From a08d71f13e54eba17bc2f6234bfe564db9545f54 Mon Sep 17 00:00:00 2001
From: hyeonsang <k98hh@naver.com>
Date: Fri, 28 Aug 2026 19:40:52 +0900
Subject: [PATCH] Disallow optional calls on import.defer

---
 tsc/internal/parser/parser.go                 |  3 +++
 .../importDeferOptionalCall.errors.txt        | 16 +++++++++++++
 .../conformance/importDeferOptionalCall.js    | 18 +++++++++++++++
 .../importDeferOptionalCall.symbols           | 16 +++++++++++++
 .../conformance/importDeferOptionalCall.types | 23 +++++++++++++++++++
 .../importDefer/importDeferOptionalCall.ts    |  9 ++++++++
 6 files changed, 85 insertions(+)
 create mode 100644 tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.errors.txt
 create mode 100644 tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.js
 create mode 100644 tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.symbols
 create mode 100644 tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.types
 create mode 100644 tsc/testdata/tests/cases/conformance/importDefer/importDeferOptionalCall.ts

diff --git a/tsc/internal/parser/parser.go b/tsc/internal/parser/parser.go
index 8b53a39b0cda3..a49ccfef55f1f 100644
--- a/tsc/internal/parser/parser.go
+++ b/tsc/internal/parser/parser.go
@@ -5241,6 +5241,9 @@ func (p *Parser) parseLeftHandSideExpressionOrHigher() *ast.Expression {
 			p.nextToken() // advance past the dot
 			expression = p.finishNode(p.factory.NewMetaProperty(ast.KindImportKeyword, p.parseIdentifierName()), pos)
 			if expression.Text() == "defer" {
+				if p.token == ast.KindQuestionDotToken && p.lookAhead((*Parser).nextTokenIsOpenParenOrLessThan) {
+					p.parseErrorAtCurrentToken(diagnostics.X_0_expected, scanner.TokenToString(ast.KindOpenParenToken))
+				}
 				if p.token == ast.KindOpenParenToken || p.token == ast.KindLessThanToken {
 					p.sourceFlags |= ast.NodeFlagsPossiblyContainsDynamicImport
 				}
diff --git a/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.errors.txt b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.errors.txt
new file mode 100644
index 0000000000000..e99e2334ca075
--- /dev/null
+++ b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.errors.txt
@@ -0,0 +1,16 @@
+b.ts(1,13): error TS1005: '(' expected.
+b.ts(2,13): error TS1005: '(' expected.
+
+
+==== x.ts (0 errors) ====
+    export const x = 1;
+    
+==== b.ts (2 errors) ====
+    import.defer?.("./x");
+                ~~
+!!! error TS1005: '(' expected.
+    import.defer?.<string>("./x");
+                ~~
+!!! error TS1005: '(' expected.
+    import.defer("./x");
+    
\ No newline at end of file
diff --git a/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.js b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.js
new file mode 100644
index 0000000000000..86e22802e0793
--- /dev/null
+++ b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.js
@@ -0,0 +1,18 @@
+//// [tests/cases/conformance/importDefer/importDeferOptionalCall.ts] ////
+
+//// [x.ts]
+export const x = 1;
+
+//// [b.ts]
+import.defer?.("./x");
+import.defer?.<string>("./x");
+import.defer("./x");
+
+
+//// [x.js]
+export const x = 1;
+//// [b.js]
+"use strict";
+import.defer?.("./x");
+import.defer?.("./x");
+import.defer("./x");
diff --git a/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.symbols b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.symbols
new file mode 100644
index 0000000000000..1c6d788e36628
--- /dev/null
+++ b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.symbols
@@ -0,0 +1,16 @@
+//// [tests/cases/conformance/importDefer/importDeferOptionalCall.ts] ////
+
+=== x.ts ===
+export const x = 1;
+>x : Symbol(x, Decl(x.ts, 0, 12))
+
+=== b.ts ===
+import.defer?.("./x");
+>"./x" : Symbol("./x", Decl(x.ts, 0, 0))
+
+import.defer?.<string>("./x");
+>"./x" : Symbol("./x", Decl(x.ts, 0, 0))
+
+import.defer("./x");
+>"./x" : Symbol("./x", Decl(x.ts, 0, 0))
+
diff --git a/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.types b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.types
new file mode 100644
index 0000000000000..cea9d6cf54487
--- /dev/null
+++ b/tsc/testdata/baselines/reference/conformance/importDeferOptionalCall.types
@@ -0,0 +1,23 @@
+//// [tests/cases/conformance/importDefer/importDeferOptionalCall.ts] ////
+
+=== x.ts ===
+export const x = 1;
+>x : 1
+>1 : 1
+
+=== b.ts ===
+import.defer?.("./x");
+>import.defer?.("./x") : Promise<typeof import("./x")>
+>defer : any
+>"./x" : "./x"
+
+import.defer?.<string>("./x");
+>import.defer?.<string>("./x") : Promise<typeof import("./x")>
+>defer : any
+>"./x" : "./x"
+
+import.defer("./x");
+>import.defer("./x") : Promise<typeof import("./x")>
+>defer : any
+>"./x" : "./x"
+
diff --git a/tsc/testdata/tests/cases/conformance/importDefer/importDeferOptionalCall.ts b/tsc/testdata/tests/cases/conformance/importDefer/importDeferOptionalCall.ts
new file mode 100644
index 0000000000000..650fec4838c50
--- /dev/null
+++ b/tsc/testdata/tests/cases/conformance/importDefer/importDeferOptionalCall.ts
@@ -0,0 +1,9 @@
+// @module: esnext
+
+// @filename: x.ts
+export const x = 1;
+
+// @filename: b.ts
+import.defer?.("./x");
+import.defer?.<string>("./x");
+import.defer("./x");