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syntax: Apply recovery for casts to type ascription

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Fix spans, add some comments
This commit is contained in:
Vadim Petrochenkov
2017-07-04 02:17:01 +03:00
parent 5fa1c1b5f3
commit 4323877e92
5 changed files with 155 additions and 79 deletions
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99
src/libsyntax/parse/parser.rs
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@@ -1081,6 +1081,16 @@ impl<'a> Parser<'a> {
None => token::CloseDelim(self.token_cursor.frame.delim),
})
}
fn look_ahead_span(&self, dist: usize) -> Span {
if dist == 0 {
return self.span
}
match self.token_cursor.frame.tree_cursor.look_ahead(dist - 1) {
Some(TokenTree::Token(span, _)) | Some(TokenTree::Delimited(span, _)) => span,
None => self.look_ahead_span(dist - 1),
}
}
pub fn fatal(&self, m: &str) -> DiagnosticBuilder<'a> {
self.sess.span_diagnostic.struct_span_fatal(self.span, m)
}
@@ -2805,13 +2815,10 @@ impl<'a> Parser<'a> {
}
// Special cases:
if op == AssocOp::As {
// Save the state of the parser before parsing type normally, in case there is a
// LessThan comparison after this cast.
lhs = self.parse_assoc_op_as(lhs, lhs_span)?;
lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
continue
} else if op == AssocOp::Colon {
let rhs = self.parse_ty_no_plus()?;
lhs = self.mk_expr(lhs_span.to(rhs.span), ExprKind::Type(lhs, rhs), ThinVec::new());
lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
continue
} else if op == AssocOp::DotDot || op == AssocOp::DotDotDot {
// If we didn’t have to handle `x..`/`x...`, it would be pretty easy to
@@ -2905,61 +2912,61 @@ impl<'a> Parser<'a> {
Ok(lhs)
}
fn parse_assoc_op_as(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
let rp = self.clone();
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>> {
let mk_expr = |this: &mut Self, rhs: P<Ty>| {
this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
};
// Save the state of the parser before parsing type normally, in case there is a
// LessThan comparison after this cast.
let parser_snapshot_before_type = self.clone();
match self.parse_ty_no_plus() {
Ok(rhs) => {
Ok(self.mk_expr(lhs_span.to(rhs.span),
ExprKind::Cast(lhs, rhs),
ThinVec::new()))
Ok(mk_expr(self, rhs))
}
Err(mut err) => {
let rp_err = self.clone();
let sp = rp_err.span.clone();
Err(mut type_err) => {
// Rewind to before attempting to parse the type with generics, to recover
// from situations like `x as usize < y` in which we first tried to parse
// `usize < y` as a type with generic arguments.
let parser_snapshot_after_type = self.clone();
mem::replace(self, parser_snapshot_before_type);
// Rewind to before attempting to parse the type with generics, to get
// arround #22644.
mem::replace(self, rp);
let lo = self.span;
match self.parse_path_without_generics(PathStyle::Type) {
Ok(path) => {
// Successfully parsed the type leaving a `<` yet to parse
err.cancel();
let codemap = self.sess.codemap();
let suggestion_span = lhs_span.to(self.prev_span);
let warn_message = match codemap.span_to_snippet(self.prev_span) {
Ok(lstring) => format!("`{}`", lstring),
_ => "a type".to_string(),
};
// Successfully parsed the type path leaving a `<` yet to parse.
type_err.cancel();
// Report non-fatal diagnostics, keep `x as usize` as an expression
// in AST and continue parsing.
let msg = format!("`<` is interpreted as a start of generic \
arguments for {}, not a comparison",
warn_message);
let mut err = self.sess.span_diagnostic.struct_span_err(sp, &msg);
err.span_label(sp, "interpreted as generic argument");
arguments for `{}`, not a comparison", path);
let mut err = self.sess.span_diagnostic.struct_span_err(self.span, &msg);
err.span_label(self.look_ahead_span(1).to(parser_snapshot_after_type.span),
"interpreted as generic arguments");
err.span_label(self.span, "not interpreted as comparison");
let suggestion = match codemap.span_to_snippet(suggestion_span) {
Ok(lstring) => format!("({})", lstring),
_ => format!("(<expression> as <type>)")
};
err.span_suggestion(suggestion_span,
let expr = mk_expr(self, P(Ty {
span: path.span,
node: TyKind::Path(None, path),
id: ast::DUMMY_NODE_ID
}));
let expr_str = self.sess.codemap().span_to_snippet(expr.span)
.unwrap_or(pprust::expr_to_string(&expr));
err.span_suggestion(expr.span,
"if you want to compare the casted value then write:",
suggestion);
format!("({})", expr_str));
err.emit();
let path = TyKind::Path(None, path);
let span = lo.to(self.prev_span);
let rhs = P(Ty { node: path, span: span, id: ast::DUMMY_NODE_ID });
// Letting the parser accept the recovered type to avoid further errors,
// but the code will still not compile due to the error emitted above.
Ok(self.mk_expr(lhs_span.to(rhs.span),
ExprKind::Cast(lhs, rhs),
ThinVec::new()))
Ok(expr)
}
Err(mut path_err) => {
// Still couldn't parse, return original error and parser state
// Couldn't parse as a path, return original error and parser state.
path_err.cancel();
mem::replace(self, rp_err);
Err(err)
mem::replace(self, parser_snapshot_after_type);
Err(type_err)
}
}
}