Parsing the .. (DOT_DOT) operator to get a range had two
issues. Trying to compile:
let block = [1,2,3,4,5];
let _rf = &block[1..];
let _rt = &block[..3];
let _rft = &block[2..4];
range.rs:4:23: error: found unexpected token ‘]’ in null denotation
4 | let _rf = &block[1..];
| ^
range.rs:4:24: error: expecting ‘]’ but ‘;’ found
4 | let _rf = &block[1..];
| ^
Since .. can represent either a range from or a range from-to it can
be followed by an expression or not. We do have a hack in our
pratt-parser so that it is allowed to return a nullptr. But even in
that case it will have swallowed the next token. Add another hack to
the pratt-parser so that if the next token is one that cannot start an
expression and the caller allows a nullptr return then don't skip the
token and return immediately.
After this patch we can parse the above range expressions, but we
still don't handle them fully:
range.rs:4:20: fatal error: Failed to lower expr: [1..]
4 | let _rf = &block[1..];
| ^
Ranges are actually syntactic sugar for std::ops::Range[From|To].
---
gcc/rust/parse/rust-parse-impl.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index be261715c6c..7b128fff157 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -12348,6 +12348,18 @@ Parser<ManagedTokenSource>::parse_expr (int
right_binding_power,
ParseRestrictions restrictions)
{
const_TokenPtr current_token = lexer.peek_token ();
+ // Special hack because we are allowed to return nullptr, in that case we
+ // don't want to skip the token, since we don't actually parse it. But if
+ // null isn't allowed it indicates an error, and we want to skip past that.
+ // So return early if it is one of the tokens that ends an expression
+ // (or at least cannot start a new expression).
+ if (restrictions.expr_can_be_null)
+ {
+ TokenId id = current_token->get_id ();
+ if (id == SEMICOLON || id == RIGHT_PAREN || id == RIGHT_CURLY
+ || id == RIGHT_SQUARE)
+ return nullptr;
+ }
lexer.skip_token ();
// parse null denotation (unary part of expression)
@@ -14028,6 +14040,9 @@
Parser<ManagedTokenSource>::parse_led_range_exclusive_expr (
{
// FIXME: this probably parses expressions accidently or whatever
// try parsing RHS (as tok has already been consumed in parse_expression)
+ // Can be nullptr, in which case it is a RangeFromExpr, otherwise a
+ // RangeFromToExpr.
+ restrictions.expr_can_be_null = true;
std::unique_ptr<AST::Expr> right
= parse_expr (LBP_DOT_DOT, AST::AttrVec (), restrictions);
--
2.32.0
--
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