From edb963e7e908535cfc9a9456609d87487f7ffd3c Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Wed, 18 Dec 2019 22:10:28 -0800
Subject: [PATCH] go/types: fixed testdata/linalg.go2 example

The new lazy method substitution code seems to work. The bug was
in the test, not in the implementation!

Change-Id: I39794743a01e9725d57f49ccd7c3751376cd01d6
---
 src/go/types/call.go             |  4 +---
 src/go/types/predicates.go       |  4 ++--
 src/go/types/subst.go            |  1 +
 src/go/types/testdata/linalg.go2 | 12 ++++--------
 src/go/types/testdata/tmp.go2    |  6 +++---
 5 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/src/go/types/call.go b/src/go/types/call.go
index f6b942da67..84bf6026f5 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -26,9 +26,7 @@ func (check *Checker) call(x *operand, e *ast.CallExpr) exprKind {
 		// conversion or type instantiation
 		T := x.typ
 		x.mode = invalid
-		// A parameterized type is only instantiated if it doesn't have an instantiation already (see named.targs).
-		// TODO(gri) This seems a bit subtle. Can we do better?
-		if named, _ := T.(*Named); named != nil && named.obj != nil && named.obj.IsParameterized() && named.targs == nil {
+		if isGeneric(T) {
 			// type instantiation
 			x.typ = check.typ(e)
 			if x.typ != Typ[Invalid] {
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 22d2a5c8cd..c7491a31f4 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -19,9 +19,9 @@ func isNamed(typ Type) bool {
 	return ok
 }
 
-// isGeneric reports whether a type is a generic, uninstantiated type
-// (generic signatures are not included).
+// isGeneric reports whether a type is a generic, uninstantiated type (generic signatures are not included).
 func isGeneric(typ Type) bool {
+	// A parameterized type is only instantiated if it doesn't have an instantiation already.
 	named, _ := typ.(*Named)
 	return named != nil && named.obj != nil && named.obj.IsParameterized() && named.targs == nil
 }
diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index e3ca4d3ab1..2c11799987 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -83,6 +83,7 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 		iface = check.subst(pos, iface, tparams, targs).(*Interface)
 
 		// update targ method signatures
+		// TODO(gri) This needs documentation and cleanups!
 		update := func(V Type, sig *Signature) *Signature {
 			V, _ = deref(V)
 			// check.dump(">>> %s: V = %s", pos, V)
diff --git a/src/go/types/testdata/linalg.go2 b/src/go/types/testdata/linalg.go2
index 1b44cfd5d1..55c671a8ce 100644
--- a/src/go/types/testdata/linalg.go2
+++ b/src/go/types/testdata/linalg.go2
@@ -61,7 +61,7 @@ contract Complex(T) {
 // ordered numeric types.
 type OrderedAbs(type T OrderedNumeric) T
 
-func (a OrderedAbs(T)) Abs() T {
+func (a OrderedAbs(T)) Abs() OrderedAbs(T) {
 	if a < 0 {
 		return -a
 	}
@@ -72,7 +72,7 @@ func (a OrderedAbs(T)) Abs() T {
 // complex types.
 type ComplexAbs(type T Complex) T
 
-func (a ComplexAbs(T)) Abs() T {
+func (a ComplexAbs(T)) Abs() ComplexAbs(T) {
 	r := float64(real(a))
 	i := float64(imag(a))
 	d := math.Sqrt(r * r + i * i)
@@ -80,13 +80,9 @@ func (a ComplexAbs(T)) Abs() T {
 }
 
 func OrderedAbsDifference(type T OrderedNumeric)(a, b T) T {
-	// TODO(gri) fix this
-	// return T(AbsDifference(OrderedAbs(T)(a), OrderedAbs(T)(b)))
-	return a
+	return T(AbsDifference(OrderedAbs(T)(a), OrderedAbs(T)(b)))
 }
 
 func ComplexAbsDifference(type T Complex)(a, b T) T {
-	// TODO(gri) fix this
-	// return T(AbsDifference(ComplexAbs(T)(a), ComplexAbs(T)(b)))
-	return a
+	return T(AbsDifference(ComplexAbs(T)(a), ComplexAbs(T)(b)))
 }
diff --git a/src/go/types/testdata/tmp.go2 b/src/go/types/testdata/tmp.go2
index 24adce03fe..4ba882f949 100644
--- a/src/go/types/testdata/tmp.go2
+++ b/src/go/types/testdata/tmp.go2
@@ -8,10 +8,10 @@ func f(type P interface{ m() P })(x P)
 
 type T(type P) P
 
-func (_ T(P)) m() P
+func (_ T(P)) m() T(P)
 
 func _(type Q)(x Q) {
-	f(T /* ERROR does not satisfy */ (Q))(T(Q)(x))
+	f(T(Q))(T(Q)(x))
 }
 
 // TODO(gri) Once the code above works, check the code below.
@@ -24,7 +24,7 @@ func AbsDifference(type T NumericAbs(T))()
 
 type OrderedAbs(type T) T
 
-func (a OrderedAbs(T)) Abs() T
+func (a OrderedAbs(T)) Abs() OrderedAbs(T)
 
 func OrderedAbsDifference(type T)() {
 	AbsDifference(OrderedAbs(T))()