[dev.typeparams] Parse a generic type arg for generic function call

Will now run "go tool compile -G=2 -W=2" on a simple generic function
with one type parameter and a call to that function with one explicit
type argument. Next change will handle multiple type arguments.

Change-Id: Ia7d17ea2a02bf99bd50e673ac80ae4aad4c48440
Reviewed-on: https://go-review.googlesource.com/c/go/+/288432
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/noder/types.go b/src/cmd/compile/internal/noder/types.go
index b4ad9cfc5b8..1e719698582 100644
--- a/src/cmd/compile/internal/noder/types.go
+++ b/src/cmd/compile/internal/noder/types.go
@@ -39,7 +39,7 @@ func (g *irgen) typ(typ types2.Type) *types.Type {
 		// Ensure we calculate the size for all concrete types seen by
 		// the frontend. This is another heavy hammer for something that
 		// should really be the backend's responsibility instead.
-		if !res.IsUntyped() {
+		if res != nil && !res.IsUntyped() && !res.IsFuncArgStruct() {
 			types.CheckSize(res)
 		}
 	}
@@ -106,6 +106,22 @@ func (g *irgen) typ0(typ types2.Type) *types.Type {
 		tp.SetSym(g.sym(typ.Obj()))
 		return tp
 
+	case *types2.Tuple:
+		// Tuples are used for the type of a function call (i.e. the
+		// return value of the function).
+		if typ == nil {
+			return (*types.Type)(nil)
+		}
+		fields := make([]*types.Field, typ.Len())
+		for i := range fields {
+			fields[i] = g.param(typ.At(i))
+		}
+		t := types.NewStruct(types.LocalPkg, fields)
+		types.CheckSize(t)
+		// Can only set after doing the types.CheckSize()
+		t.StructType().Funarg = types.FunargResults
+		return t
+
 	default:
 		base.FatalfAt(src.NoXPos, "unhandled type: %v (%T)", typ, typ)
 		panic("unreachable")