css2: Support stringifying parse errors

css2/tokenizer.cpp

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: 2021-2024 Robin Lindén <[email protected]>
+// SPDX-FileCopyrightText: 2021-2025 Robin Lindén <[email protected]>
 // SPDX-FileCopyrightText: 2022 Mikael Larsson <[email protected]>
 //
 // SPDX-License-Identifier: BSD-2-Clause
@@ -42,6 +42,21 @@ constexpr bool is_digit(std::optional<char> c) {
 
 } // namespace
 
+std::string_view to_string(ParseError e) {
+    switch (e) {
+        case ParseError::EofInComment:
+            return "EofInComment";
+        case ParseError::EofInEscapeSequence:
+            return "EofInEscapeSequence";
+        case ParseError::EofInString:
+            return "EofInString";
+        case ParseError::NewlineInString:
+            return "NewlineInString";
+    }
+
+    return "Unknown parse error";
+}
+
 void Tokenizer::run() {
     while (true) {
         switch (state_) {

css2/tokenizer.h

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: 2021-2024 Robin Lindén <[email protected]>
+// SPDX-FileCopyrightText: 2021-2025 Robin Lindén <[email protected]>
 // SPDX-FileCopyrightText: 2022 Mikael Larsson <[email protected]>
 //
 // SPDX-License-Identifier: BSD-2-Clause
@@ -39,6 +39,8 @@ enum class ParseError : std::uint8_t {
     NewlineInString,
 };
 
+std::string_view to_string(ParseError);
+
 class Tokenizer {
 public:
     Tokenizer(std::string_view input, std::function<void(Token &&)> on_emit, std::function<void(ParseError)> on_error)

css2/tokenizer_test.cpp

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: 2021-2024 Robin Lindén <[email protected]>
+// SPDX-FileCopyrightText: 2021-2025 Robin Lindén <[email protected]>
 // SPDX-FileCopyrightText: 2022 Mikael Larsson <[email protected]>
 //
 // SPDX-License-Identifier: BSD-2-Clause
@@ -68,6 +68,23 @@ void expect_error(
 
 int main() {
     etest::Suite s{};
+
+    s.add_test("to_string(ParseError)", [](etest::IActions &a) {
+        static constexpr auto kFirstError = ParseError::EofInComment;
+        static constexpr auto kLastError = ParseError::NewlineInString;
+
+        auto error = static_cast<int>(kFirstError);
+        a.expect_eq(error, 0);
+
+        while (error <= static_cast<int>(kLastError)) {
+            a.expect(to_string(static_cast<ParseError>(error)) != "Unknown parse error",
+                    std::to_string(error) + " is missing an error message");
+            error += 1;
+        }
+
+        a.expect_eq(to_string(static_cast<ParseError>(error + 1)), "Unknown parse error");
+    });
+
     s.add_test("delimiter", [](etest::IActions &a) {
         auto output = run_tokenizer(a, "?");