interp: improve handling of composed interfaces wrappers

This change implements a workaround to better support composed
interfaces in yaegi and let the interpreter define objects which
implement multiple interfaces at once.

We use the existing MapTypes to store what possible composed interface
wrapper could be used for some interfaces. When generating an interface
wrapper, the wrapper with the highest number of implemented methods is
chosen.

This is still an imperfect solution but it improves the accuracy of
interpreter in some critical cases.

This workaround could be removed in future if/when golang/go#15924
is resolved.

Fixes #1425.

_test/issue-1425.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"io"
+	"log"
+	"os"
+	"strings"
+)
+
+type WrappedReader struct {
+	reader io.Reader
+}
+
+func (wr WrappedReader) Read(p []byte) (n int, err error) {
+	return wr.reader.Read(p)
+}
+
+// Of course, this implementation is completely stupid because it does not write
+// to the intended writer, as any honest WriteTo implementation should. its
+// implemtion is just to make obvious the divergence of behaviour with yaegi.
+func (wr WrappedReader) WriteTo(w io.Writer) (n int64, err error) {
+	// Ignore w, send to Stdout to prove whether this WriteTo is used.
+	data, err := io.ReadAll(wr)
+	if err != nil {
+		return 0, err
+	}
+	nn, err := os.Stdout.Write(data)
+	return int64(nn), err
+}
+
+func main() {
+	f := strings.NewReader("hello world")
+	wr := WrappedReader{reader: f}
+
+	// behind the scenes, io.Copy is supposed to use wr.WriteTo if the implementation exists.
+	// With Go, it works as expected, i.e. the output is sent to os.Stdout.
+	// With Yaegi, it doesn't, i.e. the output is sent to io.Discard.
+	if _, err := io.Copy(io.Discard, wr); err != nil {
+		log.Fatal(err)
+	}
+}
+
+// Output:
+// hello world

internal/cmd/extract/extract.go

@@ -11,7 +11,7 @@ Output files are written in the current directory, and prefixed with the go vers
 
 Usage:
 
-    extract package...
+	extract package...
 
 The same program is used for all target operating systems and architectures.
 The GOOS and GOARCH environment variables set the desired target.

interp/doc.go

@@ -4,7 +4,7 @@ Package interp provides a complete Go interpreter.
 For the Go language itself, refer to the official Go specification
 https://golang.org/ref/spec.
 
-Importing packages
+# Importing packages
 
 Packages can be imported in source or binary form, using the standard
 Go import statement. In source form, packages are searched first in the
@@ -16,7 +16,7 @@ Binary form packages are compiled and linked with the interpreter
 executable, and exposed to scripts with the Use method. The extract
 subcommand of yaegi can be used to generate package wrappers.
 
-Custom build tags
+# Custom build tags
 
 Custom build tags allow to control which files in imported source
 packages are interpreted, in the same way as the "-tags" option of the

interp/interp.go

@@ -4,16 +4,12 @@ import (
 	"bufio"
 	"context"
 	"errors"
-	"flag"
 	"fmt"
 	"go/build"
-	"go/constant"
 	"go/scanner"
 	"go/token"
 	"io"
 	"io/fs"
-	"log"
-	"math/bits"
 	"os"
 	"os/signal"
 	"path"
@@ -547,62 +543,6 @@ func (interp *Interpreter) EvalTest(path string) error {
 	return err
 }
 
-// Symbols returns a map of interpreter exported symbol values for the given
-// import path. If the argument is the empty string, all known symbols are
-// returned.
-func (interp *Interpreter) Symbols(importPath string) Exports {
-	m := map[string]map[string]reflect.Value{}
-	interp.mutex.RLock()
-	defer interp.mutex.RUnlock()
-
-	for k, v := range interp.srcPkg {
-		if importPath != "" && k != importPath {
-			continue
-		}
-		syms := map[string]reflect.Value{}
-		for n, s := range v {
-			if !canExport(n) {
-				// Skip private non-exported symbols.
-				continue
-			}
-			switch s.kind {
-			case constSym:
-				syms[n] = s.rval
-			case funcSym:
-				syms[n] = genFunctionWrapper(s.node)(interp.frame)
-			case varSym:
-				syms[n] = interp.frame.data[s.index]
-			case typeSym:
-				syms[n] = reflect.New(s.typ.TypeOf())
-			}
-		}
-
-		if len(syms) > 0 {
-			m[k] = syms
-		}
-
-		if importPath != "" {
-			return m
-		}
-	}
-
-	if importPath != "" && len(m) > 0 {
-		return m
-	}
-
-	for k, v := range interp.binPkg {
-		if importPath != "" && k != importPath {
-			continue
-		}
-		m[k] = v
-		if importPath != "" {
-			return m
-		}
-	}
-
-	return m
-}
-
 func isFile(filesystem fs.FS, path string) bool {
 	fi, err := fs.Stat(filesystem, path)
 	return err == nil && fi.Mode().IsRegular()
@@ -664,167 +604,6 @@ func (interp *Interpreter) stop() {
 
 func (interp *Interpreter) runid() uint64 { return atomic.LoadUint64(&interp.id) }
 
-// getWrapper returns the wrapper type of the corresponding interface, or nil if not found.
-func (interp *Interpreter) getWrapper(t reflect.Type) reflect.Type {
-	if p, ok := interp.binPkg[t.PkgPath()]; ok {
-		return p["_"+t.Name()].Type().Elem()
-	}
-	return nil
-}
-
-// Use loads binary runtime symbols in the interpreter context so
-// they can be used in interpreted code.
-func (interp *Interpreter) Use(values Exports) error {
-	for k, v := range values {
-		importPath := path.Dir(k)
-		packageName := path.Base(k)
-
-		if k == "." && v["MapTypes"].IsValid() {
-			// Use mapping for special interface wrappers.
-			for kk, vv := range v["MapTypes"].Interface().(map[reflect.Value][]reflect.Type) {
-				interp.mapTypes[kk] = vv
-			}
-			continue
-		}
-
-		if importPath == "." {
-			return fmt.Errorf("export path %[1]q is missing a package name; did you mean '%[1]s/%[1]s'?", k)
-		}
-
-		if importPath == selfPrefix {
-			interp.hooks.Parse(v)
-			continue
-		}
-
-		if interp.binPkg[importPath] == nil {
-			interp.binPkg[importPath] = make(map[string]reflect.Value)
-			interp.pkgNames[importPath] = packageName
-		}
-
-		for s, sym := range v {
-			interp.binPkg[importPath][s] = sym
-		}
-		if k == selfPath {
-			interp.binPkg[importPath]["Self"] = reflect.ValueOf(interp)
-		}
-	}
-
-	// Checks if input values correspond to stdlib packages by looking for one
-	// well known stdlib package path.
-	if _, ok := values["fmt/fmt"]; ok {
-		fixStdlib(interp)
-	}
-	return nil
-}
-
-// fixStdlib redefines interpreter stdlib symbols to use the standard input,
-// output and errror assigned to the interpreter. The changes are limited to
-// the interpreter only.
-// Note that it is possible to escape the virtualized stdio by
-// read/write directly to file descriptors 0, 1, 2.
-func fixStdlib(interp *Interpreter) {
-	p := interp.binPkg["fmt"]
-	if p == nil {
-		return
-	}
-
-	stdin, stdout, stderr := interp.stdin, interp.stdout, interp.stderr
-
-	p["Print"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fprint(stdout, a...) })
-	p["Printf"] = reflect.ValueOf(func(f string, a ...interface{}) (n int, err error) { return fmt.Fprintf(stdout, f, a...) })
-	p["Println"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fprintln(stdout, a...) })
-
-	p["Scan"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fscan(stdin, a...) })
-	p["Scanf"] = reflect.ValueOf(func(f string, a ...interface{}) (n int, err error) { return fmt.Fscanf(stdin, f, a...) })
-	p["Scanln"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fscanln(stdin, a...) })
-
-	// Update mapTypes to virtualized symbols as well.
-	interp.mapTypes[p["Print"]] = interp.mapTypes[reflect.ValueOf(fmt.Print)]
-	interp.mapTypes[p["Printf"]] = interp.mapTypes[reflect.ValueOf(fmt.Printf)]
-	interp.mapTypes[p["Println"]] = interp.mapTypes[reflect.ValueOf(fmt.Println)]
-	interp.mapTypes[p["Scan"]] = interp.mapTypes[reflect.ValueOf(fmt.Scan)]
-	interp.mapTypes[p["Scanf"]] = interp.mapTypes[reflect.ValueOf(fmt.Scanf)]
-	interp.mapTypes[p["Scanln"]] = interp.mapTypes[reflect.ValueOf(fmt.Scanln)]
-
-	if p = interp.binPkg["flag"]; p != nil {
-		c := flag.NewFlagSet(os.Args[0], flag.PanicOnError)
-		c.SetOutput(stderr)
-		p["CommandLine"] = reflect.ValueOf(&c).Elem()
-	}
-
-	if p = interp.binPkg["log"]; p != nil {
-		l := log.New(stderr, "", log.LstdFlags)
-		// Restrict Fatal symbols to panic instead of exit.
-		p["Fatal"] = reflect.ValueOf(l.Panic)
-		p["Fatalf"] = reflect.ValueOf(l.Panicf)
-		p["Fatalln"] = reflect.ValueOf(l.Panicln)
-
-		p["Flags"] = reflect.ValueOf(l.Flags)
-		p["Output"] = reflect.ValueOf(l.Output)
-		p["Panic"] = reflect.ValueOf(l.Panic)
-		p["Panicf"] = reflect.ValueOf(l.Panicf)
-		p["Panicln"] = reflect.ValueOf(l.Panicln)
-		p["Prefix"] = reflect.ValueOf(l.Prefix)
-		p["Print"] = reflect.ValueOf(l.Print)
-		p["Printf"] = reflect.ValueOf(l.Printf)
-		p["Println"] = reflect.ValueOf(l.Println)
-		p["SetFlags"] = reflect.ValueOf(l.SetFlags)
-		p["SetOutput"] = reflect.ValueOf(l.SetOutput)
-		p["SetPrefix"] = reflect.ValueOf(l.SetPrefix)
-		p["Writer"] = reflect.ValueOf(l.Writer)
-
-		// Update mapTypes to virtualized symbols as well.
-		interp.mapTypes[p["Print"]] = interp.mapTypes[reflect.ValueOf(log.Print)]
-		interp.mapTypes[p["Printf"]] = interp.mapTypes[reflect.ValueOf(log.Printf)]
-		interp.mapTypes[p["Println"]] = interp.mapTypes[reflect.ValueOf(log.Println)]
-		interp.mapTypes[p["Panic"]] = interp.mapTypes[reflect.ValueOf(log.Panic)]
-		interp.mapTypes[p["Panicf"]] = interp.mapTypes[reflect.ValueOf(log.Panicf)]
-		interp.mapTypes[p["Panicln"]] = interp.mapTypes[reflect.ValueOf(log.Panicln)]
-	}
-
-	if p = interp.binPkg["os"]; p != nil {
-		p["Args"] = reflect.ValueOf(&interp.args).Elem()
-		if interp.specialStdio {
-			// Inherit streams from interpreter even if they do not have a file descriptor.
-			p["Stdin"] = reflect.ValueOf(&stdin).Elem()
-			p["Stdout"] = reflect.ValueOf(&stdout).Elem()
-			p["Stderr"] = reflect.ValueOf(&stderr).Elem()
-		} else {
-			// Inherits streams from interpreter only if they have a file descriptor and preserve original type.
-			if s, ok := stdin.(*os.File); ok {
-				p["Stdin"] = reflect.ValueOf(&s).Elem()
-			}
-			if s, ok := stdout.(*os.File); ok {
-				p["Stdout"] = reflect.ValueOf(&s).Elem()
-			}
-			if s, ok := stderr.(*os.File); ok {
-				p["Stderr"] = reflect.ValueOf(&s).Elem()
-			}
-		}
-		if !interp.unrestricted {
-			// In restricted mode, scripts can only access to a passed virtualized env, and can not write the real one.
-			getenv := func(key string) string { return interp.env[key] }
-			p["Clearenv"] = reflect.ValueOf(func() { interp.env = map[string]string{} })
-			p["ExpandEnv"] = reflect.ValueOf(func(s string) string { return os.Expand(s, getenv) })
-			p["Getenv"] = reflect.ValueOf(getenv)
-			p["LookupEnv"] = reflect.ValueOf(func(key string) (s string, ok bool) { s, ok = interp.env[key]; return })
-			p["Setenv"] = reflect.ValueOf(func(key, value string) error { interp.env[key] = value; return nil })
-			p["Unsetenv"] = reflect.ValueOf(func(key string) error { delete(interp.env, key); return nil })
-			p["Environ"] = reflect.ValueOf(func() (a []string) {
-				for k, v := range interp.env {
-					a = append(a, k+"="+v)
-				}
-				return
-			})
-		}
-	}
-
-	if p = interp.binPkg["math/bits"]; p != nil {
-		// Do not trust extracted value maybe from another arch.
-		p["UintSize"] = reflect.ValueOf(constant.MakeInt64(bits.UintSize))
-	}
-}
-
 // ignoreScannerError returns true if the error from Go scanner can be safely ignored
 // to let the caller grab one more line before retrying to parse its input.
 func ignoreScannerError(e *scanner.Error, s string) bool {

interp/interp_export_test.go

@@ -33,7 +33,6 @@ func Hi(h Helloer) {
 //
 // Only the Wrap type definition needs to be exported to the interpreter (not
 // the interfaces and methods definitions).
-//
 type Wrap struct {
 	DoHello func() // related to the Hello() method.
 	// Other interface method wrappers...

interp/run.go

@@ -1050,19 +1050,24 @@ func genInterfaceWrapper(n *node, typ reflect.Type) func(*frame) reflect.Value {
 			return value
 		}
 	}
-	mn := typ.NumMethod()
+
+	// Retrieve methods from the interface wrapper, which is a struct where all fields
+	// except the first define the methods to implement.
+	// As the field name was generated with a prefixed first character (in order to avoid
+	// collisions with method names), this first character is ignored in comparisons.
+	wrap := getWrapper(n, typ)
+	mn := wrap.NumField() - 1
 	names := make([]string, mn)
 	methods := make([]*node, mn)
 	indexes := make([][]int, mn)
 	for i := 0; i < mn; i++ {
-		names[i] = typ.Method(i).Name
+		names[i] = wrap.Field(i + 1).Name[1:]
 		methods[i], indexes[i] = n.typ.lookupMethod(names[i])
 		if methods[i] == nil && n.typ.cat != nilT {
 			// interpreted method not found, look for binary method, possibly embedded
 			_, indexes[i], _, _ = n.typ.lookupBinMethod(names[i])
 		}
 	}
-	wrap := n.interp.getWrapper(typ)
 
 	return func(f *frame) reflect.Value {
 		v := value(f)

interp/scope.go

@@ -72,7 +72,6 @@ type symbol struct {
 //
 // In symbols, the index value corresponds to the index in scope.types, and at
 // execution to the index in frame, created exactly from the types layout.
-//
 type scope struct {
 	anc         *scope             // ancestor upper scope
 	child       []*scope           // included scopes