Struct FixupContext

pub(crate) struct FixupContext {
    stmt: bool,
    leftmost_subexpression_in_stmt: bool,
    match_arm: bool,
    leftmost_subexpression_in_match_arm: bool,
    parenthesize_exterior_struct_lit: bool,
}

Fields

stmt: bool

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

leftmost_subexpression_in_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.

match_arm: 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
}

leftmost_subexpression_in_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
}

parenthesize_exterior_struct_lit: bool

This is the difference between:

if let _ = (Struct {}) {}  // needs parens

match () {
    () if let _ = Struct {} => {}  // no parens
}

Implementations

impl FixupContext

pub(crate) fn new_stmt() -> Self

Create the initial fixup for printing an expression in statement position.

pub(crate) fn new_match_arm() -> Self

Create the initial fixup for printing an expression as the right-hand side of a match arm.

pub(crate) fn new_cond() -> Self

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(crate) fn leftmost_subexpression(self) -> Self

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(crate) fn subsequent_subexpression(self) -> 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(crate) fn would_cause_statement_boundary(self, expr: &Expr) -> bool

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(crate) fn needs_par_as_let_scrutinee(self, expr: &Expr) -> bool

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”.

Trait Implementations

impl Clone for FixupContext

fn clone(&self) -> FixupContext

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FixupContext

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for FixupContext

The default amount of fixing is minimal fixing. Fixups should be turned on in a targeted fashion where needed.

fn default() -> Self

Returns the “default value” for a type.

impl Copy for FixupContext

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 5 bytes