go/types: import instance.expand and subst.go from dev.go2go

Changes from dev.go2go:
 + A potentially latent bug is fixed when nilling out tparams in an
   instantiated signature (the resulting type could be Typ[Invalid])
 + Support for pointer designation is removed
 + instantiatedHash is updated to use '[]' rather than '()'
 + Several TODOs were added for me to follow-up on, rather than address
   in this CL
 + Error callsites are updated. Deciding on error codes and better error
   messages is punted to a later CL

These changes can be reviewed by comparing with Patchset #1 of this CL.

Change-Id: Ib5869586b8395419013010e2085cab877727d2ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/276253
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/check.go

@@ -82,6 +82,7 @@ type Checker struct {
 	objMap map[Object]*declInfo       // maps package-level objects and (non-interface) methods to declaration info
 	impMap map[importKey]*Package     // maps (import path, source directory) to (complete or fake) package
 	posMap map[*Interface][]token.Pos // maps interface types to lists of embedded interface positions
+	typMap map[string]*Named          // maps an instantiated named type hash to a *Named type
 	pkgCnt map[string]int             // counts number of imported packages with a given name (for better error messages)
 
 	// information collected during type-checking of a set of package files
@@ -194,6 +195,7 @@ func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Ch
 		objMap: make(map[Object]*declInfo),
 		impMap: make(map[importKey]*Package),
 		posMap: make(map[*Interface][]token.Pos),
+		typMap: make(map[string]*Named),
 		pkgCnt: make(map[string]int),
 	}
 }

src/go/types/subst.go

@@ -0,0 +1,542 @@
+// Copyright 2018 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.
+
+// This file implements instantiation of generic types
+// through substitution of type parameters by actual
+// types.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+	"go/token"
+)
+
+// TODO(rFindley) decide error codes for the errors in this file, and check
+//                if error spans can be improved
+
+type substMap struct {
+	// The targs field is currently needed for *Named type substitution.
+	// TODO(gri) rewrite that code, get rid of this field, and make this
+	//           struct just the map (proj)
+	targs []Type
+	proj  map[*TypeParam]Type
+}
+
+// makeSubstMap creates a new substitution map mapping tpars[i] to targs[i].
+// If targs[i] is nil, tpars[i] is not substituted.
+func makeSubstMap(tpars []*TypeName, targs []Type) *substMap {
+	assert(len(tpars) == len(targs))
+	proj := make(map[*TypeParam]Type, len(tpars))
+	for i, tpar := range tpars {
+		// We must expand type arguments otherwise *instance
+		// types end up as components in composite types.
+		// TODO(gri) explain why this causes problems, if it does
+		targ := expand(targs[i]) // possibly nil
+		targs[i] = targ
+		proj[tpar.typ.(*TypeParam)] = targ
+	}
+	return &substMap{targs, proj}
+}
+
+func (m *substMap) String() string {
+	return fmt.Sprintf("%s", m.proj)
+}
+
+func (m *substMap) empty() bool {
+	return len(m.proj) == 0
+}
+
+func (m *substMap) lookup(tpar *TypeParam) Type {
+	if t := m.proj[tpar]; t != nil {
+		return t
+	}
+	return tpar
+}
+
+func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist []token.Pos) (res Type) {
+	if trace {
+		check.trace(pos, "-- instantiating %s with %s", typ, typeListString(targs))
+		check.indent++
+		defer func() {
+			check.indent--
+			var under Type
+			if res != nil {
+				// Calling under() here may lead to endless instantiations.
+				// Test case: type T[P any] T[P]
+				// TODO(gri) investigate if that's a bug or to be expected.
+				under = res.Underlying()
+			}
+			check.trace(pos, "=> %s (under = %s)", res, under)
+		}()
+	}
+
+	assert(len(poslist) <= len(targs))
+
+	// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
+	var tparams []*TypeName
+	switch t := typ.(type) {
+	case *Named:
+		tparams = t.tparams
+	case *Signature:
+		tparams = t.tparams
+		defer func() {
+			// If we had an unexpected failure somewhere don't panic below when
+			// asserting res.(*Signature). Check for *Signature in case Typ[Invalid]
+			// is returned.
+			if _, ok := res.(*Signature); !ok {
+				return
+			}
+			// If the signature doesn't use its type parameters, subst
+			// will not make a copy. In that case, make a copy now (so
+			// we can set tparams to nil w/o causing side-effects).
+			if t == res {
+				copy := *t
+				res = &copy
+			}
+			// After instantiating a generic signature, it is not generic
+			// anymore; we need to set tparams to nil.
+			res.(*Signature).tparams = nil
+		}()
+
+	default:
+		check.dump("%v: cannot instantiate %v", pos, typ)
+		unreachable() // only defined types and (defined) functions can be generic
+	}
+
+	// the number of supplied types must match the number of type parameters
+	if len(targs) != len(tparams) {
+		// TODO(gri) provide better error message
+		check.errorf(atPos(pos), 0, "got %d arguments but %d type parameters", len(targs), len(tparams))
+		return Typ[Invalid]
+	}
+
+	if len(tparams) == 0 {
+		return typ // nothing to do (minor optimization)
+	}
+
+	smap := makeSubstMap(tparams, targs)
+
+	// check bounds
+	for i, tname := range tparams {
+		tpar := tname.typ.(*TypeParam)
+		iface := tpar.Bound()
+		if iface.Empty() {
+			continue // no type bound
+		}
+
+		targ := targs[i]
+
+		// best position for error reporting
+		pos := pos
+		if i < len(poslist) {
+			pos = poslist[i]
+		}
+
+		// The type parameter bound is parameterized with the same type parameters
+		// as the instantiated type; before we can use it for bounds checking we
+		// need to instantiate it with the type arguments with which we instantiate
+		// the parameterized type.
+		iface = check.subst(pos, iface, smap).(*Interface)
+
+		// targ must implement iface (methods)
+		// - check only if we have methods
+		check.completeInterface(token.NoPos, iface)
+		if len(iface.allMethods) > 0 {
+			// If the type argument is a pointer to a type parameter, the type argument's
+			// method set is empty.
+			// TODO(gri) is this what we want? (spec question)
+			if base, isPtr := deref(targ); isPtr && asTypeParam(base) != nil {
+				check.errorf(atPos(pos), 0, "%s has no methods", targ)
+				break
+			}
+			if m, wrong := check.missingMethod(targ, iface, true); m != nil {
+				// TODO(gri) needs to print updated name to avoid major confusion in error message!
+				//           (print warning for now)
+				// Old warning:
+				// check.softErrorf(pos, "%s does not satisfy %s (warning: name not updated) = %s (missing method %s)", targ, tpar.bound, iface, m)
+				if m.name == "==" {
+					// We don't want to report "missing method ==".
+					check.softErrorf(atPos(pos), 0, "%s does not satisfy comparable", targ)
+				} else if wrong != nil {
+					// TODO(gri) This can still report uninstantiated types which makes the error message
+					//           more difficult to read then necessary.
+					check.softErrorf(atPos(pos), 0,
+						"%s does not satisfy %s: wrong method signature\n\tgot  %s\n\twant %s",
+						targ, tpar.bound, wrong, m,
+					)
+				} else {
+					check.softErrorf(atPos(pos), 0, "%s does not satisfy %s (missing method %s)", targ, tpar.bound, m.name)
+				}
+				break
+			}
+		}
+
+		// targ's underlying type must also be one of the interface types listed, if any
+		if iface.allTypes == nil {
+			continue // nothing to do
+		}
+
+		// If targ is itself a type parameter, each of its possible types, but at least one, must be in the
+		// list of iface types (i.e., the targ type list must be a non-empty subset of the iface types).
+		if targ := asTypeParam(targ); targ != nil {
+			targBound := targ.Bound()
+			if targBound.allTypes == nil {
+				check.softErrorf(atPos(pos), 0, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
+				break
+			}
+			for _, t := range unpackType(targBound.allTypes) {
+				if !iface.isSatisfiedBy(t) {
+					// TODO(gri) match this error message with the one below (or vice versa)
+					check.softErrorf(atPos(pos), 0, "%s does not satisfy %s (%s type constraint %s not found in %s)", targ, tpar.bound, targ, t, iface.allTypes)
+					break
+				}
+			}
+			break
+		}
+
+		// Otherwise, targ's type or underlying type must also be one of the interface types listed, if any.
+		if !iface.isSatisfiedBy(targ) {
+			check.softErrorf(atPos(pos), 0, "%s does not satisfy %s (%s or %s not found in %s)", targ, tpar.bound, targ, under(targ), iface.allTypes)
+			break
+		}
+	}
+
+	return check.subst(pos, typ, smap)
+}
+
+// subst returns the type typ with its type parameters tpars replaced by
+// the corresponding type arguments targs, recursively.
+// subst is functional in the sense that it doesn't modify the incoming
+// type. If a substitution took place, the result type is different from
+// from the incoming type.
+func (check *Checker) subst(pos token.Pos, typ Type, smap *substMap) Type {
+	if smap.empty() {
+		return typ
+	}
+
+	// common cases
+	switch t := typ.(type) {
+	case *Basic:
+		return typ // nothing to do
+	case *TypeParam:
+		return smap.lookup(t)
+	}
+
+	// general case
+	subst := subster{check, pos, make(map[Type]Type), smap}
+	return subst.typ(typ)
+}
+
+type subster struct {
+	check *Checker
+	pos   token.Pos
+	cache map[Type]Type
+	smap  *substMap
+}
+
+func (subst *subster) typ(typ Type) Type {
+	switch t := typ.(type) {
+	case nil:
+		// Call typOrNil if it's possible that typ is nil.
+		panic("nil typ")
+
+	case *Basic, *bottom, *top:
+		// nothing to do
+
+	case *Array:
+		elem := subst.typOrNil(t.elem)
+		if elem != t.elem {
+			return &Array{len: t.len, elem: elem}
+		}
+
+	case *Slice:
+		elem := subst.typOrNil(t.elem)
+		if elem != t.elem {
+			return &Slice{elem: elem}
+		}
+
+	case *Struct:
+		if fields, copied := subst.varList(t.fields); copied {
+			return &Struct{fields: fields, tags: t.tags}
+		}
+
+	case *Pointer:
+		base := subst.typ(t.base)
+		if base != t.base {
+			return &Pointer{base: base}
+		}
+
+	case *Tuple:
+		return subst.tuple(t)
+
+	case *Signature:
+		// TODO(gri) rethink the recv situation with respect to methods on parameterized types
+		// recv := subst.var_(t.recv) // TODO(gri) this causes a stack overflow - explain
+		recv := t.recv
+		params := subst.tuple(t.params)
+		results := subst.tuple(t.results)
+		if recv != t.recv || params != t.params || results != t.results {
+			return &Signature{
+				rparams: t.rparams,
+				// TODO(rFindley) why can't we nil out tparams here, rather than in
+				//                instantiate above?
+				tparams:  t.tparams,
+				scope:    t.scope,
+				recv:     recv,
+				params:   params,
+				results:  results,
+				variadic: t.variadic,
+			}
+		}
+
+	case *Sum:
+		types, copied := subst.typeList(t.types)
+		if copied {
+			// Don't do it manually, with a Sum literal: the new
+			// types list may not be unique and NewSum may remove
+			// duplicates.
+			return NewSum(types)
+		}
+
+	case *Interface:
+		methods, mcopied := subst.funcList(t.methods)
+		types := t.types
+		if t.types != nil {
+			types = subst.typ(t.types)
+		}
+		embeddeds, ecopied := subst.typeList(t.embeddeds)
+		if mcopied || types != t.types || ecopied {
+			iface := &Interface{methods: methods, types: types, embeddeds: embeddeds}
+			subst.check.posMap[iface] = subst.check.posMap[t] // satisfy completeInterface requirement
+			subst.check.completeInterface(token.NoPos, iface)
+			return iface
+		}
+
+	case *Map:
+		key := subst.typ(t.key)
+		elem := subst.typ(t.elem)
+		if key != t.key || elem != t.elem {
+			return &Map{key: key, elem: elem}
+		}
+
+	case *Chan:
+		elem := subst.typ(t.elem)
+		if elem != t.elem {
+			return &Chan{dir: t.dir, elem: elem}
+		}
+
+	case *Named:
+		subst.check.indent++
+		defer func() {
+			subst.check.indent--
+		}()
+		dump := func(format string, args ...interface{}) {
+			if trace {
+				subst.check.trace(subst.pos, format, args...)
+			}
+		}
+
+		if t.tparams == nil {
+			dump(">>> %s is not parameterized", t)
+			return t // type is not parameterized
+		}
+
+		var newTargs []Type
+
+		if len(t.targs) > 0 {
+			// already instantiated
+			dump(">>> %s already instantiated", t)
+			assert(len(t.targs) == len(t.tparams))
+			// For each (existing) type argument targ, determine if it needs
+			// to be substituted; i.e., if it is or contains a type parameter
+			// that has a type argument for it.
+			for i, targ := range t.targs {
+				dump(">>> %d targ = %s", i, targ)
+				newTarg := subst.typ(targ)
+				if newTarg != targ {
+					dump(">>> substituted %d targ %s => %s", i, targ, newTarg)
+					if newTargs == nil {
+						newTargs = make([]Type, len(t.tparams))
+						copy(newTargs, t.targs)
+					}
+					newTargs[i] = newTarg
+				}
+			}
+
+			if newTargs == nil {
+				dump(">>> nothing to substitute in %s", t)
+				return t // nothing to substitute
+			}
+		} else {
+			// not yet instantiated
+			dump(">>> first instantiation of %s", t)
+			// TODO(rFindley) can we instead subst the tparam types here?
+			newTargs = subst.smap.targs
+		}
+
+		// before creating a new named type, check if we have this one already
+		h := instantiatedHash(t, newTargs)
+		dump(">>> new type hash: %s", h)
+		if named, found := subst.check.typMap[h]; found {
+			dump(">>> found %s", named)
+			subst.cache[t] = named
+			return named
+		}
+
+		// create a new named type and populate caches to avoid endless recursion
+		tname := NewTypeName(subst.pos, t.obj.pkg, t.obj.name, nil)
+		named := subst.check.NewNamed(tname, t.underlying, t.methods) // method signatures are updated lazily
+		named.tparams = t.tparams                                     // new type is still parameterized
+		named.targs = newTargs
+		subst.check.typMap[h] = named
+		subst.cache[t] = named
+
+		// do the substitution
+		dump(">>> subst %s with %s (new: %s)", t.underlying, subst.smap, newTargs)
+		named.underlying = subst.typOrNil(t.underlying)
+		named.orig = named.underlying // for cycle detection (Checker.validType)
+
+		return named
+
+	case *TypeParam:
+		return subst.smap.lookup(t)
+
+	case *instance:
+		// TODO(gri) can we avoid the expansion here and just substitute the type parameters?
+		return subst.typ(t.expand())
+
+	default:
+		panic("unimplemented")
+	}
+
+	return typ
+}
+
+// TODO(gri) Eventually, this should be more sophisticated.
+//           It won't work correctly for locally declared types.
+func instantiatedHash(typ *Named, targs []Type) string {
+	var buf bytes.Buffer
+	writeTypeName(&buf, typ.obj, nil)
+	buf.WriteByte('[')
+	writeTypeList(&buf, targs, nil, nil)
+	buf.WriteByte(']')
+
+	// With respect to the represented type, whether a
+	// type is fully expanded or stored as instance
+	// does not matter - they are the same types.
+	// Remove the instanceMarkers printed for instances.
+	res := buf.Bytes()
+	i := 0
+	for _, b := range res {
+		if b != instanceMarker {
+			res[i] = b
+			i++
+		}
+	}
+
+	return string(res[:i])
+}
+
+func typeListString(list []Type) string {
+	var buf bytes.Buffer
+	writeTypeList(&buf, list, nil, nil)
+	return buf.String()
+}
+
+// typOrNil is like typ but if the argument is nil it is replaced with Typ[Invalid].
+// A nil type may appear in pathological cases such as type T[P any] []func(_ T([]_))
+// where an array/slice element is accessed before it is set up.
+func (subst *subster) typOrNil(typ Type) Type {
+	if typ == nil {
+		return Typ[Invalid]
+	}
+	return subst.typ(typ)
+}
+
+func (subst *subster) var_(v *Var) *Var {
+	if v != nil {
+		if typ := subst.typ(v.typ); typ != v.typ {
+			copy := *v
+			copy.typ = typ
+			return &copy
+		}
+	}
+	return v
+}
+
+func (subst *subster) tuple(t *Tuple) *Tuple {
+	if t != nil {
+		if vars, copied := subst.varList(t.vars); copied {
+			return &Tuple{vars: vars}
+		}
+	}
+	return t
+}
+
+func (subst *subster) varList(in []*Var) (out []*Var, copied bool) {
+	out = in
+	for i, v := range in {
+		if w := subst.var_(v); w != v {
+			if !copied {
+				// first variable that got substituted => allocate new out slice
+				// and copy all variables
+				new := make([]*Var, len(in))
+				copy(new, out)
+				out = new
+				copied = true
+			}
+			out[i] = w
+		}
+	}
+	return
+}
+
+func (subst *subster) func_(f *Func) *Func {
+	if f != nil {
+		if typ := subst.typ(f.typ); typ != f.typ {
+			copy := *f
+			copy.typ = typ
+			return &copy
+		}
+	}
+	return f
+}
+
+func (subst *subster) funcList(in []*Func) (out []*Func, copied bool) {
+	out = in
+	for i, f := range in {
+		if g := subst.func_(f); g != f {
+			if !copied {
+				// first function that got substituted => allocate new out slice
+				// and copy all functions
+				new := make([]*Func, len(in))
+				copy(new, out)
+				out = new
+				copied = true
+			}
+			out[i] = g
+		}
+	}
+	return
+}
+
+func (subst *subster) typeList(in []Type) (out []Type, copied bool) {
+	out = in
+	for i, t := range in {
+		if u := subst.typ(t); u != t {
+			if !copied {
+				// first function that got substituted => allocate new out slice
+				// and copy all functions
+				new := make([]Type, len(in))
+				copy(new, out)
+				out = new
+				copied = true
+			}
+			out[i] = u
+		}
+	}
+	return
+}

src/go/types/type.go

@@ -313,7 +313,6 @@ type Interface struct {
 	allTypes   Type    // intersection of all embedded and locally declared types  (TODO(gri) need better field name)
 
 	obj Object // type declaration defining this interface; or nil (for better error messages)
-
 }
 
 // unpack unpacks a type into a list of types.
@@ -669,6 +668,14 @@ func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
 	return typ
 }
 
+func (check *Checker) NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
+	typ := &Named{check: check, obj: obj, orig: underlying, underlying: underlying, methods: methods}
+	if obj.typ == nil {
+		obj.typ = typ
+	}
+	return typ
+}
+
 // Obj returns the type name for the named type t.
 func (t *Named) Obj() *TypeName { return t.obj }
 
@@ -713,16 +720,15 @@ func (t *Named) AddMethod(m *Func) {
 type TypeParam struct {
 	check *Checker  // for lazy type bound completion
 	id    uint64    // unique id
-	ptr   bool      // pointer designation
 	obj   *TypeName // corresponding type name
 	index int       // parameter index
 	bound Type      // *Named or *Interface; underlying type is always *Interface
 }
 
 // NewTypeParam returns a new TypeParam.
-func (check *Checker) NewTypeParam(ptr bool, obj *TypeName, index int, bound Type) *TypeParam {
+func (check *Checker) NewTypeParam(obj *TypeName, index int, bound Type) *TypeParam {
 	assert(bound != nil)
-	typ := &TypeParam{check: check, id: check.nextId, ptr: ptr, obj: obj, index: index, bound: bound}
+	typ := &TypeParam{check: check, id: check.nextId, obj: obj, index: index, bound: bound}
 	check.nextId++
 	if obj.typ == nil {
 		obj.typ = typ
@@ -783,8 +789,19 @@ type instance struct {
 // The result is either an instantiated *Named type, or
 // Typ[Invalid] if there was an error.
 func (t *instance) expand() Type {
-	// TODO(rFindley) add this in a follow-up CL.
+	v := t.value
-	panic("not implemented")
+	if v == nil {
+		v = t.check.instantiate(t.pos, t.base, t.targs, t.poslist)
+		if v == nil {
+			v = Typ[Invalid]
+		}
+		t.value = v
+	}
+	// After instantiation we must have an invalid or a *Named type.
+	if debug && v != Typ[Invalid] {
+		_ = v.(*Named)
+	}
+	return v
 }
 
 // expand expands a type instance into its instantiated

src/go/types/typestring.go

@@ -333,9 +333,6 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 		prev = b
 
 		if t, _ := p.typ.(*TypeParam); t != nil {
-			if t.ptr {
-				buf.WriteByte('*')
-			}
 			writeType(buf, t, qf, visited)
 		} else {
 			buf.WriteString(p.name)