bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

let_chains: Add support for parsing let expressions.

Browse source
This commit is contained in:
Mazdak Farrokhzad 2019-05-15 16:03:22 +02:00
parent 3fc9642014
commit dff1e379fc
3 changed files with 21 additions and 52 deletions
Download patch file Download diff file Expand all files Collapse all files

65
src/libsyntax/parse/parser.rs
View file

@ -2215,13 +2215,8 @@ impl<'a> Parser<'a> {
} else {
ex = ExprKind::Yield(None);
}
} else if self.token.is_keyword(kw::Let) {
// Catch this syntax error here, instead of in `parse_ident`, so
// that we can explicitly mention that let is not to be used as an expression
let mut db = self.fatal("expected expression, found statement (`let`)");
db.span_label(self.token.span, "expected expression");
db.note("variable declaration using `let` is a statement");
return Err(db);
} else if self.eat_keyword(kw::Let) {
return self.parse_let_expr(attrs);
} else if is_span_rust_2018 && self.eat_keyword(kw::Await) {
let (await_hi, e_kind) = self.parse_await_macro_or_alt(lo, self.prev_span)?;
hi = await_hi;
@ -2483,15 +2478,13 @@ impl<'a> Parser<'a> {
attrs.extend::<Vec<_>>(expr.attrs.into());
expr.attrs = attrs;
match expr.node {
ExprKind::If(..) | ExprKind::IfLet(..) => {
if !expr.attrs.is_empty() {
// Just point to the first attribute in there...
let span = expr.attrs[0].span;
ExprKind::If(..) if !expr.attrs.is_empty() => {
// Just point to the first attribute in there...
let span = expr.attrs[0].span;
self.span_err(span,
"attributes are not yet allowed on `if` \
expressions");
}
self.span_err(span,
"attributes are not yet allowed on `if` \
expressions");
}
_ => {}
}
@ -3163,9 +3156,6 @@ impl<'a> Parser<'a> {
/// Parses an `if` or `if let` expression (`if` token already eaten).
fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
if self.check_keyword(kw::Let) {
return self.parse_if_let_expr(attrs);
}
let lo = self.prev_span;
let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
@ -3197,22 +3187,18 @@ impl<'a> Parser<'a> {
Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
}
/// Parses an `if let` expression (`if` token already eaten).
fn parse_if_let_expr(&mut self, attrs: ThinVec<Attribute>)
-> PResult<'a, P<Expr>> {
/// Parses a `let $pats = $expr` pseudo-expression.
/// The `let` token has already been eaten.
fn parse_let_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
let lo = self.prev_span;
self.expect_keyword(kw::Let)?;
let pats = self.parse_pats()?;
self.expect(&token::Eq)?;
let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
let thn = self.parse_block()?;
let (hi, els) = if self.eat_keyword(kw::Else) {
let expr = self.parse_else_expr()?;
(expr.span, Some(expr))
} else {
(thn.span, None)
};
Ok(self.mk_expr(lo.to(hi), ExprKind::IfLet(pats, expr, thn, els), attrs))
let expr = self.with_res(
Restrictions::NO_STRUCT_LITERAL,
|this| this.parse_assoc_expr_with(1 + AssocOp::LAnd.precedence(), None.into())
)?;
Ok(self.mk_expr(lo.to(expr.span), ExprKind::Let(pats, expr), attrs))
}
/// Parses `move |args| expr`.
@ -3299,9 +3285,6 @@ impl<'a> Parser<'a> {
fn parse_while_expr(&mut self, opt_label: Option<Label>,
span_lo: Span,
mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
if self.token.is_keyword(kw::Let) {
return self.parse_while_let_expr(opt_label, span_lo, attrs);
}
let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
let (iattrs, body) = self.parse_inner_attrs_and_block()?;
attrs.extend(iattrs);
@ -3309,20 +3292,6 @@ impl<'a> Parser<'a> {
return Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs));
}
/// Parses a `while let` expression (`while` token already eaten).
fn parse_while_let_expr(&mut self, opt_label: Option<Label>,
span_lo: Span,
mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
self.expect_keyword(kw::Let)?;
let pats = self.parse_pats()?;
self.expect(&token::Eq)?;
let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
let (iattrs, body) = self.parse_inner_attrs_and_block()?;
attrs.extend(iattrs);
let span = span_lo.to(body.span);
return Ok(self.mk_expr(span, ExprKind::WhileLet(pats, expr, body, opt_label), attrs));
}
// parse `loop {...}`, `loop` token already eaten
fn parse_loop_expr(&mut self, opt_label: Option<Label>,
span_lo: Span,