From 4796ece77dba3b84b1d6913b2d34d059609f3ccf Mon Sep 17 00:00:00 2001
From: overlookmotel <557937+overlookmotel@users.noreply.github.com>
Date: Mon, 19 Aug 2024 20:59:43 +0000
Subject: [PATCH] refactor(transformer): TS annotations transform use
 `move_expression` (#4982)

Follow on after #4920. #4920 removed a usage of `AstBuilder::copy` and replaced with 2 new methods `AstBuilder::move_identifier_reference` and `AstBuilder:: move_member_expression`.

We can instead use `AstBuilder::move_expression` earlier and then unpack the enum again. Hopefully the compiler can see that the 2 `unreachable!()` branches are indeed unreachable and elide them.

`move_expression` is preferable to `move_member_expression` as it only creates 1 temporary `Box<Expression::NullLiteral>` instead of 2.
---
 crates/oxc_ast/src/ast_builder_impl.rs        | 22 -------------------
 .../src/typescript/annotations.rs             | 18 +++++++++------
 2 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/crates/oxc_ast/src/ast_builder_impl.rs b/crates/oxc_ast/src/ast_builder_impl.rs
index 4f4a7f030..3dc648715 100644
--- a/crates/oxc_ast/src/ast_builder_impl.rs
+++ b/crates/oxc_ast/src/ast_builder_impl.rs
@@ -69,16 +69,6 @@ impl<'a> AstBuilder<'a> {
         unsafe { std::mem::transmute_copy(src) }
     }
 
-    /// Moves the identifier reference out by replacing it with a dummy identifier reference.
-    #[inline]
-    pub fn move_identifier_reference(
-        self,
-        expr: &mut IdentifierReference<'a>,
-    ) -> IdentifierReference<'a> {
-        let dummy = self.identifier_reference(expr.span(), Atom::empty());
-        mem::replace(expr, dummy)
-    }
-
     /// Moves the expression out by replacing it with a null expression.
     #[inline]
     pub fn move_expression(self, expr: &mut Expression<'a>) -> Expression<'a> {
@@ -86,18 +76,6 @@ impl<'a> AstBuilder<'a> {
         mem::replace(expr, null_expr)
     }
 
-    /// Moves the member expression out by replacing it with a dummy expression.
-    #[inline]
-    pub fn move_member_expression(self, expr: &mut MemberExpression<'a>) -> MemberExpression<'a> {
-        let dummy = self.member_expression_computed(
-            expr.span(),
-            self.expression_null_literal(expr.span()),
-            self.expression_null_literal(expr.span()),
-            false,
-        );
-        mem::replace(expr, dummy)
-    }
-
     #[inline]
     pub fn move_statement(self, stmt: &mut Statement<'a>) -> Statement<'a> {
         let empty_stmt = self.empty_statement(stmt.span());
diff --git a/crates/oxc_transformer/src/typescript/annotations.rs b/crates/oxc_transformer/src/typescript/annotations.rs
index f96e51fd0..0f1c67a79 100644
--- a/crates/oxc_transformer/src/typescript/annotations.rs
+++ b/crates/oxc_transformer/src/typescript/annotations.rs
@@ -226,16 +226,20 @@ impl<'a> TypeScriptAnnotations<'a> {
         if let Some(expr) = target.get_expression_mut() {
             match expr.get_inner_expression_mut() {
                 // `foo!++` to `foo++`
-                Expression::Identifier(ident) => {
-                    *target = self.ctx.ast.simple_assignment_target_from_identifier_reference(
-                        self.ctx.ast.move_identifier_reference(ident),
-                    );
+                inner_expr @ Expression::Identifier(_) => {
+                    let inner_expr = self.ctx.ast.move_expression(inner_expr);
+                    let Expression::Identifier(ident) = inner_expr else {
+                        unreachable!();
+                    };
+                    *target = SimpleAssignmentTarget::AssignmentTargetIdentifier(ident);
                 }
                 // `foo.bar!++` to `foo.bar++`
                 inner_expr @ match_member_expression!(Expression) => {
-                    *target = SimpleAssignmentTarget::from(
-                        self.ctx.ast.move_member_expression(inner_expr.to_member_expression_mut()),
-                    );
+                    let inner_expr = self.ctx.ast.move_expression(inner_expr);
+                    let Ok(member_expr) = MemberExpression::try_from(inner_expr) else {
+                        unreachable!();
+                    };
+                    *target = SimpleAssignmentTarget::from(member_expr);
                 }
                 _ => {
                     // This should be never hit until more syntax is added to the JavaScript/TypeScrips