go/internal/gcimporter: rewrite interface receiver parameters

Tracking changes in go repo for unified IR.

See CL 421355.

Change-Id: Idc0d2afeb6f2241f3608cbdb0fbc128f8755ec55
Reviewed-on: https://go-review.googlesource.com/c/tools/+/421255
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

go/internal/gcimporter/gcimporter_test.go

@@ -372,14 +372,6 @@ func verifyInterfaceMethodRecvs(t *testing.T, named *types.Named, level int) {
 		return // not an interface
 	}
 
-	// The unified IR importer always sets interface method receiver
-	// parameters to point to the Interface type, rather than the Named.
-	// See #49906.
-	var want types.Type = named
-	if unifiedIR {
-		want = iface
-	}
-
 	// check explicitly declared methods
 	for i := 0; i < iface.NumExplicitMethods(); i++ {
 		m := iface.ExplicitMethod(i)
@@ -388,8 +380,8 @@ func verifyInterfaceMethodRecvs(t *testing.T, named *types.Named, level int) {
 			t.Errorf("%s: missing receiver type", m)
 			continue
 		}
-		if recv.Type() != want {
-			t.Errorf("%s: got recv type %s; want %s", m, recv.Type(), want)
+		if recv.Type() != named {
+			t.Errorf("%s: got recv type %s; want %s", m, recv.Type(), named)
 		}
 	}
 

go/internal/gcimporter/ureader_yes.go

@@ -512,10 +512,6 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types.Package, string) {
 
 			named.SetTypeParams(r.typeParamNames())
 
-			// TODO(mdempsky): Rewrite receiver types to underlying is an
-			// Interface? The go/types importer does this (I think because
-			// unit tests expected that), but cmd/compile doesn't care
-			// about it, so maybe we can avoid worrying about that here.
 			rhs := r.typ()
 			pk := r.p
 			pk.laterFor(named, func() {
@@ -527,6 +523,28 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types.Package, string) {
 					f()                        // initialize RHS
 				}
 				underlying := rhs.Underlying()
+
+				// If the underlying type is an interface, we need to
+				// duplicate its methods so we can replace the receiver
+				// parameter's type (#49906).
+				if iface, ok := underlying.(*types.Interface); ok && iface.NumExplicitMethods() != 0 {
+					methods := make([]*types.Func, iface.NumExplicitMethods())
+					for i := range methods {
+						fn := iface.ExplicitMethod(i)
+						sig := fn.Type().(*types.Signature)
+
+						recv := types.NewVar(fn.Pos(), fn.Pkg(), "", named)
+						methods[i] = types.NewFunc(fn.Pos(), fn.Pkg(), fn.Name(), types.NewSignature(recv, sig.Params(), sig.Results(), sig.Variadic()))
+					}
+
+					embeds := make([]types.Type, iface.NumEmbeddeds())
+					for i := range embeds {
+						embeds[i] = iface.EmbeddedType(i)
+					}
+
+					underlying = types.NewInterfaceType(methods, embeds)
+				}
+
 				named.SetUnderlying(underlying)
 			})