build: move e2e dependencies into e2e/go.mod

Several packages are only used while running the e2e suite. These
packages are less important to update, as the they can not influence the
final executable that is part of the Ceph-CSI container-image.

By moving these dependencies out of the main Ceph-CSI go.mod, it is
easier to identify if a reported CVE affects Ceph-CSI, or only the
testing (like most of the Kubernetes CVEs).

Signed-off-by: Niels de Vos <ndevos@ibm.com>

e2e/vendor/github.com/google/cel-go/common/decls/BUILD.bazel

@@ -0,0 +1,39 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+package(
+    default_visibility = ["//visibility:public"],
+    licenses = ["notice"],  # Apache 2.0
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "decls.go",
+    ],
+    importpath = "github.com/google/cel-go/common/decls",
+    deps = [
+        "//checker/decls:go_default_library",
+        "//common/functions:go_default_library",
+        "//common/types:go_default_library",
+        "//common/types/ref:go_default_library",
+        "//common/types/traits:go_default_library",
+        "@org_golang_google_genproto_googleapis_api//expr/v1alpha1:go_default_library",
+    ],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = [
+        "decls_test.go",
+    ],
+    embed = [":go_default_library"],
+    deps = [
+        "//checker/decls:go_default_library",
+        "//common/overloads:go_default_library",
+        "//common/types:go_default_library",
+        "//common/types/ref:go_default_library",
+        "//common/types/traits:go_default_library",
+        "@org_golang_google_genproto_googleapis_api//expr/v1alpha1:go_default_library",
+        "@org_golang_google_protobuf//proto:go_default_library",
+    ],
+)

e2e/vendor/github.com/google/cel-go/common/decls/decls.go

@@ -0,0 +1,846 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package decls contains function and variable declaration structs and helper methods.
+package decls
+
+import (
+	"fmt"
+	"strings"
+
+	chkdecls "github.com/google/cel-go/checker/decls"
+	"github.com/google/cel-go/common/functions"
+	"github.com/google/cel-go/common/types"
+	"github.com/google/cel-go/common/types/ref"
+
+	exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
+)
+
+// NewFunction creates a new function declaration with a set of function options to configure overloads
+// and function definitions (implementations).
+//
+// Functions are checked for name collisions and singleton redefinition.
+func NewFunction(name string, opts ...FunctionOpt) (*FunctionDecl, error) {
+	fn := &FunctionDecl{
+		name:             name,
+		overloads:        map[string]*OverloadDecl{},
+		overloadOrdinals: []string{},
+	}
+	var err error
+	for _, opt := range opts {
+		fn, err = opt(fn)
+		if err != nil {
+			return nil, err
+		}
+	}
+	if len(fn.overloads) == 0 {
+		return nil, fmt.Errorf("function %s must have at least one overload", name)
+	}
+	return fn, nil
+}
+
+// FunctionDecl defines a function name, overload set, and optionally a singleton definition for all
+// overload instances.
+type FunctionDecl struct {
+	name string
+
+	// overloads associated with the function name.
+	overloads map[string]*OverloadDecl
+
+	// singleton implementation of the function for all overloads.
+	//
+	// If this option is set, an error will occur if any overloads specify a per-overload implementation
+	// or if another function with the same name attempts to redefine the singleton.
+	singleton *functions.Overload
+
+	// disableTypeGuards is a performance optimization to disable detailed runtime type checks which could
+	// add overhead on common operations. Setting this option true leaves error checks and argument checks
+	// intact.
+	disableTypeGuards bool
+
+	// state indicates that the binding should be provided as a declaration, as a runtime binding, or both.
+	state declarationState
+
+	// overloadOrdinals indicates the order in which the overload was declared.
+	overloadOrdinals []string
+}
+
+type declarationState int
+
+const (
+	declarationStateUnset declarationState = iota
+	declarationDisabled
+	declarationEnabled
+)
+
+// Name returns the function name in human-readable terms, e.g. 'contains' of 'math.least'
+func (f *FunctionDecl) Name() string {
+	if f == nil {
+		return ""
+	}
+	return f.name
+}
+
+// IsDeclarationDisabled indicates that the function implementation should be added to the dispatcher, but the
+// declaration should not be exposed for use in expressions.
+func (f *FunctionDecl) IsDeclarationDisabled() bool {
+	return f.state == declarationDisabled
+}
+
+// Merge combines an existing function declaration with another.
+//
+// If a function is extended, by say adding new overloads to an existing function, then it is merged with the
+// prior definition of the function at which point its overloads must not collide with pre-existing overloads
+// and its bindings (singleton, or per-overload) must not conflict with previous definitions either.
+func (f *FunctionDecl) Merge(other *FunctionDecl) (*FunctionDecl, error) {
+	if f == other {
+		return f, nil
+	}
+	if f.Name() != other.Name() {
+		return nil, fmt.Errorf("cannot merge unrelated functions. %s and %s", f.Name(), other.Name())
+	}
+	merged := &FunctionDecl{
+		name:             f.Name(),
+		overloads:        make(map[string]*OverloadDecl, len(f.overloads)),
+		singleton:        f.singleton,
+		overloadOrdinals: make([]string, len(f.overloads)),
+		// if one function is expecting type-guards and the other is not, then they
+		// must not be disabled.
+		disableTypeGuards: f.disableTypeGuards && other.disableTypeGuards,
+		// default to the current functions declaration state.
+		state: f.state,
+	}
+	// If the other state indicates that the declaration should be explicitly enabled or
+	// disabled, then update the merged state with the most recent value.
+	if other.state != declarationStateUnset {
+		merged.state = other.state
+	}
+	// baseline copy of the overloads and their ordinals
+	copy(merged.overloadOrdinals, f.overloadOrdinals)
+	for oID, o := range f.overloads {
+		merged.overloads[oID] = o
+	}
+	// overloads and their ordinals are added from the left
+	for _, oID := range other.overloadOrdinals {
+		o := other.overloads[oID]
+		err := merged.AddOverload(o)
+		if err != nil {
+			return nil, fmt.Errorf("function declaration merge failed: %v", err)
+		}
+	}
+	if other.singleton != nil {
+		if merged.singleton != nil && merged.singleton != other.singleton {
+			return nil, fmt.Errorf("function already has a singleton binding: %s", f.Name())
+		}
+		merged.singleton = other.singleton
+	}
+	return merged, nil
+}
+
+// AddOverload ensures that the new overload does not collide with an existing overload signature;
+// however, if the function signatures are identical, the implementation may be rewritten as its
+// difficult to compare functions by object identity.
+func (f *FunctionDecl) AddOverload(overload *OverloadDecl) error {
+	if f == nil {
+		return fmt.Errorf("nil function cannot add overload: %s", overload.ID())
+	}
+	for oID, o := range f.overloads {
+		if oID != overload.ID() && o.SignatureOverlaps(overload) {
+			return fmt.Errorf("overload signature collision in function %s: %s collides with %s", f.Name(), oID, overload.ID())
+		}
+		if oID == overload.ID() {
+			if o.SignatureEquals(overload) && o.IsNonStrict() == overload.IsNonStrict() {
+				// Allow redefinition of an overload implementation so long as the signatures match.
+				if overload.hasBinding() {
+					f.overloads[oID] = overload
+				}
+				return nil
+			}
+			return fmt.Errorf("overload redefinition in function. %s: %s has multiple definitions", f.Name(), oID)
+		}
+	}
+	f.overloadOrdinals = append(f.overloadOrdinals, overload.ID())
+	f.overloads[overload.ID()] = overload
+	return nil
+}
+
+// OverloadDecls returns the overload declarations in the order in which they were declared.
+func (f *FunctionDecl) OverloadDecls() []*OverloadDecl {
+	if f == nil {
+		return []*OverloadDecl{}
+	}
+	overloads := make([]*OverloadDecl, 0, len(f.overloads))
+	for _, oID := range f.overloadOrdinals {
+		overloads = append(overloads, f.overloads[oID])
+	}
+	return overloads
+}
+
+// Bindings produces a set of function bindings, if any are defined.
+func (f *FunctionDecl) Bindings() ([]*functions.Overload, error) {
+	if f == nil {
+		return []*functions.Overload{}, nil
+	}
+	overloads := []*functions.Overload{}
+	nonStrict := false
+	for _, oID := range f.overloadOrdinals {
+		o := f.overloads[oID]
+		if o.hasBinding() {
+			overload := &functions.Overload{
+				Operator:     o.ID(),
+				Unary:        o.guardedUnaryOp(f.Name(), f.disableTypeGuards),
+				Binary:       o.guardedBinaryOp(f.Name(), f.disableTypeGuards),
+				Function:     o.guardedFunctionOp(f.Name(), f.disableTypeGuards),
+				OperandTrait: o.OperandTrait(),
+				NonStrict:    o.IsNonStrict(),
+			}
+			overloads = append(overloads, overload)
+			nonStrict = nonStrict || o.IsNonStrict()
+		}
+	}
+	if f.singleton != nil {
+		if len(overloads) != 0 {
+			return nil, fmt.Errorf("singleton function incompatible with specialized overloads: %s", f.Name())
+		}
+		overloads = []*functions.Overload{
+			{
+				Operator:     f.Name(),
+				Unary:        f.singleton.Unary,
+				Binary:       f.singleton.Binary,
+				Function:     f.singleton.Function,
+				OperandTrait: f.singleton.OperandTrait,
+			},
+		}
+		// fall-through to return single overload case.
+	}
+	if len(overloads) == 0 {
+		return overloads, nil
+	}
+	// Single overload. Replicate an entry for it using the function name as well.
+	if len(overloads) == 1 {
+		if overloads[0].Operator == f.Name() {
+			return overloads, nil
+		}
+		return append(overloads, &functions.Overload{
+			Operator:     f.Name(),
+			Unary:        overloads[0].Unary,
+			Binary:       overloads[0].Binary,
+			Function:     overloads[0].Function,
+			NonStrict:    overloads[0].NonStrict,
+			OperandTrait: overloads[0].OperandTrait,
+		}), nil
+	}
+	// All of the defined overloads are wrapped into a top-level function which
+	// performs dynamic dispatch to the proper overload based on the argument types.
+	bindings := append([]*functions.Overload{}, overloads...)
+	funcDispatch := func(args ...ref.Val) ref.Val {
+		for _, oID := range f.overloadOrdinals {
+			o := f.overloads[oID]
+			// During dynamic dispatch over multiple functions, signature agreement checks
+			// are preserved in order to assist with the function resolution step.
+			switch len(args) {
+			case 1:
+				if o.unaryOp != nil && o.matchesRuntimeSignature(f.disableTypeGuards, args...) {
+					return o.unaryOp(args[0])
+				}
+			case 2:
+				if o.binaryOp != nil && o.matchesRuntimeSignature(f.disableTypeGuards, args...) {
+					return o.binaryOp(args[0], args[1])
+				}
+			}
+			if o.functionOp != nil && o.matchesRuntimeSignature(f.disableTypeGuards, args...) {
+				return o.functionOp(args...)
+			}
+			// eventually this will fall through to the noSuchOverload below.
+		}
+		return MaybeNoSuchOverload(f.Name(), args...)
+	}
+	function := &functions.Overload{
+		Operator:  f.Name(),
+		Function:  funcDispatch,
+		NonStrict: nonStrict,
+	}
+	return append(bindings, function), nil
+}
+
+// MaybeNoSuchOverload determines whether to propagate an error if one is provided as an argument, or
+// to return an unknown set, or to produce a new error for a missing function signature.
+func MaybeNoSuchOverload(funcName string, args ...ref.Val) ref.Val {
+	argTypes := make([]string, len(args))
+	var unk *types.Unknown = nil
+	for i, arg := range args {
+		if types.IsError(arg) {
+			return arg
+		}
+		if types.IsUnknown(arg) {
+			unk = types.MergeUnknowns(arg.(*types.Unknown), unk)
+		}
+		argTypes[i] = arg.Type().TypeName()
+	}
+	if unk != nil {
+		return unk
+	}
+	signature := strings.Join(argTypes, ", ")
+	return types.NewErr("no such overload: %s(%s)", funcName, signature)
+}
+
+// FunctionOpt defines a functional option for mutating a function declaration.
+type FunctionOpt func(*FunctionDecl) (*FunctionDecl, error)
+
+// DisableTypeGuards disables automatically generated function invocation guards on direct overload calls.
+// Type guards remain on during dynamic dispatch for parsed-only expressions.
+func DisableTypeGuards(value bool) FunctionOpt {
+	return func(fn *FunctionDecl) (*FunctionDecl, error) {
+		fn.disableTypeGuards = value
+		return fn, nil
+	}
+}
+
+// DisableDeclaration indicates that the function declaration should be disabled, but the runtime function
+// binding should be provided. Marking a function as runtime-only is a safe way to manage deprecations
+// of function declarations while still preserving the runtime behavior for previously compiled expressions.
+func DisableDeclaration(value bool) FunctionOpt {
+	return func(fn *FunctionDecl) (*FunctionDecl, error) {
+		if value {
+			fn.state = declarationDisabled
+		} else {
+			fn.state = declarationEnabled
+		}
+		return fn, nil
+	}
+}
+
+// SingletonUnaryBinding creates a singleton function definition to be used for all function overloads.
+//
+// Note, this approach works well if operand is expected to have a specific trait which it implements,
+// e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.
+func SingletonUnaryBinding(fn functions.UnaryOp, traits ...int) FunctionOpt {
+	trait := 0
+	for _, t := range traits {
+		trait = trait | t
+	}
+	return func(f *FunctionDecl) (*FunctionDecl, error) {
+		if f.singleton != nil {
+			return nil, fmt.Errorf("function already has a singleton binding: %s", f.Name())
+		}
+		f.singleton = &functions.Overload{
+			Operator:     f.Name(),
+			Unary:        fn,
+			OperandTrait: trait,
+		}
+		return f, nil
+	}
+}
+
+// SingletonBinaryBinding creates a singleton function definition to be used with all function overloads.
+//
+// Note, this approach works well if operand is expected to have a specific trait which it implements,
+// e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.
+func SingletonBinaryBinding(fn functions.BinaryOp, traits ...int) FunctionOpt {
+	trait := 0
+	for _, t := range traits {
+		trait = trait | t
+	}
+	return func(f *FunctionDecl) (*FunctionDecl, error) {
+		if f.singleton != nil {
+			return nil, fmt.Errorf("function already has a singleton binding: %s", f.Name())
+		}
+		f.singleton = &functions.Overload{
+			Operator:     f.Name(),
+			Binary:       fn,
+			OperandTrait: trait,
+		}
+		return f, nil
+	}
+}
+
+// SingletonFunctionBinding creates a singleton function definition to be used with all function overloads.
+//
+// Note, this approach works well if operand is expected to have a specific trait which it implements,
+// e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.
+func SingletonFunctionBinding(fn functions.FunctionOp, traits ...int) FunctionOpt {
+	trait := 0
+	for _, t := range traits {
+		trait = trait | t
+	}
+	return func(f *FunctionDecl) (*FunctionDecl, error) {
+		if f.singleton != nil {
+			return nil, fmt.Errorf("function already has a singleton binding: %s", f.Name())
+		}
+		f.singleton = &functions.Overload{
+			Operator:     f.Name(),
+			Function:     fn,
+			OperandTrait: trait,
+		}
+		return f, nil
+	}
+}
+
+// Overload defines a new global overload with an overload id, argument types, and result type. Through the
+// use of OverloadOpt options, the overload may also be configured with a binding, an operand trait, and to
+// be non-strict.
+//
+// Note: function bindings should be commonly configured with Overload instances whereas operand traits and
+// strict-ness should be rare occurrences.
+func Overload(overloadID string,
+	args []*types.Type, resultType *types.Type,
+	opts ...OverloadOpt) FunctionOpt {
+	return newOverload(overloadID, false, args, resultType, opts...)
+}
+
+// MemberOverload defines a new receiver-style overload (or member function) with an overload id, argument types,
+// and result type. Through the use of OverloadOpt options, the overload may also be configured with a binding,
+// an operand trait, and to be non-strict.
+//
+// Note: function bindings should be commonly configured with Overload instances whereas operand traits and
+// strict-ness should be rare occurrences.
+func MemberOverload(overloadID string,
+	args []*types.Type, resultType *types.Type,
+	opts ...OverloadOpt) FunctionOpt {
+	return newOverload(overloadID, true, args, resultType, opts...)
+}
+
+func newOverload(overloadID string,
+	memberFunction bool, args []*types.Type, resultType *types.Type,
+	opts ...OverloadOpt) FunctionOpt {
+	return func(f *FunctionDecl) (*FunctionDecl, error) {
+		overload, err := newOverloadInternal(overloadID, memberFunction, args, resultType, opts...)
+		if err != nil {
+			return nil, err
+		}
+		err = f.AddOverload(overload)
+		if err != nil {
+			return nil, err
+		}
+		return f, nil
+	}
+}
+
+func newOverloadInternal(overloadID string,
+	memberFunction bool, args []*types.Type, resultType *types.Type,
+	opts ...OverloadOpt) (*OverloadDecl, error) {
+	overload := &OverloadDecl{
+		id:               overloadID,
+		argTypes:         args,
+		resultType:       resultType,
+		isMemberFunction: memberFunction,
+	}
+	var err error
+	for _, opt := range opts {
+		overload, err = opt(overload)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return overload, nil
+}
+
+// OverloadDecl contains the definition of a single overload id with a specific signature, and an optional
+// implementation.
+type OverloadDecl struct {
+	id               string
+	argTypes         []*types.Type
+	resultType       *types.Type
+	isMemberFunction bool
+	// nonStrict indicates that the function will accept error and unknown arguments as inputs.
+	nonStrict bool
+	// operandTrait indicates whether the member argument should have a specific type-trait.
+	//
+	// This is useful for creating overloads which operate on a type-interface rather than a concrete type.
+	operandTrait int
+
+	// Function implementation options. Optional, but encouraged.
+	// unaryOp is a function binding that takes a single argument.
+	unaryOp functions.UnaryOp
+	// binaryOp is a function binding that takes two arguments.
+	binaryOp functions.BinaryOp
+	// functionOp is a catch-all for zero-arity and three-plus arity functions.
+	functionOp functions.FunctionOp
+}
+
+// ID mirrors the overload signature and provides a unique id which may be referenced within the type-checker
+// and interpreter to optimize performance.
+//
+// The ID format is usually one of two styles:
+// global: <functionName>_<argType>_<argTypeN>
+// member: <memberType>_<functionName>_<argType>_<argTypeN>
+func (o *OverloadDecl) ID() string {
+	if o == nil {
+		return ""
+	}
+	return o.id
+}
+
+// ArgTypes contains the set of argument types expected by the overload.
+//
+// For member functions ArgTypes[0] represents the member operand type.
+func (o *OverloadDecl) ArgTypes() []*types.Type {
+	if o == nil {
+		return emptyArgs
+	}
+	return o.argTypes
+}
+
+// IsMemberFunction indicates whether the overload is a member function
+func (o *OverloadDecl) IsMemberFunction() bool {
+	if o == nil {
+		return false
+	}
+	return o.isMemberFunction
+}
+
+// IsNonStrict returns whether the overload accepts errors and unknown values as arguments.
+func (o *OverloadDecl) IsNonStrict() bool {
+	if o == nil {
+		return false
+	}
+	return o.nonStrict
+}
+
+// OperandTrait returns the trait mask of the first operand to the overload call, e.g.
+// `traits.Indexer`
+func (o *OverloadDecl) OperandTrait() int {
+	if o == nil {
+		return 0
+	}
+	return o.operandTrait
+}
+
+// ResultType indicates the output type from calling the function.
+func (o *OverloadDecl) ResultType() *types.Type {
+	if o == nil {
+		// *types.Type is nil-safe
+		return nil
+	}
+	return o.resultType
+}
+
+// TypeParams returns the type parameter names associated with the overload.
+func (o *OverloadDecl) TypeParams() []string {
+	typeParams := map[string]struct{}{}
+	collectParamNames(typeParams, o.ResultType())
+	for _, arg := range o.ArgTypes() {
+		collectParamNames(typeParams, arg)
+	}
+	params := make([]string, 0, len(typeParams))
+	for param := range typeParams {
+		params = append(params, param)
+	}
+	return params
+}
+
+// SignatureEquals determines whether the incoming overload declaration signature is equal to the current signature.
+//
+// Result type, operand trait, and strict-ness are not considered as part of signature equality.
+func (o *OverloadDecl) SignatureEquals(other *OverloadDecl) bool {
+	if o == other {
+		return true
+	}
+	if o.ID() != other.ID() || o.IsMemberFunction() != other.IsMemberFunction() || len(o.ArgTypes()) != len(other.ArgTypes()) {
+		return false
+	}
+	for i, at := range o.ArgTypes() {
+		oat := other.ArgTypes()[i]
+		if !at.IsEquivalentType(oat) {
+			return false
+		}
+	}
+	return o.ResultType().IsEquivalentType(other.ResultType())
+}
+
+// SignatureOverlaps indicates whether two functions have non-equal, but overloapping function signatures.
+//
+// For example, list(dyn) collides with list(string) since the 'dyn' type can contain a 'string' type.
+func (o *OverloadDecl) SignatureOverlaps(other *OverloadDecl) bool {
+	if o.IsMemberFunction() != other.IsMemberFunction() || len(o.ArgTypes()) != len(other.ArgTypes()) {
+		return false
+	}
+	argsOverlap := true
+	for i, argType := range o.ArgTypes() {
+		otherArgType := other.ArgTypes()[i]
+		argsOverlap = argsOverlap &&
+			(argType.IsAssignableType(otherArgType) ||
+				otherArgType.IsAssignableType(argType))
+	}
+	return argsOverlap
+}
+
+// hasBinding indicates whether the overload already has a definition.
+func (o *OverloadDecl) hasBinding() bool {
+	return o != nil && (o.unaryOp != nil || o.binaryOp != nil || o.functionOp != nil)
+}
+
+// guardedUnaryOp creates an invocation guard around the provided unary operator, if one is defined.
+func (o *OverloadDecl) guardedUnaryOp(funcName string, disableTypeGuards bool) functions.UnaryOp {
+	if o.unaryOp == nil {
+		return nil
+	}
+	return func(arg ref.Val) ref.Val {
+		if !o.matchesRuntimeUnarySignature(disableTypeGuards, arg) {
+			return MaybeNoSuchOverload(funcName, arg)
+		}
+		return o.unaryOp(arg)
+	}
+}
+
+// guardedBinaryOp creates an invocation guard around the provided binary operator, if one is defined.
+func (o *OverloadDecl) guardedBinaryOp(funcName string, disableTypeGuards bool) functions.BinaryOp {
+	if o.binaryOp == nil {
+		return nil
+	}
+	return func(arg1, arg2 ref.Val) ref.Val {
+		if !o.matchesRuntimeBinarySignature(disableTypeGuards, arg1, arg2) {
+			return MaybeNoSuchOverload(funcName, arg1, arg2)
+		}
+		return o.binaryOp(arg1, arg2)
+	}
+}
+
+// guardedFunctionOp creates an invocation guard around the provided variadic function binding, if one is provided.
+func (o *OverloadDecl) guardedFunctionOp(funcName string, disableTypeGuards bool) functions.FunctionOp {
+	if o.functionOp == nil {
+		return nil
+	}
+	return func(args ...ref.Val) ref.Val {
+		if !o.matchesRuntimeSignature(disableTypeGuards, args...) {
+			return MaybeNoSuchOverload(funcName, args...)
+		}
+		return o.functionOp(args...)
+	}
+}
+
+// matchesRuntimeUnarySignature indicates whether the argument type is runtime assiganble to the overload's expected argument.
+func (o *OverloadDecl) matchesRuntimeUnarySignature(disableTypeGuards bool, arg ref.Val) bool {
+	return matchRuntimeArgType(o.IsNonStrict(), disableTypeGuards, o.ArgTypes()[0], arg) &&
+		matchOperandTrait(o.OperandTrait(), arg)
+}
+
+// matchesRuntimeBinarySignature indicates whether the argument types are runtime assiganble to the overload's expected arguments.
+func (o *OverloadDecl) matchesRuntimeBinarySignature(disableTypeGuards bool, arg1, arg2 ref.Val) bool {
+	return matchRuntimeArgType(o.IsNonStrict(), disableTypeGuards, o.ArgTypes()[0], arg1) &&
+		matchRuntimeArgType(o.IsNonStrict(), disableTypeGuards, o.ArgTypes()[1], arg2) &&
+		matchOperandTrait(o.OperandTrait(), arg1)
+}
+
+// matchesRuntimeSignature indicates whether the argument types are runtime assiganble to the overload's expected arguments.
+func (o *OverloadDecl) matchesRuntimeSignature(disableTypeGuards bool, args ...ref.Val) bool {
+	if len(args) != len(o.ArgTypes()) {
+		return false
+	}
+	if len(args) == 0 {
+		return true
+	}
+	for i, arg := range args {
+		if !matchRuntimeArgType(o.IsNonStrict(), disableTypeGuards, o.ArgTypes()[i], arg) {
+			return false
+		}
+	}
+	return matchOperandTrait(o.OperandTrait(), args[0])
+}
+
+func matchRuntimeArgType(nonStrict, disableTypeGuards bool, argType *types.Type, arg ref.Val) bool {
+	if nonStrict && (disableTypeGuards || types.IsUnknownOrError(arg)) {
+		return true
+	}
+	if types.IsUnknownOrError(arg) {
+		return false
+	}
+	return disableTypeGuards || argType.IsAssignableRuntimeType(arg)
+}
+
+func matchOperandTrait(trait int, arg ref.Val) bool {
+	return trait == 0 || arg.Type().HasTrait(trait) || types.IsUnknownOrError(arg)
+}
+
+// OverloadOpt is a functional option for configuring a function overload.
+type OverloadOpt func(*OverloadDecl) (*OverloadDecl, error)
+
+// UnaryBinding provides the implementation of a unary overload. The provided function is protected by a runtime
+// type-guard which ensures runtime type agreement between the overload signature and runtime argument types.
+func UnaryBinding(binding functions.UnaryOp) OverloadOpt {
+	return func(o *OverloadDecl) (*OverloadDecl, error) {
+		if o.hasBinding() {
+			return nil, fmt.Errorf("overload already has a binding: %s", o.ID())
+		}
+		if len(o.ArgTypes()) != 1 {
+			return nil, fmt.Errorf("unary function bound to non-unary overload: %s", o.ID())
+		}
+		o.unaryOp = binding
+		return o, nil
+	}
+}
+
+// BinaryBinding provides the implementation of a binary overload. The provided function is protected by a runtime
+// type-guard which ensures runtime type agreement between the overload signature and runtime argument types.
+func BinaryBinding(binding functions.BinaryOp) OverloadOpt {
+	return func(o *OverloadDecl) (*OverloadDecl, error) {
+		if o.hasBinding() {
+			return nil, fmt.Errorf("overload already has a binding: %s", o.ID())
+		}
+		if len(o.ArgTypes()) != 2 {
+			return nil, fmt.Errorf("binary function bound to non-binary overload: %s", o.ID())
+		}
+		o.binaryOp = binding
+		return o, nil
+	}
+}
+
+// FunctionBinding provides the implementation of a variadic overload. The provided function is protected by a runtime
+// type-guard which ensures runtime type agreement between the overload signature and runtime argument types.
+func FunctionBinding(binding functions.FunctionOp) OverloadOpt {
+	return func(o *OverloadDecl) (*OverloadDecl, error) {
+		if o.hasBinding() {
+			return nil, fmt.Errorf("overload already has a binding: %s", o.ID())
+		}
+		o.functionOp = binding
+		return o, nil
+	}
+}
+
+// OverloadIsNonStrict enables the function to be called with error and unknown argument values.
+//
+// Note: do not use this option unless absoluately necessary as it should be an uncommon feature.
+func OverloadIsNonStrict() OverloadOpt {
+	return func(o *OverloadDecl) (*OverloadDecl, error) {
+		o.nonStrict = true
+		return o, nil
+	}
+}
+
+// OverloadOperandTrait configures a set of traits which the first argument to the overload must implement in order to be
+// successfully invoked.
+func OverloadOperandTrait(trait int) OverloadOpt {
+	return func(o *OverloadDecl) (*OverloadDecl, error) {
+		o.operandTrait = trait
+		return o, nil
+	}
+}
+
+// NewConstant creates a new constant declaration.
+func NewConstant(name string, t *types.Type, v ref.Val) *VariableDecl {
+	return &VariableDecl{name: name, varType: t, value: v}
+}
+
+// NewVariable creates a new variable declaration.
+func NewVariable(name string, t *types.Type) *VariableDecl {
+	return &VariableDecl{name: name, varType: t}
+}
+
+// VariableDecl defines a variable declaration which may optionally have a constant value.
+type VariableDecl struct {
+	name    string
+	varType *types.Type
+	value   ref.Val
+}
+
+// Name returns the fully-qualified variable name
+func (v *VariableDecl) Name() string {
+	if v == nil {
+		return ""
+	}
+	return v.name
+}
+
+// Type returns the types.Type value associated with the variable.
+func (v *VariableDecl) Type() *types.Type {
+	if v == nil {
+		// types.Type is nil-safe
+		return nil
+	}
+	return v.varType
+}
+
+// Value returns the constant value associated with the declaration.
+func (v *VariableDecl) Value() ref.Val {
+	if v == nil {
+		return nil
+	}
+	return v.value
+}
+
+// DeclarationIsEquivalent returns true if one variable declaration has the same name and same type as the input.
+func (v *VariableDecl) DeclarationIsEquivalent(other *VariableDecl) bool {
+	if v == other {
+		return true
+	}
+	return v.Name() == other.Name() && v.Type().IsEquivalentType(other.Type())
+}
+
+// TypeVariable creates a new type identifier for use within a types.Provider
+func TypeVariable(t *types.Type) *VariableDecl {
+	return NewVariable(t.TypeName(), types.NewTypeTypeWithParam(t))
+}
+
+// variableDeclToExprDecl converts a go-native variable declaration into a protobuf-type variable declaration.
+func variableDeclToExprDecl(v *VariableDecl) (*exprpb.Decl, error) {
+	varType, err := types.TypeToExprType(v.Type())
+	if err != nil {
+		return nil, err
+	}
+	return chkdecls.NewVar(v.Name(), varType), nil
+}
+
+// functionDeclToExprDecl converts a go-native function declaration into a protobuf-typed function declaration.
+func functionDeclToExprDecl(f *FunctionDecl) (*exprpb.Decl, error) {
+	overloads := make([]*exprpb.Decl_FunctionDecl_Overload, len(f.overloads))
+	for i, oID := range f.overloadOrdinals {
+		o := f.overloads[oID]
+		paramNames := map[string]struct{}{}
+		argTypes := make([]*exprpb.Type, len(o.ArgTypes()))
+		for j, a := range o.ArgTypes() {
+			collectParamNames(paramNames, a)
+			at, err := types.TypeToExprType(a)
+			if err != nil {
+				return nil, err
+			}
+			argTypes[j] = at
+		}
+		collectParamNames(paramNames, o.ResultType())
+		resultType, err := types.TypeToExprType(o.ResultType())
+		if err != nil {
+			return nil, err
+		}
+		if len(paramNames) == 0 {
+			if o.IsMemberFunction() {
+				overloads[i] = chkdecls.NewInstanceOverload(oID, argTypes, resultType)
+			} else {
+				overloads[i] = chkdecls.NewOverload(oID, argTypes, resultType)
+			}
+		} else {
+			params := []string{}
+			for pn := range paramNames {
+				params = append(params, pn)
+			}
+			if o.IsMemberFunction() {
+				overloads[i] = chkdecls.NewParameterizedInstanceOverload(oID, argTypes, resultType, params)
+			} else {
+				overloads[i] = chkdecls.NewParameterizedOverload(oID, argTypes, resultType, params)
+			}
+		}
+	}
+	return chkdecls.NewFunction(f.Name(), overloads...), nil
+}
+
+func collectParamNames(paramNames map[string]struct{}, arg *types.Type) {
+	if arg.Kind() == types.TypeParamKind {
+		paramNames[arg.TypeName()] = struct{}{}
+	}
+	for _, param := range arg.Parameters() {
+		collectParamNames(paramNames, param)
+	}
+}
+
+var (
+	emptyArgs = []*types.Type{}
+)