all: Add build constants for runtime.GOOS comparisons (#8442)

all: Add package runtimeos for runtime.GOOS comparisons

I grew tired of hand written string comparisons. This adds generated
constants for the GOOS values, and predefined Is$OS constants that can
be iffed on. In a couple of places I rewrote trivial switch:es to if:s,
and added Illumos where we checked for Solaris (because they are
effectively the same, and if we're going to target one of them that
would be Illumos...).

lib/osutil/atomic.go

@@ -9,8 +9,8 @@ package osutil
 import (
 	"errors"
 	"path/filepath"
-	"runtime"
 
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/fs"
 )
 
@@ -97,7 +97,7 @@ func (w *AtomicWriter) Close() error {
 		return infoErr
 	}
 	err := w.fs.Rename(w.next.Name(), w.path)
-	if runtime.GOOS == "windows" && fs.IsPermission(err) {
+	if build.IsWindows && fs.IsPermission(err) {
 		// On Windows, we might not be allowed to rename over the file
 		// because it's read-only. Get us some write permissions and try
 		// again.

lib/osutil/osutil.go

@@ -9,9 +9,9 @@ package osutil
 
 import (
 	"path/filepath"
-	"runtime"
 	"strings"
 
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/fs"
 	"github.com/syncthing/syncthing/lib/sync"
 )
@@ -90,7 +90,7 @@ func withPreparedTarget(filesystem fs.Filesystem, from, to string, f func() erro
 	}
 
 	// On Windows, make sure the destination file is writeable (or we can't delete it)
-	if runtime.GOOS == "windows" {
+	if build.IsWindows {
 		filesystem.Chmod(to, 0666)
 		if !strings.EqualFold(from, to) {
 			err := filesystem.Remove(to)

lib/osutil/osutil_test.go

@@ -10,10 +10,10 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strings"
 	"testing"
 
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/fs"
 	"github.com/syncthing/syncthing/lib/osutil"
 )
@@ -51,7 +51,7 @@ func TestIsDeleted(t *testing.T) {
 		}
 		fd.Close()
 	}
-	if runtime.GOOS != "windows" {
+	if !build.IsWindows {
 		// Can't create unreadable dir on windows
 		testFs.MkdirAll("inacc", 0777)
 		if err := testFs.Chmod("inacc", 0000); err == nil {
@@ -63,7 +63,7 @@ func TestIsDeleted(t *testing.T) {
 	}
 	for _, n := range []string{"Dir", "File", "Del"} {
 		if err := fs.DebugSymlinkForTestsOnly(testFs, testFs, strings.ToLower(n), "linkTo"+n); err != nil {
-			if runtime.GOOS == "windows" {
+			if build.IsWindows {
 				t.Skip("Symlinks aren't working")
 			}
 			t.Fatal(err)

lib/osutil/replacingwriter.go

@@ -9,7 +9,8 @@ package osutil
 import (
 	"bytes"
 	"io"
-	"runtime"
+
+	"github.com/syncthing/syncthing/lib/build"
 )
 
 type ReplacingWriter struct {
@@ -51,7 +52,7 @@ func (w ReplacingWriter) Write(bs []byte) (int, error) {
 // LineEndingsWriter returns a writer that writes platform-appropriate line
 // endings. (This is a no-op on non-Windows platforms.)
 func LineEndingsWriter(w io.Writer) io.Writer {
-	if runtime.GOOS != "windows" {
+	if !build.IsWindows {
 		return w
 	}
 	return &ReplacingWriter{

lib/osutil/rlimit_unix.go

@@ -10,8 +10,9 @@
 package osutil
 
 import (
-	"runtime"
 	"syscall"
+
+	"github.com/syncthing/syncthing/lib/build"
 )
 
 const (
@@ -36,7 +37,7 @@ func MaximizeOpenFileLimit() (int, error) {
 
 	// macOS doesn't like a soft limit greater then OPEN_MAX
 	// See also: man setrlimit
-	if runtime.GOOS == "darwin" && lim.Max > darwinOpenMax {
+	if build.IsDarwin && lim.Max > darwinOpenMax {
 		lim.Max = darwinOpenMax
 	}
 

lib/osutil/traversessymlink_test.go

@@ -9,9 +9,9 @@ package osutil_test
 import (
 	"os"
 	"path/filepath"
-	"runtime"
 	"testing"
 
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/fs"
 	"github.com/syncthing/syncthing/lib/osutil"
 )
@@ -22,7 +22,7 @@ func TestTraversesSymlink(t *testing.T) {
 	testFs := fs.NewFilesystem(fs.FilesystemTypeBasic, tmpDir)
 	testFs.MkdirAll("a/b/c", 0755)
 	if err := fs.DebugSymlinkForTestsOnly(testFs, testFs, filepath.Join("a", "b"), filepath.Join("a", "l")); err != nil {
-		if runtime.GOOS == "windows" {
+		if build.IsWindows {
 			t.Skip("Symlinks aren't working")
 		}
 		t.Fatal(err)
@@ -71,7 +71,7 @@ func TestIssue4875(t *testing.T) {
 	testFs := fs.NewFilesystem(fs.FilesystemTypeBasic, tmpDir)
 	testFs.MkdirAll(filepath.Join("a", "b", "c"), 0755)
 	if err := fs.DebugSymlinkForTestsOnly(testFs, testFs, filepath.Join("a", "b"), filepath.Join("a", "l")); err != nil {
-		if runtime.GOOS == "windows" {
+		if build.IsWindows {
 			t.Skip("Symlinks aren't working")
 		}
 		t.Fatal(err)