Struct rustc_ast_pretty::pprust::state::fixup::FixupContext

source ·
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§

source§

impl FixupContext

source

pub fn new_stmt() -> Self

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

source

pub fn new_match_arm() -> Self

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

source

pub 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.

source

pub 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.

source

pub 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).

source

pub 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.

source

pub 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§

source§

impl Clone for FixupContext

source§

fn clone(&self) -> FixupContext

Returns a copy of the value. Read more
1.0.0 · source§

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

Performs copy-assignment from source. Read more
source§

impl Debug for FixupContext

source§

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

Formats the value using the given formatter. Read more
source§

impl Default for FixupContext

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

source§

fn default() -> Self

Returns the “default value” for a type. Read more
source§

impl Copy for FixupContext

Auto Trait Implementations§

Blanket Implementations§

source§

impl<T> Aligned for T

source§

const ALIGN: Alignment = _

Alignment of Self.
source§

impl<T> Any for T
where T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T> Borrow<T> for T
where T: ?Sized,

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T> Instrument for T

source§

fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
source§

fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
source§

impl<T, U> Into<U> for T
where U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

source§

impl<T> IntoEither for T

source§

fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts self into a Left variant of Either<Self, Self> if into_left is true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
source§

fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts self into a Left variant of Either<Self, Self> if into_left(&self) returns true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
source§

impl<T> Pointable for T

source§

const ALIGN: usize = _

The alignment of pointer.
§

type Init = T

The type for initializers.
source§

unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
source§

unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
source§

unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
source§

unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
source§

impl<T> Same for T

§

type Output = T

Should always be Self
source§

impl<T> ToOwned for T
where T: Clone,

§

type Owned = T

The resulting type after obtaining ownership.
source§

fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
source§

fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
source§

impl<T> WithSubscriber for T

source§

fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
source§

fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
source§

impl<'a, T> Captures<'a> for T
where T: ?Sized,

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