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extract should_continue_as_assoc_expr

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This commit is contained in:
Mazdak Farrokhzad 2019-12-03 09:04:36 +01:00
parent be463cbc2b
commit 903c9dfd18
1 changed files with 55 additions and 45 deletions
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100
src/librustc_parse/parser/expr.rs
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@ -155,53 +155,13 @@ pub(super) fn parse_assoc_expr_with(
};
let last_type_ascription_set = self.last_type_ascription.is_some();
match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) {
(true, None) => {
self.last_type_ascription = None;
// Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071
return Ok(lhs);
}
(false, _) => {} // continue parsing the expression
// An exhaustive check is done in the following block, but these are checked first
// because they *are* ambiguous but also reasonable looking incorrect syntax, so we
// want to keep their span info to improve diagnostics in these cases in a later stage.
(true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
(true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
(true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475)
(true, Some(AssocOp::Add)) // `{ 42 } + 42
// If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
// `if x { a } else { b } && if y { c } else { d }`
if !self.look_ahead(1, |t| t.is_reserved_ident()) => {
self.last_type_ascription = None;
// These cases are ambiguous and can't be identified in the parser alone
let sp = self.sess.source_map().start_point(self.token.span);
self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
return Ok(lhs);
}
(true, Some(ref op)) if !op.can_continue_expr_unambiguously() => {
self.last_type_ascription = None;
return Ok(lhs);
}
(true, Some(_)) => {
// We've found an expression that would be parsed as a statement, but the next
// token implies this should be parsed as an expression.
// For example: `if let Some(x) = x { x } else { 0 } / 2`
let mut err = self.struct_span_err(self.token.span, &format!(
"expected expression, found `{}`",
pprust::token_to_string(&self.token),
));
err.span_label(self.token.span, "expected expression");
self.sess.expr_parentheses_needed(
&mut err,
lhs.span,
Some(pprust::expr_to_string(&lhs),
));
err.emit();
}
if !self.should_continue_as_assoc_expr(&lhs) {
self.last_type_ascription = None;
return Ok(lhs);
}
self.expected_tokens.push(TokenType::Operator);
while let Some(op) = AssocOp::from_token(&self.token) {
self.expected_tokens.push(TokenType::Operator);
while let Some(op) = self.check_assoc_op() {
// Adjust the span for interpolated LHS to point to the `$lhs` token and not to what
// it refers to. Interpolated identifiers are unwrapped early and never show up here
// as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process
@ -338,6 +298,56 @@ pub(super) fn parse_assoc_expr_with(
Ok(lhs)
}
fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
match (self.expr_is_complete(lhs), self.check_assoc_op()) {
// Semi-statement forms are odd:
// See https://github.com/rust-lang/rust/issues/29071
(true, None) => false,
(false, _) => true, // Continue parsing the expression.
// An exhaustive check is done in the following block, but these are checked first
// because they *are* ambiguous but also reasonable looking incorrect syntax, so we
// want to keep their span info to improve diagnostics in these cases in a later stage.
(true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
(true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
(true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475)
(true, Some(AssocOp::Add)) // `{ 42 } + 42
// If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
// `if x { a } else { b } && if y { c } else { d }`
if !self.look_ahead(1, |t| t.is_reserved_ident()) => {
// These cases are ambiguous and can't be identified in the parser alone.
let sp = self.sess.source_map().start_point(self.token.span);
self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
false
}
(true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
(true, Some(_)) => {
self.error_found_expr_would_be_stmt(lhs);
true
}
}
}
/// We've found an expression that would be parsed as a statement,
/// but the next token implies this should be parsed as an expression.
/// For example: `if let Some(x) = x { x } else { 0 } / 2`.
fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
let mut err = self.struct_span_err(self.token.span, &format!(
"expected expression, found `{}`",
pprust::token_to_string(&self.token),
));
err.span_label(self.token.span, "expected expression");
self.sess.expr_parentheses_needed(&mut err, lhs.span, Some(pprust::expr_to_string(&lhs)));
err.emit();
}
/// Possibly translate the current token to an associative operator.
/// The method does not advance the current token.
///
/// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
fn check_assoc_op(&self) -> Option<AssocOp> {
AssocOp::from_token(&self.token)
}
/// Checks if this expression is a successfully parsed statement.
fn expr_is_complete(&self, e: &Expr) -> bool {
self.restrictions.contains(Restrictions::STMT_EXPR) &&