From 64ee83d67ec10561803c75b5fe76589f040c7098 Mon Sep 17 00:00:00 2001
From: "Matthew \"strager\" Glazar" <strager.nds@gmail.com>
Date: Fri, 3 Nov 2023 22:28:06 -0400
Subject: [PATCH] fix(typescript): don't treat 'case await a: b;' as arrow
 function

quick-lint-js's error detection for 'async a: b => c' is too
optimistic. Disable it when the keyword prior is 'await' instead of
'async', fixing false positives for valid code such as the following:

    async function f() {
      switch (x) {
      case await y:
        z;
        break;
      }
    }
---
 docs/CHANGELOG.md                         |  2 +
 src/quick-lint-js/fe/parse-expression.cpp |  3 +-
 test/CMakeLists.txt                       |  1 +
 test/test-parse-typescript-statement.cpp  | 64 +++++++++++++++++++++++
 4 files changed, 69 insertions(+), 1 deletion(-)
 create mode 100644 test/test-parse-typescript-statement.cpp

diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index e6f2c0f69e..81879ea155 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -12,6 +12,8 @@ Semantic Versioning.
 
 * TypeScript support (still experimental):
   * `export as namespace` statements are now parsed.
+  * `case await x:` no longer treats `:` as if it was a type annotation colon in
+    an arrow function parameter list.
 
 ## 2.18.0 (2023-11-03)
 
diff --git a/src/quick-lint-js/fe/parse-expression.cpp b/src/quick-lint-js/fe/parse-expression.cpp
index a8ff40c322..22799f1280 100644
--- a/src/quick-lint-js/fe/parse-expression.cpp
+++ b/src/quick-lint-js/fe/parse-expression.cpp
@@ -1105,7 +1105,8 @@ Expression* Parser::parse_async_expression_only(
     }
 
     std::optional<Source_Code_Span> type_colon_span;
-    if (this->peek().type == Token_Type::colon && this->options_.typescript) {
+    if (is_async && this->peek().type == Token_Type::colon &&
+        this->options_.typescript) {
       // async param: Type => {}  // Invalid.
       type_colon_span = this->peek().span();
       Buffering_Visitor type_visits(&this->type_expression_memory_);
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 88b3bfff22..947457ffe3 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -167,6 +167,7 @@ quick_lint_js_add_executable(
   test-parse-typescript-module.cpp
   test-parse-typescript-namespace.cpp
   test-parse-typescript-object.cpp
+  test-parse-typescript-statement.cpp
   test-parse-typescript-this-parameters.cpp
   test-parse-typescript-type-alias.cpp
   test-parse-typescript-type.cpp
diff --git a/test/test-parse-typescript-statement.cpp b/test/test-parse-typescript-statement.cpp
new file mode 100644
index 0000000000..55c30723d1
--- /dev/null
+++ b/test/test-parse-typescript-statement.cpp
@@ -0,0 +1,64 @@
+// Copyright (C) 2020  Matthew "strager" Glazar
+// See end of file for extended copyright information.
+
+#include <algorithm>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <iterator>
+#include <quick-lint-js/array.h>
+#include <quick-lint-js/cli/cli-location.h>
+#include <quick-lint-js/container/concat.h>
+#include <quick-lint-js/container/padded-string.h>
+#include <quick-lint-js/container/string-view.h>
+#include <quick-lint-js/diag-collector.h>
+#include <quick-lint-js/diag-matcher.h>
+#include <quick-lint-js/diag/diagnostic-types.h>
+#include <quick-lint-js/fe/language.h>
+#include <quick-lint-js/fe/parse.h>
+#include <quick-lint-js/parse-support.h>
+#include <quick-lint-js/port/char8.h>
+#include <quick-lint-js/spy-visitor.h>
+#include <string>
+#include <string_view>
+#include <vector>
+
+using ::testing::ElementsAreArray;
+
+namespace quick_lint_js {
+namespace {
+class Test_Parse_TypeScript_Statement : public ::testing::Test {};
+
+TEST_F(Test_Parse_TypeScript_Statement,
+       await_in_case_is_not_arrow_function_with_missing_parens) {
+  // This code used to confuse
+  // Diag_Arrow_Parameter_With_Type_Annotation_Requires_Parentheses detection.
+  {
+    Spy_Visitor p = test_parse_and_visit_statement(
+        u8"switch (x) { case await a: b => c; }"_sv, no_diags,
+        typescript_options);
+    EXPECT_THAT(p.variable_uses,
+                ElementsAreArray({u8"x"_sv, u8"a"_sv, u8"c"_sv}));
+    EXPECT_THAT(p.variable_declarations,
+                ElementsAreArray({arrow_param_decl(u8"b"_sv)}));
+  }
+}
+}
+}
+
+// quick-lint-js finds bugs in JavaScript programs.
+// Copyright (C) 2020  Matthew "strager" Glazar
+//
+// This file is part of quick-lint-js.
+//
+// quick-lint-js is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// quick-lint-js is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with quick-lint-js.  If not, see <https://www.gnu.org/licenses/>.