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Rollup merge of #59150 - estebank:type-ascription, r=varkor

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Expand suggestions for type ascription parse errors

Fix #51222. CC #48016, #47666, #54516, #34255.
This commit is contained in:
Mazdak Farrokhzad 2019-03-26 09:05:39 +01:00 • committed by GitHub
commit b316514dbd
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21 changed files with 302 additions and 22 deletions
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75
src/libsyntax/parse/parser.rs
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@ -3538,22 +3538,19 @@ impl<'a> Parser<'a> {
lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
continue
} else if op == AssocOp::Colon {
let maybe_path = self.could_ascription_be_path(&lhs.node);
let next_sp = self.span;
lhs = match self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type) {
Ok(lhs) => lhs,
Err(mut err) => {
err.span_label(self.span,
"expecting a type here because of type ascription");
let cm = self.sess.source_map();
let cur_pos = cm.lookup_char_pos(self.span.lo());
let op_pos = cm.lookup_char_pos(cur_op_span.hi());
if cur_pos.line != op_pos.line {
err.span_suggestion(
cur_op_span,
"try using a semicolon",
";".to_string(),
Applicability::MaybeIncorrect // speculative
);
}
self.bad_type_ascription(
&mut err,
lhs_span,
cur_op_span,
next_sp,
maybe_path,
);
return Err(err);
}
};
@ -3658,6 +3655,58 @@ impl<'a> Parser<'a> {
Ok(lhs)
}
fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
self.token.is_ident() &&
if let ast::ExprKind::Path(..) = node { true } else { false } &&
!self.token.is_reserved_ident() && // v `foo:bar(baz)`
self.look_ahead(1, |t| t == &token::OpenDelim(token::Paren)) ||
self.look_ahead(1, |t| t == &token::Lt) && // `foo:bar<baz`
self.look_ahead(2, |t| t.is_ident()) ||
self.look_ahead(1, |t| t == &token::Colon) && // `foo:bar:baz`
self.look_ahead(2, |t| t.is_ident()) ||
self.look_ahead(1, |t| t == &token::ModSep) && // `foo:bar::baz`
self.look_ahead(2, |t| t.is_ident())
}
fn bad_type_ascription(
&self,
err: &mut DiagnosticBuilder<'a>,
lhs_span: Span,
cur_op_span: Span,
next_sp: Span,
maybe_path: bool,
) {
err.span_label(self.span, "expecting a type here because of type ascription");
let cm = self.sess.source_map();
let next_pos = cm.lookup_char_pos(next_sp.lo());
let op_pos = cm.lookup_char_pos(cur_op_span.hi());
if op_pos.line != next_pos.line {
err.span_suggestion(
cur_op_span,
"try using a semicolon",
";".to_string(),
Applicability::MaybeIncorrect,
);
} else {
if maybe_path {
err.span_suggestion(
cur_op_span,
"maybe you meant to write a path separator here",
"::".to_string(),
Applicability::MaybeIncorrect,
);
} else {
err.note("type ascription is a nightly-only feature that lets \
you annotate an expression with a type: `<expr>: <type>`");
err.span_note(
lhs_span,
"this expression expects an ascribed type after the colon",
);
err.help("this might be indicative of a syntax error elsewhere");
}
}
}
fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
-> PResult<'a, P<Expr>> {