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use crate::classify;
use crate::expr::Expr;
use crate::precedence::Precedence;
pub(crate) struct FixupContext {
// Print expression such that it can be parsed back as a statement
// consisting of the original expression.
//
// The effect of this is for binary operators in statement position to set
// `leftmost_subexpression_in_stmt` when printing their left-hand operand.
//
// (match x {}) - 1; // match needs parens when LHS of binary operator
//
// match x {}; // not when its own statement
//
stmt: bool,
// This is the difference between:
//
// (match x {}) - 1; // subexpression needs parens
//
// let _ = match x {} - 1; // no parens
//
// There are 3 distinguishable contexts in which `print_expr` might be
// called with the expression `$match` as its argument, where `$match`
// represents an expression of kind `ExprKind::Match`:
//
// - stmt=false leftmost_subexpression_in_stmt=false
//
// Example: `let _ = $match - 1;`
//
// No parentheses required.
//
// - stmt=false leftmost_subexpression_in_stmt=true
//
// Example: `$match - 1;`
//
// Must parenthesize `($match)`, otherwise parsing back the output as a
// statement would terminate the statement after the closing brace of
// the match, parsing `-1;` as a separate statement.
//
// - stmt=true leftmost_subexpression_in_stmt=false
//
// Example: `$match;`
//
// No parentheses required.
leftmost_subexpression_in_stmt: bool,
// Print expression such that it can be parsed as a match arm.
//
// This is almost equivalent to `stmt`, but the grammar diverges a tiny bit
// between statements and match arms when it comes to braced macro calls.
// Macro calls with brace delimiter terminate a statement without a
// semicolon, but do not terminate a match-arm without comma.
//
// m! {} - 1; // two statements: a macro call followed by -1 literal
//
// match () {
// _ => m! {} - 1, // binary subtraction operator
// }
//
match_arm: bool,
// This is almost equivalent to `leftmost_subexpression_in_stmt`, other than
// for braced macro calls.
//
// If we have `m! {} - 1` as an expression, the leftmost subexpression
// `m! {}` will need to be parenthesized in the statement case but not the
// match-arm case.
//
// (m! {}) - 1; // subexpression needs parens
//
// match () {
// _ => m! {} - 1, // no parens
// }
//
leftmost_subexpression_in_match_arm: bool,
// This is the difference between:
//
// if let _ = (Struct {}) {} // needs parens
//
// match () {
// () if let _ = Struct {} => {} // no parens
// }
//
parenthesize_exterior_struct_lit: bool,
}
impl FixupContext {
/// The default amount of fixing is minimal fixing. Fixups should be turned
/// on in a targeted fashion where needed.
pub const NONE: Self = FixupContext {
stmt: false,
leftmost_subexpression_in_stmt: false,
match_arm: false,
leftmost_subexpression_in_match_arm: false,
parenthesize_exterior_struct_lit: false,
};
/// Create the initial fixup for printing an expression in statement
/// position.
pub fn new_stmt() -> Self {
FixupContext {
stmt: true,
..FixupContext::NONE
}
}
/// Create the initial fixup for printing an expression as the right-hand
/// side of a match arm.
pub fn new_match_arm() -> Self {
FixupContext {
match_arm: true,
..FixupContext::NONE
}
}
/// Create the initial fixup for printing an expression as the "condition"
/// of an `if` or `while`. There are a few other positions which are
/// grammatically equivalent and also use this, such as the iterator
/// expression in `for` and the scrutinee in `match`.
pub fn new_condition() -> Self {
FixupContext {
parenthesize_exterior_struct_lit: true,
..FixupContext::NONE
}
}
/// Transform this fixup into the one that should apply when printing the
/// leftmost subexpression of the current expression.
///
/// The leftmost subexpression is any subexpression that has the same first
/// token as the current expression, but has a different last token.
///
/// For example in `$a + $b` and `$a.method()`, the subexpression `$a` is a
/// leftmost subexpression.
///
/// Not every expression has a leftmost subexpression. For example neither
/// `-$a` nor `[$a]` have one.
pub fn leftmost_subexpression(self) -> Self {
FixupContext {
stmt: false,
leftmost_subexpression_in_stmt: self.stmt || self.leftmost_subexpression_in_stmt,
match_arm: false,
leftmost_subexpression_in_match_arm: self.match_arm
|| self.leftmost_subexpression_in_match_arm,
..self
}
}
/// Transform this fixup into the one that should apply when printing a
/// leftmost subexpression followed by a `.` or `?` token, which confer
/// different statement boundary rules compared to other leftmost
/// subexpressions.
pub fn leftmost_subexpression_with_dot(self) -> Self {
FixupContext {
stmt: self.stmt || self.leftmost_subexpression_in_stmt,
leftmost_subexpression_in_stmt: false,
match_arm: self.match_arm || self.leftmost_subexpression_in_match_arm,
leftmost_subexpression_in_match_arm: false,
..self
}
}
/// Transform this fixup into the one that should apply when printing any
/// subexpression that is neither a leftmost subexpression nor surrounded in
/// delimiters.
///
/// This is for any subexpression that has a different first token than the
/// current expression, and is not surrounded by a paren/bracket/brace. For
/// example the `$b` in `$a + $b` and `-$b`, but not the one in `[$b]` or
/// `$a.f($b)`.
pub fn subsequent_subexpression(self) -> Self {
FixupContext {
stmt: false,
leftmost_subexpression_in_stmt: false,
match_arm: false,
leftmost_subexpression_in_match_arm: false,
..self
}
}
/// Determine whether parentheses are needed around the given expression to
/// head off an unintended statement boundary.
///
/// The documentation on `FixupContext::leftmost_subexpression_in_stmt` has
/// examples.
pub fn would_cause_statement_boundary(self, expr: &Expr) -> bool {
(self.leftmost_subexpression_in_stmt && !classify::requires_semi_to_be_stmt(expr))
|| (self.leftmost_subexpression_in_match_arm
&& !classify::requires_comma_to_be_match_arm(expr))
}
/// Determine whether parentheses are needed around the given `let`
/// scrutinee.
///
/// In `if let _ = $e {}`, some examples of `$e` that would need parentheses
/// are:
///
/// - `Struct {}.f()`, because otherwise the `{` would be misinterpreted
/// as the opening of the if's then-block.
///
/// - `true && false`, because otherwise this would be misinterpreted as a
/// "let chain".
pub fn needs_group_as_let_scrutinee(self, expr: &Expr) -> bool {
self.parenthesize_exterior_struct_lit && classify::confusable_with_adjacent_block(expr)
|| Precedence::of_rhs(expr) <= Precedence::And
}
}
impl Copy for FixupContext {}
impl Clone for FixupContext {
fn clone(&self) -> Self {
*self
}
}