Compare against expected output for formatting tests

The formatting request tests currently test for the specific list
of changes returned by the server, but that list is tied to the
differences algorithm used by the standard library, which isn't
guaranteed to be stable. This change compares the expected result
with a new string generated by applying the list of changes, which
is stable.

Author: natecook1000

Sources/SKTestSupport/String+applyingTextEdits.swift

@@ -0,0 +1,65 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+package import LanguageServerProtocol
+
+extension String {
+  /// Returns a new string obtained by applying the given text edits to this
+  /// string.
+  package func applying(_ edits: [TextEdit]) -> String {
+    let sortedEdits = edits.sorted { lhs, rhs in
+      lhs.range.lowerBound < rhs.range.lowerBound
+    }
+
+    let lines = self.split(separator: /\v/, omittingEmptySubsequences: false)
+    var result = ""
+    var currentLine = 0
+    var currentPos = lines[0].startIndex
+
+    Edits: for edit in sortedEdits {
+      // Copy any unchanged lines into the result
+      while currentLine < edit.range.lowerBound.line {
+        result.append(String(lines[currentLine][currentPos...]))
+        result.append("\n")
+        currentLine += 1
+        if currentLine == lines.count { break Edits }
+        currentPos = lines[currentLine].startIndex
+      }
+
+      // Copy any prefix in this line into the result
+      let editStart = lines[currentLine].utf16
+        .index(lines[currentLine].startIndex, offsetBy: edit.range.lowerBound.utf16index)
+      let prefixRange = currentPos..<editStart
+      let prefix = lines[currentLine][prefixRange]
+      result += prefix
+
+      // Add the new text (if any)
+      result += edit.newText
+
+      // Prepare the next cursor position
+      currentLine = edit.range.upperBound.line
+      currentPos = lines[currentLine].utf16
+        .index(lines[currentLine].startIndex, offsetBy: edit.range.upperBound.utf16index)
+    }
+
+    // Copy any remainder
+    while currentLine < lines.count {
+      result.append(String(lines[currentLine][currentPos...]))
+      result.append("\n")
+      currentLine += 1
+      if currentLine == lines.count { break }
+      currentPos = lines[currentLine].startIndex
+    }
+
+    return result
+  }
+}

Tests/SourceKitLSPTests/FormattingTests.swift

@@ -25,15 +25,13 @@ final class FormattingTests: XCTestCase {
     let testClient = try await TestSourceKitLSPClient()
     let uri = DocumentURI(for: .swift)
 
-    let positions = testClient.openDocument(
-      """
+    let source = """
       struct S {
       1️⃣var foo: 2️⃣ 3️⃣Int
       4️⃣var bar: Int
       }5️⃣
-      """,
-      uri: uri
-    )
+      """
+    testClient.openDocument(source, uri: uri)
 
     let response = try await testClient.send(
       DocumentFormattingRequest(
@@ -43,14 +41,19 @@ final class FormattingTests: XCTestCase {
     )
 
     let edits = try XCTUnwrap(response)
+    let (_, unmarkedSource) = extractMarkers(source)
+    let formattedSource = unmarkedSource.applying(edits)
+
     XCTAssertEqual(
-      edits,
-      [
-        TextEdit(range: Range(positions["1️⃣"]), newText: "   "),
-        TextEdit(range: positions["2️⃣"]..<positions["3️⃣"], newText: ""),
-        TextEdit(range: Range(positions["4️⃣"]), newText: "   "),
-        TextEdit(range: Range(positions["5️⃣"]), newText: "\n"),
-      ]
+      formattedSource,
+      """
+      struct S {
+         var foo: Int
+         var bar: Int
+      }
+
+
+      """
     )
   }
 
@@ -217,15 +220,13 @@ final class FormattingTests: XCTestCase {
     let testClient = try await TestSourceKitLSPClient()
     let uri = DocumentURI(for: .swift)
 
-    let positions = testClient.openDocument(
-      """
+    let source = """
       1️⃣public 2️⃣extension Example {
         3️⃣func function() {}
       }
 
-      """,
-      uri: uri
-    )
+      """
+    testClient.openDocument(source, uri: uri)
 
     let response = try await testClient.send(
       DocumentFormattingRequest(
@@ -235,21 +236,26 @@ final class FormattingTests: XCTestCase {
     )
 
     let edits = try XCTUnwrap(response)
+    let (_, unmarkedSource) = extractMarkers(source)
+    let formattedSource = unmarkedSource.applying(edits)
+
     XCTAssertEqual(
-      edits,
-      [
-        TextEdit(range: positions["1️⃣"]..<positions["2️⃣"], newText: ""),
-        TextEdit(range: Range(positions["3️⃣"]), newText: "public "),
-      ]
+      formattedSource,
+      """
+      extension Example {
+        public func function() {}
+      }
+
+
+      """
     )
   }
 
   func testMultiLineStringInsertion() async throws {
     let testClient = try await TestSourceKitLSPClient()
     let uri = DocumentURI(for: .swift)
 
-    let positions = testClient.openDocument(
-      #"""
+    let source = #"""
       _ = [
         Node(
           documentation: """
@@ -268,9 +274,8 @@ final class FormattingTests: XCTestCase {
         )
       ]
 
-      """#,
-      uri: uri
-    )
+      """#
+    testClient.openDocument(source, uri: uri)
 
     let response = try await testClient.send(
       DocumentFormattingRequest(
@@ -280,18 +285,32 @@ final class FormattingTests: XCTestCase {
     )
 
     let edits = try XCTUnwrap(response)
+    let (_, unmarkedSource) = extractMarkers(source)
+    let formattedSource = unmarkedSource.applying(edits)
+
     XCTAssertEqual(
-      edits,
-      [
-        TextEdit(range: Range(positions["1️⃣"]), newText: "  "),
-        TextEdit(range: Range(positions["2️⃣"]), newText: "  "),
-        TextEdit(range: Range(positions["3️⃣"]), newText: "  "),
-        TextEdit(range: Range(positions["4️⃣"]), newText: "  "),
-        TextEdit(range: Range(positions["5️⃣"]), newText: "  "),
-        TextEdit(range: Range(positions["6️⃣"]), newText: "\n"),
-        TextEdit(range: positions["7️⃣"]..<positions["8️⃣"], newText: ""),
-        TextEdit(range: positions["9️⃣"]..<positions["🔟"], newText: ""),
+      formattedSource,
+      #"""
+      _ = [
+        Node(
+          documentation: """
+            A
+            B
+            C
+            """,
+          children: [
+            Child(
+              documentation: """
+                A
+
+                """
+            )
+          ]
+        )
       ]
+
+
+      """#
     )
   }