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Diffstat (limited to 'rust/syn/fixup.rs')
| -rw-r--r-- | rust/syn/fixup.rs | 775 |
1 files changed, 775 insertions, 0 deletions
diff --git a/rust/syn/fixup.rs b/rust/syn/fixup.rs new file mode 100644 index 000000000000..79b6d7618bb7 --- /dev/null +++ b/rust/syn/fixup.rs @@ -0,0 +1,775 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +use crate::classify; +use crate::expr::Expr; +#[cfg(feature = "full")] +use crate::expr::{ + ExprBreak, ExprRange, ExprRawAddr, ExprReference, ExprReturn, ExprUnary, ExprYield, +}; +use crate::precedence::Precedence; +#[cfg(feature = "full")] +use crate::ty::ReturnType; + +pub(crate) struct FixupContext { + #[cfg(feature = "full")] + previous_operator: Precedence, + #[cfg(feature = "full")] + next_operator: Precedence, + + // 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 + // + #[cfg(feature = "full")] + 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. + #[cfg(feature = "full")] + 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 + // } + // + #[cfg(feature = "full")] + 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 + // } + // + #[cfg(feature = "full")] + leftmost_subexpression_in_match_arm: bool, + + // This is the difference between: + // + // if let _ = (Struct {}) {} // needs parens + // + // match () { + // () if let _ = Struct {} => {} // no parens + // } + // + #[cfg(feature = "full")] + condition: bool, + + // This is the difference between: + // + // if break Struct {} == (break) {} // needs parens + // + // if break break == Struct {} {} // no parens + // + #[cfg(feature = "full")] + rightmost_subexpression_in_condition: bool, + + // This is the difference between: + // + // if break ({ x }).field + 1 {} needs parens + // + // if break 1 + { x }.field {} // no parens + // + #[cfg(feature = "full")] + leftmost_subexpression_in_optional_operand: bool, + + // This is the difference between: + // + // let _ = (return) - 1; // without paren, this would return -1 + // + // let _ = return + 1; // no paren because '+' cannot begin expr + // + #[cfg(feature = "full")] + next_operator_can_begin_expr: bool, + + // This is the difference between: + // + // let _ = 1 + return 1; // no parens if rightmost subexpression + // + // let _ = 1 + (return 1) + 1; // needs parens + // + #[cfg(feature = "full")] + next_operator_can_continue_expr: bool, + + // This is the difference between: + // + // let _ = x as u8 + T; + // + // let _ = (x as u8) < T; + // + // Without parens, the latter would want to parse `u8<T...` as a type. + next_operator_can_begin_generics: 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 { + #[cfg(feature = "full")] + previous_operator: Precedence::MIN, + #[cfg(feature = "full")] + next_operator: Precedence::MIN, + #[cfg(feature = "full")] + stmt: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_stmt: false, + #[cfg(feature = "full")] + match_arm: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_match_arm: false, + #[cfg(feature = "full")] + condition: false, + #[cfg(feature = "full")] + rightmost_subexpression_in_condition: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_optional_operand: false, + #[cfg(feature = "full")] + next_operator_can_begin_expr: false, + #[cfg(feature = "full")] + next_operator_can_continue_expr: false, + next_operator_can_begin_generics: false, + }; + + /// Create the initial fixup for printing an expression in statement + /// position. + #[cfg(feature = "full")] + 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. + #[cfg(feature = "full")] + 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`. + #[cfg(feature = "full")] + pub fn new_condition() -> Self { + FixupContext { + condition: true, + rightmost_subexpression_in_condition: 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_with_operator( + self, + expr: &Expr, + #[cfg(feature = "full")] next_operator_can_begin_expr: bool, + next_operator_can_begin_generics: bool, + #[cfg(feature = "full")] precedence: Precedence, + ) -> (Precedence, Self) { + let fixup = FixupContext { + #[cfg(feature = "full")] + next_operator: precedence, + #[cfg(feature = "full")] + stmt: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_stmt: self.stmt || self.leftmost_subexpression_in_stmt, + #[cfg(feature = "full")] + match_arm: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_match_arm: self.match_arm + || self.leftmost_subexpression_in_match_arm, + #[cfg(feature = "full")] + rightmost_subexpression_in_condition: false, + #[cfg(feature = "full")] + next_operator_can_begin_expr, + #[cfg(feature = "full")] + next_operator_can_continue_expr: true, + next_operator_can_begin_generics, + ..self + }; + + (fixup.leftmost_subexpression_precedence(expr), fixup) + } + + /// 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, expr: &Expr) -> (Precedence, Self) { + let fixup = FixupContext { + #[cfg(feature = "full")] + next_operator: Precedence::Unambiguous, + #[cfg(feature = "full")] + stmt: self.stmt || self.leftmost_subexpression_in_stmt, + #[cfg(feature = "full")] + leftmost_subexpression_in_stmt: false, + #[cfg(feature = "full")] + match_arm: self.match_arm || self.leftmost_subexpression_in_match_arm, + #[cfg(feature = "full")] + leftmost_subexpression_in_match_arm: false, + #[cfg(feature = "full")] + rightmost_subexpression_in_condition: false, + #[cfg(feature = "full")] + next_operator_can_begin_expr: false, + #[cfg(feature = "full")] + next_operator_can_continue_expr: true, + next_operator_can_begin_generics: false, + ..self + }; + + (fixup.leftmost_subexpression_precedence(expr), fixup) + } + + fn leftmost_subexpression_precedence(self, expr: &Expr) -> Precedence { + #[cfg(feature = "full")] + if !self.next_operator_can_begin_expr || self.next_operator == Precedence::Range { + if let Scan::Bailout = scan_right(expr, self, Precedence::MIN, 0, 0) { + if scan_left(expr, self) { + return Precedence::Unambiguous; + } + } + } + + self.precedence(expr) + } + + /// Transform this fixup into the one that should apply when printing the + /// rightmost subexpression of the current expression. + /// + /// The rightmost subexpression is any subexpression that has a different + /// first token than the current expression, but has the same last token. + /// + /// For example in `$a + $b` and `-$b`, the subexpression `$b` is a + /// rightmost subexpression. + /// + /// Not every expression has a rightmost subexpression. For example neither + /// `[$b]` nor `$a.f($b)` have one. + pub fn rightmost_subexpression( + self, + expr: &Expr, + #[cfg(feature = "full")] precedence: Precedence, + ) -> (Precedence, Self) { + let fixup = self.rightmost_subexpression_fixup( + #[cfg(feature = "full")] + false, + #[cfg(feature = "full")] + false, + #[cfg(feature = "full")] + precedence, + ); + (fixup.rightmost_subexpression_precedence(expr), fixup) + } + + pub fn rightmost_subexpression_fixup( + self, + #[cfg(feature = "full")] reset_allow_struct: bool, + #[cfg(feature = "full")] optional_operand: bool, + #[cfg(feature = "full")] precedence: Precedence, + ) -> Self { + FixupContext { + #[cfg(feature = "full")] + previous_operator: precedence, + #[cfg(feature = "full")] + stmt: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_stmt: false, + #[cfg(feature = "full")] + match_arm: false, + #[cfg(feature = "full")] + leftmost_subexpression_in_match_arm: false, + #[cfg(feature = "full")] + condition: self.condition && !reset_allow_struct, + #[cfg(feature = "full")] + leftmost_subexpression_in_optional_operand: self.condition && optional_operand, + ..self + } + } + + pub fn rightmost_subexpression_precedence(self, expr: &Expr) -> Precedence { + let default_prec = self.precedence(expr); + + #[cfg(feature = "full")] + if match self.previous_operator { + Precedence::Assign | Precedence::Let | Precedence::Prefix => { + default_prec < self.previous_operator + } + _ => default_prec <= self.previous_operator, + } && match self.next_operator { + Precedence::Range | Precedence::Or | Precedence::And => true, + _ => !self.next_operator_can_begin_expr, + } { + if let Scan::Bailout | Scan::Fail = scan_right(expr, self, self.previous_operator, 1, 0) + { + if scan_left(expr, self) { + return Precedence::Prefix; + } + } + } + + default_prec + } + + /// Determine whether parentheses are needed around the given expression to + /// head off the early termination of a statement or condition. + #[cfg(feature = "full")] + pub fn parenthesize(self, expr: &Expr) -> bool { + (self.leftmost_subexpression_in_stmt && !classify::requires_semi_to_be_stmt(expr)) + || ((self.stmt || self.leftmost_subexpression_in_stmt) && matches!(expr, Expr::Let(_))) + || (self.leftmost_subexpression_in_match_arm + && !classify::requires_comma_to_be_match_arm(expr)) + || (self.condition && matches!(expr, Expr::Struct(_))) + || (self.rightmost_subexpression_in_condition + && matches!( + expr, + Expr::Return(ExprReturn { expr: None, .. }) + | Expr::Yield(ExprYield { expr: None, .. }) + )) + || (self.rightmost_subexpression_in_condition + && !self.condition + && matches!( + expr, + Expr::Break(ExprBreak { expr: None, .. }) + | Expr::Path(_) + | Expr::Range(ExprRange { end: None, .. }) + )) + || (self.leftmost_subexpression_in_optional_operand + && matches!(expr, Expr::Block(expr) if expr.attrs.is_empty() && expr.label.is_none())) + } + + /// Determines the effective precedence of a subexpression. Some expressions + /// have higher or lower precedence when adjacent to particular operators. + fn precedence(self, expr: &Expr) -> Precedence { + #[cfg(feature = "full")] + if self.next_operator_can_begin_expr { + // Decrease precedence of value-less jumps when followed by an + // operator that would otherwise get interpreted as beginning a + // value for the jump. + if let Expr::Break(ExprBreak { expr: None, .. }) + | Expr::Return(ExprReturn { expr: None, .. }) + | Expr::Yield(ExprYield { expr: None, .. }) = expr + { + return Precedence::Jump; + } + } + + #[cfg(feature = "full")] + if !self.next_operator_can_continue_expr { + match expr { + // Increase precedence of expressions that extend to the end of + // current statement or group. + Expr::Break(_) + | Expr::Closure(_) + | Expr::Let(_) + | Expr::Return(_) + | Expr::Yield(_) => { + return Precedence::Prefix; + } + Expr::Range(e) if e.start.is_none() => return Precedence::Prefix, + _ => {} + } + } + + if self.next_operator_can_begin_generics { + if let Expr::Cast(cast) = expr { + if classify::trailing_unparameterized_path(&cast.ty) { + return Precedence::MIN; + } + } + } + + Precedence::of(expr) + } +} + +impl Copy for FixupContext {} + +impl Clone for FixupContext { + fn clone(&self) -> Self { + *self + } +} + +#[cfg(feature = "full")] +enum Scan { + Fail, + Bailout, + Consume, +} + +#[cfg(feature = "full")] +impl Copy for Scan {} + +#[cfg(feature = "full")] +impl Clone for Scan { + fn clone(&self) -> Self { + *self + } +} + +#[cfg(feature = "full")] +impl PartialEq for Scan { + fn eq(&self, other: &Self) -> bool { + *self as u8 == *other as u8 + } +} + +#[cfg(feature = "full")] +fn scan_left(expr: &Expr, fixup: FixupContext) -> bool { + match expr { + Expr::Assign(_) => fixup.previous_operator <= Precedence::Assign, + Expr::Binary(e) => match Precedence::of_binop(&e.op) { + Precedence::Assign => fixup.previous_operator <= Precedence::Assign, + binop_prec => fixup.previous_operator < binop_prec, + }, + Expr::Cast(_) => fixup.previous_operator < Precedence::Cast, + Expr::Range(e) => e.start.is_none() || fixup.previous_operator < Precedence::Assign, + _ => true, + } +} + +#[cfg(feature = "full")] +fn scan_right( + expr: &Expr, + fixup: FixupContext, + precedence: Precedence, + fail_offset: u8, + bailout_offset: u8, +) -> Scan { + let consume_by_precedence = if match precedence { + Precedence::Assign | Precedence::Compare => precedence <= fixup.next_operator, + _ => precedence < fixup.next_operator, + } || fixup.next_operator == Precedence::MIN + { + Scan::Consume + } else { + Scan::Bailout + }; + if fixup.parenthesize(expr) { + return consume_by_precedence; + } + match expr { + Expr::Assign(e) if e.attrs.is_empty() => { + if match fixup.next_operator { + Precedence::Unambiguous => fail_offset >= 2, + _ => bailout_offset >= 1, + } { + return Scan::Consume; + } + let right_fixup = fixup.rightmost_subexpression_fixup(false, false, Precedence::Assign); + let scan = scan_right( + &e.right, + right_fixup, + Precedence::Assign, + match fixup.next_operator { + Precedence::Unambiguous => fail_offset, + _ => 1, + }, + 1, + ); + if let Scan::Bailout | Scan::Consume = scan { + Scan::Consume + } else if let Precedence::Unambiguous = fixup.next_operator { + Scan::Fail + } else { + Scan::Bailout + } + } + Expr::Binary(e) if e.attrs.is_empty() => { + if match fixup.next_operator { + Precedence::Unambiguous => { + fail_offset >= 2 + && (consume_by_precedence == Scan::Consume || bailout_offset >= 1) + } + _ => bailout_offset >= 1, + } { + return Scan::Consume; + } + let binop_prec = Precedence::of_binop(&e.op); + if binop_prec == Precedence::Compare && fixup.next_operator == Precedence::Compare { + return Scan::Consume; + } + let right_fixup = fixup.rightmost_subexpression_fixup(false, false, binop_prec); + let scan = scan_right( + &e.right, + right_fixup, + binop_prec, + match fixup.next_operator { + Precedence::Unambiguous => fail_offset, + _ => 1, + }, + consume_by_precedence as u8 - Scan::Bailout as u8, + ); + match scan { + Scan::Fail => {} + Scan::Bailout => return consume_by_precedence, + Scan::Consume => return Scan::Consume, + } + let right_needs_group = binop_prec != Precedence::Assign + && right_fixup.rightmost_subexpression_precedence(&e.right) <= binop_prec; + if right_needs_group { + consume_by_precedence + } else if let (Scan::Fail, Precedence::Unambiguous) = (scan, fixup.next_operator) { + Scan::Fail + } else { + Scan::Bailout + } + } + Expr::RawAddr(ExprRawAddr { expr, .. }) + | Expr::Reference(ExprReference { expr, .. }) + | Expr::Unary(ExprUnary { expr, .. }) => { + if match fixup.next_operator { + Precedence::Unambiguous => { + fail_offset >= 2 + && (consume_by_precedence == Scan::Consume || bailout_offset >= 1) + } + _ => bailout_offset >= 1, + } { + return Scan::Consume; + } + let right_fixup = fixup.rightmost_subexpression_fixup(false, false, Precedence::Prefix); + let scan = scan_right( + expr, + right_fixup, + precedence, + match fixup.next_operator { + Precedence::Unambiguous => fail_offset, + _ => 1, + }, + consume_by_precedence as u8 - Scan::Bailout as u8, + ); + match scan { + Scan::Fail => {} + Scan::Bailout => return consume_by_precedence, + Scan::Consume => return Scan::Consume, + } + if right_fixup.rightmost_subexpression_precedence(expr) < Precedence::Prefix { + consume_by_precedence + } else if let (Scan::Fail, Precedence::Unambiguous) = (scan, fixup.next_operator) { + Scan::Fail + } else { + Scan::Bailout + } + } + Expr::Range(e) if e.attrs.is_empty() => match &e.end { + Some(end) => { + if fail_offset >= 2 { + return Scan::Consume; + } + let right_fixup = + fixup.rightmost_subexpression_fixup(false, true, Precedence::Range); + let scan = scan_right( + end, + right_fixup, + Precedence::Range, + fail_offset, + match fixup.next_operator { + Precedence::Assign | Precedence::Range => 0, + _ => 1, + }, + ); + if match (scan, fixup.next_operator) { + (Scan::Fail, _) => false, + (Scan::Bailout, Precedence::Assign | Precedence::Range) => false, + (Scan::Bailout | Scan::Consume, _) => true, + } { + return Scan::Consume; + } + if right_fixup.rightmost_subexpression_precedence(end) <= Precedence::Range { + Scan::Consume + } else { + Scan::Fail + } + } + None => { + if fixup.next_operator_can_begin_expr { + Scan::Consume + } else { + Scan::Fail + } + } + }, + Expr::Break(e) => match &e.expr { + Some(value) => { + if bailout_offset >= 1 || e.label.is_none() && classify::expr_leading_label(value) { + return Scan::Consume; + } + let right_fixup = fixup.rightmost_subexpression_fixup(true, true, Precedence::Jump); + match scan_right(value, right_fixup, Precedence::Jump, 1, 1) { + Scan::Fail => Scan::Bailout, + Scan::Bailout | Scan::Consume => Scan::Consume, + } + } + None => match fixup.next_operator { + Precedence::Assign if precedence > Precedence::Assign => Scan::Fail, + _ => Scan::Consume, + }, + }, + Expr::Return(ExprReturn { expr, .. }) | Expr::Yield(ExprYield { expr, .. }) => match expr { + Some(e) => { + if bailout_offset >= 1 { + return Scan::Consume; + } + let right_fixup = + fixup.rightmost_subexpression_fixup(true, false, Precedence::Jump); + match scan_right(e, right_fixup, Precedence::Jump, 1, 1) { + Scan::Fail => Scan::Bailout, + Scan::Bailout | Scan::Consume => Scan::Consume, + } + } + None => match fixup.next_operator { + Precedence::Assign if precedence > Precedence::Assign => Scan::Fail, + _ => Scan::Consume, + }, + }, + Expr::Closure(e) => { + if matches!(e.output, ReturnType::Default) + || matches!(&*e.body, Expr::Block(body) if body.attrs.is_empty() && body.label.is_none()) + { + if bailout_offset >= 1 { + return Scan::Consume; + } + let right_fixup = + fixup.rightmost_subexpression_fixup(false, false, Precedence::Jump); + match scan_right(&e.body, right_fixup, Precedence::Jump, 1, 1) { + Scan::Fail => Scan::Bailout, + Scan::Bailout | Scan::Consume => Scan::Consume, + } + } else { + Scan::Consume + } + } + Expr::Let(e) => { + if bailout_offset >= 1 { + return Scan::Consume; + } + let right_fixup = fixup.rightmost_subexpression_fixup(false, false, Precedence::Let); + let scan = scan_right( + &e.expr, + right_fixup, + Precedence::Let, + 1, + if fixup.next_operator < Precedence::Let { + 0 + } else { + 1 + }, + ); + match scan { + Scan::Fail | Scan::Bailout if fixup.next_operator < Precedence::Let => { + return Scan::Bailout; + } + Scan::Consume => return Scan::Consume, + _ => {} + } + if right_fixup.rightmost_subexpression_precedence(&e.expr) < Precedence::Let { + Scan::Consume + } else if let Scan::Fail = scan { + Scan::Bailout + } else { + Scan::Consume + } + } + Expr::Array(_) + | Expr::Assign(_) + | Expr::Async(_) + | Expr::Await(_) + | Expr::Binary(_) + | Expr::Block(_) + | Expr::Call(_) + | Expr::Cast(_) + | Expr::Const(_) + | Expr::Continue(_) + | Expr::Field(_) + | Expr::ForLoop(_) + | Expr::Group(_) + | Expr::If(_) + | Expr::Index(_) + | Expr::Infer(_) + | Expr::Lit(_) + | Expr::Loop(_) + | Expr::Macro(_) + | Expr::Match(_) + | Expr::MethodCall(_) + | Expr::Paren(_) + | Expr::Path(_) + | Expr::Range(_) + | Expr::Repeat(_) + | Expr::Struct(_) + | Expr::Try(_) + | Expr::TryBlock(_) + | Expr::Tuple(_) + | Expr::Unsafe(_) + | Expr::Verbatim(_) + | Expr::While(_) => match fixup.next_operator { + Precedence::Assign | Precedence::Range if precedence == Precedence::Range => Scan::Fail, + _ if precedence == Precedence::Let && fixup.next_operator < Precedence::Let => { + Scan::Fail + } + _ => consume_by_precedence, + }, + } +} |