[dev.typeparams] cmd/compile: allow generic funcs to call other generic funcs for stenciling

 - Handle generic function calling itself or another generic function in
   stenciling. This is easy - after it is created, just scan an
   instantiated generic function for function instantiations (that may
   needed to be stenciled), just like non-generic functions. The types
   in the function instantiation will already have been set by the
   stenciling.

 - Handle OTYPE nodes in subster.node() (allows for generic type
   conversions).

 - Eliminated some duplicated work in subster.typ().

 - Added new test case fact.go that tests a generic function calling
   itself, and simple generic type conversions.

 - Cause an error if a generic function is to be exported (which we
   don't handle yet).

 - Fixed some suggested changes in the add.go test case that I missed in
   the last review.

Change-Id: I5d61704254c27962f358d5a3d2e0c62a5099f148
Reviewed-on: https://go-review.googlesource.com/c/go/+/290469
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/test/typeparam/fact.go b/test/typeparam/fact.go
new file mode 100644
index 0000000000..e5e0ad4ff3
--- /dev/null
+++ b/test/typeparam/fact.go
@@ -0,0 +1,35 @@
+// 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
+
+import (
+	"fmt"
+)
+
+
+func fact[T interface { type float64 }](n T) T {
+	if n == T(1) {
+		return T(1)
+	}
+	return n * fact(n - T(1))
+}
+
+func main() {
+	got := fact(4.0)
+	want := 24.0
+	if got != want {
+		panic(fmt.Sprintf("Got %f, want %f", got, want))
+	}
+
+	// Re-enable when types2 bug is fixed (can't do T(1) with more than one
+	// type in the type list).
+	//got = fact(5)
+	//want = 120
+	//if want != got {
+	//	panic(fmt.Sprintf("Want %d, got %d", want, got))
+	//}
+}