[5.7] Cherry pick a RegexBuilder and StringProcessing change

Sources/RegexBuilder/Algorithms.swift

@@ -11,11 +11,6 @@
 
 @_spi(RegexBuilder) import _StringProcessing
 
-// FIXME(rdar://92459215): We should be using 'some RegexComponent' instead of
-// <R: RegexComponent> for the methods below that don't impose any additional
-// requirements on the type. Currently the generic parameter is needed to work
-// around a compiler issue.
-
 extension BidirectionalCollection where SubSequence == Substring {
   /// Matches a regex in its entirety, where the regex is created by
   /// the given closure.

Sources/RegexBuilder/Builder.swift

@@ -18,8 +18,10 @@ public enum RegexComponentBuilder {
     _RegexFactory().empty()
   }
 
-  public static func buildPartialBlock<R: RegexComponent>(first: R ) -> R {
-    first
+  public static func buildPartialBlock<R: RegexComponent>(
+    first component: R
+  ) -> Regex<R.RegexOutput> {
+    component.regex
   }
 
   public static func buildExpression<R: RegexComponent>(_ regex: R) -> R {

Sources/_StringProcessing/Regex/Match.swift

@@ -164,7 +164,7 @@ extension BidirectionalCollection where SubSequence == Substring {
   public func wholeMatch<R: RegexComponent>(
     of r: R
   ) -> Regex<R.RegexOutput>.Match? {
-    try? r.regex.wholeMatch(in: self[...].base)
+    try? r.regex.wholeMatch(in: self[...])
   }
 
   /// Checks for a match against the string, starting at its beginning.

Tests/RegexBuilderTests/AlgorithmsTests.swift

@@ -170,6 +170,16 @@ class AlgorithmsResultBuilderTests: XCTestCase {
   }
 
   func testMatches() throws {
+    do {
+      let regex = Regex { OneOrMore(.any) }
+      XCTAssertEqual("abc".wholeMatch(of: regex)!.0, "abc")
+      XCTAssertEqual("abc".prefixMatch(of: regex)!.0, "abc")
+      XCTAssertEqual("abc".firstMatch(of: regex)!.0, "abc")
+      XCTAssertEqual("abc".suffix(1).wholeMatch(of: regex)!.0, "c")
+      XCTAssertEqual("abc".suffix(1).prefixMatch(of: regex)!.0, "c")
+      XCTAssertEqual("abc".suffix(1).firstMatch(of: regex)!.0, "c")
+    }
+
     let int = Capture(OneOrMore(.digit)) { Int($0)! }
 
     // Test syntax

Tests/RegexBuilderTests/RegexDSLTests.swift

@@ -1052,7 +1052,7 @@ class RegexDSLTests: XCTestCase {
       XCTAssertEqual(str.wholeMatch(of: parser)?.1, version)
     }
   }
-  
+
   func testZeroWidthConsumer() throws {
     struct Trace: CustomConsumingRegexComponent {
       typealias RegexOutput = Void
@@ -1088,6 +1088,26 @@ class RegexDSLTests: XCTestCase {
 
       """)
   }
+
+  func testRegexComponentBuilderResultType() {
+    // Test that the user can declare a closure or computed property marked with
+    // `@RegexComponentBuilder` with `Regex` as the result type.
+    @RegexComponentBuilder
+    var unaryWithSingleNonRegex: Regex<Substring> {
+      OneOrMore("a")
+    }
+    @RegexComponentBuilder
+    var multiComponent: Regex<Substring> {
+      OneOrMore("a")
+      "b"
+    }
+    struct MyCustomRegex: RegexComponent {
+      @RegexComponentBuilder
+      var regex: Regex<Substring> {
+        OneOrMore("a")
+      }
+    }
+  }
 }
 
 extension Unicode.Scalar {