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//! Term-level parsing: atoms, function application, and `.`/`or` selection.
use super::Parser;
use crate::ast::{Expression, Selector, Term, Token};
use crate::error::{ParseError, Result};
impl Parser {
/// Parse function application (left-associative)
/// Apply only consumes TERMS, not unary expressions
pub(super) fn parse_application(&mut self) -> Result<Expression> {
// Prefix unary operators recurse so that postfix `?` (handled below) binds tighter.
match &self.current.value {
Token::Minus => {
let op = self.take_and_advance()?;
let inner = self.parse_application()?;
return Ok(Expression::Negation {
minus: op,
expr: Box::new(inner),
});
}
Token::Not => {
let op = self.take_and_advance()?;
let inner = self.parse_application()?;
return Ok(Expression::Not {
bang: op,
expr: Box::new(inner),
});
}
_ => {}
}
let mut expr = Expression::Term(self.parse_term()?);
// Keep applying while we see more TERMS (not unary ops)
// IMPORTANT: Don't treat binary operators as term starts even if they could start paths
while self.is_term_start() && !self.is_binary_op() && !self.is_expression_end() {
let arg = Expression::Term(self.parse_term()?);
expr = Expression::Apply {
func: Box::new(expr),
arg: Box::new(arg),
};
}
// Postfix `?` has higher precedence than prefix `!`/`-`; checking it here ensures
// `!a ? b` parses as `!(a ? b)`, not `(!a) ? b`.
if matches!(self.current.value, Token::Question) {
let question = self.take_and_advance()?;
let selectors = self.parse_selector_path()?;
expr = Expression::HasAttr {
lhs: Box::new(expr),
question,
path: selectors,
};
}
Ok(expr)
}
/// Check if current token starts a term
pub(super) fn is_term_start(&self) -> bool {
match &self.current.value {
Token::Identifier(_)
| Token::Integer(_)
| Token::Float(_)
| Token::EnvPath(_)
| Token::BraceOpen
| Token::Rec
| Token::BrackOpen
| Token::ParenOpen
| Token::DoubleQuote
| Token::DoubleSingleQuote => true,
// These can start paths, but only in specific contexts
Token::Dot | Token::Div | Token::Tilde => self.looks_like_path(),
_ => false,
}
}
/// Check if we're at the end of an expression
pub(super) const fn is_expression_end(&self) -> bool {
matches!(
self.current.value,
Token::Semicolon
| Token::Then
| Token::Else
| Token::In
| Token::ParenClose
| Token::BraceClose
| Token::BrackClose
| Token::Sof
)
}
/// Parse a term (atom), including postfix selection
pub(super) fn parse_term(&mut self) -> Result<Term> {
if self.looks_like_uri() {
return self.parse_uri();
}
if self.looks_like_path() {
return self.parse_path();
}
let base_term = match &self.current.value {
Token::Identifier(_) | Token::Integer(_) | Token::Float(_) | Token::EnvPath(_) => {
self.parse_token_term()
}
Token::BraceOpen | Token::Rec | Token::Let => self.parse_set(),
Token::BrackOpen => self.parse_list(),
Token::ParenOpen => self.parse_parenthesized(),
Token::DoubleQuote => self.parse_simple_string(),
Token::DoubleSingleQuote => self.parse_indented_string(),
_ => Err(ParseError::unexpected(
self.current.span,
vec![
"identifier".to_string(),
"number".to_string(),
"string".to_string(),
"set".to_string(),
"list".to_string(),
"path".to_string(),
],
format!("'{}'", self.current.value.text()),
)),
}?;
self.parse_postfix_selection(base_term)
}
/// Parse postfix selection: term.attr.attr or term.attr or term
pub(super) fn parse_postfix_selection(&mut self, base_term: Term) -> Result<Term> {
let mut selectors = Vec::new();
while matches!(self.current.value, Token::Dot) {
let saved_state = self.save_state();
self.advance()?;
if !self.is_simple_selector_start() {
self.restore_state(saved_state);
break;
}
let dot_token = saved_state.current;
let simple_sel = self.parse_simple_selector()?;
selectors.push(Selector {
dot: Some(dot_token),
selector: simple_sel,
});
}
// `or` is only the selection-default operator after at least one
// selector; otherwise it is the (deprecated) identifier `or` and
// must be left for the application parser.
let or_default = if !selectors.is_empty() && self.is_or_token() {
let mut or_tok = self.take_current();
// is_or_token() guarantees this is either OrDefault or Identifier("or").
or_tok.value = Token::OrDefault;
self.advance()?;
// Nix requires a default expression here; `a.b or ]`/`a.b or;`
// are syntax errors, so do not backtrack to or-as-identifier.
if !self.is_term_start() {
return Err(ParseError::unexpected(
self.current.span,
vec!["expression".to_string()],
format!("'{}'", self.current.value.text()),
));
}
let default_term = self.parse_term()?;
Some(crate::ast::SetDefault {
or_kw: or_tok,
value: Box::new(default_term),
})
} else {
None
};
if selectors.is_empty() && or_default.is_none() {
Ok(base_term)
} else {
Ok(Term::Selection {
base: Box::new(base_term),
selectors,
default: or_default,
})
}
}
/// Parse a single-token term (identifier, integer, float, env path).
fn parse_token_term(&mut self) -> Result<Term> {
let token_ann = self.take_and_advance()?;
Ok(Term::Token(token_ann))
}
}