutsu Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Parser for the fileset language.

use std::error;
use std::sync::LazyLock;

use itertools::Itertools as _;
use pest::Parser as _;
use pest::iterators::Pair;
use pest::pratt_parser::Assoc;
use pest::pratt_parser::Op;
use pest::pratt_parser::PrattParser;
use pest_derive::Parser;
use thiserror::Error;

use crate::dsl_util;
use crate::dsl_util::AliasDeclaration;
use crate::dsl_util::AliasDeclarationParser;
use crate::dsl_util::AliasDefinitionParser;
use crate::dsl_util::AliasExpandError;
use crate::dsl_util::AliasExpandableExpression;
use crate::dsl_util::AliasId;
use crate::dsl_util::AliasesMap;
use crate::dsl_util::Diagnostics;
use crate::dsl_util::ExpressionFolder;
use crate::dsl_util::FoldableExpression;
use crate::dsl_util::InvalidArguments;
use crate::dsl_util::StringLiteralParser;

#[derive(Parser)]
#[grammar = "fileset.pest"]
struct FilesetParser;

const STRING_LITERAL_PARSER: StringLiteralParser<Rule> = StringLiteralParser {
    content_rule: Rule::string_content,
    escape_rule: Rule::string_escape,
};

impl Rule {
    fn to_symbol(self) -> Option<&'static str> {
        match self {
            Self::EOI => None,
            Self::whitespace => None,
            Self::identifier => None,
            Self::strict_identifier_part => None,
            Self::strict_identifier => None,
            Self::bare_string => None,
            Self::string_escape => None,
            Self::string_content_char => None,
            Self::string_content => None,
            Self::string_literal => None,
            Self::raw_string_content => None,
            Self::raw_string_literal => None,
            Self::pattern_kind_op => Some(":"),
            Self::negate_op => Some("~"),
            Self::union_op => Some("|"),
            Self::intersection_op => Some("&"),
            Self::difference_op => Some("~"),
            Self::prefix_ops => None,
            Self::infix_ops => None,
            Self::function => None,
            Self::function_name => None,
            Self::function_arguments => None,
            Self::formal_parameters => None,
            Self::pattern => None,
            Self::bare_string_pattern => None,
            Self::primary => None,
            Self::expression => None,
            Self::program => None,
            Self::program_or_bare_string => None,
            Self::function_alias_declaration => None,
            Self::pattern_alias_declaration => None,
            Self::alias_declaration => None,
        }
    }
}

/// Manages diagnostic messages emitted during fileset parsing and name
/// resolution.
pub type FilesetDiagnostics = Diagnostics<FilesetParseError>;

/// Result of fileset parsing and name resolution.
pub type FilesetParseResult<T> = Result<T, FilesetParseError>;

/// Error occurred during fileset parsing and name resolution.
#[derive(Debug, Error)]
#[error("{pest_error}")]
pub struct FilesetParseError {
    kind: FilesetParseErrorKind,
    pest_error: Box<pest::error::Error<Rule>>,
    source: Option<Box<dyn error::Error + Send + Sync>>,
}

/// Categories of fileset parsing and name resolution error.
#[expect(missing_docs)]
#[derive(Clone, Debug, Eq, Error, PartialEq)]
pub enum FilesetParseErrorKind {
    #[error("Syntax error")]
    SyntaxError,
    #[error("Function `{name}` doesn't exist")]
    NoSuchFunction {
        name: String,
        candidates: Vec<String>,
    },
    #[error("Function `{name}`: {message}")]
    InvalidArguments { name: String, message: String },
    #[error("Redefinition of function parameter")]
    RedefinedFunctionParameter,
    #[error("{0}")]
    Expression(String),
    #[error("In alias `{0}`")]
    InAliasExpansion(String),
    #[error("In function parameter `{0}`")]
    InParameterExpansion(String),
    #[error("Alias `{0}` expanded recursively")]
    RecursiveAlias(String),
}

impl FilesetParseError {
    pub(super) fn new(kind: FilesetParseErrorKind, span: pest::Span<'_>) -> Self {
        let message = kind.to_string();
        let pest_error = Box::new(pest::error::Error::new_from_span(
            pest::error::ErrorVariant::CustomError { message },
            span,
        ));
        Self {
            kind,
            pest_error,
            source: None,
        }
    }

    pub(super) fn with_source(
        mut self,
        source: impl Into<Box<dyn error::Error + Send + Sync>>,
    ) -> Self {
        self.source = Some(source.into());
        self
    }

    /// Some other expression error.
    pub(super) fn expression(message: impl Into<String>, span: pest::Span<'_>) -> Self {
        Self::new(FilesetParseErrorKind::Expression(message.into()), span)
    }

    /// Category of the underlying error.
    pub fn kind(&self) -> &FilesetParseErrorKind {
        &self.kind
    }
}

impl AliasExpandError for FilesetParseError {
    fn invalid_arguments(err: InvalidArguments<'_>) -> Self {
        err.into()
    }

    fn recursive_expansion(id: AliasId<'_>, span: pest::Span<'_>) -> Self {
        Self::new(FilesetParseErrorKind::RecursiveAlias(id.to_string()), span)
    }

    fn within_alias_expansion(self, id: AliasId<'_>, span: pest::Span<'_>) -> Self {
        let kind = match id {
            AliasId::Symbol(_) | AliasId::Pattern(..) | AliasId::Function(..) => {
                FilesetParseErrorKind::InAliasExpansion(id.to_string())
            }
            AliasId::Parameter(_) => FilesetParseErrorKind::InParameterExpansion(id.to_string()),
        };
        Self::new(kind, span).with_source(self)
    }
}

impl From<pest::error::Error<Rule>> for FilesetParseError {
    fn from(err: pest::error::Error<Rule>) -> Self {
        Self {
            kind: FilesetParseErrorKind::SyntaxError,
            pest_error: Box::new(rename_rules_in_pest_error(err)),
            source: None,
        }
    }
}

impl From<InvalidArguments<'_>> for FilesetParseError {
    fn from(err: InvalidArguments<'_>) -> Self {
        let kind = FilesetParseErrorKind::InvalidArguments {
            name: err.name.to_owned(),
            message: err.message,
        };
        Self::new(kind, err.span)
    }
}

fn rename_rules_in_pest_error(err: pest::error::Error<Rule>) -> pest::error::Error<Rule> {
    err.renamed_rules(|rule| {
        rule.to_symbol()
            .map(|sym| format!("`{sym}`"))
            .unwrap_or_else(|| format!("<{rule:?}>"))
    })
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ExpressionKind<'i> {
    Identifier(&'i str),
    String(String),
    /// `<name>:<value>` where `<value>` is usually `Identifier` or `String`.
    Pattern(Box<PatternNode<'i>>),
    Unary(UnaryOp, Box<ExpressionNode<'i>>),
    Binary(BinaryOp, Box<ExpressionNode<'i>>, Box<ExpressionNode<'i>>),
    /// `x | y | ..`
    UnionAll(Vec<ExpressionNode<'i>>),
    FunctionCall(Box<FunctionCallNode<'i>>),
    /// Identity node to preserve the span in the source text.
    AliasExpanded(AliasId<'i>, Box<ExpressionNode<'i>>),
}

impl<'i> FoldableExpression<'i> for ExpressionKind<'i> {
    fn fold<F>(self, folder: &mut F, span: pest::Span<'i>) -> Result<Self, F::Error>
    where
        F: ExpressionFolder<'i, Self> + ?Sized,
    {
        match self {
            Self::Identifier(name) => folder.fold_identifier(name, span),
            Self::String(_) => Ok(self),
            Self::Pattern(pattern) => folder.fold_pattern(pattern, span),
            Self::Unary(op, arg) => {
                let arg = Box::new(folder.fold_expression(*arg)?);
                Ok(Self::Unary(op, arg))
            }
            Self::Binary(op, lhs, rhs) => {
                let lhs = Box::new(folder.fold_expression(*lhs)?);
                let rhs = Box::new(folder.fold_expression(*rhs)?);
                Ok(Self::Binary(op, lhs, rhs))
            }
            Self::UnionAll(nodes) => {
                let nodes = dsl_util::fold_expression_nodes(folder, nodes)?;
                Ok(Self::UnionAll(nodes))
            }
            Self::FunctionCall(function) => folder.fold_function_call(function, span),
            Self::AliasExpanded(id, subst) => {
                let subst = Box::new(folder.fold_expression(*subst)?);
                Ok(Self::AliasExpanded(id, subst))
            }
        }
    }
}

impl<'i> AliasExpandableExpression<'i> for ExpressionKind<'i> {
    fn identifier(name: &'i str) -> Self {
        Self::Identifier(name)
    }

    fn pattern(pattern: Box<PatternNode<'i>>) -> Self {
        Self::Pattern(pattern)
    }

    fn function_call(function: Box<FunctionCallNode<'i>>) -> Self {
        Self::FunctionCall(function)
    }

    fn alias_expanded(id: AliasId<'i>, subst: Box<ExpressionNode<'i>>) -> Self {
        Self::AliasExpanded(id, subst)
    }
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum UnaryOp {
    /// `~`
    Negate,
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum BinaryOp {
    /// `&`
    Intersection,
    /// `~`
    Difference,
}

pub type ExpressionNode<'i> = dsl_util::ExpressionNode<'i, ExpressionKind<'i>>;
pub type FunctionCallNode<'i> = dsl_util::FunctionCallNode<'i, ExpressionKind<'i>>;
pub type PatternNode<'i> = dsl_util::PatternNode<'i, ExpressionKind<'i>>;

fn union_nodes<'i>(lhs: ExpressionNode<'i>, rhs: ExpressionNode<'i>) -> ExpressionNode<'i> {
    let span = lhs.span.start_pos().span(&rhs.span.end_pos());
    let expr = match lhs.kind {
        // Flatten "x | y | z" to save recursion stack. Machine-generated query
        // might have long chain of unions.
        ExpressionKind::UnionAll(mut nodes) => {
            nodes.push(rhs);
            ExpressionKind::UnionAll(nodes)
        }
        _ => ExpressionKind::UnionAll(vec![lhs, rhs]),
    };
    ExpressionNode::new(expr, span)
}

fn parse_function_call_node(pair: Pair<Rule>) -> FilesetParseResult<FunctionCallNode> {
    assert_eq!(pair.as_rule(), Rule::function);
    let [name_pair, args_pair] = pair.into_inner().collect_array().unwrap();
    assert_eq!(name_pair.as_rule(), Rule::function_name);
    assert_eq!(args_pair.as_rule(), Rule::function_arguments);
    let name_span = name_pair.as_span();
    let args_span = args_pair.as_span();
    let name = name_pair.as_str();
    let args = args_pair
        .into_inner()
        .map(parse_expression_node)
        .try_collect()?;
    Ok(FunctionCallNode {
        name,
        name_span,
        args,
        keyword_args: vec![], // unsupported
        args_span,
    })
}

fn parse_as_string_literal(pair: Pair<Rule>) -> String {
    match pair.as_rule() {
        Rule::identifier => pair.as_str().to_owned(),
        Rule::string_literal => STRING_LITERAL_PARSER.parse(pair.into_inner()),
        Rule::raw_string_literal => {
            let [content] = pair.into_inner().collect_array().unwrap();
            assert_eq!(content.as_rule(), Rule::raw_string_content);
            content.as_str().to_owned()
        }
        r => panic!("unexpected string literal rule: {r:?}"),
    }
}

fn parse_primary_node(pair: Pair<Rule>) -> FilesetParseResult<ExpressionNode> {
    assert_eq!(pair.as_rule(), Rule::primary);
    let span = pair.as_span();
    let first = pair.into_inner().next().unwrap();
    let expr = match first.as_rule() {
        // Ignore inner span to preserve parenthesized expression as such.
        Rule::expression => parse_expression_node(first)?.kind,
        Rule::function => {
            let function = Box::new(parse_function_call_node(first)?);
            ExpressionKind::FunctionCall(function)
        }
        Rule::pattern => {
            let [lhs, op, rhs] = first.into_inner().collect_array().unwrap();
            assert_eq!(lhs.as_rule(), Rule::strict_identifier);
            assert_eq!(op.as_rule(), Rule::pattern_kind_op);
            let pattern = Box::new(PatternNode {
                name: lhs.as_str(),
                name_span: lhs.as_span(),
                value: parse_primary_node(rhs)?,
            });
            ExpressionKind::Pattern(pattern)
        }
        Rule::identifier => ExpressionKind::Identifier(first.as_str()),
        Rule::string_literal | Rule::raw_string_literal => {
            ExpressionKind::String(parse_as_string_literal(first))
        }
        r => panic!("unexpected primary rule: {r:?}"),
    };
    Ok(ExpressionNode::new(expr, span))
}

fn parse_expression_node(pair: Pair<Rule>) -> FilesetParseResult<ExpressionNode> {
    assert_eq!(pair.as_rule(), Rule::expression);
    static PRATT: LazyLock<PrattParser<Rule>> = LazyLock::new(|| {
        PrattParser::new()
            .op(Op::infix(Rule::union_op, Assoc::Left))
            .op(Op::infix(Rule::intersection_op, Assoc::Left)
                | Op::infix(Rule::difference_op, Assoc::Left))
            .op(Op::prefix(Rule::negate_op))
    });
    PRATT
        .map_primary(parse_primary_node)
        .map_prefix(|op, rhs| {
            let op_kind = match op.as_rule() {
                Rule::negate_op => UnaryOp::Negate,
                r => panic!("unexpected prefix operator rule {r:?}"),
            };
            let rhs = Box::new(rhs?);
            let span = op.as_span().start_pos().span(&rhs.span.end_pos());
            let expr = ExpressionKind::Unary(op_kind, rhs);
            Ok(ExpressionNode::new(expr, span))
        })
        .map_infix(|lhs, op, rhs| {
            let op_kind = match op.as_rule() {
                Rule::union_op => return Ok(union_nodes(lhs?, rhs?)),
                Rule::intersection_op => BinaryOp::Intersection,
                Rule::difference_op => BinaryOp::Difference,
                r => panic!("unexpected infix operator rule {r:?}"),
            };
            let lhs = Box::new(lhs?);
            let rhs = Box::new(rhs?);
            let span = lhs.span.start_pos().span(&rhs.span.end_pos());
            let expr = ExpressionKind::Binary(op_kind, lhs, rhs);
            Ok(ExpressionNode::new(expr, span))
        })
        .parse(pair.into_inner())
}

/// Parses text into expression tree. No name resolution is made at this stage.
pub fn parse_program(text: &str) -> FilesetParseResult<ExpressionNode<'_>> {
    let mut pairs = FilesetParser::parse(Rule::program, text)?;
    let first = pairs.next().unwrap();
    parse_expression_node(first)
}

/// Parses text into expression tree with bare string fallback. No name
/// resolution is made at this stage.
///
/// If the text can't be parsed as a fileset expression, and if it doesn't
/// contain any operator-like characters, it will be parsed as a file path.
pub fn parse_program_or_bare_string(text: &str) -> FilesetParseResult<ExpressionNode<'_>> {
    let mut pairs = FilesetParser::parse(Rule::program_or_bare_string, text)?;
    let first = pairs.next().unwrap();
    let span = first.as_span();
    let expr = match first.as_rule() {
        Rule::expression => return parse_expression_node(first),
        Rule::bare_string_pattern => {
            let [lhs, op, rhs] = first.into_inner().collect_array().unwrap();
            assert_eq!(lhs.as_rule(), Rule::strict_identifier);
            assert_eq!(op.as_rule(), Rule::pattern_kind_op);
            assert_eq!(rhs.as_rule(), Rule::bare_string);
            let name_span = lhs.as_span();
            let value_span = rhs.as_span();
            let name = lhs.as_str();
            let value_expr = ExpressionKind::String(rhs.as_str().to_owned());
            let pattern = Box::new(PatternNode {
                name,
                name_span,
                value: ExpressionNode::new(value_expr, value_span),
            });
            ExpressionKind::Pattern(pattern)
        }
        Rule::bare_string => ExpressionKind::String(first.as_str().to_owned()),
        r => panic!("unexpected program or bare string rule: {r:?}"),
    };
    Ok(ExpressionNode::new(expr, span))
}

/// Map of fileset aliases.
pub type FilesetAliasesMap = AliasesMap<FilesetAliasParser, String>;

#[derive(Clone, Debug, Default)]
pub struct FilesetAliasParser;

impl AliasDeclarationParser for FilesetAliasParser {
    type Error = FilesetParseError;

    fn parse_declaration(&self, source: &str) -> Result<AliasDeclaration, Self::Error> {
        let mut pairs = FilesetParser::parse(Rule::alias_declaration, source)?;
        let first = pairs.next().unwrap();
        match first.as_rule() {
            Rule::strict_identifier => Ok(AliasDeclaration::Symbol(first.as_str().to_owned())),
            Rule::pattern_alias_declaration => {
                let [name_pair, op, param_pair] = first.into_inner().collect_array().unwrap();
                assert_eq!(name_pair.as_rule(), Rule::strict_identifier);
                assert_eq!(op.as_rule(), Rule::pattern_kind_op);
                assert_eq!(param_pair.as_rule(), Rule::strict_identifier);
                let name = name_pair.as_str().to_owned();
                let param = param_pair.as_str().to_owned();
                Ok(AliasDeclaration::Pattern(name, param))
            }
            Rule::function_alias_declaration => {
                let [name_pair, params_pair] = first.into_inner().collect_array().unwrap();
                assert_eq!(name_pair.as_rule(), Rule::function_name);
                assert_eq!(params_pair.as_rule(), Rule::formal_parameters);
                let name = name_pair.as_str().to_owned();
                let params_span = params_pair.as_span();
                let params = params_pair
                    .into_inner()
                    .map(|pair| match pair.as_rule() {
                        Rule::strict_identifier => pair.as_str().to_owned(),
                        r => panic!("unexpected formal parameter rule {r:?}"),
                    })
                    .collect_vec();
                if params.iter().all_unique() {
                    Ok(AliasDeclaration::Function(name, params))
                } else {
                    Err(FilesetParseError::new(
                        FilesetParseErrorKind::RedefinedFunctionParameter,
                        params_span,
                    ))
                }
            }
            r => panic!("unexpected alias declaration rule {r:?}"),
        }
    }
}

impl AliasDefinitionParser for FilesetAliasParser {
    type Output<'i> = ExpressionKind<'i>;
    type Error = FilesetParseError;

    fn parse_definition<'i>(&self, source: &'i str) -> Result<ExpressionNode<'i>, Self::Error> {
        parse_program(source)
    }
}

pub fn expand_aliases<'i>(
    node: ExpressionNode<'i>,
    aliases_map: &'i FilesetAliasesMap,
) -> FilesetParseResult<ExpressionNode<'i>> {
    dsl_util::expand_aliases(node, aliases_map)
}

pub(super) fn expect_string_literal<'a>(
    type_name: &str,
    node: &'a ExpressionNode<'_>,
) -> FilesetParseResult<&'a str> {
    catch_aliases_no_diagnostics(node, |node| match &node.kind {
        ExpressionKind::Identifier(name) => Ok(*name),
        ExpressionKind::String(name) => Ok(name),
        _ => Err(FilesetParseError::expression(
            format!("Expected {type_name}"),
            node.span,
        )),
    })
}

/// Applies the given function to the innermost `node` by unwrapping alias
/// expansion nodes. Appends alias expansion stack to error and diagnostics.
pub(super) fn catch_aliases<'a, 'i, T>(
    diagnostics: &mut FilesetDiagnostics,
    node: &'a ExpressionNode<'i>,
    f: impl FnOnce(&mut FilesetDiagnostics, &'a ExpressionNode<'i>) -> Result<T, FilesetParseError>,
) -> Result<T, FilesetParseError> {
    let (node, stack) = skip_aliases(node);
    if stack.is_empty() {
        f(diagnostics, node)
    } else {
        let mut inner_diagnostics = FilesetDiagnostics::new();
        let result = f(&mut inner_diagnostics, node);
        diagnostics.extend_with(inner_diagnostics, |diag| attach_aliases_err(diag, &stack));
        result.map_err(|err| attach_aliases_err(err, &stack))
    }
}

fn catch_aliases_no_diagnostics<'a, 'i, T>(
    node: &'a ExpressionNode<'i>,
    f: impl FnOnce(&'a ExpressionNode<'i>) -> Result<T, FilesetParseError>,
) -> Result<T, FilesetParseError> {
    let (node, stack) = skip_aliases(node);
    f(node).map_err(|err| attach_aliases_err(err, &stack))
}

fn skip_aliases<'a, 'i>(
    mut node: &'a ExpressionNode<'i>,
) -> (&'a ExpressionNode<'i>, Vec<(AliasId<'i>, pest::Span<'i>)>) {
    let mut stack = Vec::new();
    while let ExpressionKind::AliasExpanded(id, subst) = &node.kind {
        stack.push((*id, node.span));
        node = subst;
    }
    (node, stack)
}

fn attach_aliases_err(
    err: FilesetParseError,
    stack: &[(AliasId<'_>, pest::Span<'_>)],
) -> FilesetParseError {
    stack
        .iter()
        .rfold(err, |err, &(id, span)| err.within_alias_expansion(id, span))
}

#[cfg(test)]
mod tests {
    use assert_matches::assert_matches;

    use super::*;
    use crate::dsl_util::KeywordArgument;
    use crate::tests::TestResult;

    #[derive(Debug)]
    struct WithFilesetAliasesMap {
        aliases_map: FilesetAliasesMap,
    }

    impl WithFilesetAliasesMap {
        fn parse<'i>(&'i self, text: &'i str) -> FilesetParseResult<ExpressionNode<'i>> {
            let node = parse_program(text)?;
            expand_aliases(node, &self.aliases_map)
        }

        fn parse_normalized<'i>(&'i self, text: &'i str) -> ExpressionNode<'i> {
            normalize_tree(self.parse(text).unwrap())
        }
    }

    fn with_aliases(
        aliases: impl IntoIterator<Item = (impl AsRef<str>, impl Into<String>)>,
    ) -> WithFilesetAliasesMap {
        let mut aliases_map = FilesetAliasesMap::new();
        for (decl, defn) in aliases {
            aliases_map.insert(decl, defn).unwrap();
        }
        WithFilesetAliasesMap { aliases_map }
    }

    fn parse_into_kind(text: &str) -> Result<ExpressionKind<'_>, FilesetParseErrorKind> {
        parse_program(text)
            .map(|node| node.kind)
            .map_err(|err| err.kind)
    }

    fn parse_maybe_bare_into_kind(text: &str) -> Result<ExpressionKind<'_>, FilesetParseErrorKind> {
        parse_program_or_bare_string(text)
            .map(|node| node.kind)
            .map_err(|err| err.kind)
    }

    fn parse_normalized(text: &str) -> ExpressionNode<'_> {
        normalize_tree(parse_program(text).unwrap())
    }

    fn parse_maybe_bare_normalized(text: &str) -> ExpressionNode<'_> {
        normalize_tree(parse_program_or_bare_string(text).unwrap())
    }

    /// Drops auxiliary data from parsed tree so it can be compared with other.
    fn normalize_tree(node: ExpressionNode) -> ExpressionNode {
        fn empty_span() -> pest::Span<'static> {
            pest::Span::new("", 0, 0).unwrap()
        }

        fn normalize_list(nodes: Vec<ExpressionNode>) -> Vec<ExpressionNode> {
            nodes.into_iter().map(normalize_tree).collect()
        }

        fn normalize_function_call(function: FunctionCallNode) -> FunctionCallNode {
            FunctionCallNode {
                name: function.name,
                name_span: empty_span(),
                args: normalize_list(function.args),
                keyword_args: function
                    .keyword_args
                    .into_iter()
                    .map(|arg| KeywordArgument {
                        name: arg.name,
                        name_span: empty_span(),
                        value: normalize_tree(arg.value),
                    })
                    .collect(),
                args_span: empty_span(),
            }
        }

        let normalized_kind = match node.kind {
            ExpressionKind::Identifier(_) | ExpressionKind::String(_) => node.kind,
            ExpressionKind::Pattern(pattern) => {
                let pattern = Box::new(PatternNode {
                    name: pattern.name,
                    name_span: empty_span(),
                    value: normalize_tree(pattern.value),
                });
                ExpressionKind::Pattern(pattern)
            }
            ExpressionKind::Unary(op, arg) => {
                let arg = Box::new(normalize_tree(*arg));
                ExpressionKind::Unary(op, arg)
            }
            ExpressionKind::Binary(op, lhs, rhs) => {
                let lhs = Box::new(normalize_tree(*lhs));
                let rhs = Box::new(normalize_tree(*rhs));
                ExpressionKind::Binary(op, lhs, rhs)
            }
            ExpressionKind::UnionAll(nodes) => {
                let nodes = normalize_list(nodes);
                ExpressionKind::UnionAll(nodes)
            }
            ExpressionKind::FunctionCall(function) => {
                let function = Box::new(normalize_function_call(*function));
                ExpressionKind::FunctionCall(function)
            }
            ExpressionKind::AliasExpanded(_, subst) => normalize_tree(*subst).kind,
        };
        ExpressionNode {
            kind: normalized_kind,
            span: empty_span(),
        }
    }

    #[test]
    fn test_parse_tree_eq() {
        assert_eq!(
            parse_normalized(r#" foo( x ) | ~bar:"baz" "#),
            parse_normalized(r#"(foo(x))|(~(bar:"baz"))"#)
        );
        assert_ne!(parse_normalized(r#" foo "#), parse_normalized(r#" "foo" "#));
    }

    #[test]
    fn test_parse_invalid_function_name() {
        assert_eq!(
            parse_into_kind("5foo(x)"),
            Err(FilesetParseErrorKind::SyntaxError)
        );
    }

    #[test]
    fn test_parse_whitespace() {
        let ascii_whitespaces: String = ('\x00'..='\x7f')
            .filter(char::is_ascii_whitespace)
            .collect();
        assert_eq!(
            parse_normalized(&format!("{ascii_whitespaces}f()")),
            parse_normalized("f()")
        );
    }

    #[test]
    fn test_parse_identifier() {
        assert_eq!(
            parse_into_kind("dir/foo-bar_0.baz"),
            Ok(ExpressionKind::Identifier("dir/foo-bar_0.baz"))
        );
        assert_eq!(
            parse_into_kind("cli-reference@.md.snap"),
            Ok(ExpressionKind::Identifier("cli-reference@.md.snap"))
        );
        assert_eq!(
            parse_into_kind("柔術.jj"),
            Ok(ExpressionKind::Identifier("柔術.jj"))
        );
        assert_eq!(
            parse_into_kind(r#"Windows\Path"#),
            Ok(ExpressionKind::Identifier(r#"Windows\Path"#))
        );
        assert_eq!(
            parse_into_kind("glob*[chars]?"),
            Ok(ExpressionKind::Identifier("glob*[chars]?"))
        );
    }

    #[test]
    fn test_parse_string_literal() {
        // "\<char>" escapes
        assert_eq!(
            parse_into_kind(r#" "\t\r\n\"\\\0\e" "#),
            Ok(ExpressionKind::String("\t\r\n\"\\\0\u{1b}".to_owned())),
        );

        // Invalid "\<char>" escape
        assert_eq!(
            parse_into_kind(r#" "\y" "#),
            Err(FilesetParseErrorKind::SyntaxError),
        );

        // Single-quoted raw string
        assert_eq!(
            parse_into_kind(r#" '' "#),
            Ok(ExpressionKind::String("".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#" 'a\n' "#),
            Ok(ExpressionKind::String(r"a\n".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#" '\' "#),
            Ok(ExpressionKind::String(r"\".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#" '"' "#),
            Ok(ExpressionKind::String(r#"""#.to_owned())),
        );

        // Hex bytes
        assert_eq!(
            parse_into_kind(r#""\x61\x65\x69\x6f\x75""#),
            Ok(ExpressionKind::String("aeiou".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#""\xe0\xe8\xec\xf0\xf9""#),
            Ok(ExpressionKind::String("àèìðù".to_owned())),
        );
        assert_eq!(
            parse_into_kind(r#""\x""#),
            Err(FilesetParseErrorKind::SyntaxError),
        );
        assert_eq!(
            parse_into_kind(r#""\xf""#),
            Err(FilesetParseErrorKind::SyntaxError),
        );
        assert_eq!(
            parse_into_kind(r#""\xgg""#),
            Err(FilesetParseErrorKind::SyntaxError),
        );
    }

    #[test]
    fn test_parse_pattern() -> TestResult {
        fn unwrap_pattern(kind: ExpressionKind<'_>) -> (&str, ExpressionKind<'_>) {
            match kind {
                ExpressionKind::Pattern(pattern) => (pattern.name, pattern.value.kind),
                _ => panic!("unexpected expression: {kind:?}"),
            }
        }

        assert_eq!(
            unwrap_pattern(parse_into_kind(r#" foo:bar "#)?),
            ("foo", ExpressionKind::Identifier("bar"))
        );
        assert_eq!(
            unwrap_pattern(parse_into_kind(" foo:glob*[chars]? ")?),
            ("foo", ExpressionKind::Identifier("glob*[chars]?"))
        );
        assert_eq!(
            unwrap_pattern(parse_into_kind(r#" foo:"bar" "#)?),
            ("foo", ExpressionKind::String("bar".to_owned()))
        );
        assert_eq!(
            unwrap_pattern(parse_into_kind(r#" foo:"" "#)?),
            ("foo", ExpressionKind::String("".to_owned()))
        );
        assert_eq!(
            unwrap_pattern(parse_into_kind(r#" foo:'\' "#)?),
            ("foo", ExpressionKind::String(r"\".to_owned()))
        );
        assert_eq!(
            parse_into_kind(r#" foo: "#),
            Err(FilesetParseErrorKind::SyntaxError)
        );

        // Whitespace isn't allowed in between
        assert_eq!(
            parse_into_kind(r#" foo: "" "#),
            Err(FilesetParseErrorKind::SyntaxError)
        );
        assert_eq!(
            parse_into_kind(r#" foo :"" "#),
            Err(FilesetParseErrorKind::SyntaxError)
        );
        // Whitespace is allowed in parenthesized value expression
        assert_eq!(
            parse_normalized("foo:( 'bar' )"),
            parse_normalized("foo:'bar'")
        );

        // Functions are allowed
        assert_eq!(parse_normalized("x:f(y)"), parse_normalized("x:(f(y))"));
        // Logical operators have lower binding strength
        assert_eq!(parse_normalized("x:y&z"), parse_normalized("(x:y)&(z)"));
        assert_matches!(
            parse_into_kind("x:~y"), // (x:) ~ (y)
            Err(FilesetParseErrorKind::SyntaxError)
        );

        // Pattern prefix is like (type)x cast, so is evaluated from right
        assert_eq!(parse_normalized("x:y:z"), parse_normalized("x:(y:z)"));
        Ok(())
    }

    #[test]
    fn test_parse_operator() -> TestResult {
        assert_matches!(
            parse_into_kind("~x"),
            Ok(ExpressionKind::Unary(UnaryOp::Negate, _))
        );
        assert_matches!(
            parse_into_kind("x|y"),
            Ok(ExpressionKind::UnionAll(nodes)) if nodes.len() == 2
        );
        assert_matches!(
            parse_into_kind("x|y|z"),
            Ok(ExpressionKind::UnionAll(nodes)) if nodes.len() == 3
        );
        assert_matches!(
            parse_into_kind("x&y"),
            Ok(ExpressionKind::Binary(BinaryOp::Intersection, _, _))
        );
        assert_matches!(
            parse_into_kind("x~y"),
            Ok(ExpressionKind::Binary(BinaryOp::Difference, _, _))
        );

        // Set operator associativity/precedence
        assert_eq!(parse_normalized("~x|y"), parse_normalized("(~x)|y"));
        assert_eq!(parse_normalized("x&~y"), parse_normalized("x&(~y)"));
        assert_eq!(parse_normalized("x~~y"), parse_normalized("x~(~y)"));
        assert_eq!(parse_normalized("x~~~y"), parse_normalized("x~(~(~y))"));
        assert_eq!(parse_normalized("x|y|z"), parse_normalized("(x|y)|z"));
        assert_eq!(parse_normalized("x&y|z"), parse_normalized("(x&y)|z"));
        assert_eq!(parse_normalized("x|y&z"), parse_normalized("x|(y&z)"));
        assert_eq!(parse_normalized("x|y~z"), parse_normalized("x|(y~z)"));
        assert_eq!(parse_normalized("~x:y"), parse_normalized("~(x:y)"));
        assert_eq!(parse_normalized("x|y:z"), parse_normalized("x|(y:z)"));

        // Expression span
        assert_eq!(parse_program(" ~ x ")?.span.as_str(), "~ x");
        assert_eq!(parse_program(" x |y ")?.span.as_str(), "x |y");
        assert_eq!(parse_program(" (x) ")?.span.as_str(), "(x)");
        assert_eq!(parse_program("~( x|y) ")?.span.as_str(), "~( x|y)");
        Ok(())
    }

    #[test]
    fn test_parse_function_call() -> TestResult {
        fn unwrap_function_call(node: ExpressionNode<'_>) -> Box<FunctionCallNode<'_>> {
            match node.kind {
                ExpressionKind::FunctionCall(function) => function,
                _ => panic!("unexpected expression: {node:?}"),
            }
        }

        assert_matches!(
            parse_into_kind("foo()"),
            Ok(ExpressionKind::FunctionCall(_))
        );

        // Trailing comma isn't allowed for empty argument
        assert!(parse_into_kind("foo(,)").is_err());

        // Trailing comma is allowed for the last argument
        assert_eq!(parse_normalized("foo(a,)"), parse_normalized("foo(a)"));
        assert_eq!(parse_normalized("foo(a ,  )"), parse_normalized("foo(a)"));
        assert!(parse_into_kind("foo(,a)").is_err());
        assert!(parse_into_kind("foo(a,,)").is_err());
        assert!(parse_into_kind("foo(a  , , )").is_err());
        assert_eq!(parse_normalized("foo(a,b,)"), parse_normalized("foo(a,b)"));
        assert!(parse_into_kind("foo(a,,b)").is_err());

        // Expression span
        let function = unwrap_function_call(parse_program("foo( a, (b) , ~(c) )")?);
        assert_eq!(function.name_span.as_str(), "foo");
        assert_eq!(function.args_span.as_str(), "a, (b) , ~(c)");
        assert_eq!(function.args[0].span.as_str(), "a");
        assert_eq!(function.args[1].span.as_str(), "(b)");
        assert_eq!(function.args[2].span.as_str(), "~(c)");
        Ok(())
    }

    #[test]
    fn test_parse_bare_string() -> TestResult {
        fn unwrap_pattern(kind: ExpressionKind<'_>) -> (&str, ExpressionKind<'_>) {
            match kind {
                ExpressionKind::Pattern(pattern) => (pattern.name, pattern.value.kind),
                _ => panic!("unexpected expression: {kind:?}"),
            }
        }

        // Valid expression should be parsed as such
        assert_eq!(
            parse_maybe_bare_into_kind(" valid "),
            Ok(ExpressionKind::Identifier("valid"))
        );
        assert_eq!(
            parse_maybe_bare_normalized("f(x)&y"),
            parse_normalized("f(x)&y")
        );
        assert_eq!(
            unwrap_pattern(parse_maybe_bare_into_kind("foo:bar")?),
            ("foo", ExpressionKind::Identifier("bar"))
        );

        // Bare string
        assert_eq!(
            parse_maybe_bare_into_kind("Foo Bar.txt"),
            Ok(ExpressionKind::String("Foo Bar.txt".to_owned()))
        );
        assert_eq!(
            parse_maybe_bare_into_kind(r#"Windows\Path with space"#),
            Ok(ExpressionKind::String(
                r#"Windows\Path with space"#.to_owned()
            ))
        );
        assert_eq!(
            parse_maybe_bare_into_kind("柔 術 . j j"),
            Ok(ExpressionKind::String("柔 術 . j j".to_owned()))
        );
        assert_eq!(
            parse_maybe_bare_into_kind("Unicode emoji 💩"),
            Ok(ExpressionKind::String("Unicode emoji 💩".to_owned()))
        );
        assert_eq!(
            parse_maybe_bare_into_kind("looks like & expression"),
            Err(FilesetParseErrorKind::SyntaxError)
        );
        assert_eq!(
            parse_maybe_bare_into_kind("unbalanced_parens("),
            Err(FilesetParseErrorKind::SyntaxError)
        );

        // Bare string pattern
        assert_eq!(
            unwrap_pattern(parse_maybe_bare_into_kind("foo: bar baz")?),
            ("foo", ExpressionKind::String(" bar baz".to_owned()))
        );
        assert_eq!(
            unwrap_pattern(parse_maybe_bare_into_kind("foo:glob * [chars]?")?),
            ("foo", ExpressionKind::String("glob * [chars]?".to_owned()))
        );
        assert_eq!(
            parse_maybe_bare_into_kind("foo: bar:baz"),
            Err(FilesetParseErrorKind::SyntaxError)
        );
        assert_eq!(
            parse_maybe_bare_into_kind("foo:"),
            Err(FilesetParseErrorKind::SyntaxError)
        );
        assert_eq!(
            parse_maybe_bare_into_kind(r#"foo:"unclosed quote"#),
            Err(FilesetParseErrorKind::SyntaxError)
        );

        // Surrounding spaces are simply preserved. They could be trimmed, but
        // space is valid bare_string character.
        assert_eq!(
            parse_maybe_bare_into_kind(" No trim "),
            Ok(ExpressionKind::String(" No trim ".to_owned()))
        );
        Ok(())
    }

    #[test]
    fn test_parse_error() {
        insta::assert_snapshot!(parse_program("foo|").unwrap_err().to_string(), @"
         --> 1:5
          |
        1 | foo|
          |     ^---
          |
          = expected `~` or <primary>
        ");
    }

    #[test]
    fn test_parse_alias_symbol_decl() -> TestResult {
        let mut aliases_map = FilesetAliasesMap::new();
        aliases_map.insert("sym", "symbol")?;
        assert_eq!(aliases_map.symbol_names().count(), 1);
        let (id, defn) = aliases_map.get_symbol("sym").unwrap();
        assert_eq!(id, AliasId::Symbol("sym"));
        assert_eq!(defn, "symbol");

        // Non-ASCII character isn't allowed in alias symbol. This rule can be
        // relaxed if needed.
        assert!(aliases_map.insert("柔術", "none()").is_err());
        Ok(())
    }

    #[test]
    fn test_parse_alias_pattern_decl() -> TestResult {
        let mut aliases_map = FilesetAliasesMap::new();
        assert!(aliases_map.insert("pat:", "bad_pattern").is_err());
        aliases_map.insert("pat:a", "pattern_a")?;
        aliases_map.insert("pat:b", "pattern_b")?;
        assert_eq!(aliases_map.pattern_names().count(), 1);
        let (id, param, defn) = aliases_map.get_pattern("pat").unwrap();
        assert_eq!(id, AliasId::Pattern("pat", "b"));
        assert_eq!(param, "b");
        assert_eq!(defn, "pattern_b");

        // Non-ASCII character isn't allowed. This rule can be relaxed if
        // needed.
        assert!(aliases_map.insert("柔術:x", "none()").is_err());
        assert!(aliases_map.insert("x:柔術", "none()").is_err());
        Ok(())
    }

    #[test]
    fn test_parse_alias_func_decl() -> TestResult {
        let mut aliases_map = FilesetAliasesMap::new();
        assert!(aliases_map.insert("5func()", "bad_function").is_err());
        aliases_map.insert("func()", "function_0")?;
        aliases_map.insert("func(a)", "function_1a")?;
        aliases_map.insert("func(b)", "function_1b")?;
        aliases_map.insert("func(a, b)", "function_2")?;
        assert_eq!(aliases_map.function_names().count(), 1);

        let (id, params, defn) = aliases_map.get_function("func", 0).unwrap();
        assert_eq!(id, AliasId::Function("func", &[]));
        assert!(params.is_empty());
        assert_eq!(defn, "function_0");

        let (id, params, defn) = aliases_map.get_function("func", 1).unwrap();
        assert_eq!(id, AliasId::Function("func", &["b".to_owned()]));
        assert_eq!(params, ["b"]);
        assert_eq!(defn, "function_1b");

        let (id, params, defn) = aliases_map.get_function("func", 2).unwrap();
        assert_eq!(
            id,
            AliasId::Function("func", &["a".to_owned(), "b".to_owned()])
        );
        assert_eq!(params, ["a", "b"]);
        assert_eq!(defn, "function_2");

        assert!(aliases_map.get_function("func", 3).is_none());
        Ok(())
    }

    #[test]
    fn test_parse_alias_formal_parameter() {
        let mut aliases_map = FilesetAliasesMap::new();
        // Formal parameter 'a' can't be redefined
        assert_eq!(
            aliases_map.insert("f(a, a)", "bad").unwrap_err().kind,
            FilesetParseErrorKind::RedefinedFunctionParameter
        );
        // Trailing comma isn't allowed for empty parameter
        assert!(aliases_map.insert("f(,)", "bad").is_err());
        // Trailing comma is allowed for the last parameter
        assert!(aliases_map.insert("g(a,)", "bad").is_ok());
        assert!(aliases_map.insert("h(a ,  )", "bad").is_ok());
        assert!(aliases_map.insert("i(,a)", "bad").is_err());
        assert!(aliases_map.insert("j(a,,)", "bad").is_err());
        assert!(aliases_map.insert("k(a  , , )", "bad").is_err());
        assert!(aliases_map.insert("l(a,b,)", "bad").is_ok());
        assert!(aliases_map.insert("m(a,,b)", "bad").is_err());
    }

    #[test]
    fn test_expand_symbol_alias() {
        assert_eq!(
            with_aliases([("AB", "a&b")]).parse_normalized("AB|c"),
            parse_normalized("(a&b)|c")
        );
        assert_eq!(
            with_aliases([("AB", "a|b")]).parse_normalized("AB~f(AB)"),
            parse_normalized("(a|b)~f(a|b)")
        );

        // Not string substitution 'a&b|c', but tree substitution.
        assert_eq!(
            with_aliases([("BC", "b|c")]).parse_normalized("a&BC"),
            parse_normalized("a&(b|c)")
        );

        // String literal should not be substituted with alias.
        assert_eq!(
            with_aliases([("A", "a")]).parse_normalized(r#"A|"A"|'A'"#),
            parse_normalized("a|'A'|'A'")
        );

        // Kind of string pattern should not be substituted, which is similar to
        // function name.
        assert_eq!(
            with_aliases([("A", "a")]).parse_normalized("A:b"),
            parse_normalized("A:b")
        );

        // Value of string pattern can be substituted if it's an identifier.
        assert_eq!(
            with_aliases([("A", "a")]).parse_normalized("p:A"),
            parse_normalized("p:a")
        );
        assert_eq!(
            with_aliases([("A", "a")]).parse_normalized("p:'A'"),
            parse_normalized("p:'A'")
        );

        // Multi-level substitution.
        assert_eq!(
            with_aliases([("A", "BC"), ("BC", "b|C"), ("C", "c")]).parse_normalized("A"),
            parse_normalized("b|c")
        );

        // Infinite recursion, where the top-level error isn't of RecursiveAlias kind.
        assert_eq!(
            with_aliases([("A", "A")]).parse("A").unwrap_err().kind,
            FilesetParseErrorKind::InAliasExpansion("A".to_owned())
        );
        assert_eq!(
            with_aliases([("A", "B"), ("B", "b|C"), ("C", "c|B")])
                .parse("A")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InAliasExpansion("A".to_owned())
        );

        // Error in alias definition.
        assert_eq!(
            with_aliases([("A", "a(")]).parse("A").unwrap_err().kind,
            FilesetParseErrorKind::InAliasExpansion("A".to_owned())
        );
    }

    #[test]
    fn test_expand_pattern_alias() {
        assert_eq!(
            with_aliases([("P:x", "x")]).parse_normalized("P:a"),
            parse_normalized("a")
        );

        // Argument should be resolved in the current scope.
        assert_eq!(
            with_aliases([("P:x", "x|a")]).parse_normalized("P:x"),
            parse_normalized("x|a")
        );
        // P:a -> (Q:a)&y -> (x|a)&y
        assert_eq!(
            with_aliases([("P:x", "(Q:x)&y"), ("Q:y", "x|y")]).parse_normalized("P:a"),
            parse_normalized("(x|a)&y")
        );

        // Pattern parameter should precede the symbol alias.
        assert_eq!(
            with_aliases([("P:X", "X"), ("X", "x")]).parse_normalized("(P:a)|X"),
            parse_normalized("a|x")
        );

        // Pattern parameter shouldn't be expanded in symbol alias.
        assert_eq!(
            with_aliases([("P:x", "x|A"), ("A", "x")]).parse_normalized("P:a"),
            parse_normalized("a|x")
        );

        // String literal should not be substituted with pattern parameter.
        assert_eq!(
            with_aliases([("P:x", "x|'x'")]).parse_normalized("P:a"),
            parse_normalized("a|'x'")
        );

        // Pattern and symbol aliases reside in separate namespaces.
        assert_eq!(
            with_aliases([("A:x", "A"), ("A", "a")]).parse_normalized("A:x"),
            parse_normalized("a")
        );

        // Infinite recursion, where the top-level error isn't of RecursiveAlias kind.
        assert_eq!(
            with_aliases([("P:x", "Q:x"), ("Q:x", "R:x"), ("R:x", "P:x")])
                .parse("P:a")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InAliasExpansion("P:x".to_owned())
        );
    }

    #[test]
    fn test_expand_function_alias() {
        assert_eq!(
            with_aliases([("F(  )", "a")]).parse_normalized("F()"),
            parse_normalized("a")
        );
        assert_eq!(
            with_aliases([("F( x  )", "x")]).parse_normalized("F(a)"),
            parse_normalized("a")
        );
        assert_eq!(
            with_aliases([("F( x,  y )", "x|y")]).parse_normalized("F(a, b)"),
            parse_normalized("a|b")
        );

        // Not recursion because functions are overloaded by arity.
        assert_eq!(
            with_aliases([("F(x)", "F(x,b)"), ("F(x,y)", "x|y")]).parse_normalized("F(a)"),
            parse_normalized("a|b")
        );

        // Arguments should be resolved in the current scope.
        assert_eq!(
            with_aliases([("F(x,y)", "x|y")]).parse_normalized("F(a~y,b~x)"),
            parse_normalized("(a~y)|(b~x)")
        );
        // F(a) -> G(a)&y -> (x|a)&y
        assert_eq!(
            with_aliases([("F(x)", "G(x)&y"), ("G(y)", "x|y")]).parse_normalized("F(a)"),
            parse_normalized("(x|a)&y")
        );
        // F(G(a)) -> F(x|a) -> G(x|a)&y -> (x|(x|a))&y
        assert_eq!(
            with_aliases([("F(x)", "G(x)&y"), ("G(y)", "x|y")]).parse_normalized("F(G(a))"),
            parse_normalized("(x|(x|a))&y")
        );

        // Function parameter should precede the symbol alias.
        assert_eq!(
            with_aliases([("F(X)", "X"), ("X", "x")]).parse_normalized("F(a)|X"),
            parse_normalized("a|x")
        );

        // Function parameter shouldn't be expanded in symbol alias.
        assert_eq!(
            with_aliases([("F(x)", "x|A"), ("A", "x")]).parse_normalized("F(a)"),
            parse_normalized("a|x")
        );

        // String literal should not be substituted with function parameter.
        assert_eq!(
            with_aliases([("F(x)", "x|'x'")]).parse_normalized("F(a)"),
            parse_normalized("a|'x'")
        );

        // Function and symbol aliases reside in separate namespaces.
        assert_eq!(
            with_aliases([("A()", "A"), ("A", "a")]).parse_normalized("A()"),
            parse_normalized("a")
        );

        // Invalid number of arguments.
        assert_eq!(
            with_aliases([("F()", "x")]).parse("F(a)").unwrap_err().kind,
            FilesetParseErrorKind::InvalidArguments {
                name: "F".to_owned(),
                message: "Expected 0 arguments".to_owned()
            }
        );
        assert_eq!(
            with_aliases([("F(x)", "x")]).parse("F()").unwrap_err().kind,
            FilesetParseErrorKind::InvalidArguments {
                name: "F".to_owned(),
                message: "Expected 1 arguments".to_owned()
            }
        );
        assert_eq!(
            with_aliases([("F(x,y)", "x|y")])
                .parse("F(a,b,c)")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InvalidArguments {
                name: "F".to_owned(),
                message: "Expected 2 arguments".to_owned()
            }
        );
        assert_eq!(
            with_aliases([("F(x)", "x"), ("F(x,y)", "x|y")])
                .parse("F()")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InvalidArguments {
                name: "F".to_owned(),
                message: "Expected 1 to 2 arguments".to_owned()
            }
        );
        assert_eq!(
            with_aliases([("F()", "x"), ("F(x,y)", "x|y")])
                .parse("F(a)")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InvalidArguments {
                name: "F".to_owned(),
                message: "Expected 0, 2 arguments".to_owned()
            }
        );

        // Infinite recursion, where the top-level error isn't of RecursiveAlias kind.
        assert_eq!(
            with_aliases([("F(x)", "G(x)"), ("G(x)", "H(x)"), ("H(x)", "F(x)")])
                .parse("F(a)")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InAliasExpansion("F(x)".to_owned())
        );
        assert_eq!(
            with_aliases([("F(x)", "F(x,b)"), ("F(x,y)", "F(x|y)")])
                .parse("F(a)")
                .unwrap_err()
                .kind,
            FilesetParseErrorKind::InAliasExpansion("F(x)".to_owned())
        );
    }
}