cmd/compile/internal/types2: consolidate verification logic

Change an internal call of instantiateLazy to call Instantiate, so that
we can consolidate the logic for invoking verification.

This made verification of signatures lazy, which is not necessary but
should be harmless.

Change-Id: I2e59b04ac859e08c2e2910ded3c183093d1e34a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/342149
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/cmd/compile/internal/types2/instantiate.go

@@ -26,12 +26,12 @@ import (
 // instantiated.
 func (check *Checker) Instantiate(pos syntax.Pos, typ Type, targs []Type, posList []syntax.Pos, verify bool) (res Type) {
 	// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
-	var tparams []*TypeName
+	var inst Type
 	switch t := typ.(type) {
 	case *Named:
-		return check.instantiateLazy(pos, t, targs, posList, verify)
+		inst = check.instantiateLazy(pos, t, targs)
 	case *Signature:
-		tparams = t.TParams().list()
+		tparams := t.TParams().list()
 		defer func() {
 			// If we had an unexpected failure somewhere don't panic below when
 			// asserting res.(*Signature). Check for *Signature in case Typ[Invalid]
@@ -50,18 +50,35 @@ func (check *Checker) Instantiate(pos syntax.Pos, typ Type, targs []Type, posLis
 			// anymore; we need to set tparams to nil.
 			res.(*Signature).tparams = nil
 		}()
+		inst = check.instantiate(pos, typ, tparams, targs, nil)
 	default:
 		// only types and functions can be generic
 		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
 	}
-	inst := check.instantiate(pos, typ, tparams, targs, nil)
 
 	if verify {
-		assert(len(posList) <= len(targs))
+		if check == nil {
-		if len(tparams) == len(targs) {
+			panic("cannot have nil Checker if verifying constraints")
-			check.verify(pos, tparams, targs, posList)
 		}
+		assert(len(posList) <= len(targs))
+		check.later(func() {
+			// Collect tparams again because lazily loaded *Named types may not have
+			// had tparams set up above.
+			var tparams []*TypeName
+			switch t := typ.(type) {
+			case *Named:
+				tparams = t.TParams().list()
+			case *Signature:
+				tparams = t.TParams().list()
+			}
+			// Avoid duplicate errors; instantiate will have complained if tparams
+			// and targs do not have the same length.
+			if len(tparams) == len(targs) {
+				check.verify(pos, tparams, targs, posList)
+			}
+		})
 	}
+
 	return inst
 }
 
@@ -101,20 +118,7 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, tparams []*TypeName,
 
 // instantiateLazy avoids actually instantiating the type until needed. typ
 // must be a *Named type.
-func (check *Checker) instantiateLazy(pos syntax.Pos, orig *Named, targs []Type, posList []syntax.Pos, verify bool) Type {
+func (check *Checker) instantiateLazy(pos syntax.Pos, orig *Named, targs []Type) Type {
-	if verify {
-		if check == nil {
-			// Provide a more useful panic instead of panicking at check.later below.
-			panic("cannot have nil Checker if verifying constraints")
-		}
-		assert(len(posList) <= len(targs))
-		if orig.TParams().Len() == len(targs) {
-			check.later(func() {
-				check.verify(pos, orig.tparams.list(), targs, posList)
-			})
-		}
-	}
-
 	h := instantiatedHash(orig, targs)
 	if check != nil {
 		// typ may already have been instantiated with identical type arguments. In
@@ -136,9 +140,6 @@ func (check *Checker) instantiateLazy(pos syntax.Pos, orig *Named, targs []Type,
 }
 
 func (check *Checker) verify(pos syntax.Pos, tparams []*TypeName, targs []Type, posList []syntax.Pos) {
-	if check == nil {
-		panic("cannot have nil Checker if verifying constraints")
-	}
 	smap := makeSubstMap(tparams, targs)
 	for i, tname := range tparams {
 		// best position for error reporting

src/cmd/compile/internal/types2/typexpr.go

@@ -444,7 +444,7 @@ func (check *Checker) instantiatedType(x syntax.Expr, targsx []syntax.Expr, def
 		posList[i] = syntax.StartPos(arg)
 	}
 
-	typ := check.instantiateLazy(x.Pos(), base, targs, posList, true)
+	typ := check.Instantiate(x.Pos(), base, targs, posList, true)
 	def.setUnderlying(typ)
 
 	// make sure we check instantiation works at least once