bjoernager/rust
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Fix a bug in diagnostics for x as usize < y

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Improve diagnostics for `x as usize << y`
This commit is contained in:
Vadim Petrochenkov 2017-10-09 20:02:17 +03:00
parent 72d65019c7
commit 3e4d9df02b
5 changed files with 75 additions and 6 deletions
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19
src/libsyntax/parse/parser.rs
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@ -2890,17 +2890,30 @@ impl<'a> Parser<'a> {
match self.parse_path(PathStyle::Expr) {
Ok(path) => {
let (op_noun, op_verb) = match self.token {
token::Lt => ("comparison", "comparing"),
token::BinOp(token::Shl) => ("shift", "shifting"),
_ => {
// We can end up here even without `<` being the next token, for
// example because `parse_ty_no_plus` returns `Err` on keywords,
// but `parse_path` returns `Ok` on them due to error recovery.
// Return original error and parser state.
mem::replace(self, parser_snapshot_after_type);
return Err(type_err);
}
};
// 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", path);
arguments for `{}`, not a {}", path, op_noun);
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");
err.span_label(self.span, format!("not interpreted as {}", op_noun));
let expr = mk_expr(self, P(Ty {
span: path.span,
@ -2911,7 +2924,7 @@ impl<'a> Parser<'a> {
let expr_str = self.sess.codemap().span_to_snippet(expr.span)
.unwrap_or(pprust::expr_to_string(&expr));
err.span_suggestion(expr.span,
"try comparing the casted value",
&format!("try {} the casted value", op_verb),
format!("({})", expr_str));
err.emit();