net: adjust build tags for darwin libc calls

Support for direct libc calls was added in CL 446178 but the build
tags weren't quite activating it when cgo was not enabled. Adjust them
and add a new supporting file for darwin.

This should use the new direct libc calls with both CGO_ENABLED=0 and
CGO_ENABLED=1 when building for darwin.

Updates #12524

Change-Id: Ieee4b298dee13f389ed3a63c0a4a3a18c9180163
Reviewed-on: https://go-review.googlesource.com/c/go/+/448020
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Dan Peterson <danp@danp.net>
Auto-Submit: Ian Lance Taylor <iant@google.com>

Author: danp

src/net/cgo_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build cgo && !netgo && (darwin || dragonfly || freebsd)
+//go:build cgo && !netgo && (dragonfly || freebsd)
 
 package net
 

src/net/cgo_darwin.go

@@ -0,0 +1,9 @@
+// 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 net
+
+import "internal/syscall/unix"
+
+const cgoAddrInfoFlags = (unix.AI_CANONNAME | unix.AI_V4MAPPED | unix.AI_ALL) & unix.AI_MASK

src/net/cgo_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !cgo || netgo
+//go:build (!cgo && !darwin) || netgo
 
 package net
 

src/net/cgo_unix.go

@@ -7,7 +7,7 @@
 // Instead of C.foo it uses _C_foo, which is defined in either
 // cgo_unix_cgo.go or cgo_unix_syscall.go
 
-//go:build cgo && !netgo && unix
+//go:build !netgo && ((cgo && unix) || darwin)
 
 package net
 

src/net/cgo_unix_syscall.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build cgo && !netgo && darwin
+//go:build !netgo && darwin
 
 package net
 

src/net/cgo_unix_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build cgo && !netgo && unix
+//go:build (cgo || darwin) && !netgo && unix
 
 package net
 

src/net/netgo.go

@@ -4,9 +4,9 @@
 
 // Default netGo to true if the netgo build tag is being used, or the
 // C library DNS routines are not available. Note that the C library
-// routines are always available on Windows.
+// routines are always available on Darwin and Windows.
 
-//go:build netgo || (!cgo && !windows)
+//go:build netgo || (!cgo && !darwin && !windows)
 
 package net
 

src/net/netgo_unix_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (!cgo || netgo) && (darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris)
+//go:build (!cgo || netgo) && (dragonfly || freebsd || linux || netbsd || openbsd || solaris)
 
 package net