Fix an issue with 'DynamicCaptures' where there is no captures.

Author: rxwei

Diff for: Sources/_StringProcessing/RegexDSL/Core.swift

@@ -87,7 +87,13 @@ extension RegexProtocol {
     guard let result = executor.execute(input: input) else {
       return nil
     }
-    return RegexMatch(range: result.range, captures: () as! Capture)
+    let convertedCapture: Capture
+    if Capture.self == DynamicCaptures.self {
+      convertedCapture = DynamicCaptures.tuple([]) as! Capture
+    } else {
+      convertedCapture = () as! Capture
+    }
+    return RegexMatch(range: result.range, captures: convertedCapture)
   }
 }
 

Diff for: Sources/_StringProcessing/RegexDSL/DynamicCaptures.swift

@@ -12,6 +12,10 @@ public enum DynamicCaptures: Equatable {
   indirect case optional(DynamicCaptures?)
   indirect case array([DynamicCaptures])
 
+  public static var empty: Self {
+    .tuple([])
+  }
+
   internal init(_ capture: Capture) {
     switch capture {
     case .atom(let atom):

Diff for: Tests/RegexDSLTests/RegexDSLTests.swift

@@ -184,13 +184,25 @@ class RegexDSLTests: XCTestCase {
   }
 
   func testDynamicCaptures() throws {
-    let regex = try Regex(#"([0-9A-F]+)(?:\.\.([0-9A-F]+))?\s+;\s+(\w+).*"#)
-    let line = """
-      A6F0..A6F1    ; Extend # Mn   [2] BAMUM COMBINING MARK KOQNDON..BAMUM COMBINING MARK TUKWENTIS
-      """
-    let captures = try XCTUnwrap(line.match(regex)?.captures)
-    XCTAssertEqual(
-        captures,
-        .tuple([.substring("A6F0"), .optional(.substring("A6F1")), .substring("Extend")]))
+    do {
+      let regex = try Regex("aabcc.")
+      let line = "aabccd"
+      let captures = try XCTUnwrap(line.match(regex)?.captures)
+      XCTAssertEqual(captures, .empty)
+    }
+    do {
+      let regex = try Regex(#"([0-9A-F]+)(?:\.\.([0-9A-F]+))?\s+;\s+(\w+).*"#)
+      let line = """
+        A6F0..A6F1    ; Extend # Mn   [2] BAMUM COMBINING MARK KOQNDON..BAMUM \
+        COMBINING MARK TUKWENTIS
+        """
+      let captures = try XCTUnwrap(line.match(regex)?.captures)
+      XCTAssertEqual(
+          captures,
+          .tuple([
+            .substring("A6F0"),
+            .optional(.substring("A6F1")),
+            .substring("Extend")]))
+    }
   }
 }