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use rustc_ast::util::{classify, parser};
use rustc_ast::Expr;
#[derive(Copy, Clone, Debug)]
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.
///
/// ```ignore (illustrative)
/// (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:
///
/// ```ignore (illustrative)
/// (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,
/// This is the difference between:
///
/// ```ignore (illustrative)
/// if let _ = (Struct {}) {} // needs parens
///
/// match () {
/// () if let _ = Struct {} => {} // no parens
/// }
/// ```
parenthesize_exterior_struct_lit: bool,
}
/// The default amount of fixing is minimal fixing. Fixups should be turned on
/// in a targeted fashion where needed.
impl Default for FixupContext {
fn default() -> Self {
FixupContext {
stmt: false,
leftmost_subexpression_in_stmt: false,
parenthesize_exterior_struct_lit: false,
}
}
}
impl FixupContext {
/// Create the initial fixup for printing an expression in statement
/// position.
///
/// This is currently also used for printing an expression as a match-arm,
/// but this is incorrect and leads to over-parenthesizing.
pub fn new_stmt() -> Self {
FixupContext { stmt: true, ..FixupContext::default() }
}
/// 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_cond() -> Self {
FixupContext { parenthesize_exterior_struct_lit: true, ..FixupContext::default() }
}
/// 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 `[$a]` have one.
pub fn leftmost_subexpression(self) -> Self {
FixupContext {
stmt: false,
leftmost_subexpression_in_stmt: self.stmt || self.leftmost_subexpression_in_stmt,
..self
}
}
/// Transform this fixup into the one that should apply when printing any
/// subexpression that is neither a leftmost subexpression nor surrounded in
/// delimiters.
///
/// This is for any subexpression that has a different first token than the
/// current expression, and is not surrounded by a paren/bracket/brace. For
/// example the `$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, ..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::expr_requires_semi_to_be_stmt(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_par_as_let_scrutinee(self, expr: &Expr) -> bool {
self.parenthesize_exterior_struct_lit && parser::contains_exterior_struct_lit(expr)
|| parser::needs_par_as_let_scrutinee(expr.precedence().order())
}
}
|
