Repository: apple/swift-argument-parser (swift)

Issue:
Repeated flags with FlagExclusivity.chooseFirst error instead of choosing first.
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Repeated flags defined with `FlagExclusivity.chooseFirst` error instead of choosing first.

**ArgumentParser version:** `master` at https://github.com/apple/swift-argument-parser/commit/58660b05c444b6916df980e7ad1e8f047cf14977
**Swift version:** Apple Swift version 5.2 (swiftlang-1103.0.30 clang-1103.0.30)

### Checklist
- [x] If possible, I've reproduced the issue using the `master` branch of this package
- [x] I've searched for [existing GitHub issues](https://github.com/apple/swift-argument-parser/issues)

### Steps to Reproduce
Use this simple program:
```
enum Enum: String, CaseIterable { case s, t, u }

struct Options: ParsableCommand {
  @Flag(name: .short, exclusivity: .chooseFirst)
  var flag1: Enum
}

let options = Options.parseOrExit()
print(options.flag1)
```
```
$ options -s -t
```
### Expected behavior
It should print "s" by itself, on a line

### Actual behavior
```
$ options -s -t
Error: Unknown option '-t'
Usage: options -s -t -u
```

Pull request description:
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Previously, using a set of flags declared with FlagExclusivity.chooseFirst would result in an error instead of choosing the first from the command line. (See https://github.com/apple/swift-argument-parser/issues/66).

### Detailed Design
Added a case handling repeating arguments in the `ArgumentSet.updateFlag` function.
The previous behaviour had the repeating-arguments-with-.chooseFirst situation going through the `default` case, which didn't add the current argument to the list of used arguments, which later caused an error due to the argument being incorrectly deemed to have not been used.

### Documentation Plan
No change to documentation is needed.

### Test Plan
Tests added to `FlagsEndToEndTests.testParsing_invert` and `FlagsEndToEndTests.testParsingCaseIterable_RepeatableFlags`.

### Source Impact
None.

### Checklist
- [x] I've added at least one test that validates that my change is working, if appropriate
- [x] I've followed the code style of the rest of the project
- [x] I've read the [Contribution Guidelines](CONTRIBUTING.md)
- [x] I've updated the documentation if necessary

This PR fixes https://github.com/apple/swift-argument-parser/issues/66

Patch:
diff --git a/Sources/ArgumentParser/Parsing/ArgumentSet.swift b/Sources/ArgumentParser/Parsing/ArgumentSet.swift
index 976f8223d..06edd0526 100644
--- a/Sources/ArgumentParser/Parsing/ArgumentSet.swift
+++ b/Sources/ArgumentParser/Parsing/ArgumentSet.swift
@@ -176,12 +176,14 @@ extension ArgumentSet {
     case(true, let previous?, .exclusive):
       // This value has already been set.
       throw ParserError.duplicateExclusiveValues(previous: previous.inputOrigin, duplicate: origin, originalInput: values.originalInput)
+    case (true, _, .chooseFirst):
+      values.update(forKey: key, inputOrigin: origin, initial: value, closure: { _ in })
     case (false, _, _), (_, _, .chooseLast):
       values.set(value, forKey: key, inputOrigin: origin)
-      return true
     default:
-      return hasUpdated
+      break
     }
+    return true
   }
   
   /// Creates an argument set for a pair of inverted Boolean flags.


Test patch:
diff --git a/Tests/EndToEndTests/FlagsEndToEndTests.swift b/Tests/EndToEndTests/FlagsEndToEndTests.swift
index 86cb9bf84..198f95fe2 100644
--- a/Tests/EndToEndTests/FlagsEndToEndTests.swift
+++ b/Tests/EndToEndTests/FlagsEndToEndTests.swift
@@ -80,10 +80,9 @@ extension FlagsEndToEndTests {
     AssertParse(Bar.self, ["--enable-logging"]) { options in
       XCTAssertEqual(options.logging, true)
     }
-// Can't test this yet, because .chooseFirst flags don't work
-//    AssertParse(Bar.self, ["--enable-logging", "--disable-logging"]) { options in
-//      XCTAssertEqual(options.logging, false)
-//    }
+    AssertParse(Bar.self, ["--disable-logging", "--enable-logging"]) { options in
+      XCTAssertEqual(options.logging, false)
+    }
   }
 }
 
@@ -263,3 +262,25 @@ extension FlagsEndToEndTests {
     XCTAssertThrowsError(try Qux.parse(["--pink", "--small", "--bloop"]))
   }
 }
+
+fileprivate struct RepeatOK: ParsableArguments {
+  @Flag(exclusivity: .chooseFirst)
+  var color: Color
+
+  @Flag(exclusivity: .chooseLast)
+  var shape: Shape
+}
+
+extension FlagsEndToEndTests {
+  func testParsingCaseIterable_RepeatableFlags() throws {
+    AssertParse(RepeatOK.self, ["--pink", "--purple", "--square"]) { options in
+      XCTAssertEqual(options.color, .pink)
+      XCTAssertEqual(options.shape, .square)
+    }
+
+    AssertParse(RepeatOK.self, ["--round", "--oblong", "--silver"]) { options in
+      XCTAssertEqual(options.color, .silver)
+      XCTAssertEqual(options.shape, .oblong)
+    }
+  }
+}