[dev.typeparams] go/types: replace types2.Instantiate with Checker.Instantiate

This is a partial port of CL 333569 containing just changes to go/types.
Changes to the importer wil be made in a separate CL.

Change-Id: I9383e260b76402875ca6eb23c4478a6a3e8c1f0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/335071
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/go/types/api_test.go

@@ -1833,7 +1833,9 @@ func TestInstantiate(t *testing.T) {
 	}
 
 	// instantiation should succeed (no endless recursion)
-	res := Instantiate(token.NoPos, T, []Type{Typ[Int]})
+	// even with a nil *Checker
+	var check *Checker
+	res := check.Instantiate(token.NoPos, T, []Type{Typ[Int]}, nil, false)
 
 	// instantiated type should point to itself
 	if res.Underlying().(*Pointer).Elem() != res {

src/go/types/call.go

@@ -60,7 +60,7 @@ func (check *Checker) funcInst(x *operand, ix *typeparams.IndexExpr) {
 	}
 
 	// instantiate function signature
-	res := check.instantiate(x.Pos(), sig, targs, poslist).(*Signature)
+	res := check.Instantiate(x.Pos(), sig, targs, poslist, true).(*Signature)
 	assert(res.tparams == nil) // signature is not generic anymore
 	if inferred {
 		check.recordInferred(ix.Orig, targs, res)
@@ -333,7 +333,7 @@ func (check *Checker) arguments(call *ast.CallExpr, sig *Signature, targs []Type
 		}
 
 		// compute result signature
-		rsig = check.instantiate(call.Pos(), sig, targs, nil).(*Signature)
+		rsig = check.Instantiate(call.Pos(), sig, targs, nil, true).(*Signature)
 		assert(rsig.tparams == nil) // signature is not generic anymore
 		check.recordInferred(call, targs, rsig)
 

src/go/types/instance.go

@@ -16,6 +16,7 @@ type instance struct {
 	base    *Named      // parameterized type to be instantiated
 	targs   []Type      // type arguments
 	poslist []token.Pos // position of each targ; for error reporting only
+	verify  bool        // if set, constraint satisfaction is verified
 	value   Type        // base[targs...] after instantiation or Typ[Invalid]; nil if not yet set
 }
 
@@ -25,7 +26,7 @@ type instance struct {
 func (t *instance) expand() Type {
 	v := t.value
 	if v == nil {
-		v = t.check.instantiate(t.pos, t.base, t.targs, t.poslist)
+		v = t.check.Instantiate(t.pos, t.base, t.targs, t.poslist, t.verify)
 		if v == nil {
 			v = Typ[Invalid]
 		}

src/go/types/instantiate.go

@@ -9,71 +9,19 @@ import (
 	"go/token"
 )
 
-// Instantiate instantiates the type typ with the given type arguments.
-// typ must be a *Named or a *Signature type, it must be generic, and
-// its number of type parameters must match the number of provided type
-// arguments. The result is a new, instantiated (not generic) type of
-// the same kind (either a *Named or a *Signature). The type arguments
-// are not checked against the constraints of the type parameters.
-// Any methods attached to a *Named are simply copied; they are not
-// instantiated.
-func Instantiate(pos token.Pos, typ Type, targs []Type) (res Type) {
-	// TODO(gri) This code is basically identical to the prolog
-	//           in Checker.instantiate. Factor.
-	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:
-		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
-	}
-
-	// the number of supplied types must match the number of type parameters
-	if len(targs) != len(tparams) {
-		panic(fmt.Sprintf("%v: got %d arguments but %d type parameters", pos, len(targs), len(tparams)))
-	}
-
-	if len(tparams) == 0 {
-		return typ // nothing to do (minor optimization)
-	}
-
-	smap := makeSubstMap(tparams, targs)
-	return (*Checker)(nil).subst(pos, typ, smap)
-}
-
 // InstantiateLazy is like Instantiate, but avoids actually
 // instantiating the type until needed.
-func (check *Checker) InstantiateLazy(pos token.Pos, typ Type, targs []Type) (res Type) {
+func (check *Checker) InstantiateLazy(pos token.Pos, typ Type, targs []Type, verify bool) (res Type) {
 	base := asNamed(typ)
 	if base == nil {
 		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
 	}
 
 	return &instance{
-		check: check,
-		pos:   pos,
-		base:  base,
-		targs: targs,
+		check:  check,
+		pos:    pos,
+		base:   base,
+		targs:  targs,
+		verify: verify,
 	}
 }

src/go/types/sizeof_test.go

@@ -32,7 +32,7 @@ func TestSizeof(t *testing.T) {
 		{Chan{}, 12, 24},
 		{Named{}, 84, 160},
 		{TypeParam{}, 28, 48},
-		{instance{}, 44, 88},
+		{instance{}, 48, 96},
 		{top{}, 0, 0},
 
 		// Objects

src/go/types/subst.go

@@ -56,8 +56,24 @@ func (m *substMap) lookup(tpar *TypeParam) Type {
 	return tpar
 }
 
-func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist []token.Pos) (res Type) {
-	if trace {
+// Instantiate instantiates the type typ with the given type arguments
+// targs. To check type constraint satisfaction, verify must be set.
+// pos and posList correspond to the instantiation and type argument
+// positions respectively; posList may be nil or shorter than the number
+// of type arguments provided.
+// typ must be a *Named or a *Signature type, and its number of type
+// parameters must match the number of provided type arguments.
+// The receiver (check) may be nil if and only if verify is not set.
+// The result is a new, instantiated (not generic) type of the same kind
+// (either a *Named or a *Signature).
+// Any methods attached to a *Named are simply copied; they are not
+// instantiated.
+func (check *Checker) Instantiate(pos token.Pos, typ Type, targs []Type, posList []token.Pos, verify bool) (res Type) {
+	if verify && check == nil {
+		panic("cannot have nil receiver if verify is set")
+	}
+
+	if check != nil && trace {
 		check.trace(pos, "-- instantiating %s with %s", typ, typeListString(targs))
 		check.indent++
 		defer func() {
@@ -73,7 +89,7 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 		}()
 	}
 
-	assert(len(poslist) <= len(targs))
+	assert(len(posList) <= len(targs))
 
 	// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
 	var tparams []*TypeName
@@ -100,17 +116,19 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 			// 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
+		// only types and functions can be generic
+		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
 	}
 
 	// 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), _Todo, "got %d arguments but %d type parameters", len(targs), len(tparams))
-		return Typ[Invalid]
+		if check != nil {
+			check.errorf(atPos(pos), _Todo, "got %d arguments but %d type parameters", len(targs), len(tparams))
+			return Typ[Invalid]
+		}
+		panic(fmt.Sprintf("%v: got %d arguments but %d type parameters", pos, len(targs), len(tparams)))
 	}
 
 	if len(tparams) == 0 {
@@ -120,16 +138,18 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 	smap := makeSubstMap(tparams, targs)
 
 	// check bounds
-	for i, tname := range tparams {
-		// best position for error reporting
-		pos := pos
-		if i < len(poslist) {
-			pos = poslist[i]
-		}
+	if verify {
+		for i, tname := range tparams {
+			// best position for error reporting
+			pos := pos
+			if i < len(posList) {
+				pos = posList[i]
+			}
 
-		// stop checking bounds after the first failure
-		if !check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap) {
-			break
+			// stop checking bounds after the first failure
+			if !check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap) {
+				break
+			}
 		}
 	}
 

src/go/types/typexpr.go

@@ -413,12 +413,14 @@ func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *Named) Typ
 	// create a new type instance rather than instantiate the type
 	// TODO(gri) should do argument number check here rather than
 	//           when instantiating the type?
+	// TODO(gri) use InstantiateLazy here (cleanup)
 	typ := new(instance)
 	def.setUnderlying(typ)
 
 	typ.check = check
 	typ.pos = ix.X.Pos()
 	typ.base = base
+	typ.verify = true
 
 	// evaluate arguments (always)
 	typ.targs = check.typeList(ix.Indices)