From fa2ffe2dd16871a893701b7771df729156d9d6f7 Mon Sep 17 00:00:00 2001
From: Sysix <3897725+Sysix@users.noreply.github.com>
Date: Sun, 18 Jan 2026 10:40:19 +0000
Subject: [PATCH] feat(parser): add ts error 1266 for `TSTupleElement` (#18145)

---
 crates/oxc_parser/src/diagnostics.rs            |  9 +++++++++
 crates/oxc_parser/src/ts/types.rs               |  9 +++++++++
 tasks/coverage/snapshots/parser_typescript.snap | 10 ++++++++++
 3 files changed, 28 insertions(+)

diff --git a/crates/oxc_parser/src/diagnostics.rs b/crates/oxc_parser/src/diagnostics.rs
index 0fd7e7c786f43..c4844405e73cd 100644
--- a/crates/oxc_parser/src/diagnostics.rs
+++ b/crates/oxc_parser/src/diagnostics.rs
@@ -353,6 +353,15 @@ pub fn rest_element_cannot_follow_another_rest_element(
         .with_labels([span.label("Second rest element here"), seen_span.label("First seen here")])
 }
 
+/// An optional element cannot follow a rest element. ts(1266)
+#[cold]
+pub fn optional_element_cannot_follow_rest_element(span: Span, rest_span: Span) -> OxcDiagnostic {
+    ts_error("1266", "An optional element cannot follow a rest element.").with_labels([
+        span.label("Optional element here"),
+        rest_span.label("Rest element seen here"),
+    ])
+}
+
 // A type-only import can specify a default import or named bindings, but not both. ts(1363)
 #[cold]
 pub fn type_only_import_default_and_named(specifier_span: Span) -> OxcDiagnostic {
diff --git a/crates/oxc_parser/src/ts/types.rs b/crates/oxc_parser/src/ts/types.rs
index a3faee59cf185..37cb6b05aca3b 100644
--- a/crates/oxc_parser/src/ts/types.rs
+++ b/crates/oxc_parser/src/ts/types.rs
@@ -926,6 +926,15 @@ impl<'a> ParserImpl<'a> {
                     }
                     seen_type_span = Some(tuple.span());
                 }
+
+                if let Some(seen_rest_span) = seen_type_span
+                    && matches!(tuple, TSTupleElement::TSOptionalType(_))
+                {
+                    me.error(diagnostics::optional_element_cannot_follow_rest_element(
+                        tuple.span(),
+                        seen_rest_span,
+                    ));
+                }
                 tuple
             });
         self.expect(Kind::RBrack);
diff --git a/tasks/coverage/snapshots/parser_typescript.snap b/tasks/coverage/snapshots/parser_typescript.snap
index d03b7576b2fc7..ad5de38b74bce 100644
--- a/tasks/coverage/snapshots/parser_typescript.snap
+++ b/tasks/coverage/snapshots/parser_typescript.snap
@@ -26514,6 +26514,16 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
  8 │ type V11 = [number, ...string[], boolean?];  // Error
    ╰────
 
+  × TS(1266): An optional element cannot follow a rest element.
+   ╭─[typescript/tests/cases/conformance/types/tuple/variadicTuples2.ts:8:21]
+ 7 │ type V10 = [number, ...string[], ...boolean[]];  // Error
+ 8 │ type V11 = [number, ...string[], boolean?];  // Error
+   ·                     ─────┬─────  ────┬───
+   ·                          │           ╰── Optional element here
+   ·                          ╰── Rest element seen here
+ 9 │ type V12 = [number, string?, boolean];  // Error
+   ╰────
+
   × TS(1265): A rest element cannot follow another rest element.
     ╭─[typescript/tests/cases/conformance/types/tuple/variadicTuples2.ts:11:13]
  10 │