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Fix range precedence edge cases #1820

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merged 4 commits into from
Dec 31, 2024
Merged

Fix range precedence edge cases #1820

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cd75e10
Allow binops to terminate a range endpoint
dtolnay Dec 31, 2024
223540c
Fix unambiguous RangeFull parenthesization
dtolnay Dec 31, 2024
f3d8f8d
Add test of range precedence with binop
dtolnay Dec 31, 2024
f7b0d72
Disallow binop with a range lhs
dtolnay Dec 31, 2024
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20 changes: 11 additions & 9 deletions src/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1315,9 +1315,8 @@ pub(crate) mod parsing {
) -> Result<Expr> {
loop {
let ahead = input.fork();
if let Expr::Range(ExprRange { end: Some(_), .. }) = lhs {
// A range with an upper bound cannot be the left-hand side of
// another binary operator.
if let Expr::Range(_) = lhs {
// A range cannot be the left-hand side of another binary operator.
break;
} else if let Ok(op) = ahead.parse::<BinOp>() {
let precedence = Precedence::of_binop(&op);
Expand Down Expand Up @@ -2886,17 +2885,20 @@ pub(crate) mod parsing {
|| input.peek(Token![?])
|| input.peek(Token![=>])
|| !allow_struct.0 && input.peek(token::Brace)
|| input.peek(Token![=]) && !input.peek(Token![==])
|| input.peek(Token![+=])
|| input.peek(Token![=])
|| input.peek(Token![+])
|| input.peek(Token![/])
|| input.peek(Token![%])
|| input.peek(Token![^])
|| input.peek(Token![>])
|| input.peek(Token![<=])
|| input.peek(Token![!=])
|| input.peek(Token![-=])
|| input.peek(Token![*=])
|| input.peek(Token![/=])
|| input.peek(Token![%=])
|| input.peek(Token![^=])
|| input.peek(Token![&=])
|| input.peek(Token![|=])
|| input.peek(Token![<<=])
|| input.peek(Token![>>=]))
|| input.peek(Token![as]))
{
Ok(None)
} else {
Expand Down
31 changes: 29 additions & 2 deletions src/fixup.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,15 @@ pub(crate) struct FixupContext {
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: bool,

// This is the difference between:
//
// (..) + x // parens because range cannot be lhs of a binop
//
// &.. + x // no parens because range is a right subexpression
//
#[cfg(feature = "full")]
rightmost_subexpression: bool,

// This is the difference between:
//
// if let _ = (Struct {}) {} // needs parens
Expand Down Expand Up @@ -133,6 +142,8 @@ impl FixupContext {
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: false,
#[cfg(feature = "full")]
rightmost_subexpression: false,
#[cfg(feature = "full")]
parenthesize_exterior_struct_lit: false,
#[cfg(feature = "full")]
next_operator_can_begin_expr: false,
Expand Down Expand Up @@ -196,6 +207,8 @@ impl FixupContext {
leftmost_subexpression_in_match_arm: self.match_arm
|| self.leftmost_subexpression_in_match_arm,
#[cfg(feature = "full")]
rightmost_subexpression: false,
#[cfg(feature = "full")]
next_operator_can_begin_expr: false,
#[cfg(feature = "full")]
next_operator_can_continue_expr: true,
Expand All @@ -219,6 +232,8 @@ impl FixupContext {
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: false,
#[cfg(feature = "full")]
rightmost_subexpression: false,
#[cfg(feature = "full")]
next_operator_can_begin_expr: false,
#[cfg(feature = "full")]
next_operator_can_continue_expr: true,
Expand Down Expand Up @@ -264,6 +279,8 @@ impl FixupContext {
match_arm: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: false,
#[cfg(feature = "full")]
rightmost_subexpression: true,
..self
}
}
Expand Down Expand Up @@ -309,6 +326,12 @@ impl FixupContext {
if let Expr::Break(_) | Expr::Return(_) | Expr::Yield(_) = expr {
return Precedence::Jump;
}
} else if self.rightmost_subexpression {
if let Expr::Range(range) = expr {
if range.start.is_none() && range.end.is_none() {
return Precedence::Unambiguous;
}
}
}
#[cfg(feature = "full")]
if !self.next_operator_can_continue_expr {
Expand Down Expand Up @@ -348,7 +371,7 @@ impl Clone for FixupContext {
#[cfg(feature = "full")]
#[test]
fn test_leftmost_rightmost_invariant() {
const BITS: usize = 8;
const BITS: usize = 9;

for bits in 0u16..1 << BITS {
let mut i = 0;
Expand All @@ -362,6 +385,7 @@ fn test_leftmost_rightmost_invariant() {
leftmost_subexpression_in_stmt: bit(),
match_arm: bit(),
leftmost_subexpression_in_match_arm: bit(),
rightmost_subexpression: bit(),
parenthesize_exterior_struct_lit: bit(),
next_operator_can_begin_expr: bit(),
next_operator_can_continue_expr: bit(),
Expand All @@ -370,7 +394,10 @@ fn test_leftmost_rightmost_invariant() {
assert_eq!(i, BITS);
assert_eq!(
fixup.leftmost_subexpression().rightmost_subexpression(),
fixup.rightmost_subexpression().leftmost_subexpression(),
FixupContext {
rightmost_subexpression: true,
..fixup.rightmost_subexpression().leftmost_subexpression()
},
);
}
}
13 changes: 13 additions & 0 deletions tests/test_expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -400,6 +400,19 @@ fn test_range_precedence() {
}
"#);

snapshot!("() = .. + ()" as Expr, @r"
Expr::Binary {
left: Expr::Assign {
left: Expr::Tuple,
right: Expr::Range {
limits: RangeLimits::HalfOpen,
},
},
op: BinOp::Add,
right: Expr::Tuple,
}
");

// A range with a lower bound cannot be the upper bound of another range,
// and a range with an upper bound cannot be the lower bound of another
// range.
Expand Down
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