main.go: Custom `Required()` for `--project` argument

As far as I've been able to figure out, Kingpin doesn't have a mechanism
for dependent arguments or conditional requireds. Thus there's no way to
say "--position is only required if --write-config isn't passed".

In that case, write our own "required" check, to enforce the presence of
"--project" only if "--write-config" isn't passed. We duplicate the
message that Kingpin provides from `Required()` and leverage its error
formatting (we should probably use this for our other error messages
too).

The only difference is that `--position=POSITION` won't appear on the
first line of the Help text, which would have emphasised the fact that
it's required. It's possible to configure Kingpin's help text via
templates, but I don't think that's worth the trouble at this point.

1 files changed, 4 insertions, 1 deletions

diff --git a/main.go b/main.go
index 90bb653..38cd527 100644
--- a/main.go
+++ b/main.go
@@ -32,7 +32,6 @@ func main() {
 		"Project alias defined in config.toml.",
 	).
 		Short('p').
-		Required().
 		String()
 	time_spent := kingpin.Flag("time", "Time spent working on project.").
 		Short('t').
@@ -53,6 +52,10 @@ func main() {
 	kingpin.Version(VERSION)
 	kingpin.Parse()
 
+	if *project_alias == "" && !*write_config {
+		kingpin.Fatalf("required flag --project not provided, try --help")
+	}
+
 	if *write_config {
 		err = maybeWriteConfig()
 		if err != nil {