[dev.typeparams] cmd/compile: make sure closures inside generic funcs are not compiled

Closures inside generic functions were being added to the g.target.Decls
list during noding, just like other closures. We remove generic
functions/methods from g.target.Decls, so they don't get compiled
(they're only available for export and stenciling). Most closures inside
generic functions/methods were similarly being removed from
g.target.Decls, because they have a generic parameter. But we need to
ensure no closures in generic function/methods are left remaining in
g.target.Decls, since we don't want them transformed and compiled.

So, we set a flag in (*irgen) that records when we are noding a
top-level generic function/method, and don't add any closures to
g.target.Decls when the flag is true.

Updates #47514

Change-Id: Id66b4c41d307ffa8f54cab6ce3646ade81606862
Reviewed-on: https://go-review.googlesource.com/c/go/+/340258
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/test/typeparam/issue47514.go b/test/typeparam/issue47514.go
new file mode 100644
index 0000000000..947f254003
--- /dev/null
+++ b/test/typeparam/issue47514.go
@@ -0,0 +1,20 @@
+// 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.
+
+// Test that closures inside a generic function are not exported,
+// even though not themselves generic.
+
+package main
+
+func Do[T any]() {
+	_ = func() string {
+		return ""
+	}
+}
+
+func main() {
+	Do[int]()
+}