argparse: allow positional args to be optional

Add 'optional' property to 'argparse.positionalArg'. This leads to the
following behavior if an arg isn't specified on the command line:

- If 'required' is true, exit with the appropriate usage message.
- If 'required' is false, stop processing positional arguments. The arg
  values are never set, leaving them with the default values with which they
  were originally specified.

For now, mark all existing positional arguments as required to avoid changes
to behavior.

Signed-off-by: Victoria Dye <[email protected]>

Author: vdye

cmd/git-bundle-server/delete.go

@@ -34,7 +34,7 @@ data.`
 
 func (d *deleteCmd) Run(ctx context.Context, args []string) error {
 	parser := argparse.NewArgParser(d.logger, "git-bundle-server delete <route>")
-	route := parser.PositionalString("route", "the route to delete")
+	route := parser.PositionalString("route", "the route to delete", true)
 	parser.Parse(ctx, args)
 
 	repoProvider := utils.GetDependency[core.RepositoryProvider](ctx, d.container)

cmd/git-bundle-server/init.go

@@ -36,9 +36,9 @@ should be hosted at '<route>'.`
 
 func (i *initCmd) Run(ctx context.Context, args []string) error {
 	parser := argparse.NewArgParser(i.logger, "git-bundle-server init <url> <route>")
-	url := parser.PositionalString("url", "the URL of a repository to clone")
+	url := parser.PositionalString("url", "the URL of a repository to clone", true)
 	// TODO: allow parsing <route> out of <url>
-	route := parser.PositionalString("route", "the route to host the specified repo")
+	route := parser.PositionalString("route", "the route to host the specified repo", true)
 	parser.Parse(ctx, args)
 
 	repoProvider := utils.GetDependency[core.RepositoryProvider](ctx, i.container)

cmd/git-bundle-server/start.go

@@ -34,7 +34,7 @@ specified '<route>'.`
 
 func (s *startCmd) Run(ctx context.Context, args []string) error {
 	parser := argparse.NewArgParser(s.logger, "git-bundle-server start <route>")
-	route := parser.PositionalString("route", "the route for which bundles should be generated")
+	route := parser.PositionalString("route", "the route for which bundles should be generated", true)
 	parser.Parse(ctx, args)
 
 	repoProvider := utils.GetDependency[core.RepositoryProvider](ctx, s.container)

cmd/git-bundle-server/stop.go

@@ -33,7 +33,7 @@ specified '<route>'.`
 
 func (s *stopCmd) Run(ctx context.Context, args []string) error {
 	parser := argparse.NewArgParser(s.logger, "git-bundle-server stop <route>")
-	route := parser.PositionalString("route", "the route for which bundles should stop being generated")
+	route := parser.PositionalString("route", "the route for which bundles should stop being generated", true)
 	parser.Parse(ctx, args)
 
 	repoProvider := utils.GetDependency[core.RepositoryProvider](ctx, s.container)

cmd/git-bundle-server/update.go

@@ -36,7 +36,7 @@ bundles, and update the bundle list.`
 
 func (u *updateCmd) Run(ctx context.Context, args []string) error {
 	parser := argparse.NewArgParser(u.logger, "git-bundle-server update <route>")
-	route := parser.PositionalString("route", "the route to update")
+	route := parser.PositionalString("route", "the route to update", true)
 	parser.Parse(ctx, args)
 
 	repoProvider := utils.GetDependency[core.RepositoryProvider](ctx, u.container)

internal/argparse/argparse.go

@@ -15,6 +15,7 @@ const usageExitCode int = 2
 type positionalArg struct {
 	name        string
 	description string
+	required    bool
 	value       interface{}
 }
 
@@ -93,31 +94,33 @@ func (a *argParser) Subcommand(subcommand Subcommand) {
 	a.subcommands[subcommand.Name()] = subcommand
 }
 
-func (a *argParser) PositionalStringVar(name string, description string, arg *string) {
+func (a *argParser) PositionalStringVar(name string, description string, arg *string, required bool) {
 	a.positionalArgs = append(a.positionalArgs, &positionalArg{
 		name:        name,
 		description: description,
+		required:    required,
 		value:       arg,
 	})
 }
 
-func (a *argParser) PositionalString(name string, description string) *string {
+func (a *argParser) PositionalString(name string, description string, required bool) *string {
 	arg := new(string)
-	a.PositionalStringVar(name, description, arg)
+	a.PositionalStringVar(name, description, arg, required)
 	return arg
 }
 
-func (a *argParser) PositionalListVar(name string, description string, arg *[]string) {
+func (a *argParser) PositionalListVar(name string, description string, arg *[]string, required bool) {
 	a.positionalArgs = append(a.positionalArgs, &positionalArg{
 		name:        name,
 		description: description,
+		required:    required,
 		value:       arg,
 	})
 }
 
-func (a *argParser) PositionalList(name string, description string) *[]string {
+func (a *argParser) PositionalList(name string, description string, required bool) *[]string {
 	arg := &[]string{}
-	a.PositionalListVar(name, description, arg)
+	a.PositionalListVar(name, description, arg, required)
 	return arg
 }
 
@@ -131,7 +134,14 @@ func (a *argParser) Parse(ctx context.Context, args []string) {
 	if len(a.subcommands) > 0 && len(a.positionalArgs) > 0 {
 		panic("cannot mix subcommands and positional args")
 	}
+
+	mustBeOptional := false
 	for i, positionalArg := range a.positionalArgs {
+		mustBeOptional = mustBeOptional || !positionalArg.required
+		if mustBeOptional && positionalArg.required {
+			panic("cannot have required args after optional args")
+		}
+
 		if i < len(a.positionalArgs)-1 {
 			// Only the last positional arg can be a list
 			_, isList := positionalArg.value.(*[]string)
@@ -165,13 +175,17 @@ func (a *argParser) Parse(ctx context.Context, args []string) {
 	} else {
 		// Handle positional args
 		for _, arg := range a.positionalArgs {
-			// First, try single string case
-			sPtr, isStr := arg.value.(*string)
-			if isStr {
-				if a.NArg() == 0 {
+			if a.NArg() == 0 {
+				if arg.required {
 					a.Usage(ctx, "No value specified for required argument '%s'", arg.name)
+				} else {
+					break
 				}
+			}
 
+			// First, try single string case
+			sPtr, isStr := arg.value.(*string)
+			if isStr {
 				*sPtr = a.Arg(0)
 				a.argOffset++
 				continue