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flags : reflection-powered general ParseArgs : uglier than tidy switch statements per cmd, but much easier to add new flags

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This commit is contained in:
bth 2026-01-21 11:44:14 -08:00
commit 6f9f5dbb23
5 changed files with 93 additions and 87 deletions
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82
flags/flags.go
View file

@ -11,6 +11,8 @@ import (
"github.com/brtholomy/um/go/cmd"
)
const INTERNAL_ERR_PREFIX = "um internal err: ParseArgs"
type Arg struct {
Val string
Help string
@ -61,9 +63,9 @@ func missingValue(args []string, i int) bool {
}
// if no value ahead in the args, print error and exit
func validValueOrExit(args []string, i int) {
func validValueOrExit(sub cmd.Subcommand, args []string, i int) {
if missingValue(args, i) {
log.Printf("um: %s needs a value assignment\n", args[i])
log.Printf("um %s: %s needs a value assignment\n", sub, args[i])
log.Fatal("try: um [cmd] --help")
}
}
@ -71,8 +73,8 @@ func validValueOrExit(args []string, i int) {
// 1. validate a Flag[string] by looking ahead in args, if missing, os.Exit(1)
// 2. increment the i to skip that value and return
// 3. fetch that value and return
func ValidateIncrementFetchOrExit(args []string, i int) (int, string) {
validValueOrExit(args, i)
func ValidateIncrementFetchOrExit(sub cmd.Subcommand, args []string, i int) (int, string) {
validValueOrExit(sub, args, i)
return i + 1, args[i+1]
}
@ -88,6 +90,9 @@ func HelpInvalidArg(sub cmd.Subcommand, arg string) {
// and os.Exit(0)
func Help(sub cmd.Subcommand, summary string, opts any) {
v := reflect.ValueOf(opts)
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
t := v.Type()
// everything should go to either stderr or stdout:
@ -118,3 +123,72 @@ func Help(sub cmd.Subcommand, summary string, opts any) {
w.Flush()
os.Exit(0)
}
// parse the commandline args
//
// reflect on the incoming opts struct filled out with flags.Arg, flags.Flag[string], flags.Flag[string]
// and fill their "Val" field appropriately.
//
// WARN: incoming opts must be a pointer!
// WORB: opts struct must list its Arg types first and in expected order
// NOTE: uglier than the pretty switch statements I had per cmd, but much more convenient.
func ParseArgs(sub cmd.Subcommand, summary string, args []string, opts any) {
// immediately get the underlying value of the incoming pointer:
v := reflect.ValueOf(opts)
if v.Kind() == reflect.Ptr {
v = v.Elem()
} else {
log.Fatalf("%s needs a pointer to a struct: %#v", INTERNAL_ERR_PREFIX, opts)
}
if v.Kind() != reflect.Struct {
log.Fatalf("%s needs an underlying struct: %#v", INTERNAL_ERR_PREFIX, opts)
}
// for all args, iterate through all opts fields and reflect on type
argloop:
for i := 0; i < len(args); i++ {
arg := args[i]
for j := 0; j < v.NumField(); j++ {
field := v.Field(j)
if field.Kind() != reflect.Struct {
log.Fatalf("%s needs a struct of flag types: %#v is type: %s", INTERNAL_ERR_PREFIX, field, field.Kind())
}
val := field.FieldByName("Val")
// NORT: FieldByName().String() won't panic if not present, as with Arg type, just prints "<invalid Value>"
long := field.FieldByName("Long").String()
short := field.FieldByName("Short").String()
if !val.CanSet() {
log.Fatalf("%s failed to set flag value: %#v", INTERNAL_ERR_PREFIX, field)
}
switch field.Interface().(type) {
case Arg:
// NOTE: we assume the opts struct lists its Arg types first and in order
if j == i && !HasDashPrefix(arg) {
val.SetString(arg)
continue argloop
}
case Flag[bool]:
if arg == long || arg == short {
val.SetBool(true)
if long == "--help" {
Help(sub, summary, opts)
}
continue argloop
}
case Flag[string]:
if arg == long || arg == short {
fetch := ""
i, fetch = ValidateIncrementFetchOrExit(sub, args, i)
val.SetString(fetch)
continue argloop
}
default:
log.Fatalf("um internal err: unrecognized flag type in opts struct: %#v", field)
}
}
// BLAK: if we didn't skip ahead, arg didn't match:
HelpInvalidArg(sub, arg)
Help(sub, summary, opts)
}
}

18
last/last.go
View file

@ -31,20 +31,6 @@ func initOpts() options {
}
}
func parseArgs(args []string) options {
opts := initOpts()
for _, arg := range args {
switch {
case arg == opts.Help.Long || arg == opts.Help.Short:
flags.Help(CMD, SUMMARY, opts)
default:
flags.HelpInvalidArg(CMD, arg)
flags.Help(CMD, SUMMARY, opts)
}
}
return opts
}
// get the lexical last file from GLOB
func GlobLast(glob string) (string, error) {
// NOTE: filepath.Glob is more reliable than a manual ls call:
@ -59,7 +45,9 @@ func GlobLast(glob string) (string, error) {
}
func Last(args []string) {
_ = parseArgs(args)
opts := initOpts()
flags.ParseArgs(CMD, SUMMARY, args, &opts)
s, err := GlobLast(GLOB)
if err != nil {
log.Fatalf("um %s: %v", cmd.Last, err)

22
next/next.go
View file

@ -36,24 +36,6 @@ func initOpts() options {
}
}
func parseArgs(args []string) options {
opts := initOpts()
for i, arg := range args {
switch {
case i == 0 && !flags.HasDashPrefix(arg):
opts.Descriptor.Val = arg
case i == 1 && !flags.HasDashPrefix(arg):
opts.Tags.Val = arg
case arg == opts.Help.Long || arg == opts.Help.Short:
flags.Help(CMD, SUMMARY, opts)
default:
flags.HelpInvalidArg(CMD, arg)
flags.Help(CMD, SUMMARY, opts)
}
}
return opts
}
// takes the complete last file string
// returns the number as string
func numFromLast(l string) (string, error) {
@ -116,7 +98,9 @@ func emacsNext(f string, tags string) error {
}
func Next(args []string) {
opts := parseArgs(args)
opts := initOpts()
flags.ParseArgs(CMD, SUMMARY, args, &opts)
l, err := last.GlobLast(last.GLOB)
if err != nil {
log.Fatalf("um %s: %v", CMD, err)

33
sort/sort.go
View file

@ -33,31 +33,6 @@ func initOpts() options {
}
}
func parseArgs(args []string) options {
opts := initOpts()
for i := 0; i < len(args); i++ {
arg := args[i]
switch {
case arg == opts.Source.Long || arg == opts.Source.Short:
i, opts.Source.Val = flags.ValidateIncrementFetchOrExit(args, i)
case arg == opts.Key.Long || arg == opts.Key.Short:
i, opts.Key.Val = flags.ValidateIncrementFetchOrExit(args, i)
case arg == opts.Write.Long || arg == opts.Write.Short:
opts.Write.Val = true
case arg == opts.Help.Long || arg == opts.Help.Short:
flags.Help(CMD, SUMMARY, opts)
default:
flags.HelpInvalidArg(CMD, arg)
flags.Help(CMD, SUMMARY, opts)
}
}
if !opts.Key.IsSet() {
flags.HelpRequired(CMD, opts.Key.Long)
flags.Help(CMD, SUMMARY, opts)
}
return opts
}
// reads files from stdin if present, otherwise from the filename:
func fileListSplitMaybeStdin(f string) []string {
filelist, err := pipe.GetStdin()
@ -112,7 +87,13 @@ func write(file string, content string) {
}
func Sort(args []string) {
opts := parseArgs(args)
opts := initOpts()
flags.ParseArgs(CMD, SUMMARY, args, &opts)
// BORK: by hand for now:
if !opts.Key.IsSet() {
flags.HelpRequired(CMD, opts.Key.Long)
flags.Help(CMD, SUMMARY, opts)
}
sslice := fileListSplitMaybeStdin(opts.Source.Val)
kslice := fileListSplit(opts.Key.Val)

27
tag/tag.go
View file

@ -31,31 +31,10 @@ func initOpts() options {
}
}
func parseArgs(args []string) options {
opts := initOpts()
for i := 0; i < len(args); i++ {
arg := args[i]
switch {
case i == 0 && !flags.HasDashPrefix(arg):
opts.Query.Val = arg
case arg == opts.Invert.Long || arg == opts.Invert.Short:
opts.Invert.Val = true
case arg == opts.Verbose.Long || arg == opts.Verbose.Short:
opts.Verbose.Val = true
case arg == opts.Date.Long || arg == opts.Date.Short:
i, opts.Date.Val = flags.ValidateIncrementFetchOrExit(args, i)
case arg == opts.Help.Long || arg == opts.Help.Short:
flags.Help(CMD, SUMMARY, opts)
default:
flags.HelpInvalidArg(CMD, arg)
flags.Help(CMD, SUMMARY, opts)
}
}
return opts
}
func Tag(args []string) {
opts := parseArgs(args)
opts := initOpts()
flags.ParseArgs(CMD, SUMMARY, args, &opts)
queries := parseQuery(opts.Query.Val)
entries := entriesGlobOrStdin(last.GLOB)