[dev.regabi] cmd/compile: exporting, importing, and inlining functions with OCLOSURE

I have exporting, importing, and inlining of functions with closures
working in all cases (issue #28727). all.bash runs successfully without
errors.

Approach:
  - Write out the Func type, Dcls, ClosureVars, and Body when exporting
    an OCLOSURE.

  - When importing an OCLOSURE, read in the type, dcls, closure vars,
    and body, and then do roughly equivalent code to (*noder).funcLit

  - During inlining of a closure within inlined function, create new
    nodes for all params and local variables (including closure
    variables), so they can have a new Curfn and some other field
    values. Must substitute not only on the Nbody of the closure, but
    also the Type, Cvars, and Dcl fields.

Fixes #28727

Change-Id: I4da1e2567c3fa31a5121afbe82dc4e5ee32b3170
Reviewed-on: https://go-review.googlesource.com/c/go/+/283112
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Trust: Dan Scales <danscales@google.com>

2 files changed, 26 insertions, 0 deletions

diff --git a/test/closure5.dir/a.go b/test/closure5.dir/a.go
new file mode 100644
index 0000000000..de8082b7b1
--- /dev/null
+++ b/test/closure5.dir/a.go
@@ -0,0 +1,11 @@
+// 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.
+
+// Check correctness of various closure corner cases
+// that are expected to be inlined
+
+package a
+
+func f() bool               { return true }
+func G() func() func() bool { return func() func() bool { return f } }
diff --git a/test/closure5.dir/main.go b/test/closure5.dir/main.go
new file mode 100644
index 0000000000..ee5dba6481
--- /dev/null
+++ b/test/closure5.dir/main.go
@@ -0,0 +1,15 @@
+// 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.
+
+// Check correctness of various closure corner cases
+// that are expected to be inlined
+package main
+
+import "a"
+
+func main() {
+	if !a.G()()() {
+		panic("FAIL")
+	}
+}