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Add signature generation functions for types and function overloads #36

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2 changes: 1 addition & 1 deletion MODULE.bazel
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ bazel_dep(name = "bazel_skylib", version = "1.8.2")
# https://registry.bazel.build/modules/cel-cpp
bazel_dep(name = "cel-cpp", version = "0.14.0", repo_name = "com_google_cel_cpp")

# 03/30/2026
# 04/01/2026
_CEL_CPP_COMMIT = "5a3463337cf2a9b90b53833af2bbc1f35da90d64"

_CEL_CPP_SHA256 = "299be398d1495340eb92da31f9a0667e1351479752e8a567ac31c385e4aea73c"
Expand Down
112 changes: 90 additions & 22 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,76 @@ Resulting message type: <class '...TestAllTypes'>
Resulting message value: 123
```

### Custom functions

When configuring `cel.Env` you can supply custom functions. For each function
there needs to be a declaration and an implementation. The implementation, which
is a Python function, can be provided either as part of the declaration
or separately.

Let's say we want to be able to invoke this function from CEL expressions:
```python
def good_time_of_day(ampm, arg):
if ampm == 'am':
time_of_day = 'morning'
else:
time_of_day = 'afternoon'
return f"Good {time_of_day}, {arg}"
```

The implementation can be supplied along with the declaration:
```python
cel_env = cel.NewEnv(functions=[
cel.FunctionDecl(
"hello",
[
cel.Overload(
"hello(string,string)",
return_type=cel.Type.STRING,
parameters=[
cel.Type.STRING,
cel.Type.STRING,
],
impl=good_time_of_day,
)
],
)
])
```

It can also be provided separately in a dictionary that maps overload IDs to
their respective implementations:

```python
cel_env = cel.NewEnv(functions=[
cel.FunctionDecl(
"hello",
[
cel.Overload(
"hello(string,string)",
return_type=cel.Type.STRING,
parameters=[
cel.Type.STRING,
cel.Type.STRING,
],
)
],
)
],
function_impls={
"hello(string,string)": good_time_of_day,
})
```

Now that the function implementation is bound to the CEL environment,
we can invoke it from CEL like this:
```python
result = env.compile("hello('am', 'breakfast is ready!')").eval()
print(result.value()) # Good morning, breakfast is ready!
result = env.compile("hello('pm', 'tea is served.')").eval()
print(result.value()) # Good afternoon, tea is served.
```

### Extensions

#### Standard extensions
Expand Down Expand Up @@ -234,36 +304,34 @@ expr = cel_env.compile("my_func(1)")

To define a custom extension in C++, define a class extending
`cel_python::CelExtension`. There are two methods you will need to implement:
`ConfigureCompiler` and `ConfigureRuntime`. The implementations of these methods
use the same API as extensions written for the C++ CEL runtime. In fact,
`GetCompilerLibrary` and `ConfigureRuntime`. The implementations of these
methods use the same API as extensions written for the C++ CEL runtime. In fact,
extensions written for the C++ runtime can be used unchanged with
cel-expr-python - you would just need to write a trivial wrapper class invoking
the registration functions defined by the C++ extension.

```cpp
absl::Status ConfigureCompiler(
cel::CompilerBuilder& compiler_builder,
const proto2::DescriptorPool& descriptor_pool);
```
This method adds extension function definitions to the provided
`CompilerBuilder`, for example:

```cpp
absl::Status ConfigureCompiler(
cel::CompilerBuilder& compiler_builder,
const proto2::DescriptorPool& descriptor_pool) {
CEL_PYTHON_ASSIGN_OR_RETURN(
auto func_translate,
cel::MakeFunctionDecl("translate",
cel::MakeMemberOverloadDecl("translate_inst",
/*return_type=*/cel::StringType(),
/*target=*/cel::StringType(),
/*from_lang=*/cel::StringType(),
/*to_lang=*/cel::StringType())));
CEL_PYTHON_RETURN_IF_ERROR(
compiler_builder.GetCheckerBuilder().AddFunction(func_translate));
return absl::OkStatus();
}
cel::CompilerLibrary GetCompilerLibrary() {
return cel::CompilerLibrary(
"translate-ext",
[](cel::TypeCheckerBuilder& checker_builder) -> absl::Status {
CEL_PYTHON_ASSIGN_OR_RETURN(
auto func_translate,
cel::MakeFunctionDecl(
"translate",
cel::MakeMemberOverloadDecl("translate_inst",
/*return_type=*/cel::StringType(),
/*target=*/cel::StringType(),
/*from_lang=*/cel::StringType(),
/*to_lang=*/cel::StringType())));
CEL_PYTHON_RETURN_IF_ERROR(
checker_builder.AddFunction(func_translate));
return absl::OkStatus();
});
}
```

The other method registers the actual implementation
Expand Down
26 changes: 23 additions & 3 deletions cel_expr_python/BUILD
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,7 @@ pybind_extension(
"@com_google_absl//absl/types:optional",
"@com_google_absl//absl/types:span",
"@com_google_cel_cpp//checker:type_checker_builder",
"@com_google_cel_cpp//checker:type_checker_builder_factory",
"@com_google_cel_cpp//checker:validation_result",
"@com_google_cel_cpp//common:ast",
"@com_google_cel_cpp//common:ast_proto",
Expand All @@ -78,8 +79,13 @@ pybind_extension(
"@com_google_cel_cpp//compiler",
"@com_google_cel_cpp//env",
"@com_google_cel_cpp//env:config",
"@com_google_cel_cpp//env:env_runtime",
"@com_google_cel_cpp//env:env_std_extensions",
"@com_google_cel_cpp//env:env_yaml",
"@com_google_cel_cpp//env:runtime_std_extensions",
"@com_google_cel_cpp//extensions/protobuf:runtime_adapter",
"@com_google_cel_cpp//parser",
"@com_google_cel_cpp//parser:options",
"@com_google_cel_cpp//parser:parser_interface",
"@com_google_cel_cpp//runtime",
"@com_google_cel_cpp//runtime:activation",
Expand All @@ -88,7 +94,6 @@ pybind_extension(
"@com_google_cel_cpp//runtime:reference_resolver",
"@com_google_cel_cpp//runtime:runtime_builder",
"@com_google_cel_cpp//runtime:runtime_options",
"@com_google_cel_cpp//runtime:standard_runtime_builder_factory",
"@com_google_cel_spec//proto/cel/expr:checked_cc_proto",
"@com_google_cel_spec//proto/cel/expr:syntax_cc_proto",
"@com_google_protobuf//:protobuf",
Expand All @@ -99,14 +104,25 @@ pybind_extension(
# For pybind11-based CEL extensions.
pybind_library(
name = "cel_extension",
hdrs = ["cel_extension.h"],
srcs = [
"py_error_status.cc",
],
hdrs = [
"cel_extension.h",
"py_error_status.h",
],
visibility = ["//visibility:public"],
deps = [
":status_macros",
"@com_google_absl//absl/base:no_destructor",
"@com_google_absl//absl/container:flat_hash_map",
"@com_google_absl//absl/log:absl_check",
"@com_google_absl//absl/log:absl_log",
"@com_google_absl//absl/status",
"@com_google_absl//absl/status:statusor",
"@com_google_cel_cpp//compiler",
"@com_google_cel_cpp//runtime:runtime_builder",
"@com_google_cel_cpp//runtime:runtime_options",
"@com_google_protobuf//:protobuf",
],
)

Expand Down Expand Up @@ -135,6 +151,10 @@ py_test(
srcs = ["cel_env_test.py"],
deps = [
":cel",
"//cel_expr_python/ext:ext_bindings",
"//cel_expr_python/ext:ext_math",
"//cel_expr_python/ext:ext_optional",
"//cel_expr_python/ext:ext_strings",
"//testing:proto2_test_all_types_py_pb2",
"@com_google_absl_py//absl/testing:absltest",
],
Expand Down
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