[dev.typeparams] cmd/compile: call transformArgs before early typecheckaste in noder

In the cases where we do an early call to typecheckaste() in noder to
expose CONVIFACE nodes, we need a preceding call to transformArgs().
This is needed to allow typecheckaste() to run correctly, in the case of
f(g()), where g has multiple return values.

I also cleaned up the code a bit and commented the code in Call(), and
we do the call to typecheckaste() in several more cases.

In stencil.go:stencil(), I moved the transformCall earlier for the
OCALLMETH/ODOTMETH case, just as I did in my previous CL for
OCALL/OFUNCINST. By doing this, transformArgs no longer needs to deal
with the extra dictionary args. Therefore, I was able to simply
transformArgs() to look like typecheckargs() again, and make use of
RewriteMultiValue directly.

Updates #47514

Change-Id: I49eb82ac05707e50c2e2fb03e39458a70491d406
Reviewed-on: https://go-review.googlesource.com/c/go/+/340531
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/typeparam/issue47514b.go b/test/typeparam/issue47514b.go
new file mode 100644
index 0000000000..5428a0edc5
--- /dev/null
+++ b/test/typeparam/issue47514b.go
@@ -0,0 +1,19 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func Do[T any](do func() (T, string)) {
+	_ = func() (T, string) {
+		return do()
+	}
+}
+
+func main() {
+	Do[int](func() (int, string) {
+		return 3, "3"
+	})
+}