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feat: Add runtime function overload resolution based on Type information
## Motivation Currently, CEL-C++ only supports Type-level function overload resolution during the type-checking phase, while runtime function dispatch is limited to Kind-level resolution. This limitation prevents runtime selection of the most appropriate function overload when dealing with complex type hierarchies or when type information is available but not fully determined during static analysis. As described in issue #1484, the FunctionRegistry cannot distinguish overloads differing only by container parameter types (e.g., `list<int>` vs `list<string>`) because the current implementation only compares `cel::Kind` rather than precise `cel::Type` information during function registration and dispatch. ## Objective Enable runtime function overload resolution based on precise Type information by propagating overload IDs from the type-checking phase to the runtime execution phase. This enhancement allows the runtime to make more informed decisions about which function overload to invoke, improving both correctness and performance in scenarios where multiple overloads are available. ## Implementation ### Core Changes 1. **Enhanced Function Interface** - Extended `Function::Invoke()` method signature to accept an optional `overload_id` parameter (`absl::Span<const std::string>`) with default empty value - Updated all function adapter classes (Nullary, Unary, Binary, Ternary, Quaternary) to propagate overload ID information - Modified `CelFunction` implementation to support the new interface 2. **FlatExpr Builder Integration** - Added `reference_map_` field to `FlatExprVisitor` to access type-checking reference information during expression compilation - Implemented `FindReference()` helper method to retrieve overload IDs associated with specific expressions - Updated `CreateFunctionStep()` and `CreateDirectFunctionStep()` calls to pass overload ID information from the reference map - Added default parameter values to maintain backward compatibility 3. **Function Step Enhancement** - Extended `AbstractFunctionStep` constructor to accept overload IDs with move semantics - Updated both eager (`EagerFunctionStep`) and lazy (`LazyFunctionStep`) function step implementations to store overload ID information - Modified direct execution steps (`DirectFunctionStepImpl`) to store and utilize overload ID information - Enhanced the `Invoke()` helper function to pass overload IDs to the underlying function implementation ### Technical Details - **Backward Compatibility**: All function creation methods provide default empty overload ID parameters, ensuring existing code continues to work without modification ## Benefits 1. **Enhanced Precision**: Runtime can select optimal function overloads based on complete type information rather than just value kinds 2. **Better Performance**: Reduced need for runtime type checks and fallback mechanisms when precise overload information is available 3. **Improved Extensibility**: Framework for future enhancements requiring type-aware runtime behavior 4. **Maintained Compatibility**: All existing functionality preserved while adding new capabilities 5. **Resolves Container Type Disambiguation**: Enables proper handling of function overloads that differ only in container element types, addressing the "empty container" problem described in the issue ## Testing This change maintains full API and ABI compatibility through default parameter values. All existing tests should continue to pass without modification, and new tests can be added to verify type-aware overload resolution behavior. Closes #1484
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+89
-39
lines changed

11 files changed

+89
-39
lines changed

‎eval/compiler/flat_expr_builder.cc‎

Lines changed: 20 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -515,6 +515,7 @@ class FlatExprVisitor : public cel::AstVisitor {
515515
resolved_select_expr_(nullptr),
516516
options_(options),
517517
program_optimizers_(std::move(program_optimizers)),
518+
reference_map_(reference_map),
518519
issue_collector_(issue_collector),
519520
program_builder_(program_builder),
520521
extension_context_(extension_context),
@@ -1667,6 +1668,15 @@ class FlatExprVisitor : public cel::AstVisitor {
16671668
suppressed_branches_.insert(expr);
16681669
}
16691670

1671+
const cel::ast_internal::Reference& FindReference(const cel::Expr* expr) const {
1672+
auto it = reference_map_.find(expr->id());
1673+
if (it == reference_map_.end()) {
1674+
static const cel::ast_internal::Reference no_reference;
1675+
return no_reference;
1676+
}
1677+
return it->second;
1678+
}
1679+
16701680
void AddResolvedFunctionStep(const cel::CallExpr* call_expr,
16711681
const cel::Expr* expr,
16721682
absl::string_view function) {
@@ -1684,12 +1694,14 @@ class FlatExprVisitor : public cel::AstVisitor {
16841694
auto args = program_builder_.current()->ExtractRecursiveDependencies();
16851695
SetRecursiveStep(CreateDirectLazyFunctionStep(
16861696
expr->id(), *call_expr, std::move(args),
1687-
std::move(lazy_overloads)),
1697+
std::move(lazy_overloads),
1698+
FindReference(expr).overload_id()),
16881699
*depth + 1);
16891700
return;
16901701
}
16911702
AddStep(CreateFunctionStep(*call_expr, expr->id(),
1692-
std::move(lazy_overloads)));
1703+
std::move(lazy_overloads),
1704+
FindReference(expr).overload_id()));
16931705
return;
16941706
}
16951707

@@ -1718,11 +1730,14 @@ class FlatExprVisitor : public cel::AstVisitor {
17181730
auto args = program_builder_.current()->ExtractRecursiveDependencies();
17191731
SetRecursiveStep(
17201732
CreateDirectFunctionStep(expr->id(), *call_expr, std::move(args),
1721-
std::move(overloads)),
1733+
std::move(overloads),
1734+
FindReference(expr).overload_id()),
17221735
*recursion_depth + 1);
17231736
return;
17241737
}
1725-
AddStep(CreateFunctionStep(*call_expr, expr->id(), std::move(overloads)));
1738+
AddStep(CreateFunctionStep(*call_expr, expr->id(),
1739+
std::move(overloads),
1740+
FindReference(expr).overload_id()));
17261741
}
17271742

17281743
// Add a step to the program, taking ownership. If successful, returns the
@@ -1960,6 +1975,7 @@ class FlatExprVisitor : public cel::AstVisitor {
19601975
absl::flat_hash_set<const cel::Expr*> suppressed_branches_;
19611976
const cel::Expr* resume_from_suppressed_branch_ = nullptr;
19621977
std::vector<std::unique_ptr<ProgramOptimizer>> program_optimizers_;
1978+
const absl::flat_hash_map<int64_t, cel::ast_internal::Reference>& reference_map_;
19631979
IssueCollector& issue_collector_;
19641980

19651981
ProgramBuilder& program_builder_;

‎eval/compiler/flat_expr_builder_test.cc‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2397,7 +2397,8 @@ class UnknownFunctionImpl : public cel::Function {
23972397
absl::StatusOr<Value> Invoke(absl::Span<const Value> args,
23982398
const google::protobuf::DescriptorPool* ABSL_NONNULL,
23992399
google::protobuf::MessageFactory* ABSL_NONNULL,
2400-
google::protobuf::Arena* ABSL_NONNULL) const override {
2400+
google::protobuf::Arena* ABSL_NONNULL,
2401+
absl::Span<const std::string> overload_id) const override {
24012402
return cel::UnknownValue();
24022403
}
24032404
};

‎eval/eval/function_step.cc‎

Lines changed: 37 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -150,10 +150,11 @@ class AbstractFunctionStep : public ExpressionStepBase {
150150
public:
151151
// Constructs FunctionStep that uses overloads specified.
152152
AbstractFunctionStep(const std::string& name, size_t num_arguments,
153-
int64_t expr_id)
153+
int64_t expr_id, std::vector<std::string>&& overload_id)
154154
: ExpressionStepBase(expr_id),
155155
name_(name),
156-
num_arguments_(num_arguments) {}
156+
num_arguments_(num_arguments),
157+
overload_id_(std::move(overload_id)) {}
157158

158159
absl::Status Evaluate(ExecutionFrame* frame) const override;
159160

@@ -172,15 +173,18 @@ class AbstractFunctionStep : public ExpressionStepBase {
172173
protected:
173174
std::string name_;
174175
size_t num_arguments_;
176+
std::vector<std::string> overload_id_;
175177
};
176178

177179
inline absl::StatusOr<Value> Invoke(
178180
const cel::FunctionOverloadReference& overload, int64_t expr_id,
179-
absl::Span<const cel::Value> args, ExecutionFrameBase& frame) {
181+
absl::Span<const cel::Value> args, ExecutionFrameBase& frame,
182+
absl::Span<const std::string> overload_id) {
180183
CEL_ASSIGN_OR_RETURN(
181184
Value result,
182185
overload.implementation.Invoke(args, frame.descriptor_pool(),
183-
frame.message_factory(), frame.arena()));
186+
frame.message_factory(), frame.arena(),
187+
overload_id));
184188

185189
if (frame.unknown_function_results_enabled() &&
186190
IsUnknownFunctionResultError(result)) {
@@ -240,7 +244,7 @@ absl::StatusOr<Value> AbstractFunctionStep::DoEvaluate(
240244
// Overload found and is allowed to consume the arguments.
241245
if (matched_function.has_value() &&
242246
ShouldAcceptOverload(matched_function->descriptor, input_args)) {
243-
return Invoke(*matched_function, id(), input_args, *frame);
247+
return Invoke(*matched_function, id(), input_args, *frame, overload_id_);
244248
}
245249

246250
return NoOverloadResult(name_, input_args, *frame);
@@ -323,8 +327,9 @@ absl::StatusOr<ResolveResult> ResolveLazy(
323327
class EagerFunctionStep : public AbstractFunctionStep {
324328
public:
325329
EagerFunctionStep(std::vector<cel::FunctionOverloadReference> overloads,
326-
const std::string& name, size_t num_args, int64_t expr_id)
327-
: AbstractFunctionStep(name, num_args, expr_id),
330+
const std::string& name, size_t num_args, int64_t expr_id,
331+
std::vector<std::string>&& overload_id)
332+
: AbstractFunctionStep(name, num_args, expr_id, std::move(overload_id)),
328333
overloads_(std::move(overloads)) {}
329334

330335
absl::StatusOr<ResolveResult> ResolveFunction(
@@ -344,8 +349,9 @@ class LazyFunctionStep : public AbstractFunctionStep {
344349
LazyFunctionStep(const std::string& name, size_t num_args,
345350
bool receiver_style,
346351
std::vector<cel::FunctionRegistry::LazyOverload> providers,
347-
int64_t expr_id)
348-
: AbstractFunctionStep(name, num_args, expr_id),
352+
int64_t expr_id,
353+
std::vector<std::string>&& overload_id)
354+
: AbstractFunctionStep(name, num_args, expr_id, std::move(overload_id)),
349355
receiver_style_(receiver_style),
350356
providers_(std::move(providers)) {}
351357

@@ -404,10 +410,12 @@ class DirectFunctionStepImpl : public DirectExpressionStep {
404410
DirectFunctionStepImpl(
405411
int64_t expr_id, const std::string& name,
406412
std::vector<std::unique_ptr<DirectExpressionStep>> arg_steps,
407-
Resolver&& resolver)
413+
Resolver&& resolver,
414+
std::vector<std::string>&& overload_id)
408415
: DirectExpressionStep(expr_id),
409416
name_(name),
410417
arg_steps_(std::move(arg_steps)),
418+
overload_id_(std::move(overload_id)),
411419
resolver_(std::forward<Resolver>(resolver)) {}
412420

413421
absl::Status Evaluate(ExecutionFrameBase& frame, cel::Value& result,
@@ -439,7 +447,8 @@ class DirectFunctionStepImpl : public DirectExpressionStep {
439447
if (resolved_function.has_value() &&
440448
ShouldAcceptOverload(resolved_function->descriptor, args)) {
441449
CEL_ASSIGN_OR_RETURN(result,
442-
Invoke(*resolved_function, expr_id_, args, frame));
450+
Invoke(*resolved_function, expr_id_, args, frame,
451+
overload_id_));
443452

444453
return absl::OkStatus();
445454
}
@@ -468,6 +477,7 @@ class DirectFunctionStepImpl : public DirectExpressionStep {
468477
friend Resolver;
469478
std::string name_;
470479
std::vector<std::unique_ptr<DirectExpressionStep>> arg_steps_;
480+
std::vector<std::string> overload_id_;
471481
Resolver resolver_;
472482
};
473483

@@ -476,39 +486,47 @@ class DirectFunctionStepImpl : public DirectExpressionStep {
476486
std::unique_ptr<DirectExpressionStep> CreateDirectFunctionStep(
477487
int64_t expr_id, const cel::CallExpr& call,
478488
std::vector<std::unique_ptr<DirectExpressionStep>> deps,
479-
std::vector<cel::FunctionOverloadReference> overloads) {
489+
std::vector<cel::FunctionOverloadReference> overloads,
490+
std::vector<std::string> overload_id) {
480491
return std::make_unique<DirectFunctionStepImpl<StaticResolver>>(
481492
expr_id, call.function(), std::move(deps),
482-
StaticResolver(std::move(overloads)));
493+
StaticResolver(std::move(overloads)),
494+
std::move(overload_id));
483495
}
484496

485497
std::unique_ptr<DirectExpressionStep> CreateDirectLazyFunctionStep(
486498
int64_t expr_id, const cel::CallExpr& call,
487499
std::vector<std::unique_ptr<DirectExpressionStep>> deps,
488-
std::vector<cel::FunctionRegistry::LazyOverload> providers) {
500+
std::vector<cel::FunctionRegistry::LazyOverload> providers,
501+
std::vector<std::string> overload_id) {
489502
return std::make_unique<DirectFunctionStepImpl<LazyResolver>>(
490503
expr_id, call.function(), std::move(deps),
491-
LazyResolver(std::move(providers), call.function(), call.has_target()));
504+
LazyResolver(std::move(providers), call.function(), call.has_target()),
505+
std::move(overload_id));
492506
}
493507

494508
absl::StatusOr<std::unique_ptr<ExpressionStep>> CreateFunctionStep(
495509
const cel::CallExpr& call_expr, int64_t expr_id,
496-
std::vector<cel::FunctionRegistry::LazyOverload> lazy_overloads) {
510+
std::vector<cel::FunctionRegistry::LazyOverload> lazy_overloads,
511+
std::vector<std::string> overload_id) {
497512
bool receiver_style = call_expr.has_target();
498513
size_t num_args = call_expr.args().size() + (receiver_style ? 1 : 0);
499514
const std::string& name = call_expr.function();
500515
return std::make_unique<LazyFunctionStep>(name, num_args, receiver_style,
501-
std::move(lazy_overloads), expr_id);
516+
std::move(lazy_overloads), expr_id,
517+
std::move(overload_id));
502518
}
503519

504520
absl::StatusOr<std::unique_ptr<ExpressionStep>> CreateFunctionStep(
505521
const cel::CallExpr& call_expr, int64_t expr_id,
506-
std::vector<cel::FunctionOverloadReference> overloads) {
522+
std::vector<cel::FunctionOverloadReference> overloads,
523+
std::vector<std::string> overload_id) {
507524
bool receiver_style = call_expr.has_target();
508525
size_t num_args = call_expr.args().size() + (receiver_style ? 1 : 0);
509526
const std::string& name = call_expr.function();
510527
return std::make_unique<EagerFunctionStep>(std::move(overloads), name,
511-
num_args, expr_id);
528+
num_args, expr_id,
529+
std::move(overload_id));
512530
}
513531

514532
} // namespace google::api::expr::runtime

‎eval/eval/function_step.h‎

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -20,28 +20,32 @@ namespace google::api::expr::runtime {
2020
std::unique_ptr<DirectExpressionStep> CreateDirectFunctionStep(
2121
int64_t expr_id, const cel::CallExpr& call,
2222
std::vector<std::unique_ptr<DirectExpressionStep>> deps,
23-
std::vector<cel::FunctionOverloadReference> overloads);
23+
std::vector<cel::FunctionOverloadReference> overloads,
24+
std::vector<std::string> overload_id = {});
2425

2526
// Factory method for Call-based execution step where the function has been
2627
// statically resolved from a set of lazy functions configured in the
2728
// CelFunctionRegistry.
2829
std::unique_ptr<DirectExpressionStep> CreateDirectLazyFunctionStep(
2930
int64_t expr_id, const cel::CallExpr& call,
3031
std::vector<std::unique_ptr<DirectExpressionStep>> deps,
31-
std::vector<cel::FunctionRegistry::LazyOverload> providers);
32+
std::vector<cel::FunctionRegistry::LazyOverload> providers,
33+
std::vector<std::string> overload_id = {});
3234

3335
// Factory method for Call-based execution step where the function will be
3436
// resolved at runtime (lazily) from an input Activation.
3537
absl::StatusOr<std::unique_ptr<ExpressionStep>> CreateFunctionStep(
3638
const cel::CallExpr& call, int64_t expr_id,
37-
std::vector<cel::FunctionRegistry::LazyOverload> lazy_overloads);
39+
std::vector<cel::FunctionRegistry::LazyOverload> lazy_overloads,
40+
std::vector<std::string> overload_id = {});
3841

3942
// Factory method for Call-based execution step where the function has been
4043
// statically resolved from a set of eagerly functions configured in the
4144
// CelFunctionRegistry.
4245
absl::StatusOr<std::unique_ptr<ExpressionStep>> CreateFunctionStep(
4346
const cel::CallExpr& call, int64_t expr_id,
44-
std::vector<cel::FunctionOverloadReference> overloads);
47+
std::vector<cel::FunctionOverloadReference> overloads,
48+
std::vector<std::string> overload_id = {});
4549

4650
} // namespace google::api::expr::runtime
4751

‎eval/public/cel_function.cc‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -57,7 +57,8 @@ absl::StatusOr<Value> CelFunction::Invoke(
5757
absl::Span<const cel::Value> arguments,
5858
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
5959
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
60-
google::protobuf::Arena* ABSL_NONNULL arena) const {
60+
google::protobuf::Arena* ABSL_NONNULL arena,
61+
absl::Span<const std::string> overload_id) const {
6162
std::vector<CelValue> legacy_args;
6263
legacy_args.reserve(arguments.size());
6364

‎eval/public/cel_function.h‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -69,7 +69,8 @@ class CelFunction : public ::cel::Function {
6969
absl::Span<const cel::Value> arguments,
7070
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
7171
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
72-
google::protobuf::Arena* ABSL_NONNULL arena) const override;
72+
google::protobuf::Arena* ABSL_NONNULL arena,
73+
absl::Span<const std::string> overload_id) const override;
7374

7475
// CelFunction descriptor
7576
const CelFunctionDescriptor& descriptor() const { return descriptor_; }

‎runtime/activation_test.cc‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -69,7 +69,8 @@ class FunctionImpl : public cel::Function {
6969
absl::StatusOr<Value> Invoke(absl::Span<const Value> args,
7070
const google::protobuf::DescriptorPool* ABSL_NONNULL,
7171
google::protobuf::MessageFactory* ABSL_NONNULL,
72-
google::protobuf::Arena* ABSL_NONNULL) const override {
72+
google::protobuf::Arena* ABSL_NONNULL,
73+
absl::Span<const std::string> overload_id) const override {
7374
return NullValue();
7475
}
7576
};

‎runtime/function.h‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -47,7 +47,8 @@ class Function {
4747
absl::Span<const Value> args,
4848
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
4949
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
50-
google::protobuf::Arena* ABSL_NONNULL arena) const = 0;
50+
google::protobuf::Arena* ABSL_NONNULL arena,
51+
absl::Span<const std::string> overload_id = {}) const = 0;
5152
};
5253

5354
} // namespace cel

‎runtime/function_adapter.h‎

Lines changed: 10 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -228,7 +228,8 @@ class NullaryFunctionAdapter
228228
absl::Span<const Value> args,
229229
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
230230
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
231-
google::protobuf::Arena* ABSL_NONNULL arena) const override {
231+
google::protobuf::Arena* ABSL_NONNULL arena,
232+
absl::Span<const std::string> overload_id) const override {
232233
if (args.size() != 0) {
233234
return absl::InvalidArgumentError(
234235
"unexpected number of arguments for nullary function");
@@ -305,7 +306,8 @@ class UnaryFunctionAdapter : public RegisterHelper<UnaryFunctionAdapter<T, U>> {
305306
absl::Span<const Value> args,
306307
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
307308
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
308-
google::protobuf::Arena* ABSL_NONNULL arena) const override {
309+
google::protobuf::Arena* ABSL_NONNULL arena,
310+
absl::Span<const std::string> overload_id) const override {
309311
using ArgTraits = runtime_internal::AdaptedTypeTraits<U>;
310312
if (args.size() != 1) {
311313
return absl::InvalidArgumentError(
@@ -437,7 +439,8 @@ class BinaryFunctionAdapter
437439
absl::Span<const Value> args,
438440
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
439441
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
440-
google::protobuf::Arena* ABSL_NONNULL arena) const override {
442+
google::protobuf::Arena* ABSL_NONNULL arena,
443+
absl::Span<const std::string> overload_id) const override {
441444
using Arg1Traits = runtime_internal::AdaptedTypeTraits<U>;
442445
using Arg2Traits = runtime_internal::AdaptedTypeTraits<V>;
443446
if (args.size() != 2) {
@@ -509,7 +512,8 @@ class TernaryFunctionAdapter
509512
absl::Span<const Value> args,
510513
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
511514
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
512-
google::protobuf::Arena* ABSL_NONNULL arena) const override {
515+
google::protobuf::Arena* ABSL_NONNULL arena,
516+
absl::Span<const std::string> overload_id) const override {
513517
using Arg1Traits = runtime_internal::AdaptedTypeTraits<U>;
514518
using Arg2Traits = runtime_internal::AdaptedTypeTraits<V>;
515519
using Arg3Traits = runtime_internal::AdaptedTypeTraits<W>;
@@ -588,7 +592,8 @@ class QuaternaryFunctionAdapter
588592
absl::Span<const Value> args,
589593
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
590594
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
591-
google::protobuf::Arena* ABSL_NONNULL arena) const override {
595+
google::protobuf::Arena* ABSL_NONNULL arena,
596+
absl::Span<const std::string> overload_id) const override {
592597
using Arg1Traits = runtime_internal::AdaptedTypeTraits<U>;
593598
using Arg2Traits = runtime_internal::AdaptedTypeTraits<V>;
594599
using Arg3Traits = runtime_internal::AdaptedTypeTraits<W>;

‎runtime/function_registry_test.cc‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -54,7 +54,8 @@ class ConstIntFunction : public cel::Function {
5454
absl::Span<const Value> args,
5555
const google::protobuf::DescriptorPool* ABSL_NONNULL descriptor_pool,
5656
google::protobuf::MessageFactory* ABSL_NONNULL message_factory,
57-
google::protobuf::Arena* ABSL_NONNULL arena) const override {
57+
google::protobuf::Arena* ABSL_NONNULL arena,
58+
absl::Span<const std::string> overload_id) const override {
5859
return IntValue(42);
5960
}
6061
};

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