cmd/compile: fix import of functions of multiple nested closure

For import of functions with closures, the connections among closure
variables are constructed on-the-fly via CaptureName(). For multiple
nested closures, we need to temporarily set r.curfn to each closure we
construct, so that the processing of closure variables will be correct
for any nested closure inside that closure.

Fixes #44335

Change-Id: I34f99e2822250542528ff6b2232bf36756140868
Reviewed-on: https://go-review.googlesource.com/c/go/+/294212
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/typecheck/iimport.go

@@ -986,15 +986,19 @@ func (r *importReader) node() ir.Node {
 		fn.ClosureVars = cvars
 		r.allClosureVars = append(r.allClosureVars, cvars...)
 
-		fn.Dcl = r.readFuncDcls(fn)
-		body := r.stmtList()
+		fn.Inl = &ir.Inline{}
+		// Read in the Dcls and Body of the closure after temporarily
+		// setting r.curfn to fn.
+		r.funcBody(fn)
+		fn.Dcl = fn.Inl.Dcl
+		fn.Body = fn.Inl.Body
+		fn.Inl = nil
+
 		ir.FinishCaptureNames(pos, r.curfn, fn)
 
 		clo := ir.NewClosureExpr(pos, fn)
 		fn.OClosure = clo
 
-		fn.Body = body
-
 		return clo
 
 	// case OPTRLIT:

test/fixedbugs/issue44335.dir/a.go

@@ -0,0 +1,17 @@
+// 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 a
+
+type W struct {
+	M func(string) string
+}
+
+func FM(m string) func(W) {
+	return func(pw W) {
+		pw.M = func(string) string {
+			return m
+		}
+	}
+}

test/fixedbugs/issue44335.dir/b.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.
+
+package b
+
+import "./a"
+
+func F() {
+	a.FM("")
+}

test/fixedbugs/issue44335.go

@@ -0,0 +1,7 @@
+// compiledir
+
+// 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 ignored