From 3684fe9c1b8d1fe3eabd6b285d535c5602562539 Mon Sep 17 00:00:00 2001
From: Nate Cook <natecook@apple.com>
Date: Wed, 15 Jun 2022 17:12:26 -0500
Subject: [PATCH 1/2] Add tests for substring / anchor interaction

^ and $ should match the start and end of the callee, even if that
callee is a substring. Right now ^ and $ match the start and end of
the callee's base string, instead. In addition, ^ and $ should only
match the start and end of the callee when replacing a subrange, not
the start and end of the subrange.
---
 Tests/RegexTests/MatchTests.swift | 32 +++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Tests/RegexTests/MatchTests.swift b/Tests/RegexTests/MatchTests.swift
index e0f391507..e4e8b78a6 100644
--- a/Tests/RegexTests/MatchTests.swift
+++ b/Tests/RegexTests/MatchTests.swift
@@ -1397,6 +1397,38 @@ extension RegexTests {
     XCTAssertEqual(allRanges.count, 5)
   }
   
+  func testSubstringAnchors() throws {
+    let string = "123abc456def789"
+    let trimmed = string.dropFirst(3).dropLast(3) // "abc456def"
+    let prefixLetters = try Regex(#"^[a-z]+"#, as: Substring.self)
+    let postfixLetters = try Regex(#"[a-z]+$"#, as: Substring.self)
+
+    XCTExpectFailure {
+      // start anchor (^) should match beginning of substring
+      XCTAssertEqual(trimmed.firstMatch(of: prefixLetters)?.output, "abc")
+      XCTAssertEqual(trimmed.replacing(prefixLetters, with: ""), "456def")
+      
+      // end anchor ($) should match end of substring
+      XCTAssertEqual(trimmed.firstMatch(of: postfixLetters)?.output, "def")
+      XCTAssertEqual(trimmed.replacing(postfixLetters, with: ""), "abc456")
+    }
+
+    // start anchor (^) should _not_ match beginning of subrange
+    XCTAssertEqual(
+      string.replacing(
+        prefixLetters,
+        with: "",
+        subrange: trimmed.startIndex..<trimmed.endIndex),
+      string)
+    // end anchor ($) should _not_ match beginning of subrange
+    XCTAssertEqual(
+      string.replacing(
+        postfixLetters,
+        with: "",
+        subrange: trimmed.startIndex..<trimmed.endIndex),
+      string)
+  }
+  
   func testMatchingOptionsScope() {
     // `.` only matches newlines when the 's' option (single-line mode)
     // is turned on. Standalone option-setting groups (e.g. `(?s)`) are

From 2c03b87717a095768d8cbc53ce08c3eb5131a58f Mon Sep 17 00:00:00 2001
From: Nate Cook <natecook@apple.com>
Date: Wed, 15 Jun 2022 23:26:43 -0500
Subject: [PATCH 2/2] One test failure per expectFailure

---
 Tests/RegexTests/MatchTests.swift | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/Tests/RegexTests/MatchTests.swift b/Tests/RegexTests/MatchTests.swift
index e4e8b78a6..3c5ac96eb 100644
--- a/Tests/RegexTests/MatchTests.swift
+++ b/Tests/RegexTests/MatchTests.swift
@@ -1403,13 +1403,19 @@ extension RegexTests {
     let prefixLetters = try Regex(#"^[a-z]+"#, as: Substring.self)
     let postfixLetters = try Regex(#"[a-z]+$"#, as: Substring.self)
 
+    // start anchor (^) should match beginning of substring
     XCTExpectFailure {
-      // start anchor (^) should match beginning of substring
       XCTAssertEqual(trimmed.firstMatch(of: prefixLetters)?.output, "abc")
+    }
+    XCTExpectFailure {
       XCTAssertEqual(trimmed.replacing(prefixLetters, with: ""), "456def")
-      
-      // end anchor ($) should match end of substring
+    }
+    
+    // end anchor ($) should match end of substring
+    XCTExpectFailure {
       XCTAssertEqual(trimmed.firstMatch(of: postfixLetters)?.output, "def")
+    }
+    XCTExpectFailure {
       XCTAssertEqual(trimmed.replacing(postfixLetters, with: ""), "abc456")
     }