Add is_contextual flag to FunctionDescriptor.

common/function_descriptor.h

@@ -26,30 +26,68 @@
 
 namespace cel {
 
+struct FunctionDescriptorOptions {
+  // If true (strict, default), error or unknown arguments are propagated
+  // instead of calling the function. if false (non-strict), the function may
+  // receive error or unknown values as arguments.
+  bool is_strict = true;
+
+  // Whether the function is impure or context-sensitive.
+  //
+  // Impure functions depend on state other than the arguments received during
+  // the CEL expression evaluation or have visible side effects. This breaks
+  // some of the assumptions of the CEL evaluation model. This flag is used as a
+  // hint to the planner that some optimizations are not safe or not effective.
+  bool is_contextual = false;
+};
+
 // Coarsely describes a function for the purpose of runtime resolution of
 // overloads.
 class FunctionDescriptor final {
  public:
   FunctionDescriptor(absl::string_view name, bool receiver_style,
-                     std::vector<Kind> types, bool is_strict = true)
-      : impl_(std::make_shared<Impl>(name, receiver_style, std::move(types),
-                                     is_strict)) {}
+                     std::vector<Kind> types, bool is_strict)
+      : impl_(std::make_shared<Impl>(
+            name, std::move(types), receiver_style,
+            FunctionDescriptorOptions{is_strict,
+                                      /*is_contextual=*/false})) {}
+
+  FunctionDescriptor(absl::string_view name, bool receiver_style,
+                     std::vector<Kind> types, bool is_strict,
+                     bool is_contextual)
+      : impl_(std::make_shared<Impl>(
+            name, std::move(types), receiver_style,
+            FunctionDescriptorOptions{is_strict, is_contextual})) {}
+
+  FunctionDescriptor(absl::string_view name, bool is_receiver_style,
+                     std::vector<Kind> types,
+                     FunctionDescriptorOptions options = {})
+      : impl_(std::make_shared<Impl>(name, std::move(types), is_receiver_style,
+                                     options)) {}
 
   // Function name.
   const std::string& name() const { return impl_->name; }
 
   // Whether function is receiver style i.e. true means arg0.name(args[1:]...).
-  bool receiver_style() const { return impl_->receiver_style; }
+  bool receiver_style() const { return impl_->is_receiver_style; }
 
-  // The argmument types the function accepts.
+  // The argument types the function accepts.
   //
   // TODO(uncreated-issue/17): make this kinds
   const std::vector<Kind>& types() const { return impl_->types; }
 
   // if true (strict, default), error or unknown arguments are propagated
   // instead of calling the function. if false (non-strict), the function may
   // receive error or unknown values as arguments.
-  bool is_strict() const { return impl_->is_strict; }
+  bool is_strict() const { return impl_->options.is_strict; }
+
+  // Whether the function is contextual (impure).
+  //
+  // Contextual functions depend on state other than the arguments received in
+  // the CEL expression evaluation or have visible side effects. This breaks
+  // some of the assumptions of CEL. This flag is used as a hint to the planner
+  // that some optimizations are not safe or not effective.
+  bool is_contextual() const { return impl_->options.is_contextual; }
 
   // Helper for matching a descriptor. This tests that the shape is the same --
   // |other| accepts the same number and types of arguments and is the same call
@@ -65,17 +103,17 @@ class FunctionDescriptor final {
 
  private:
   struct Impl final {
-    Impl(absl::string_view name, bool receiver_style, std::vector<Kind> types,
-         bool is_strict)
+    Impl(absl::string_view name, std::vector<Kind> types,
+         bool is_receiver_style, FunctionDescriptorOptions options)
         : name(name),
           types(std::move(types)),
-          receiver_style(receiver_style),
-          is_strict(is_strict) {}
+          is_receiver_style(is_receiver_style),
+          options(options) {}
 
     std::string name;
     std::vector<Kind> types;
-    bool receiver_style;
-    bool is_strict;
+    bool is_receiver_style;
+    FunctionDescriptorOptions options;
   };
 
   std::shared_ptr<const Impl> impl_;

eval/compiler/constant_folding.cc

@@ -155,6 +155,17 @@ IsConst IsConstExpr(const Expr& expr, const Resolver& resolver) {
         return IsConst::kNonConst;
       }
 
+      auto overloads =
+          resolver.FindOverloads(call.function(), call.has_target(), arg_len);
+      // Check for any contextual overloads. If there are any, we cowardly
+      // avoid constant folding instead of trying to check if one of the
+      // overloads would be safe to use.
+      for (const auto& overload : overloads) {
+        if (overload.descriptor.is_contextual()) {
+          return IsConst::kNonConst;
+        }
+      }
+
       return IsConst::kConditional;
     }
     case ExprKindCase::kUnspecifiedExpr:

runtime/BUILD

@@ -116,6 +116,7 @@ cc_library(
     deps =
         [
             ":function_registry",
+            "//common:function_descriptor",
             "@com_google_absl//absl/status",
             "@com_google_absl//absl/strings",
         ],
@@ -320,7 +321,7 @@ cc_library(
     deps = [
         ":runtime",
         ":runtime_builder",
-        "//common:native_type",
+        "//common:typeinfo",
         "//eval/compiler:constant_folding",
         "//internal:casts",
         "//internal:noop_delete",
@@ -342,11 +343,14 @@ cc_test(
     deps = [
         ":activation",
         ":constant_folding",
+        ":function",
         ":register_function_helper",
         ":runtime_builder",
         ":runtime_options",
         ":standard_runtime_builder_factory",
         "//base:function_adapter",
+        "//common:function_descriptor",
+        "//common:kind",
         "//common:value",
         "//extensions/protobuf:runtime_adapter",
         "//internal:testing",

runtime/constant_folding.cc

@@ -22,7 +22,7 @@
 #include "absl/log/absl_check.h"
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
-#include "common/native_type.h"
+#include "common/typeinfo.h"
 #include "eval/compiler/constant_folding.h"
 #include "internal/casts.h"
 #include "internal/noop_delete.h"
@@ -44,8 +44,7 @@ using ::cel::runtime_internal::RuntimeImpl;
 absl::StatusOr<RuntimeImpl* absl_nonnull> RuntimeImplFromBuilder(
     RuntimeBuilder& builder ABSL_ATTRIBUTE_LIFETIME_BOUND) {
   Runtime& runtime = RuntimeFriendAccess::GetMutableRuntime(builder);
-  if (RuntimeFriendAccess::RuntimeTypeId(runtime) !=
-      NativeTypeId::For<RuntimeImpl>()) {
+  if (RuntimeFriendAccess::RuntimeTypeId(runtime) != TypeId<RuntimeImpl>()) {
     return absl::UnimplementedError(
         "constant folding only supported on the default cel::Runtime "
         "implementation.");

runtime/constant_folding_test.cc

@@ -14,6 +14,7 @@
 
 #include "runtime/constant_folding.h"
 
+#include <memory>
 #include <string>
 #include <utility>
 #include <vector>
@@ -25,13 +26,13 @@
 #include "absl/strings/match.h"
 #include "absl/strings/str_cat.h"
 #include "base/function_adapter.h"
+#include "common/function_descriptor.h"
 #include "common/value.h"
 #include "extensions/protobuf/runtime_adapter.h"
 #include "internal/testing.h"
 #include "internal/testing_descriptor_pool.h"
 #include "parser/parser.h"
 #include "runtime/activation.h"
-#include "runtime/register_function_helper.h"
 #include "runtime/runtime_builder.h"
 #include "runtime/runtime_options.h"
 #include "runtime/standard_runtime_builder_factory.h"
@@ -82,8 +83,8 @@ TEST_P(ConstantFoldingExtTest, Runner) {
                        CreateStandardRuntimeBuilder(
                            internal::GetTestingDescriptorPool(), options));
 
-  auto status = RegisterHelper<BinaryFunctionAdapter<
-      absl::StatusOr<Value>, const StringValue&, const StringValue&>>::
+  auto status = BinaryFunctionAdapter<absl::StatusOr<Value>, const StringValue&,
+                                      const StringValue&>::
       RegisterGlobalOverload(
           "prepend",
           [](const StringValue& value, const StringValue& prefix) {
@@ -129,14 +130,99 @@ INSTANTIATE_TEST_SUITE_P(
          IsBoolValue(true)},
         {"runtime_error", "[1, 2, 3, 4].exists(x, ['4'].all(y, y <= x))",
          IsErrorValue("No matching overloads")},
-        // TODO(uncreated-issue/32): Depends on map creation
-        // {"map_create", "{'abc': 'def', 'abd': 'deg'}.size()", 2},
+        {"map_create", "{'abc': 'def', 'abd': 'deg'}.size()", IsIntValue(2)},
         {"custom_function", "prepend('def', 'abc') == 'abcdef'",
          IsBoolValue(true)}}),
 
     [](const testing::TestParamInfo<TestCase>& info) {
       return info.param.name;
     });
 
+TEST(ConstantFoldingExtTest, LazyFunctionNotFolded) {
+  google::protobuf::Arena arena;
+  RuntimeOptions options;
+
+  ASSERT_OK_AND_ASSIGN(cel::RuntimeBuilder builder,
+                       CreateStandardRuntimeBuilder(
+                           internal::GetTestingDescriptorPool(), options));
+  int call_count = 0;
+  using FunctionAdapter =
+      BinaryFunctionAdapter<absl::StatusOr<Value>, const StringValue&,
+                            const StringValue&>;
+  auto fn = FunctionAdapter::WrapFunction(
+      [&call_count](const StringValue& value, const StringValue& prefix) {
+        call_count++;
+        return StringValue(absl::StrCat(prefix.ToString(), value.ToString()));
+      });
+  FunctionDescriptor descriptor = FunctionAdapter::CreateDescriptor(
+      "lazy_prepend", /*receiver_style=*/false);
+  ASSERT_THAT(builder.function_registry().RegisterLazyFunction(descriptor),
+              IsOk());
+
+  ASSERT_THAT(EnableConstantFolding(builder), IsOk());
+
+  ASSERT_OK_AND_ASSIGN(auto runtime, std::move(builder).Build());
+
+  ASSERT_OK_AND_ASSIGN(ParsedExpr parsed_expr,
+                       Parse("lazy_prepend('def', 'abc') == 'abcdef'"));
+
+  ASSERT_OK_AND_ASSIGN(auto program, ProtobufRuntimeAdapter::CreateProgram(
+                                         *runtime, parsed_expr));
+  EXPECT_EQ(call_count, 0);
+  Activation activation;
+  activation.InsertFunction(descriptor, std::move(fn));
+
+  ASSERT_OK_AND_ASSIGN(Value result, program->Evaluate(&arena, activation));
+  EXPECT_EQ(call_count, 1);
+  EXPECT_THAT(result, IsBoolValue(true));
+
+  ASSERT_OK_AND_ASSIGN(result, program->Evaluate(&arena, activation));
+  EXPECT_EQ(call_count, 2);
+  EXPECT_THAT(result, IsBoolValue(true));
+}
+
+TEST(ConstantFoldingExtTest, ContextualFunctionNotFolded) {
+  google::protobuf::Arena arena;
+  RuntimeOptions options;
+  ASSERT_OK_AND_ASSIGN(cel::RuntimeBuilder builder,
+                       CreateStandardRuntimeBuilder(
+                           internal::GetTestingDescriptorPool(), options));
+  int call_count = 0;
+
+  auto status = BinaryFunctionAdapter<
+      absl::StatusOr<Value>, const StringValue&,
+      const StringValue&>::Register("contextual_prepend",
+                                    /*receiver_style=*/false,
+                                    [&call_count](const StringValue& value,
+                                                  const StringValue& prefix) {
+                                      call_count++;
+                                      return StringValue(absl::StrCat(
+                                          prefix.ToString(), value.ToString()));
+                                    },
+                                    builder.function_registry(),
+                                    {/*.is_strict=*/true,
+                                     /*is_contextual=*/true});
+  ASSERT_THAT(status, IsOk());
+
+  ASSERT_THAT(EnableConstantFolding(builder), IsOk());
+
+  ASSERT_OK_AND_ASSIGN(auto runtime, std::move(builder).Build());
+
+  ASSERT_OK_AND_ASSIGN(ParsedExpr parsed_expr,
+                       Parse("contextual_prepend('def', 'abc') == 'abcdef'"));
+
+  ASSERT_OK_AND_ASSIGN(auto program, ProtobufRuntimeAdapter::CreateProgram(
+                                         *runtime, parsed_expr));
+  EXPECT_EQ(call_count, 0);
+  Activation activation;
+  ASSERT_OK_AND_ASSIGN(Value value, program->Evaluate(&arena, activation));
+  EXPECT_EQ(call_count, 1);
+  EXPECT_THAT(value, IsBoolValue(true));
+
+  ASSERT_OK_AND_ASSIGN(value, program->Evaluate(&arena, activation));
+  EXPECT_EQ(call_count, 2);
+  EXPECT_THAT(value, IsBoolValue(true));
+}
+
 }  // namespace
 }  // namespace cel::extensions