[release-branch.go1.18] cmd/compile: fix re-export closure

For hidden closure built during stenciling to implement a function
instantiation, the function may come from other package, not local
package, which causes the ICE for code that re-export the hidden closure
after inlining.

To fix it, use the closure package for export writer when writing out
the closure itself.

Fixes #51423

Change-Id: I23b067ba14e2d602a0fc3b2e99bd9317afbe53ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/391574
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 9743e9b6d8)
Reviewed-on: https://go-review.googlesource.com/c/go/+/391774
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -1851,7 +1851,10 @@ func (w *exportWriter) expr(n ir.Node) {
 		n := n.(*ir.ClosureExpr)
 		w.op(ir.OCLOSURE)
 		w.pos(n.Pos())
+		old := w.currPkg
+		w.setPkg(n.Type().Pkg(), true)
 		w.signature(n.Type())
+		w.setPkg(old, true)
 
 		// Write out id for the Outer of each conditional variable. The
 		// conditional variable itself for this closure will be re-created

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

@@ -1374,7 +1374,9 @@ func (r *importReader) node() ir.Node {
 	case ir.OCLOSURE:
 		//println("Importing CLOSURE")
 		pos := r.pos()
+		r.setPkg()
 		typ := r.signature(nil, nil)
+		r.setPkg()
 
 		// All the remaining code below is similar to (*noder).funcLit(), but
 		// with Dcls and ClosureVars lists already set up

test/typeparam/issue51423.dir/a.go

@@ -0,0 +1,17 @@
+// Copyright 2022 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 Comparator[T any] func(v1, v2 T) int
+
+func CompareInt[T ~int](a, b T) int {
+	if a < b {
+		return -1
+	}
+	if a == b {
+		return 0
+	}
+	return 1
+}

test/typeparam/issue51423.dir/b.go

@@ -0,0 +1,11 @@
+package b
+
+import "./a"
+
+func C() a.Comparator[int] {
+	return a.CompareInt[int]
+}
+
+func main() {
+	_ = C()(1, 2)
+}

test/typeparam/issue51423.go

@@ -0,0 +1,7 @@
+// compiledir -G=3
+
+// Copyright 2022 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