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Add support for emitting usage as a JSON schema #897

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Add support for emitting usage as a JSON schema #897

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4 changes: 4 additions & 0 deletions pkgs/args/lib/src/allow_anything_parser.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,10 @@ class AllowAnythingParser implements ArgParser {
@override
int? get usageLineLength => null;

@override
Map<String, Object?> get jsonSchema =>
const {'type': 'object', 'properties': {}};

@override
ArgParser addCommand(String name, [ArgParser? parser]) {
throw UnsupportedError(
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45 changes: 45 additions & 0 deletions pkgs/args/lib/src/arg_parser.dart
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Expand Up @@ -6,6 +6,7 @@ import 'dart:collection';

import 'allow_anything_parser.dart';
import 'arg_results.dart';
import 'json_schema.dart';
import 'option.dart';
import 'parser.dart';
import 'usage.dart';
Expand Down Expand Up @@ -392,4 +393,48 @@ class ArgParser {
/// Finds the option whose name or alias matches [name], or `null` if no
/// option has that name or alias.
Option? findByNameOrAlias(String name) => options[_aliases[name] ?? name];

Map<String, Object?> get jsonSchema {
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Documentation.

Why is this here? What can it be used for? By whom, and where?

final properties = <String, Schema>{};
final required = <String>[];
for (final option in _options.values) {
if (option.hide) continue;
var help = option.help;
final extras = <String>[];
if (option.defaultsTo != null) {
extras.add('defaults to "${option.defaultsTo}"');
}
if (option.allowed?.isNotEmpty ?? false) {
extras.add('allowed values: ${option.allowed?.join(', ')}');
}
if (extras.isNotEmpty) {
help = [
if (help != null) help,
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Can use ?help now?

...extras,
].join('\n');
}
final schema = switch (option.type) {
OptionType.flag => Schema.bool(
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@lrhn lrhn Jun 17, 2025 •
edited
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I'd just use BoolSchema directly, and probably drop the redirecting factories.

They're great for discovery, but this schema code here is completely internal, so we don't need that.

description: help,
),
OptionType.single => Schema.string(
description: help,
),
OptionType.multiple => Schema.list(
description: help,
items: Schema.string(),
),
_ => throw StateError('Unhandled Option Type: ${option.type.name}')
};

if (option.mandatory) {
required.add(option.name);
}
properties[option.name] = schema;
}
return Schema.object(
properties: properties,
required: required,
).asMap();
}
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@lrhn lrhn Jun 17, 2025 •
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So basically just:

  var properties = <String, Object?>{};
  var required = [];
  for (var option in _options.values) {
    if (option.hide) continue;
    var Option(:name, :type, :help) = option;
    final description = [?help,
      if (option.defaultsTo != null)  'defaults to "${option.defaultsTo}"'
      if (option.allowed?.isNotEmpty ?? false) 
         'allowed values: ${option.allowed?.join(', ')}'
    ].join('\n');
    properties[name] = {
       ...switch (type) {
         OptionType.bool => const { 'type': 'boolean' },
         OptionType.single => const { 'type': 'string' } ,
         OptionType.multi => const {
           'type': 'list',
           'items': {'type': 'string'},
         },
       }   
       if (description.isNotEmpty) 'description': description,
    };   
    if (option.mandatory) required.add(name);
  }  
  return {
    'type': 'object',
    'properties': properties,
    if (required.isNotEmpty) 'required': required
  };
}

I'm not sure a complete JSONSchema implementation is worth it, especially one we didn't write ourselves, but is vendoring and now have to maintain anyway.

}
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