fix: Prevent wrong invocations of needs_parens_in with non-ancestral "parent"s

crates/syntax/src/ast/prec.rs

@@ -1,5 +1,7 @@
 //! Precedence representation.
 
+use stdx::always;
+
 use crate::{
     ast::{self, BinaryOp, Expr, HasArgList, RangeItem},
     match_ast, AstNode, SyntaxNode,
@@ -140,6 +142,22 @@ pub fn precedence(expr: &ast::Expr) -> ExprPrecedence {
     }
 }
 
+fn check_ancestry(ancestor: &SyntaxNode, descendent: &SyntaxNode) -> bool {
+    let bail = || always!(false, "{} is not an ancestor of {}", ancestor, descendent);
+
+    if !ancestor.text_range().contains_range(descendent.text_range()) {
+        return bail();
+    }
+
+    for anc in descendent.ancestors() {
+        if anc == *ancestor {
+            return true;
+        }
+    }
+
+    bail()
+}
+
 impl Expr {
     pub fn precedence(&self) -> ExprPrecedence {
         precedence(self)
@@ -153,9 +171,19 @@ impl Expr {
 
     /// Returns `true` if `self` would need to be wrapped in parentheses given that its parent is `parent`.
     pub fn needs_parens_in(&self, parent: &SyntaxNode) -> bool {
+        self.needs_parens_in_place_of(parent, self.syntax())
+    }
+
+    /// Returns `true` if `self` would need to be wrapped in parentheses if it replaces `place_of`
+    /// given that `place_of`'s parent is `parent`.
+    pub fn needs_parens_in_place_of(&self, parent: &SyntaxNode, place_of: &SyntaxNode) -> bool {
+        if !check_ancestry(parent, place_of) {
+            return false;
+        }
+
         match_ast! {
             match parent {
-                ast::Expr(e) => self.needs_parens_in_expr(&e),
+                ast::Expr(e) => self.needs_parens_in_expr(&e, place_of),
                 ast::Stmt(e) => self.needs_parens_in_stmt(Some(&e)),
                 ast::StmtList(_) => self.needs_parens_in_stmt(None),
                 ast::ArgList(_) => false,
@@ -165,7 +193,7 @@ impl Expr {
         }
     }
 
-    fn needs_parens_in_expr(&self, parent: &Expr) -> bool {
+    fn needs_parens_in_expr(&self, parent: &Expr, place_of: &SyntaxNode) -> bool {
         // Parentheses are necessary when calling a function-like pointer that is a member of a struct or union
         // (e.g. `(a.f)()`).
         let is_parent_call_expr = matches!(parent, ast::Expr::CallExpr(_));
@@ -199,13 +227,17 @@ impl Expr {
 
         if self.is_paren_like()
             || parent.is_paren_like()
-            || self.is_prefix() && (parent.is_prefix() || !self.is_ordered_before(parent))
-            || self.is_postfix() && (parent.is_postfix() || self.is_ordered_before(parent))
+            || self.is_prefix()
+                && (parent.is_prefix()
+                    || !self.is_ordered_before_parent_in_place_of(parent, place_of))
+            || self.is_postfix()
+                && (parent.is_postfix()
+                    || self.is_ordered_before_parent_in_place_of(parent, place_of))
         {
             return false;
         }
 
-        let (left, right, inv) = match self.is_ordered_before(parent) {
+        let (left, right, inv) = match self.is_ordered_before_parent_in_place_of(parent, place_of) {
             true => (self, parent, false),
             false => (parent, self, true),
         };
@@ -413,13 +445,28 @@ impl Expr {
         }
     }
 
-    fn is_ordered_before(&self, other: &Expr) -> bool {
+    fn is_ordered_before_parent_in_place_of(&self, parent: &Expr, place_of: &SyntaxNode) -> bool {
+        use rowan::TextSize;
         use Expr::*;
 
-        return order(self) < order(other);
+        let self_range = self.syntax().text_range();
+        let place_of_range = place_of.text_range();
+
+        let self_order_adjusted = order(self) - self_range.start() + place_of_range.start();
+
+        let parent_order = order(parent);
+        let parent_order_adjusted = if parent_order <= place_of_range.start() {
+            parent_order
+        } else if parent_order >= place_of_range.end() {
+            parent_order - place_of_range.len() + self_range.len()
+        } else {
+            return false;
+        };
+
+        return self_order_adjusted < parent_order_adjusted;
 
         /// Returns text range that can be used to compare two expression for order (which goes first).
-        fn order(this: &Expr) -> rowan::TextSize {
+        fn order(this: &Expr) -> TextSize {
             // For non-paren-like operators: get the operator itself
             let token = match this {
                 RangeExpr(e) => e.op_token(),