From 121b5fefbc17932816f69c88edc14f8387c493e9 Mon Sep 17 00:00:00 2001
From: magic-akari <akari.ccino@gmail.com>
Date: Wed, 15 Jan 2025 22:32:10 +0800
Subject: [PATCH] fix(es/ts_strip): Handle ASI hazard in return statement
 (#9882)

**Related issue:**

- Closes /~https://github.com/swc-project/swc/issues/9878
---
 .changeset/curly-poems-dance.md               |  5 ++
 crates/swc_fast_ts_strip/src/lib.rs           | 60 ++++++++++++++++---
 .../tests/fixture/issue-9878.js               | 18 ++++++
 .../tests/fixture/issue-9878.transform.js     |  9 +++
 .../tests/fixture/issue-9878.ts               | 18 ++++++
 5 files changed, 101 insertions(+), 9 deletions(-)
 create mode 100644 .changeset/curly-poems-dance.md
 create mode 100644 crates/swc_fast_ts_strip/tests/fixture/issue-9878.js
 create mode 100644 crates/swc_fast_ts_strip/tests/fixture/issue-9878.transform.js
 create mode 100644 crates/swc_fast_ts_strip/tests/fixture/issue-9878.ts

diff --git a/.changeset/curly-poems-dance.md b/.changeset/curly-poems-dance.md
new file mode 100644
index 000000000000..b9337603b288
--- /dev/null
+++ b/.changeset/curly-poems-dance.md
@@ -0,0 +1,5 @@
+---
+swc_fast_ts_strip: minor
+---
+
+fix(es/ts_strip): Handle ASI hazard in return statement
diff --git a/crates/swc_fast_ts_strip/src/lib.rs b/crates/swc_fast_ts_strip/src/lib.rs
index 7c2f37aa3e50..930157f4e23a 100644
--- a/crates/swc_fast_ts_strip/src/lib.rs
+++ b/crates/swc_fast_ts_strip/src/lib.rs
@@ -15,10 +15,11 @@ use swc_ecma_ast::{
     Constructor, Decl, DefaultDecl, DoWhileStmt, EsVersion, ExportAll, ExportDecl,
     ExportDefaultDecl, ExportSpecifier, FnDecl, ForInStmt, ForOfStmt, ForStmt, GetterProp, IfStmt,
     ImportDecl, ImportSpecifier, NamedExport, ObjectPat, Param, Pat, PrivateMethod, PrivateProp,
-    Program, SetterProp, Stmt, TsAsExpr, TsConstAssertion, TsEnumDecl, TsExportAssignment,
-    TsImportEqualsDecl, TsIndexSignature, TsInstantiation, TsModuleDecl, TsModuleName,
-    TsNamespaceDecl, TsNonNullExpr, TsParamPropParam, TsSatisfiesExpr, TsTypeAliasDecl, TsTypeAnn,
-    TsTypeAssertion, TsTypeParamDecl, TsTypeParamInstantiation, VarDeclarator, WhileStmt,
+    Program, ReturnStmt, SetterProp, Stmt, TsAsExpr, TsConstAssertion, TsEnumDecl,
+    TsExportAssignment, TsImportEqualsDecl, TsIndexSignature, TsInstantiation, TsModuleDecl,
+    TsModuleName, TsNamespaceDecl, TsNonNullExpr, TsParamPropParam, TsSatisfiesExpr,
+    TsTypeAliasDecl, TsTypeAnn, TsTypeAssertion, TsTypeParamDecl, TsTypeParamInstantiation,
+    VarDeclarator, WhileStmt,
 };
 use swc_ecma_parser::{
     lexer::Lexer,
@@ -610,11 +611,6 @@ impl Visit for TsStrip {
     }
 
     fn visit_arrow_expr(&mut self, n: &ArrowExpr) {
-        #[inline(always)]
-        fn is_new_line(c: char) -> bool {
-            matches!(c, '\u{000A}' | '\u{000D}' | '\u{2028}' | '\u{2029}')
-        }
-
         'type_params: {
             // ```TypeScript
             // let f = async <
@@ -692,6 +688,48 @@ impl Visit for TsStrip {
         n.body.visit_with(self);
     }
 
+    fn visit_return_stmt(&mut self, n: &ReturnStmt) {
+        let Some(arg) = n.arg.as_deref() else {
+            return;
+        };
+
+        arg.visit_with(self);
+
+        if let Some(arrow_expr) = arg.as_arrow() {
+            if arrow_expr.is_async {
+                // We have already handled type parameters in `visit_arrow_expr`.
+                return;
+            }
+
+            // ```TypeScript
+            // return <T>
+            //     (v: T) => v;
+            // ```
+            //
+            // ```TypeScript
+            // return (
+            //      v   ) => v;
+            // ```
+
+            if let Some(tp) = &arrow_expr.type_params {
+                let l_paren = self.get_next_token(tp.span.hi);
+                debug_assert_eq!(l_paren.token, Token::LParen);
+
+                let slice = self.get_src_slice(tp.span.with_hi(l_paren.span.lo));
+
+                if !slice.chars().any(is_new_line) {
+                    return;
+                }
+
+                let l_paren_pos = l_paren.span.lo;
+                let l_lt_pos = tp.span.lo;
+
+                self.add_overwrite(l_paren_pos, b' ');
+                self.add_overwrite(l_lt_pos, b'(');
+            }
+        }
+    }
+
     fn visit_binding_ident(&mut self, n: &BindingIdent) {
         n.visit_children_with(self);
 
@@ -1303,6 +1341,10 @@ impl Visit for TsStrip {
     }
 }
 
+#[inline(always)]
+fn is_new_line(c: char) -> bool {
+    matches!(c, '\u{000A}' | '\u{000D}' | '\u{2028}' | '\u{2029}')
+}
 trait IsTsDecl {
     fn is_ts_declare(&self) -> bool;
 }
diff --git a/crates/swc_fast_ts_strip/tests/fixture/issue-9878.js b/crates/swc_fast_ts_strip/tests/fixture/issue-9878.js
new file mode 100644
index 000000000000..b200909d5d5b
--- /dev/null
+++ b/crates/swc_fast_ts_strip/tests/fixture/issue-9878.js
@@ -0,0 +1,18 @@
+function f() {
+	return (  
+		 x   )=>x;
+}
+
+function f2() {
+	return ( 
+	 
+		 x   )=>x;
+}
+
+
+function f3() {
+	return ( 
+	 
+		 x              
+         )=>x;
+}
\ No newline at end of file
diff --git a/crates/swc_fast_ts_strip/tests/fixture/issue-9878.transform.js b/crates/swc_fast_ts_strip/tests/fixture/issue-9878.transform.js
new file mode 100644
index 000000000000..9f663419aa98
--- /dev/null
+++ b/crates/swc_fast_ts_strip/tests/fixture/issue-9878.transform.js
@@ -0,0 +1,9 @@
+function f() {
+    return (x)=>x;
+}
+function f2() {
+    return (x)=>x;
+}
+function f3() {
+    return (x)=>x;
+}
diff --git a/crates/swc_fast_ts_strip/tests/fixture/issue-9878.ts b/crates/swc_fast_ts_strip/tests/fixture/issue-9878.ts
new file mode 100644
index 000000000000..c6fed4606be5
--- /dev/null
+++ b/crates/swc_fast_ts_strip/tests/fixture/issue-9878.ts
@@ -0,0 +1,18 @@
+function f() {
+	return <T>
+		(x: T)=>x;
+}
+
+function f2() {
+	return <T
+	>
+		(x: T)=>x;
+}
+
+
+function f3() {
+	return <T
+	>
+		(x: T): Promise<
+        T>=>x;
+}
\ No newline at end of file