cmd/compile: emit a symbol for a method expression when using -dynlink

Fixes #25065

Change-Id: Ia3db518cfd9c006caf951b51342a491ac8372e9c
Reviewed-on: https://go-review.googlesource.com/c/153297Reviewed-by: Robert Griesemer <gri@golang.org>

misc/cgo/testshared/shared_test.go

@@ -911,3 +911,9 @@ func TestGlobal(t *testing.T) {
 func TestTestInstalledShared(t *testing.T) {
 	goCmd(nil, "test", "-linkshared", "-test.short", "sync/atomic")
 }
+
+// Test generated pointer method with -linkshared.
+// Issue 25065.
+func TestGeneratedMethod(t *testing.T) {
+	goCmd(t, "install", "-buildmode=shared", "-linkshared", "issue25065")
+}

misc/cgo/testshared/src/issue25065/a.go

+// Copyright 2018 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 issue25065 has a type with a method that is
+//  1) referenced in a method expression
+//  2) not called
+//  3) not converted to an interface
+//  4) is a value method but the reference is to the pointer method
+// These cases avoid the call to makefuncsym from typecheckfunc, but we
+// still need to call makefuncsym somehow or the symbol will not be defined.
+package issue25065
+
+type T int
+
+func (t T) M() {}
+
+func F() func(*T) {
+	return (*T).M
+}

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

@@ -2514,6 +2514,12 @@ func typecheckMethodExpr(n *Node) (res *Node) {
 	n.Xoffset = 0
 	n.SetClass(PFUNC)
 	// methodSym already marked n.Sym as a function.
+
+	// Issue 25065. Make sure that we emit the symbol for a local method.
+	if Ctxt.Flag_dynlink && !inimport && (t.Sym == nil || t.Sym.Pkg == localpkg) {
+		makefuncsym(n.Sym)
+	}
+
 	return n
 }