[dev.typeparams] cmd/compile/internal/types2: replace types2.Instantiate with Checker.Instantiate

Allow Checker.Instantiate to work with a nil *Checker receiver
(for now). This opens the door to passing in a *Checker at all
times.

Also, added a verify flag to Instantiate, InstantiateLazy, and
instance, to be able to control if constraint satisfaction should
be checked or not.

Removed types2.Instantiate.

For #47103.

Change-Id: Ie00ce41b3e50a0fc4341e013922e5f874276d282
Reviewed-on: https://go-review.googlesource.com/c/go/+/333569
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

9 files changed, 56 insertions, 83 deletions

diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
index 14e64891b8..453fa40f2d 100644
--- a/src/cmd/compile/internal/importer/iimport.go
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -665,7 +665,8 @@ func (r *importReader) doType(base *types2.Named) types2.Type {
 		baseType := r.typ()
 		// The imported instantiated type doesn't include any methods, so
 		// we must always use the methods of the base (orig) type.
-		t := types2.Instantiate(pos, baseType, targs)
+		var check *types2.Checker // TODO provide a non-nil *Checker
+		t := check.Instantiate(pos, baseType, targs, nil, false)
 		return t
 
 	case unionType:
diff --git a/src/cmd/compile/internal/noder/reader2.go b/src/cmd/compile/internal/noder/reader2.go
index 89f224d389..92569ff843 100644
--- a/src/cmd/compile/internal/noder/reader2.go
+++ b/src/cmd/compile/internal/noder/reader2.go
@@ -224,7 +224,7 @@ func (r *reader2) doTyp() (res types2.Type) {
 		obj, targs := r.obj()
 		name := obj.(*types2.TypeName)
 		if len(targs) != 0 {
-			return r.p.check.InstantiateLazy(syntax.Pos{}, name.Type(), targs)
+			return r.p.check.InstantiateLazy(syntax.Pos{}, name.Type(), targs, false)
 		}
 		return name.Type()
 
diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index 1c535387d4..74e3da3fe1 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -1862,7 +1862,9 @@ func TestInstantiate(t *testing.T) {
 	}
 
 	// instantiation should succeed (no endless recursion)
-	res := Instantiate(nopos, T, []Type{Typ[Int]})
+	// even with a nil *Checker
+	var check *Checker
+	res := check.Instantiate(nopos, T, []Type{Typ[Int]}, nil, false)
 
 	// instantiated type should point to itself
 	if res.Underlying().(*Pointer).Elem() != res {
diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 3377270ef8..0d9637e696 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -56,7 +56,7 @@ func (check *Checker) funcInst(x *operand, inst *syntax.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(inst, targs, res)
@@ -326,7 +326,7 @@ func (check *Checker) arguments(call *syntax.CallExpr, sig *Signature, targs []T
 		}
 
 		// 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)
 
diff --git a/src/cmd/compile/internal/types2/instance.go b/src/cmd/compile/internal/types2/instance.go
index b133fd1e65..65c2015507 100644
--- a/src/cmd/compile/internal/types2/instance.go
+++ b/src/cmd/compile/internal/types2/instance.go
@@ -16,6 +16,7 @@ type instance struct {
 	base    *Named       // parameterized type to be instantiated
 	targs   []Type       // type arguments
 	poslist []syntax.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]
 		}
diff --git a/src/cmd/compile/internal/types2/instantiate.go b/src/cmd/compile/internal/types2/instantiate.go
index 85c897a909..b289607de6 100644
--- a/src/cmd/compile/internal/types2/instantiate.go
+++ b/src/cmd/compile/internal/types2/instantiate.go
@@ -9,71 +9,19 @@ import (
 	"fmt"
 )
 
-// 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 syntax.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 syntax.Pos, typ Type, targs []Type) (res Type) {
+func (check *Checker) InstantiateLazy(pos syntax.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,
 	}
 }
diff --git a/src/cmd/compile/internal/types2/sizeof_test.go b/src/cmd/compile/internal/types2/sizeof_test.go
index a51d0c43d5..f7f191f629 100644
--- a/src/cmd/compile/internal/types2/sizeof_test.go
+++ b/src/cmd/compile/internal/types2/sizeof_test.go
@@ -33,7 +33,7 @@ func TestSizeof(t *testing.T) {
 		{Chan{}, 12, 24},
 		{Named{}, 84, 160},
 		{TypeParam{}, 28, 48},
-		{instance{}, 52, 96},
+		{instance{}, 56, 104},
 		{top{}, 0, 0},
 
 		// Objects
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 6e4e778b20..32cf527372 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -53,8 +53,24 @@ func (m *substMap) lookup(tpar *TypeParam) Type {
 	return tpar
 }
 
-func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslist []syntax.Pos) (res Type) {
-	if check.conf.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 syntax.Pos, typ Type, targs []Type, posList []syntax.Pos, verify bool) (res Type) {
+	if verify && check == nil {
+		panic("cannot have nil receiver if verify is set")
+	}
+
+	if check != nil && check.conf.Trace {
 		check.trace(pos, "-- instantiating %s with %s", typ, typeListString(targs))
 		check.indent++
 		defer func() {
@@ -70,7 +86,7 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslis
 		}()
 	}
 
-	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
@@ -97,18 +113,19 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslis
 			// 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(pos, "got %d arguments but %d type parameters", len(targs), len(tparams))
-		return Typ[Invalid]
+		if check != nil {
+			check.errorf(pos, "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 {
@@ -118,15 +135,17 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslis
 	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]
-		}
-		// stop checking bounds after the first failure
-		if !check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap) {
-			break
+	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
+			}
 		}
 	}
 
diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index e861f7e784..d69dd3c496 100644
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -423,12 +423,14 @@ func (check *Checker) instantiatedType(x syntax.Expr, targs []syntax.Expr, def *
 	// 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 = x.Pos()
 	typ.base = base
+	typ.verify = true
 
 	// evaluate arguments (always)
 	typ.targs = check.typeList(targs)