Add native response file support

CHANGELOG.md

@@ -9,6 +9,7 @@ Add new items at the end of the relevant section under **Unreleased**.
 ### Additions
 
 - `CommandConfiguration` now accepts a `helpBanner`, a string printed verbatim above the overview on a command's help screen and inherited by its subcommands unless they provide their own banner or the empty string.
+- Commands can now opt in to response-file expansion by setting the `responseFilePrefix` property on their `CommandConfiguration` to the character that should introduce a response-file reference (for example, `static let configuration = CommandConfiguration(responseFilePrefix: "@")`). The property defaults to `nil`, meaning response-file expansion is disabled unless the root command opts in.
 
 ---
 

README.md

@@ -68,6 +68,32 @@ OPTIONS:
   -h, --help              Show help for this command.
 ```
 
+## Response Files
+
+Swift Argument Parser can expand response files, letting you store command-line arguments in text files. This is especially useful for commands with many arguments or for reusable configurations. Opt in on your root command by setting the `responseFilePrefix` property in its `CommandConfiguration` to the character that should introduce a response-file reference (commonly `@`):
+
+```swift
+struct Repeat: ParsableCommand {
+    static let configuration = CommandConfiguration(responseFilePrefix: "@")
+    // ...
+}
+```
+
+```bash
+# Store arguments in a file
+$ echo "--count 5 --include-counter hello" > args.txt
+
+# Use the response file with @filename syntax
+$ repeat @args.txt
+1: hello
+2: hello
+3: hello
+4: hello
+5: hello
+```
+
+Response files support multiple formats, comments, quoted arguments, and can even reference other response files. See the [Response Files documentation](https://swiftpackageindex.com/apple/swift-argument-parser/documentation/argumentparser/responsefiles) for complete details.
+
 ## Documentation
 
 For guides, articles, and API documentation see the

Sources/ArgumentParser/CMakeLists.txt

@@ -33,6 +33,7 @@ add_library(ArgumentParser
   Parsing/Parsed.swift
   Parsing/ParsedValues.swift
   Parsing/ParserError.swift
+  Parsing/ResponseFileExpander.swift
   Parsing/SplitArguments.swift
 
   Usage/DumpHelpGenerator.swift

Sources/ArgumentParser/Documentation.docc/ArgumentParser.md

@@ -10,7 +10,7 @@ Begin by declaring a type that defines
 the information that you need to collect from the command line.
 Decorate each stored property with one of `ArgumentParser`'s property wrappers,
 declare conformance to ``ParsableCommand``,
-and implement your command's logic in its `run()` method. 
+and implement your command's logic in its `run()` method.
 For `async` renditions of `run`, declare ``AsyncParsableCommand`` conformance instead.
 
 ```swift
@@ -33,7 +33,7 @@ struct Repeat: ParsableCommand {
 }
 ```
 
-When a user executes your command, 
+When a user executes your command,
 the `ArgumentParser` library parses the command-line arguments,
 instantiates your command type,
 and then either calls your `run()` method or exits with a useful message.
@@ -58,6 +58,7 @@ and then either calls your `run()` method or exits with a useful message.
 ### Arguments, Options, and Flags
 
 - <doc:DeclaringArguments>
+- <doc:ResponseFiles>
 - ``Argument``
 - ``Option``
 - ``Flag``