[dev.typeparams] go/types: move interface checking into separate file

This is a port of CL 321549 to go/types. Specifically, the same checker
methods were moved.

Change-Id: I491a8c5a985d71ebb23e4b34541a557da0af0cfc
Reviewed-on: https://go-review.googlesource.com/c/go/+/324752
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/interface.go

@@ -0,0 +1,321 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"go/ast"
+	"go/internal/typeparams"
+	"go/token"
+	"sort"
+)
+
+func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, def *Named) {
+	var tlist *ast.Ident // "type" name of first entry in a type list declaration
+	var types []ast.Expr
+	for _, f := range iface.Methods.List {
+		if len(f.Names) > 0 {
+			// We have a method with name f.Names[0], or a type
+			// of a type list (name.Name == "type").
+			// (The parser ensures that there's only one method
+			// and we don't care if a constructed AST has more.)
+			name := f.Names[0]
+			if name.Name == "_" {
+				check.errorf(name, _BlankIfaceMethod, "invalid method name _")
+				continue // ignore
+			}
+
+			if name.Name == "type" {
+				// Always collect all type list entries, even from
+				// different type lists, under the assumption that
+				// the author intended to include all types.
+				types = append(types, f.Type)
+				if tlist != nil && tlist != name {
+					check.errorf(name, _Todo, "cannot have multiple type lists in an interface")
+				}
+				tlist = name
+				continue
+			}
+
+			typ := check.typ(f.Type)
+			sig, _ := typ.(*Signature)
+			if sig == nil {
+				if typ != Typ[Invalid] {
+					check.invalidAST(f.Type, "%s is not a method signature", typ)
+				}
+				continue // ignore
+			}
+
+			// Always type-check method type parameters but complain if they are not enabled.
+			// (This extra check is needed here because interface method signatures don't have
+			// a receiver specification.)
+			if sig.tparams != nil {
+				var at positioner = f.Type
+				if tparams := typeparams.Get(f.Type); tparams != nil {
+					at = tparams
+				}
+				check.errorf(at, _Todo, "methods cannot have type parameters")
+			}
+
+			// use named receiver type if available (for better error messages)
+			var recvTyp Type = ityp
+			if def != nil {
+				recvTyp = def
+			}
+			sig.recv = NewVar(name.Pos(), check.pkg, "", recvTyp)
+
+			m := NewFunc(name.Pos(), check.pkg, name.Name, sig)
+			check.recordDef(name, m)
+			ityp.methods = append(ityp.methods, m)
+		} else {
+			// We have an embedded type. completeInterface will
+			// eventually verify that we have an interface.
+			ityp.embeddeds = append(ityp.embeddeds, check.typ(f.Type))
+			check.posMap[ityp] = append(check.posMap[ityp], f.Type.Pos())
+		}
+	}
+
+	// type constraints
+	ityp.types = _NewSum(check.collectTypeConstraints(iface.Pos(), types))
+
+	if len(ityp.methods) == 0 && ityp.types == nil && len(ityp.embeddeds) == 0 {
+		// empty interface
+		ityp.allMethods = markComplete
+		return
+	}
+
+	// sort for API stability
+	sortMethods(ityp.methods)
+	sortTypes(ityp.embeddeds)
+
+	check.later(func() { check.completeInterface(iface.Pos(), ityp) })
+}
+
+func (check *Checker) collectTypeConstraints(pos token.Pos, types []ast.Expr) []Type {
+	list := make([]Type, 0, len(types)) // assume all types are correct
+	for _, texpr := range types {
+		if texpr == nil {
+			check.invalidAST(atPos(pos), "missing type constraint")
+			continue
+		}
+		list = append(list, check.varType(texpr))
+	}
+
+	// Ensure that each type is only present once in the type list.  Types may be
+	// interfaces, which may not be complete yet. It's ok to do this check at the
+	// end because it's not a requirement for correctness of the code.
+	// Note: This is a quadratic algorithm, but type lists tend to be short.
+	check.later(func() {
+		for i, t := range list {
+			if t := asInterface(t); t != nil {
+				check.completeInterface(types[i].Pos(), t)
+			}
+			if includes(list[:i], t) {
+				check.softErrorf(types[i], _Todo, "duplicate type %s in type list", t)
+			}
+		}
+	})
+
+	return list
+}
+
+// includes reports whether typ is in list.
+func includes(list []Type, typ Type) bool {
+	for _, e := range list {
+		if Identical(typ, e) {
+			return true
+		}
+	}
+	return false
+}
+
+func (check *Checker) completeInterface(pos token.Pos, ityp *Interface) {
+	if ityp.allMethods != nil {
+		return
+	}
+
+	// completeInterface may be called via the LookupFieldOrMethod,
+	// MissingMethod, Identical, or IdenticalIgnoreTags external API
+	// in which case check will be nil. In this case, type-checking
+	// must be finished and all interfaces should have been completed.
+	if check == nil {
+		panic("internal error: incomplete interface")
+	}
+
+	if trace {
+		// Types don't generally have position information.
+		// If we don't have a valid pos provided, try to use
+		// one close enough.
+		if !pos.IsValid() && len(ityp.methods) > 0 {
+			pos = ityp.methods[0].pos
+		}
+
+		check.trace(pos, "complete %s", ityp)
+		check.indent++
+		defer func() {
+			check.indent--
+			check.trace(pos, "=> %s (methods = %v, types = %v)", ityp, ityp.allMethods, ityp.allTypes)
+		}()
+	}
+
+	// An infinitely expanding interface (due to a cycle) is detected
+	// elsewhere (Checker.validType), so here we simply assume we only
+	// have valid interfaces. Mark the interface as complete to avoid
+	// infinite recursion if the validType check occurs later for some
+	// reason.
+	ityp.allMethods = markComplete
+
+	// Methods of embedded interfaces are collected unchanged; i.e., the identity
+	// of a method I.m's Func Object of an interface I is the same as that of
+	// the method m in an interface that embeds interface I. On the other hand,
+	// if a method is embedded via multiple overlapping embedded interfaces, we
+	// don't provide a guarantee which "original m" got chosen for the embedding
+	// interface. See also issue #34421.
+	//
+	// If we don't care to provide this identity guarantee anymore, instead of
+	// reusing the original method in embeddings, we can clone the method's Func
+	// Object and give it the position of a corresponding embedded interface. Then
+	// we can get rid of the mpos map below and simply use the cloned method's
+	// position.
+
+	var seen objset
+	var methods []*Func
+	mpos := make(map[*Func]token.Pos) // method specification or method embedding position, for good error messages
+	addMethod := func(pos token.Pos, m *Func, explicit bool) {
+		switch other := seen.insert(m); {
+		case other == nil:
+			methods = append(methods, m)
+			mpos[m] = pos
+		case explicit:
+			check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
+			check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
+		default:
+			// We have a duplicate method name in an embedded (not explicitly declared) method.
+			// Check method signatures after all types are computed (issue #33656).
+			// If we're pre-go1.14 (overlapping embeddings are not permitted), report that
+			// error here as well (even though we could do it eagerly) because it's the same
+			// error message.
+			check.later(func() {
+				if !check.allowVersion(m.pkg, 1, 14) || !check.identical(m.typ, other.Type()) {
+					check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
+					check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
+				}
+			})
+		}
+	}
+
+	for _, m := range ityp.methods {
+		addMethod(m.pos, m, true)
+	}
+
+	// collect types
+	allTypes := ityp.types
+
+	posList := check.posMap[ityp]
+	for i, typ := range ityp.embeddeds {
+		pos := posList[i] // embedding position
+		utyp := under(typ)
+		etyp := asInterface(utyp)
+		if etyp == nil {
+			if utyp != Typ[Invalid] {
+				var format string
+				if _, ok := utyp.(*_TypeParam); ok {
+					format = "%s is a type parameter, not an interface"
+				} else {
+					format = "%s is not an interface"
+				}
+				// TODO: correct error code.
+				check.errorf(atPos(pos), _InvalidIfaceEmbed, format, typ)
+			}
+			continue
+		}
+		check.completeInterface(pos, etyp)
+		for _, m := range etyp.allMethods {
+			addMethod(pos, m, false) // use embedding position pos rather than m.pos
+		}
+		allTypes = intersect(allTypes, etyp.allTypes)
+	}
+
+	if methods != nil {
+		sort.Sort(byUniqueMethodName(methods))
+		ityp.allMethods = methods
+	}
+	ityp.allTypes = allTypes
+}
+
+// intersect computes the intersection of the types x and y.
+// Note: A incomming nil type stands for the top type. A top
+// type result is returned as nil.
+func intersect(x, y Type) (r Type) {
+	defer func() {
+		if r == theTop {
+			r = nil
+		}
+	}()
+
+	switch {
+	case x == theBottom || y == theBottom:
+		return theBottom
+	case x == nil || x == theTop:
+		return y
+	case y == nil || x == theTop:
+		return x
+	}
+
+	xtypes := unpackType(x)
+	ytypes := unpackType(y)
+	// Compute the list rtypes which includes only
+	// types that are in both xtypes and ytypes.
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix this
+	var rtypes []Type
+	for _, x := range xtypes {
+		if includes(ytypes, x) {
+			rtypes = append(rtypes, x)
+		}
+	}
+
+	if rtypes == nil {
+		return theBottom
+	}
+	return _NewSum(rtypes)
+}
+
+func sortTypes(list []Type) {
+	sort.Stable(byUniqueTypeName(list))
+}
+
+// byUniqueTypeName named type lists can be sorted by their unique type names.
+type byUniqueTypeName []Type
+
+func (a byUniqueTypeName) Len() int           { return len(a) }
+func (a byUniqueTypeName) Less(i, j int) bool { return sortName(a[i]) < sortName(a[j]) }
+func (a byUniqueTypeName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
+func sortName(t Type) string {
+	if named := asNamed(t); named != nil {
+		return named.obj.Id()
+	}
+	return ""
+}
+
+func sortMethods(list []*Func) {
+	sort.Sort(byUniqueMethodName(list))
+}
+
+func assertSortedMethods(list []*Func) {
+	if !debug {
+		panic("internal error: assertSortedMethods called outside debug mode")
+	}
+	if !sort.IsSorted(byUniqueMethodName(list)) {
+		panic("internal error: methods not sorted")
+	}
+}
+
+// byUniqueMethodName method lists can be sorted by their unique method names.
+type byUniqueMethodName []*Func
+
+func (a byUniqueMethodName) Len() int           { return len(a) }
+func (a byUniqueMethodName) Less(i, j int) bool { return a[i].Id() < a[j].Id() }
+func (a byUniqueMethodName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

src/go/types/typexpr.go

@@ -12,7 +12,6 @@ import (
 	"go/constant"
 	"go/internal/typeparams"
 	"go/token"
-	"sort"
 	"strconv"
 	"strings"
 )
@@ -758,277 +757,6 @@ func (check *Checker) declareInSet(oset *objset, pos token.Pos, obj Object) bool
 	return true
 }
 
-func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, def *Named) {
-	var tlist *ast.Ident // "type" name of first entry in a type list declaration
-	var types []ast.Expr
-	for _, f := range iface.Methods.List {
-		if len(f.Names) > 0 {
-			// We have a method with name f.Names[0], or a type
-			// of a type list (name.Name == "type").
-			// (The parser ensures that there's only one method
-			// and we don't care if a constructed AST has more.)
-			name := f.Names[0]
-			if name.Name == "_" {
-				check.errorf(name, _BlankIfaceMethod, "invalid method name _")
-				continue // ignore
-			}
-
-			if name.Name == "type" {
-				// Always collect all type list entries, even from
-				// different type lists, under the assumption that
-				// the author intended to include all types.
-				types = append(types, f.Type)
-				if tlist != nil && tlist != name {
-					check.errorf(name, _Todo, "cannot have multiple type lists in an interface")
-				}
-				tlist = name
-				continue
-			}
-
-			typ := check.typ(f.Type)
-			sig, _ := typ.(*Signature)
-			if sig == nil {
-				if typ != Typ[Invalid] {
-					check.invalidAST(f.Type, "%s is not a method signature", typ)
-				}
-				continue // ignore
-			}
-
-			// Always type-check method type parameters but complain if they are not enabled.
-			// (This extra check is needed here because interface method signatures don't have
-			// a receiver specification.)
-			if sig.tparams != nil {
-				var at positioner = f.Type
-				if tparams := typeparams.Get(f.Type); tparams != nil {
-					at = tparams
-				}
-				check.errorf(at, _Todo, "methods cannot have type parameters")
-			}
-
-			// use named receiver type if available (for better error messages)
-			var recvTyp Type = ityp
-			if def != nil {
-				recvTyp = def
-			}
-			sig.recv = NewVar(name.Pos(), check.pkg, "", recvTyp)
-
-			m := NewFunc(name.Pos(), check.pkg, name.Name, sig)
-			check.recordDef(name, m)
-			ityp.methods = append(ityp.methods, m)
-		} else {
-			// We have an embedded type. completeInterface will
-			// eventually verify that we have an interface.
-			ityp.embeddeds = append(ityp.embeddeds, check.typ(f.Type))
-			check.posMap[ityp] = append(check.posMap[ityp], f.Type.Pos())
-		}
-	}
-
-	// type constraints
-	ityp.types = _NewSum(check.collectTypeConstraints(iface.Pos(), types))
-
-	if len(ityp.methods) == 0 && ityp.types == nil && len(ityp.embeddeds) == 0 {
-		// empty interface
-		ityp.allMethods = markComplete
-		return
-	}
-
-	// sort for API stability
-	sortMethods(ityp.methods)
-	sortTypes(ityp.embeddeds)
-
-	check.later(func() { check.completeInterface(iface.Pos(), ityp) })
-}
-
-func (check *Checker) completeInterface(pos token.Pos, ityp *Interface) {
-	if ityp.allMethods != nil {
-		return
-	}
-
-	// completeInterface may be called via the LookupFieldOrMethod,
-	// MissingMethod, Identical, or IdenticalIgnoreTags external API
-	// in which case check will be nil. In this case, type-checking
-	// must be finished and all interfaces should have been completed.
-	if check == nil {
-		panic("internal error: incomplete interface")
-	}
-
-	if trace {
-		// Types don't generally have position information.
-		// If we don't have a valid pos provided, try to use
-		// one close enough.
-		if !pos.IsValid() && len(ityp.methods) > 0 {
-			pos = ityp.methods[0].pos
-		}
-
-		check.trace(pos, "complete %s", ityp)
-		check.indent++
-		defer func() {
-			check.indent--
-			check.trace(pos, "=> %s (methods = %v, types = %v)", ityp, ityp.allMethods, ityp.allTypes)
-		}()
-	}
-
-	// An infinitely expanding interface (due to a cycle) is detected
-	// elsewhere (Checker.validType), so here we simply assume we only
-	// have valid interfaces. Mark the interface as complete to avoid
-	// infinite recursion if the validType check occurs later for some
-	// reason.
-	ityp.allMethods = markComplete
-
-	// Methods of embedded interfaces are collected unchanged; i.e., the identity
-	// of a method I.m's Func Object of an interface I is the same as that of
-	// the method m in an interface that embeds interface I. On the other hand,
-	// if a method is embedded via multiple overlapping embedded interfaces, we
-	// don't provide a guarantee which "original m" got chosen for the embedding
-	// interface. See also issue #34421.
-	//
-	// If we don't care to provide this identity guarantee anymore, instead of
-	// reusing the original method in embeddings, we can clone the method's Func
-	// Object and give it the position of a corresponding embedded interface. Then
-	// we can get rid of the mpos map below and simply use the cloned method's
-	// position.
-
-	var seen objset
-	var methods []*Func
-	mpos := make(map[*Func]token.Pos) // method specification or method embedding position, for good error messages
-	addMethod := func(pos token.Pos, m *Func, explicit bool) {
-		switch other := seen.insert(m); {
-		case other == nil:
-			methods = append(methods, m)
-			mpos[m] = pos
-		case explicit:
-			check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
-			check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
-		default:
-			// We have a duplicate method name in an embedded (not explicitly declared) method.
-			// Check method signatures after all types are computed (issue #33656).
-			// If we're pre-go1.14 (overlapping embeddings are not permitted), report that
-			// error here as well (even though we could do it eagerly) because it's the same
-			// error message.
-			check.later(func() {
-				if !check.allowVersion(m.pkg, 1, 14) || !check.identical(m.typ, other.Type()) {
-					check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
-					check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
-				}
-			})
-		}
-	}
-
-	for _, m := range ityp.methods {
-		addMethod(m.pos, m, true)
-	}
-
-	// collect types
-	allTypes := ityp.types
-
-	posList := check.posMap[ityp]
-	for i, typ := range ityp.embeddeds {
-		pos := posList[i] // embedding position
-		utyp := under(typ)
-		etyp := asInterface(utyp)
-		if etyp == nil {
-			if utyp != Typ[Invalid] {
-				var format string
-				if _, ok := utyp.(*_TypeParam); ok {
-					format = "%s is a type parameter, not an interface"
-				} else {
-					format = "%s is not an interface"
-				}
-				// TODO: correct error code.
-				check.errorf(atPos(pos), _InvalidIfaceEmbed, format, typ)
-			}
-			continue
-		}
-		check.completeInterface(pos, etyp)
-		for _, m := range etyp.allMethods {
-			addMethod(pos, m, false) // use embedding position pos rather than m.pos
-		}
-		allTypes = intersect(allTypes, etyp.allTypes)
-	}
-
-	if methods != nil {
-		sort.Sort(byUniqueMethodName(methods))
-		ityp.allMethods = methods
-	}
-	ityp.allTypes = allTypes
-}
-
-// intersect computes the intersection of the types x and y.
-// Note: A incomming nil type stands for the top type. A top
-// type result is returned as nil.
-func intersect(x, y Type) (r Type) {
-	defer func() {
-		if r == theTop {
-			r = nil
-		}
-	}()
-
-	switch {
-	case x == theBottom || y == theBottom:
-		return theBottom
-	case x == nil || x == theTop:
-		return y
-	case y == nil || x == theTop:
-		return x
-	}
-
-	xtypes := unpackType(x)
-	ytypes := unpackType(y)
-	// Compute the list rtypes which includes only
-	// types that are in both xtypes and ytypes.
-	// Quadratic algorithm, but good enough for now.
-	// TODO(gri) fix this
-	var rtypes []Type
-	for _, x := range xtypes {
-		if includes(ytypes, x) {
-			rtypes = append(rtypes, x)
-		}
-	}
-
-	if rtypes == nil {
-		return theBottom
-	}
-	return _NewSum(rtypes)
-}
-
-func sortTypes(list []Type) {
-	sort.Stable(byUniqueTypeName(list))
-}
-
-// byUniqueTypeName named type lists can be sorted by their unique type names.
-type byUniqueTypeName []Type
-
-func (a byUniqueTypeName) Len() int           { return len(a) }
-func (a byUniqueTypeName) Less(i, j int) bool { return sortName(a[i]) < sortName(a[j]) }
-func (a byUniqueTypeName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
-
-func sortName(t Type) string {
-	if named := asNamed(t); named != nil {
-		return named.obj.Id()
-	}
-	return ""
-}
-
-func sortMethods(list []*Func) {
-	sort.Sort(byUniqueMethodName(list))
-}
-
-func assertSortedMethods(list []*Func) {
-	if !debug {
-		panic("internal error: assertSortedMethods called outside debug mode")
-	}
-	if !sort.IsSorted(byUniqueMethodName(list)) {
-		panic("internal error: methods not sorted")
-	}
-}
-
-// byUniqueMethodName method lists can be sorted by their unique method names.
-type byUniqueMethodName []*Func
-
-func (a byUniqueMethodName) Len() int           { return len(a) }
-func (a byUniqueMethodName) Less(i, j int) bool { return a[i].Id() < a[j].Id() }
-func (a byUniqueMethodName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
-
 func (check *Checker) tag(t *ast.BasicLit) string {
 	if t != nil {
 		if t.Kind == token.STRING {
@@ -1162,41 +890,3 @@ func embeddedFieldIdent(e ast.Expr) *ast.Ident {
 	}
 	return nil // invalid embedded field
 }
-
-func (check *Checker) collectTypeConstraints(pos token.Pos, types []ast.Expr) []Type {
-	list := make([]Type, 0, len(types)) // assume all types are correct
-	for _, texpr := range types {
-		if texpr == nil {
-			check.invalidAST(atPos(pos), "missing type constraint")
-			continue
-		}
-		list = append(list, check.varType(texpr))
-	}
-
-	// Ensure that each type is only present once in the type list.  Types may be
-	// interfaces, which may not be complete yet. It's ok to do this check at the
-	// end because it's not a requirement for correctness of the code.
-	// Note: This is a quadratic algorithm, but type lists tend to be short.
-	check.later(func() {
-		for i, t := range list {
-			if t := asInterface(t); t != nil {
-				check.completeInterface(types[i].Pos(), t)
-			}
-			if includes(list[:i], t) {
-				check.softErrorf(types[i], _Todo, "duplicate type %s in type list", t)
-			}
-		}
-	})
-
-	return list
-}
-
-// includes reports whether typ is in list.
-func includes(list []Type, typ Type) bool {
-	for _, e := range list {
-		if Identical(typ, e) {
-			return true
-		}
-	}
-	return false
-}