feat(static): add "static" package as a DCE-friendly alternative

The package is a drop-in replacement with two features removed:
- functions in environment
- Eval() method

Fix #863.

Author: vincentbernat

builtin/lib.go

@@ -560,11 +560,10 @@ func get(params ...any) (out any, err error) {
 	}
 
 	// Methods can be defined on any type.
-	if v.NumMethod() > 0 {
+	if runtime.MethodByNameHook != nil && v.NumMethod() > 0 {
 		if methodName, ok := i.(string); ok {
-			method := v.MethodByName(methodName)
-			if method.IsValid() {
-				return method.Interface(), nil
+			if m, ok := runtime.MethodByNameHook(v, methodName); ok {
+				return m, nil
 			}
 		}
 	}

checker/info.go

@@ -37,10 +37,10 @@ func MethodIndex(c *Cache, env Nature, node ast.Node) (bool, int, string) {
 		}
 	case *ast.MemberNode:
 		if name, ok := n.Property.(*ast.StringNode); ok {
-			base := n.Node.Type()
-			if base != nil && base.Kind() != reflect.Interface {
-				if m, ok := base.MethodByName(name.Value); ok {
-					return true, m.Index, name.Value
+			base := n.Node.Nature()
+			if base != nil && base.Kind != reflect.Interface {
+				if m, ok := base.MethodByName(c, name.Value); ok && m.TypeData != nil {
+					return true, m.MethodIndex, name.Value
 				}
 			}
 		}

checker/nature/nature.go

@@ -213,7 +213,7 @@ func ArrayFromType(c *Cache, t reflect.Type) Nature {
 }
 
 func (n *Nature) IsAny(c *Cache) bool {
-	return n.Type != nil && n.Kind == reflect.Interface && n.NumMethods(c) == 0
+	return n.Type != nil && n.Kind == reflect.Interface && n.Type.NumMethod() == 0
 }
 
 func (n *Nature) IsUnknown(c *Cache) bool {
@@ -294,7 +294,20 @@ func (n *Nature) NumMethods(c *Cache) int {
 	return 0
 }
 
+// MethodByNameHook, when non-nil, looks up a method on a Nature by name. If
+// nil, expressions must use Function-registered callables instead.
+var MethodByNameHook func(c *Cache, n *Nature, name string) (Nature, bool)
+
 func (n *Nature) MethodByName(c *Cache, name string) (Nature, bool) {
+	if MethodByNameHook == nil {
+		return Nature{}, false
+	}
+	return MethodByNameHook(c, n, name)
+}
+
+// LookupMethod is the reference implementation of MethodByNameHook. It
+// transitively reaches reflect.Type.Method via the methodset cache.
+func LookupMethod(c *Cache, n *Nature, name string) (Nature, bool) {
 	if s := n.getMethodset(c); s != nil {
 		if m := s.method(c, name); m != nil {
 			return m.nature, true

compiler/compiler.go

@@ -783,9 +783,12 @@ func (c *compiler) CallNode(node *ast.CallNode) {
 		switch callee := node.Callee.(type) {
 		case *ast.MemberNode:
 			if prop, ok := callee.Property.(*ast.StringNode); ok {
-				if _, ok = callee.Node.Type().MethodByName(prop.Value); ok && callee.Node.Type().Kind() != reflect.Interface {
-					fnInOffset = 1
-					fnNumIn--
+				base := callee.Node.Nature()
+				if base != nil && base.Kind != reflect.Interface {
+					if _, ok := base.MethodByName(c.ntCache, prop.Value); ok {
+						fnInOffset = 1
+						fnNumIn--
+					}
 				}
 			}
 		case *ast.IdentifierNode:

expr.go

@@ -13,7 +13,6 @@ import (
 	"github.com/expr-lang/expr/conf"
 	"github.com/expr-lang/expr/file"
 	"github.com/expr-lang/expr/optimizer"
-	"github.com/expr-lang/expr/parser"
 	"github.com/expr-lang/expr/patcher"
 	"github.com/expr-lang/expr/vm"
 )
@@ -25,7 +24,8 @@ type Option func(c *conf.Config)
 // If struct is passed, all fields will be treated as variables,
 // as well as all fields of embedded structs and struct itself.
 // If map is passed, all items will be treated as variables.
-// Methods defined on this type will be available as functions.
+// Methods defined on this type will be available as functions,
+// unless imported through github.com/expr-lang/expr/static.
 func Env(env any) Option {
 	return func(c *conf.Config) {
 		c.WithEnv(env)
@@ -264,27 +264,3 @@ func Compile(input string, ops ...Option) (*vm.Program, error) {
 func Run(program *vm.Program, env any) (any, error) {
 	return vm.Run(program, env)
 }
-
-// Eval parses, compiles and runs given input.
-func Eval(input string, env any) (any, error) {
-	if _, ok := env.(Option); ok {
-		return nil, fmt.Errorf("misused expr.Eval: second argument (env) should be passed without expr.Env")
-	}
-
-	tree, err := parser.Parse(input)
-	if err != nil {
-		return nil, err
-	}
-
-	program, err := compiler.Compile(tree, nil)
-	if err != nil {
-		return nil, err
-	}
-
-	output, err := Run(program, env)
-	if err != nil {
-		return nil, err
-	}
-
-	return output, nil
-}

reflectmethods.go

@@ -0,0 +1,71 @@
+package expr
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/expr-lang/expr/checker/nature"
+	"github.com/expr-lang/expr/compiler"
+	"github.com/expr-lang/expr/parser"
+	"github.com/expr-lang/expr/vm/runtime"
+)
+
+// This file installs the method-dispatch hooks that the shared packages
+// (vm/runtime, checker/nature, builtin) consult to perform reflective method
+// lookups. The hooks are installed only when the parent expr package is
+// imported.
+//
+// All four reflect.* method-resolution call sites that the linker treats as
+// REFLECTMETHOD live exclusively in this file (or in functions reachable
+// only from this file's hooks):
+//
+//   - reflect.Value.MethodByName  in fetchMethodByName
+//   - reflect.Value.Method        in fetchMethodIndexed
+//   - reflect.Type.Method         in nature.LookupMethod (transitively)
+//   - reflect.Type.MethodByName   not used
+
+func init() {
+	runtime.MethodByNameHook = fetchMethodByName
+	runtime.MethodIndexedHook = fetchMethodIndexed
+	nature.MethodByNameHook = nature.LookupMethod
+}
+
+func fetchMethodByName(v reflect.Value, name string) (any, bool) {
+	method := v.MethodByName(name)
+	if method.IsValid() {
+		return method.Interface(), true
+	}
+	return nil, false
+}
+
+func fetchMethodIndexed(v reflect.Value, index int) (any, bool) {
+	method := v.Method(index)
+	if method.IsValid() {
+		return method.Interface(), true
+	}
+	return nil, false
+}
+
+// Eval parses, compiles and runs given input.
+func Eval(input string, env any) (any, error) {
+	if _, ok := env.(Option); ok {
+		return nil, fmt.Errorf("misused expr.Eval: second argument (env) should be passed without expr.Env")
+	}
+
+	tree, err := parser.Parse(input)
+	if err != nil {
+		return nil, err
+	}
+
+	program, err := compiler.Compile(tree, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	output, err := Run(program, env)
+	if err != nil {
+		return nil, err
+	}
+
+	return output, nil
+}

static/docs.go

@@ -0,0 +1,11 @@
+// Package expr (imported as github.com/expr-lang/expr/static) is a
+// dead-code-elimination-friendly entry point for expr.
+//
+// It exposes the same API as the parent expr, without the `Eval()` function. It
+// does not trigger the Go linker's REFLECTMETHOD analysis and methods of every
+// reachable type can be eliminated by dead-code elimination. Calling a method
+// defined on the Env type does NOT work. Compilation fails with "unknown name
+// <method>". To expose a function, use the Function option.
+package expr
+
+//go:generate cp ../expr.go expr.go