Fix Anchor.startOfLine and Anchor.endOfLine

Introduce `startOfInput` and `endOfInput` assertion
kinds, and map the DSL to them such that they do
not depend on matching options.

rdar://97029630

Author: hamishknight

Sources/RegexBuilder/Anchor.swift

@@ -55,10 +55,10 @@ extension Anchor: RegexComponent {
       return isInverted ? .notTextSegment : .textSegment
     case .startOfLine:
       // FIXME: Inverted?
-      return .caretAnchor
+      return .startOfLine
     case .endOfLine:
       // FIXME: Inverted?
-      return .dollarAnchor
+      return .endOfLine
     case .wordBoundary:
       return isInverted ? .notWordBoundary : .wordBoundary
     }

Sources/_StringProcessing/ByteCodeGen.swift

@@ -113,6 +113,32 @@ fileprivate extension Compiler.ByteCodeGen {
     }
   }
 
+  mutating func emitStartOfLine() {
+    builder.buildAssert { [semanticLevel = options.semanticLevel]
+        (_, _, input, pos, subjectBounds) in
+      if pos == subjectBounds.lowerBound { return true }
+      switch semanticLevel {
+      case .graphemeCluster:
+        return input[input.index(before: pos)].isNewline
+      case .unicodeScalar:
+        return input.unicodeScalars[input.unicodeScalars.index(before: pos)].isNewline
+      }
+    }
+  }
+
+  mutating func emitEndOfLine() {
+    builder.buildAssert { [semanticLevel = options.semanticLevel]
+      (_, _, input, pos, subjectBounds) in
+      if pos == subjectBounds.upperBound { return true }
+      switch semanticLevel {
+      case .graphemeCluster:
+        return input[pos].isNewline
+      case .unicodeScalar:
+        return input.unicodeScalars[pos].isNewline
+      }
+    }
+  }
+
   mutating func emitAssertion(
     _ kind: DSLTree.Atom.Assertion
   ) throws {
@@ -170,44 +196,24 @@ fileprivate extension Compiler.ByteCodeGen {
         !input.isOnGraphemeClusterBoundary(pos)
       }
 
+    case .startOfLine:
+      emitStartOfLine()
+
+    case .endOfLine:
+      emitEndOfLine()
+
     case .caretAnchor:
-      // FIXME: Anchor.startOfLine must always use this first branch
-      // The behavior of `^` should depend on `anchorsMatchNewlines`, but
-      // the DSL-based `.startOfLine` anchor should always match the start
-      // of a line. Right now we don't distinguish between those anchors.
       if options.anchorsMatchNewlines {
-        builder.buildAssert { [semanticLevel = options.semanticLevel]
-            (_, _, input, pos, subjectBounds) in
-          if pos == subjectBounds.lowerBound { return true }
-          switch semanticLevel {
-          case .graphemeCluster:
-            return input[input.index(before: pos)].isNewline
-          case .unicodeScalar:
-            return input.unicodeScalars[input.unicodeScalars.index(before: pos)].isNewline
-          }
-        }
+        emitStartOfLine()
       } else {
         builder.buildAssert { (_, _, input, pos, subjectBounds) in
           pos == subjectBounds.lowerBound
         }
       }
-      
+
     case .dollarAnchor:
-      // FIXME: Anchor.endOfLine must always use this first branch
-      // The behavior of `$` should depend on `anchorsMatchNewlines`, but
-      // the DSL-based `.endOfLine` anchor should always match the end
-      // of a line. Right now we don't distinguish between those anchors.
       if options.anchorsMatchNewlines {
-        builder.buildAssert { [semanticLevel = options.semanticLevel]
-            (_, _, input, pos, subjectBounds) in
-          if pos == subjectBounds.upperBound { return true }
-          switch semanticLevel {
-          case .graphemeCluster:
-            return input[pos].isNewline
-          case .unicodeScalar:
-            return input.unicodeScalars[pos].isNewline
-          }
-        }
+        emitEndOfLine()
       } else {
         builder.buildAssert { (_, _, input, pos, subjectBounds) in
           pos == subjectBounds.upperBound

Sources/_StringProcessing/PrintAsPattern.swift

@@ -627,12 +627,16 @@ extension DSLTree.Atom.Assertion {
   // TODO: Some way to integrate this with conversion...
   var _patternBase: String {
     switch self {
-    case .caretAnchor:
-      // FIXME: The DSL doesn't have a way of representing this.
+    case .startOfLine:
       return "Anchor.startOfLine"
-    case .dollarAnchor:
-      // FIXME: The DSL doesn't have a way of representing this.
+    case .endOfLine:
       return "Anchor.endOfLine"
+    case .caretAnchor:
+      // The DSL doesn't have an equivalent to this, so print as regex.
+      return "/^/"
+    case .dollarAnchor:
+      // The DSL doesn't have an equivalent to this, so print as regex.
+      return "/$/"
     case .wordBoundary:
       return "Anchor.wordBoundary"
     case .notWordBoundary:

Sources/_StringProcessing/Regex/DSLTree.swift

@@ -287,6 +287,14 @@ extension DSLTree.Atom {
     /// \Y
     case notTextSegment
 
+    /// The DSL's Anchor.startOfLine, which matches the start of a line
+    /// even if `anchorsMatchNewlines` is false.
+    case startOfLine
+
+    /// The DSL's Anchor.endOfLine, which matches the end of a line
+    /// even if `anchorsMatchNewlines` is false.
+    case endOfLine
+
     /// ^
     case caretAnchor
 

Tests/RegexBuilderTests/RegexDSLTests.swift

@@ -815,19 +815,40 @@ class RegexDSLTests: XCTestCase {
         Anchor.endOfSubject
       }.anchorsMatchLineEndings()
     }
-    
-    // FIXME: Anchor.start/endOfLine needs to always match line endings,
-    // even when the `anchorsMatchLineEndings()` option is turned off.
+
     try _testDSLCaptures(
-      ("\naaa", "aaa"),
-      ("aaa\n", "aaa"),
-      ("\naaa\n", "aaa"),
-      matchType: Substring.self, ==, xfail: true)
+      ("\naaa", "\naaa"),
+      ("aaa\n", "aaa\n"),
+      ("\naaa\n", "\naaa\n"),
+      matchType: Substring.self, ==)
     {
       Regex {
+        Optionally { "\n" }
         Anchor.startOfLine
         Repeat("a", count: 3)
         Anchor.endOfLine
+        Optionally { "\n" }
+      }
+    }
+
+    // startOfLine/endOfLine apply regardless of mode.
+    for matchLineEndings in [true, false] {
+      for mode in [RegexSemanticLevel.graphemeCluster, .unicodeScalar] {
+        let r = Regex {
+          Anchor.startOfLine
+          Repeat("a", count: 3)
+          Anchor.endOfLine
+        }.anchorsMatchLineEndings(matchLineEndings).matchingSemantics(mode)
+
+        XCTAssertNotNil(try r.firstMatch(in: "\naaa"))
+        XCTAssertNotNil(try r.firstMatch(in: "aaa\n"))
+        XCTAssertNotNil(try r.firstMatch(in: "\naaa\n"))
+        XCTAssertNotNil(try r.firstMatch(in: "\naaa\r\n"))
+        XCTAssertNotNil(try r.firstMatch(in: "\r\naaa\n"))
+        XCTAssertNotNil(try r.firstMatch(in: "\r\naaa\r\n"))
+
+        XCTAssertNil(try r.firstMatch(in: "\nbaaa\n"))
+        XCTAssertNil(try r.firstMatch(in: "\naaab\n"))
       }
     }
   }

Tests/RegexTests/RenderDSLTests.swift

@@ -85,7 +85,21 @@ extension RenderDSLTests {
       }
       """#)
   }
-  
+
+  func testAnchor() throws {
+    try testConversion(#"^(?:a|b|c)$"#, #"""
+      Regex {
+        /^/
+        ChoiceOf {
+          "a"
+          "b"
+          "c"
+        }
+        /$/
+      }
+      """#)
+  }
+
   func testOptions() throws {
     try XCTExpectFailure("Options like '(?i)' aren't converted") {
       try testConversion(#"(?i)abc"#, """