Apply two upstream CL to mkwinsyscall (#278)

* Apply CL463216: write source to temp file if formatting fails

This change writes the unformatted Go source code to a temp file if
"format.Source" fails. Print the temp file path to the console to make
it easy to find. The source code is what causes formatting errors, and
it can be difficult to diagnose them without this context.

CL link: https://go-review.googlesource.com/c/sys/+/463216
commit: 4112509618ee88519f899be20efc6882496b57c8

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

* Apply CL463215: support "." and "-" in DLL name

This change adds "." and "-" support for DLL filenames in "//sys".

Supporting "." requires a change in how mkwinsyscall handles the
"= <filename>.<function>" syntax. Instead of assuming that only one "."
can appear in this string, now mkwinsyscall assumes that any additional
"." belongs to the filename.

Supporting "." also requires changing how Go identifiers are created for
each DLL. This change also allows mkwinsyscall to support "-". When
creating a Go identifier, "." and "-" in the DLL filename are replaced
with "_". Otherwise, mkwinsyscall would produce invalid Go code, causing
"format.Source" to fail.

CL link: https://go-review.googlesource.com/c/sys/+/463215
commit: 71da6904945ac440253cb5c132d64712f80ca497

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

---------

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

tools/mkwinsyscall/mkwinsyscall.go

@@ -477,15 +477,14 @@ func newFn(s string) (*Fn, error) {
 		return nil, errors.New("Could not extract dll name from \"" + f.src + "\"")
 	}
 	s = trim(s[1:])
-	a := strings.Split(s, ".")
-	switch len(a) {
-	case 1:
-		f.dllfuncname = a[0]
-	case 2:
-		f.dllname = a[0]
-		f.dllfuncname = a[1]
-	default:
-		return nil, errors.New("Could not extract dll name from \"" + f.src + "\"")
+	if i := strings.LastIndex(s, "."); i >= 0 {
+		f.dllname = s[:i]
+		f.dllfuncname = s[i+1:]
+	} else {
+		f.dllfuncname = s
+	}
+	if f.dllfuncname == "" {
+		return nil, fmt.Errorf("function name is not specified in %q", s)
 	}
 	if n := f.dllfuncname; endsIn(n, '?') {
 		f.dllfuncname = n[:len(n)-1]
@@ -502,7 +501,23 @@ func (f *Fn) DLLName() string {
 	return f.dllname
 }
 
-// DLLName returns DLL function name for function f.
+// DLLVar returns a valid Go identifier that represents DLLName.
+func (f *Fn) DLLVar() string {
+	id := strings.Map(func(r rune) rune {
+		switch r {
+		case '.', '-':
+			return '_'
+		default:
+			return r
+		}
+	}, f.DLLName())
+	if !token.IsIdentifier(id) {
+		panic(fmt.Errorf("could not create Go identifier for DLLName %q", f.DLLName()))
+	}
+	return id
+}
+
+// DLLFuncName returns DLL function name for function f.
 func (f *Fn) DLLFuncName() string {
 	if f.dllfuncname == "" {
 		return f.Name
@@ -648,6 +663,13 @@ func (f *Fn) HelperName() string {
 	return "_" + f.Name
 }
 
+// DLL is a DLL's filename and a string that is valid in a Go identifier that should be used when
+// naming a variable that refers to the DLL.
+type DLL struct {
+	Name string
+	Var  string
+}
+
 // Source files and functions.
 type Source struct {
 	Funcs           []*Fn
@@ -697,18 +719,20 @@ func ParseFiles(fs []string) (*Source, error) {
 }
 
 // DLLs return dll names for a source set src.
-func (src *Source) DLLs() []string {
+func (src *Source) DLLs() []DLL {
 	uniq := make(map[string]bool)
-	r := make([]string, 0)
+	r := make([]DLL, 0)
 	for _, f := range src.Funcs {
-		name := f.DLLName()
-		if _, found := uniq[name]; !found {
-			uniq[name] = true
-			r = append(r, name)
+		id := f.DLLVar()
+		if _, found := uniq[id]; !found {
+			uniq[id] = true
+			r = append(r, DLL{f.DLLName(), id})
 		}
 	}
 	if *sortdecls {
-		sort.Strings(r)
+		sort.Slice(r, func(i, j int) bool {
+			return r[i].Var < r[j].Var
+		})
 	}
 	return r
 }
@@ -878,6 +902,22 @@ func (src *Source) Generate(w io.Writer) error {
 	return nil
 }
 
+func writeTempSourceFile(data []byte) (string, error) {
+	f, err := os.CreateTemp("", "mkwinsyscall-generated-*.go")
+	if err != nil {
+		return "", err
+	}
+	_, err = f.Write(data)
+	if closeErr := f.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		os.Remove(f.Name()) // best effort
+		return "", err
+	}
+	return f.Name(), nil
+}
+
 func usage() {
 	fmt.Fprintf(os.Stderr, "usage: mkwinsyscall [flags] [path ...]\n")
 	flag.PrintDefaults()
@@ -904,7 +944,12 @@ func main() {
 
 	data, err := format.Source(buf.Bytes())
 	if err != nil {
-		log.Fatal(err)
+		log.Printf("failed to format source: %v", err)
+		f, err := writeTempSourceFile(buf.Bytes())
+		if err != nil {
+			log.Fatalf("failed to write unformatted source to file: %v", err)
+		}
+		log.Fatalf("for diagnosis, wrote unformatted source to %v", f)
 	}
 	if *filename == "" {
 		_, err = os.Stdout.Write(data)
@@ -970,10 +1015,10 @@ var (
 
 {{/* help functions */}}
 
-{{define "dlls"}}{{range .DLLs}}	mod{{.}} = {{newlazydll .}}
+{{define "dlls"}}{{range .DLLs}}	mod{{.Var}} = {{newlazydll .Name}}
 {{end}}{{end}}
 
-{{define "funcnames"}}{{range .DLLFuncNames}}	proc{{.DLLFuncName}} = mod{{.DLLName}}.NewProc("{{.DLLFuncName}}")
+{{define "funcnames"}}{{range .DLLFuncNames}}	proc{{.DLLFuncName}} = mod{{.DLLVar}}.NewProc("{{.DLLFuncName}}")
 {{end}}{{end}}
 
 {{define "helperbody"}}