From 2b0ed605b6089978aee76394d57aafc0f630674e Mon Sep 17 00:00:00 2001
From: Tristan Swadell <tswadell@google.com>
Date: Thu, 9 Oct 2025 16:29:33 -0700
Subject: [PATCH] Introduce `string(bool)` support at runtime

PiperOrigin-RevId: 817382186
---
 eval/public/builtin_func_registrar_test.cc         | 5 +++++
 runtime/standard/type_conversion_functions.cc      | 9 +++++++++
 runtime/standard/type_conversion_functions_test.cc | 1 +
 3 files changed, 15 insertions(+)

diff --git a/eval/public/builtin_func_registrar_test.cc b/eval/public/builtin_func_registrar_test.cc
index 751dde19a..a11676a48 100644
--- a/eval/public/builtin_func_registrar_test.cc
+++ b/eval/public/builtin_func_registrar_test.cc
@@ -264,6 +264,11 @@ INSTANTIATE_TEST_SUITE_P(
          {},
          CelValue::CreateBool(true),
          OverflowChecksEnabled()},
+        {"StringToBool",
+         "string(true) + string(false)",
+         {},
+         CelValue::CreateStringView("truefalse"),
+         OverflowChecksEnabled()},
     }),
     [](const testing::TestParamInfo<BuiltinFuncParamsTest::ParamType>& info) {
       return info.param.test_name;
diff --git a/runtime/standard/type_conversion_functions.cc b/runtime/standard/type_conversion_functions.cc
index 6d47f5ba3..871f9892f 100644
--- a/runtime/standard/type_conversion_functions.cc
+++ b/runtime/standard/type_conversion_functions.cc
@@ -152,6 +152,15 @@ absl::Status RegisterStringConversionFunctions(FunctionRegistry& registry,
           registry);
   CEL_RETURN_IF_ERROR(status);
 
+  // bool -> string
+  status = UnaryFunctionAdapter<StringValue, bool>::RegisterGlobalOverload(
+      cel::builtin::kString,
+      [](bool value) -> StringValue {
+        return StringValue(value ? "true" : "false");
+      },
+      registry);
+  CEL_RETURN_IF_ERROR(status);
+
   // double -> string
   status = UnaryFunctionAdapter<StringValue, double>::RegisterGlobalOverload(
       cel::builtin::kString,
diff --git a/runtime/standard/type_conversion_functions_test.cc b/runtime/standard/type_conversion_functions_test.cc
index 1c433c7ab..ece8d454f 100644
--- a/runtime/standard/type_conversion_functions_test.cc
+++ b/runtime/standard/type_conversion_functions_test.cc
@@ -104,6 +104,7 @@ TEST(RegisterTypeConversionFunctions, RegisterStringConversionFunctions) {
   EXPECT_THAT(
       registry.FindStaticOverloads(builtin::kString, false, {Kind::kAny}),
       UnorderedElementsAre(
+          MatchesUnaryDescriptor(builtin::kString, false, Kind::kBool),
           MatchesUnaryDescriptor(builtin::kString, false, Kind::kInt),
           MatchesUnaryDescriptor(builtin::kString, false, Kind::kDouble),
           MatchesUnaryDescriptor(builtin::kString, false, Kind::kUint),