From d31a667e23333c1453a0157562263bb59aba4885 Mon Sep 17 00:00:00 2001
From: Boshen <boshenc@gmail.com>
Date: Fri, 20 Oct 2023 23:15:06 +0800
Subject: [PATCH] feat(transformer): drop `this` parameter from typescript
 functions (#1019)

---
 crates/oxc_transformer/src/lib.rs            | 10 ++++++++++
 crates/oxc_transformer/src/typescript/mod.rs |  8 ++++++++
 tasks/transform_conformance/babel.snap.md    |  6 ++----
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/crates/oxc_transformer/src/lib.rs b/crates/oxc_transformer/src/lib.rs
index 9619e641f5500..ddd2885f9e1d5 100644
--- a/crates/oxc_transformer/src/lib.rs
+++ b/crates/oxc_transformer/src/lib.rs
@@ -144,4 +144,14 @@ impl<'a> VisitMut<'a> for Transformer<'a> {
             self.visit_class_element(class_element);
         });
     }
+
+    fn visit_formal_parameters(&mut self, params: &mut FormalParameters<'a>) {
+        self.typescript.as_mut().map(|t| t.transform_formal_parameters(params));
+        for param in params.items.iter_mut() {
+            self.visit_formal_parameter(param);
+        }
+        if let Some(rest) = &mut params.rest {
+            self.visit_rest_element(rest);
+        }
+    }
 }
diff --git a/crates/oxc_transformer/src/typescript/mod.rs b/crates/oxc_transformer/src/typescript/mod.rs
index 17a6ce5b5b34a..2d9beafd2631c 100644
--- a/crates/oxc_transformer/src/typescript/mod.rs
+++ b/crates/oxc_transformer/src/typescript/mod.rs
@@ -1,3 +1,4 @@
+use oxc_ast::ast::*;
 use oxc_ast::AstBuilder;
 
 use std::rc::Rc;
@@ -15,4 +16,11 @@ impl<'a> TypeScript<'a> {
     pub fn new(_ast: Rc<AstBuilder<'a>>) -> Self {
         Self { _ast }
     }
+
+    #[allow(clippy::unused_self)]
+    pub fn transform_formal_parameters(&self, params: &mut FormalParameters<'a>) {
+        if params.items.get(0).is_some_and(|param| matches!(&param.pattern.kind, BindingPatternKind::BindingIdentifier(ident) if ident.name =="this")) {
+            params.items.remove(0);
+        }
+    }
 }
diff --git a/tasks/transform_conformance/babel.snap.md b/tasks/transform_conformance/babel.snap.md
index 02c4b89806f7e..8cef9337d37f9 100644
--- a/tasks/transform_conformance/babel.snap.md
+++ b/tasks/transform_conformance/babel.snap.md
@@ -1,4 +1,4 @@
-Passed: 160/1087
+Passed: 162/1087
 
 # All Passed:
 * babel-plugin-transform-numeric-separator
@@ -714,7 +714,7 @@ Passed: 160/1087
 * unicode-regex/negated-set/input.js
 * unicode-regex/slash/input.js
 
-# babel-plugin-transform-typescript (71/181)
+# babel-plugin-transform-typescript (73/181)
 * class/abstract-class-decorated/input.ts
 * class/abstract-class-decorated-method/input.ts
 * class/abstract-class-decorated-parameter/input.ts
@@ -749,7 +749,6 @@ Passed: 160/1087
 * enum/string-value-template/input.ts
 * enum/string-values-computed/input.ts
 * enum/ts5.0-const-foldable/input.ts
-* exports/declare-shadowed/input.ts
 * exports/declared-types/input.ts
 * exports/export-const-enums/input.ts
 * exports/export-type/input.ts
@@ -763,7 +762,6 @@ Passed: 160/1087
 * exports/type-only-export-specifier-2/input.ts
 * exports/type-only-export-specifier-3/input.ts
 * function/overloads-exports/input.mjs
-* function/this-parameter/input.ts
 * imports/elide-injected/input.ts
 * imports/elide-preact/input.ts
 * imports/elide-react/input.ts