syscall: switch go:generate directives back to mksyscall_windows.go

Adjust mksyscall_windows.go to activate module mode and set
-mod=readonly, and to suppress its own deprecation warning when run
from within GOROOT/src.

We can't vendor the mkwinsyscall tool in to the std module directly,
because std-vendored dependencies (unlike the dependencies of all
other modules) turn into actual, distinct packages in 'std' when
viewed from outside the 'std' module. We don't want to introduce a
binary in the 'std' meta-pattern, but we also don't particularly want
to add more special-cases to the 'go' command right now when we have
an existing wrapper program that can do the job.

I also regenerated the affected packages to ensure that they are
consistent with the current version of mksyscall, which produced some
declaration-order changes in
internal/syscall/windows/zsyscall_windows.go.

Fixes #41916
Updates #25922

Change-Id: If6e6f8ba3dd372a7ecd6820ee6c0ca38d55f0f35
Reviewed-on: https://go-review.googlesource.com/c/go/+/261499
Trust: Bryan C. Mills <bcmills@google.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

2 files changed, 38 insertions, 4 deletions

diff --git a/src/syscall/mksyscall_windows.go b/src/syscall/mksyscall_windows.go
index d66bf7865f..240254b2c7 100644
--- a/src/syscall/mksyscall_windows.go
+++ b/src/syscall/mksyscall_windows.go
@@ -4,9 +4,11 @@
 
 // +build ignore
 
+// mksyscall_windows wraps golang.org/x/sys/windows/mkwinsyscall.
 package main
 
 import (
+	"bytes"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -14,11 +16,43 @@ import (
 )
 
 func main() {
-	os.Stderr.WriteString("WARNING: Please switch from using:\n    go run $GOROOT/src/syscall/mksyscall_windows.go\nto using:\n    go run golang.org/x/sys/windows/mkwinsyscall\n")
-	args := append([]string{"run", "golang.org/x/sys/windows/mkwinsyscall"}, os.Args[1:]...)
-	cmd := exec.Command(filepath.Join(runtime.GOROOT(), "bin", "go"), args...)
+	goTool := filepath.Join(runtime.GOROOT(), "bin", "go")
+
+	listCmd := exec.Command(goTool, "list", "-m")
+	listCmd.Env = append(os.Environ(), "GO111MODULE=on")
+
+	var (
+		cmdEnv  []string
+		modArgs []string
+	)
+	if out, err := listCmd.Output(); err == nil && string(bytes.TrimSpace(out)) == "std" {
+		// Force module mode to use mkwinsyscall at the same version as the x/sys
+		// module vendored into the standard library.
+		cmdEnv = append(os.Environ(), "GO111MODULE=on")
+
+		// Force -mod=readonly instead of the default -mod=vendor.
+		//
+		// mkwinsyscall is not itself vendored into the standard library, and it is
+		// not feasible to do so at the moment: std-vendored libraries are included
+		// in the "std" meta-pattern (because in general they *are* linked into
+		// users binaries separately from the original import paths), and we can't
+		// allow a binary in the "std" meta-pattern.
+		modArgs = []string{"-mod=readonly"}
+	} else {
+		// Nobody outside the standard library should be using this wrapper: other
+		// modules can vendor in the mkwinsyscall tool directly (as described in
+		// https://golang.org/issue/25922), so they don't need this wrapper to
+		// set module mode and -mod=readonly explicitly.
+		os.Stderr.WriteString("WARNING: Please switch from using:\n    go run $GOROOT/src/syscall/mksyscall_windows.go\nto using:\n    go run golang.org/x/sys/windows/mkwinsyscall\n")
+	}
+
+	args := append([]string{"run"}, modArgs...)
+	args = append(args, "golang.org/x/sys/windows/mkwinsyscall")
+	args = append(args, os.Args[1:]...)
+	cmd := exec.Command(goTool, args...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
+	cmd.Env = cmdEnv
 	err := cmd.Run()
 	if err != nil {
 		os.Exit(1)
diff --git a/src/syscall/syscall.go b/src/syscall/syscall.go
index 980ef9d27f..2e7a3ae5f2 100644
--- a/src/syscall/syscall.go
+++ b/src/syscall/syscall.go
@@ -26,7 +26,7 @@
 //
 package syscall
 
-//go:generate go run golang.org/x/sys/windows/mkwinsyscall -systemdll -output zsyscall_windows.go syscall_windows.go security_windows.go
+//go:generate go run ./mksyscall_windows.go -systemdll -output zsyscall_windows.go syscall_windows.go security_windows.go
 
 // StringByteSlice converts a string to a NUL-terminated []byte,
 // If s contains a NUL byte this function panics instead of