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use rustc_ast::token::{self, Delimiter};
use rustc_ast::tokenstream::{CursorRef, TokenStream, TokenTree};
use rustc_ast::{LitIntType, LitKind};
use rustc_ast_pretty::pprust;
use rustc_errors::{Applicability, PResult};
use rustc_session::parse::ParseSess;
use rustc_span::symbol::Ident;
use rustc_span::Span;
/// A meta-variable expression, for expansions based on properties of meta-variables.
#[derive(Debug, Clone, PartialEq, Encodable, Decodable)]
pub(crate) enum MetaVarExpr {
/// The number of repetitions of an identifier, optionally limited to a number
/// of outer-most repetition depths. If the depth limit is `None` then the depth is unlimited.
Count(Ident, Option<usize>),
/// Ignore a meta-variable for repetition without expansion.
Ignore(Ident),
/// The index of the repetition at a particular depth, where 0 is the inner-most
/// repetition. The `usize` is the depth.
Index(usize),
/// The length of the repetition at a particular depth, where 0 is the inner-most
/// repetition. The `usize` is the depth.
Length(usize),
}
impl MetaVarExpr {
/// Attempt to parse a meta-variable expression from a token stream.
pub(crate) fn parse<'sess>(
input: &TokenStream,
outer_span: Span,
sess: &'sess ParseSess,
) -> PResult<'sess, MetaVarExpr> {
let mut tts = input.trees();
let ident = parse_ident(&mut tts, sess, outer_span)?;
let Some(TokenTree::Delimited(_, Delimiter::Parenthesis, args)) = tts.next() else {
let msg = "meta-variable expression parameter must be wrapped in parentheses";
return Err(sess.span_diagnostic.struct_span_err(ident.span, msg));
};
check_trailing_token(&mut tts, sess)?;
let mut iter = args.trees();
let rslt = match &*ident.as_str() {
"count" => parse_count(&mut iter, sess, ident.span)?,
"ignore" => MetaVarExpr::Ignore(parse_ident(&mut iter, sess, ident.span)?),
"index" => MetaVarExpr::Index(parse_depth(&mut iter, sess, ident.span)?),
"length" => MetaVarExpr::Length(parse_depth(&mut iter, sess, ident.span)?),
_ => {
let err_msg = "unrecognized meta-variable expression";
let mut err = sess.span_diagnostic.struct_span_err(ident.span, err_msg);
err.span_suggestion(
ident.span,
"supported expressions are count, ignore, index and length",
"",
Applicability::MachineApplicable,
);
return Err(err);
}
};
check_trailing_token(&mut iter, sess)?;
Ok(rslt)
}
pub(crate) fn ident(&self) -> Option<Ident> {
match *self {
MetaVarExpr::Count(ident, _) | MetaVarExpr::Ignore(ident) => Some(ident),
MetaVarExpr::Index(..) | MetaVarExpr::Length(..) => None,
}
}
}
// Checks if there are any remaining tokens. For example, `${ignore(ident ... a b c ...)}`
fn check_trailing_token<'sess>(
iter: &mut CursorRef<'_>,
sess: &'sess ParseSess,
) -> PResult<'sess, ()> {
if let Some(tt) = iter.next() {
let mut diag = sess
.span_diagnostic
.struct_span_err(tt.span(), &format!("unexpected token: {}", pprust::tt_to_string(tt)));
diag.span_note(tt.span(), "meta-variable expression must not have trailing tokens");
Err(diag)
} else {
Ok(())
}
}
/// Parse a meta-variable `count` expression: `count(ident[, depth])`
fn parse_count<'sess>(
iter: &mut CursorRef<'_>,
sess: &'sess ParseSess,
span: Span,
) -> PResult<'sess, MetaVarExpr> {
let ident = parse_ident(iter, sess, span)?;
let depth = if try_eat_comma(iter) { Some(parse_depth(iter, sess, span)?) } else { None };
Ok(MetaVarExpr::Count(ident, depth))
}
/// Parses the depth used by index(depth) and length(depth).
fn parse_depth<'sess>(
iter: &mut CursorRef<'_>,
sess: &'sess ParseSess,
span: Span,
) -> PResult<'sess, usize> {
let Some(tt) = iter.next() else { return Ok(0) };
let TokenTree::Token(token::Token {
kind: token::TokenKind::Literal(lit), ..
}, _) = tt else {
return Err(sess.span_diagnostic.struct_span_err(
span,
"meta-variable expression depth must be a literal"
));
};
if let Ok(lit_kind) = LitKind::from_lit_token(*lit)
&& let LitKind::Int(n_u128, LitIntType::Unsuffixed) = lit_kind
&& let Ok(n_usize) = usize::try_from(n_u128)
{
Ok(n_usize)
}
else {
let msg = "only unsuffixes integer literals are supported in meta-variable expressions";
Err(sess.span_diagnostic.struct_span_err(span, msg))
}
}
/// Parses an generic ident
fn parse_ident<'sess>(
iter: &mut CursorRef<'_>,
sess: &'sess ParseSess,
span: Span,
) -> PResult<'sess, Ident> {
if let Some(tt) = iter.next() && let TokenTree::Token(token, _) = tt {
if let Some((elem, false)) = token.ident() {
return Ok(elem);
}
let token_str = pprust::token_to_string(token);
let mut err = sess.span_diagnostic.struct_span_err(
span,
&format!("expected identifier, found `{}`", &token_str)
);
err.span_suggestion(
token.span,
&format!("try removing `{}`", &token_str),
"",
Applicability::MaybeIncorrect,
);
return Err(err);
}
Err(sess.span_diagnostic.struct_span_err(span, "expected identifier"))
}
/// Tries to move the iterator forward returning `true` if there is a comma. If not, then the
/// iterator is not modified and the result is `false`.
fn try_eat_comma(iter: &mut CursorRef<'_>) -> bool {
if let Some(TokenTree::Token(token::Token { kind: token::Comma, .. }, _)) = iter.look_ahead(0) {
let _ = iter.next();
return true;
}
false
}
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