Move precedence handling to crates/syntax

crates/syntax/src/ast/prec.rs

@@ -0,0 +1,115 @@
+//! Precedence representation.
+
+use crate::ast::{self, BinExpr, Expr};
+
+/// Precedence of an expression.
+#[derive(Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub enum ExprPrecedence {
+    // N.B.: Order is important
+    Closure,
+    Jump,
+    Range,
+    Bin(BinOpPresedence),
+    Prefix,
+    Postfix,
+    Paren,
+}
+
+/// Precedence of a binary operator.
+#[derive(Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub enum BinOpPresedence {
+    // N.B.: Order is important
+    /// `=`, `+=`, `-=`, `*=`, `/=`, `%=`, `|=`, `&=`
+    Assign,
+    /// `||`
+    LOr,
+    /// `&&`
+    LAnd,
+    /// `<`, `<=`, `>`, `>=`, `==` and `!=`
+    Cmp,
+    /// `|`
+    BitOr,
+    /// `^`
+    BitXor,
+    /// `&`
+    BitAnd,
+    /// `<<` and `>>`
+    Shift,
+    /// `+` and `-`
+    Add,
+    /// `*`, `/` and `%`
+    Mul,
+    /// `as`
+    As,
+}
+
+impl Expr {
+    /// Returns precedence of this expression.
+    /// Usefull to preserve semantics in assists.
+    ///
+    /// Returns `None` if this is a [`BinExpr`] and its [`op_kind`] returns `None`.
+    ///
+    /// [`op_kind`]: BinExpr::op_kind
+    /// [`BinExpr`]: Expr::BinExpr
+    pub fn precedence(&self) -> Option<ExprPrecedence> {
+        // Copied from <https://github.com/rust-lang/rust/blob/b6852428a8ea9728369b64b9964cad8e258403d3/compiler/rustc_ast/src/util/parser.rs#L296>
+        use Expr::*;
+
+        let prec = match self {
+            ClosureExpr(_) => ExprPrecedence::Closure,
+
+            ContinueExpr(_) | ReturnExpr(_) | YieldExpr(_) | BreakExpr(_) => ExprPrecedence::Jump,
+
+            RangeExpr(_) => ExprPrecedence::Range,
+
+            BinExpr(bin_expr) => return bin_expr.precedence().map(ExprPrecedence::Bin),
+            CastExpr(_) => ExprPrecedence::Bin(BinOpPresedence::As),
+
+            BoxExpr(_) | RefExpr(_) | LetExpr(_) | PrefixExpr(_) => ExprPrecedence::Prefix,
+
+            AwaitExpr(_) | CallExpr(_) | MethodCallExpr(_) | FieldExpr(_) | IndexExpr(_)
+            | TryExpr(_) | MacroExpr(_) => ExprPrecedence::Postfix,
+
+            ArrayExpr(_) | TupleExpr(_) | Literal(_) | PathExpr(_) | ParenExpr(_) | IfExpr(_)
+            | WhileExpr(_) | ForExpr(_) | LoopExpr(_) | MatchExpr(_) | BlockExpr(_)
+            | RecordExpr(_) | UnderscoreExpr(_) => ExprPrecedence::Paren,
+        };
+
+        Some(prec)
+    }
+}
+
+impl BinExpr {
+    /// Returns precedence of this binary expression.
+    /// Usefull to preserve semantics in assists.
+    ///
+    /// Returns `None` if [`op_kind`] returns `None`.
+    ///
+    /// [`op_kind`]: BinExpr::op_kind
+    pub fn precedence(&self) -> Option<BinOpPresedence> {
+        use ast::{ArithOp::*, BinaryOp::*, LogicOp::*};
+
+        let prec = match self.op_kind()? {
+            LogicOp(op) => match op {
+                And => BinOpPresedence::LAnd,
+                Or => BinOpPresedence::LOr,
+            },
+            ArithOp(op) => match op {
+                Add => BinOpPresedence::Add,
+                Mul => BinOpPresedence::Mul,
+                Sub => BinOpPresedence::Add,
+                Div => BinOpPresedence::Mul,
+                Rem => BinOpPresedence::Mul,
+                Shl => BinOpPresedence::Shift,
+                Shr => BinOpPresedence::Shift,
+                BitXor => BinOpPresedence::BitXor,
+                BitOr => BinOpPresedence::BitOr,
+                BitAnd => BinOpPresedence::BitAnd,
+            },
+            CmpOp(_) => BinOpPresedence::Cmp,
+            Assignment { .. } => BinOpPresedence::Assign,
+        };
+
+        Some(prec)
+    }
+}