google · TristonianJones · Feb 3, 2025 · Jan 31, 2025
diff --git a/cel/decls.go b/cel/decls.go
@@ -194,6 +194,38 @@ func Function(name string, opts ...FunctionOpt) EnvOption {
 	}
 }
 
+// OverloadSelector selects an overload associated with a given function when it returns true.
+//
+// Used in combination with the FunctionDecl.Subset method.
+type OverloadSelector = decls.OverloadSelector
+
+// IncludeOverloads defines an OverloadSelector which allow-lists a set of overloads by their ids.
+func IncludeOverloads(overloadIDs ...string) OverloadSelector {
+	return decls.IncludeOverloads(overloadIDs...)
+}
+
+// ExcludeOverloads defines an OverloadSelector which deny-lists a set of overloads by their ids.
+func ExcludeOverloads(overloadIDs ...string) OverloadSelector {
+	return decls.ExcludeOverloads(overloadIDs...)
+}
+
+// FunctionDecls provides one or more fully formed function declaration to be added to the environment.
+func FunctionDecls(funcs ...*decls.FunctionDecl) EnvOption {
+	return func(e *Env) (*Env, error) {
+		var err error
+		for _, fn := range funcs {
+			if existing, found := e.functions[fn.Name()]; found {
+				fn, err = existing.Merge(fn)
+				if err != nil {
+					return nil, err
+				}
+			}
+			e.functions[fn.Name()] = fn
+		}
+		return e, nil
+	}
+}
+
 // FunctionOpt defines a functional  option for configuring a function declaration.
 type FunctionOpt = decls.FunctionOpt
 

diff --git a/cel/decls_test.go b/cel/decls_test.go
@@ -26,6 +26,7 @@ import (
 	"github.com/google/cel-go/common/functions"
 	"github.com/google/cel-go/common/operators"
 	"github.com/google/cel-go/common/overloads"
+	"github.com/google/cel-go/common/stdlib"
 	"github.com/google/cel-go/common/types"
 	"github.com/google/cel-go/common/types/ref"
 	"github.com/google/cel-go/common/types/traits"
@@ -780,6 +781,187 @@ func TestExprDeclToDeclarationInvalid(t *testing.T) {
 	}
 }
 
+func TestFunctionDeclExcludeOverloads(t *testing.T) {
+	funcs := []*decls.FunctionDecl{}
+	for _, fn := range stdlib.Functions() {
+		if fn.Name() == operators.Add {
+			fn = fn.Subset(ExcludeOverloads(overloads.AddList, overloads.AddBytes, overloads.AddString))
+		}
+		funcs = append(funcs, fn)
+	}
+	env, err := NewCustomEnv(FunctionDecls(funcs...))
+	if err != nil {
+		t.Fatalf("NewCustomEnv() failed: %v", err)
+	}
+
+	successTests := []struct {
+		name string
+		expr string
+		want ref.Val
+	}{
+		{
+			name: "ints",
+			expr: "1 + 1",
+			want: types.Int(2),
+		},
+		{
+			name: "doubles",
+			expr: "1.5 + 1.5",
+			want: types.Double(3.0),
+		},
+		{
+			name: "uints",
+			expr: "1u + 2u",
+			want: types.Uint(3),
+		},
+		{
+			name: "timestamp plus duration",
+			expr: "timestamp('2001-01-01T00:00:00Z') + duration('1h') == timestamp('2001-01-01T01:00:00Z')",
+			want: types.True,
+		},
+		{
+			name: "durations",
+			expr: "duration('1h') + duration('1m') == duration('1h1m')",
+			want: types.True,
+		},
+	}
+	for _, tst := range successTests {
+		tc := tst
+		t.Run(tc.name, func(t *testing.T) {
+			ast, iss := env.Compile(tc.expr)
+			if iss.Err() != nil {
+				t.Fatalf("env.Compile() failed: %v", iss.Err())
+			}
+			prg, err := env.Program(ast)
+			if err != nil {
+				t.Fatalf("env.Program() failed: %v", err)
+			}
+			out, _, err := prg.Eval(NoVars())
+			if err != nil {
+				t.Fatalf("prg.Eval() errored: %v", err)
+			}
+			if out.Equal(tc.want) != types.True {
+				t.Errorf("Eval() got %v, wanted %v", out, tc.want)
+			}
+		})
+	}
+	failureTests := []struct {
+		name string
+		expr string
+	}{
+		{
+			name: "strings",
+			expr: "'a' + 'b'",
+		},
+		{
+			name: "bytes",
+			expr: "b'123' + b'456'",
+		},
+		{
+			name: "lists",
+			expr: "[1] + [2, 3]",
+		},
+	}
+	for _, tst := range failureTests {
+		tc := tst
+		t.Run(tc.name, func(t *testing.T) {
+			_, iss := env.Compile(tc.expr)
+			if iss.Err() == nil {
+				t.Error("env.Compile() got ast, wanted error")
+			}
+		})
+	}
+}
+
+func TestFunctionDeclIncludeOverloads(t *testing.T) {
+	funcs := []*decls.FunctionDecl{}
+	for _, fn := range stdlib.Functions() {
+		if fn.Name() == operators.Add {
+			fn = fn.Subset(IncludeOverloads(overloads.AddInt64, overloads.AddDouble))
+		}
+		funcs = append(funcs, fn)
+	}
+	env, err := NewCustomEnv(FunctionDecls(funcs...))
+	if err != nil {
+		t.Fatalf("NewCustomEnv() failed: %v", err)
+	}
+
+	successTests := []struct {
+		name string
+		expr string
+		want ref.Val
+	}{
+		{
+			name: "ints",
+			expr: "1 + 1",
+			want: types.Int(2),
+		},
+		{
+			name: "doubles",
+			expr: "1.5 + 1.5",
+			want: types.Double(3.0),
+		},
+	}
+	for _, tst := range successTests {
+		tc := tst
+		t.Run(tc.name, func(t *testing.T) {
+			ast, iss := env.Compile(tc.expr)
+			if iss.Err() != nil {
+				t.Fatalf("env.Compile() failed: %v", iss.Err())
+			}
+			prg, err := env.Program(ast)
+			if err != nil {
+				t.Fatalf("env.Program() failed: %v", err)
+			}
+			out, _, err := prg.Eval(NoVars())
+			if err != nil {
+				t.Fatalf("prg.Eval() errored: %v", err)
+			}
+			if out.Equal(tc.want) != types.True {
+				t.Errorf("Eval() got %v, wanted %v", out, tc.want)
+			}
+		})
+	}
+	failureTests := []struct {
+		name string
+		expr string
+	}{
+		{
+			name: "strings",
+			expr: "'a' + 'b'",
+		},
+		{
+			name: "bytes",
+			expr: "b'123' + b'456'",
+		},
+		{
+			name: "lists",
+			expr: "[1] + [2, 3]",
+		},
+		{
+			name: "uints",
+			expr: "1u + 2u",
+		},
+		{
+			name: "timestamp plus duration",
+			expr: "timestamp('2001-01-01T00:00:00Z') + duration('1h') == timestamp('2001-01-01T01:00:00Z')",
+		},
+		{
+			name: "durations",
+			expr: "duration('1h') + duration('1m') == duration('1h1m')",
+		},
+	}
+	for _, tst := range failureTests {
+		tc := tst
+		t.Run(tc.name, func(t *testing.T) {
+			_, iss := env.Compile(tc.expr)
+			if iss.Err() == nil {
+				t.Error("env.Compile() got ast, wanted error")
+			}
+		})
+	}
+}
+
 func testParse(t testing.TB, env *Env, expr string, want any) {
 	t.Helper()
 	ast, iss := env.Parse(expr)

diff --git a/common/decls/decls.go b/common/decls/decls.go
@@ -148,6 +148,60 @@ func (f *FunctionDecl) Merge(other *FunctionDecl) (*FunctionDecl, error) {
 	return merged, nil
 }
 
+// OverloadSelector selects an overload associated with a given function when it returns true.
+//
+// Used in combination with the Subset method.
+type OverloadSelector func(overload *OverloadDecl) bool
+
+// IncludeOverloads defines an OverloadSelector which allow-lists a set of overloads by their ids.
+func IncludeOverloads(overloadIDs ...string) OverloadSelector {
+	return func(overload *OverloadDecl) bool {
+		for _, oID := range overloadIDs {
+			if overload.id == oID {
+				return true
+			}
+		}
+		return false
+	}
+}
+
+// ExcludeOverloads defines an OverloadSelector which deny-lists a set of overloads by their ids.
+func ExcludeOverloads(overloadIDs ...string) OverloadSelector {
+	return func(overload *OverloadDecl) bool {
+		for _, oID := range overloadIDs {
+			if overload.id == oID {
+				return false
+			}
+		}
+		return true
+	}
+}
+
+// Subset returns a new function declaration which contains only the overloads with the specified IDs.
+func (f *FunctionDecl) Subset(selector OverloadSelector) *FunctionDecl {
+	if f == nil {
+		return nil
+	}
+	overloads := make(map[string]*OverloadDecl)
+	overloadOrdinals := make([]string, 0, len(f.overloadOrdinals))
+	for _, oID := range f.overloadOrdinals {
+		overload := f.overloads[oID]
+		if selector(overload) {
+			overloads[oID] = overload
+			overloadOrdinals = append(overloadOrdinals, oID)
+		}
+	}
+	subset := &FunctionDecl{
+		name:              f.Name(),
+		overloads:         overloads,
+		singleton:         f.singleton,
+		disableTypeGuards: f.disableTypeGuards,
+		state:             f.state,
+		overloadOrdinals:  overloadOrdinals,
+	}
+	return subset
+}
+
 // 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.