[SwiftRefactor] Fix handling of leading trivia for new elements/arguments

When inserting a new element to an array or new argument to a call
let's only copy the indentation of the previous element instead of
whole leading trivia that includes comments.

Author: xedin

Sources/SwiftRefactor/PackageManifest/SyntaxEditUtils.swift

@@ -135,9 +135,12 @@ extension LabeledExprListSyntax {
     if position > startIndex {
       let priorArgument = arguments[positionIdx - 1]
 
-      // Our leading trivia will be based on the prior argument's leading
-      // trivia.
-      leadingTrivia = priorArgument.leadingTrivia
+      // Our indentation will be based on the prior argument's.
+      if priorArgument.leadingTrivia.hasNewlines {
+        leadingTrivia = .newline + (priorArgument.firstToken(viewMode: .sourceAccurate)?.indentationOfLine ?? Trivia())
+      } else {
+        leadingTrivia = priorArgument.leadingTrivia.indentation(isOnNewline: false) ?? Trivia()
+      }
 
       // If the prior argument is missing a trailing comma, add one.
       if priorArgument.trailingComma == nil {
@@ -221,9 +224,13 @@ extension ArrayExprSyntax {
     let trailingTrivia: Trivia
     let leftSquareTrailingTrivia: Trivia
     if let last = elements.last {
-      // The leading trivia of the new element should match that of the
+      // The leading indentation of the new element should match that of the
       // last element.
-      leadingTrivia = last.leadingTrivia.onlyLastLine
+      if last.leadingTrivia.hasNewlines {
+        leadingTrivia = .newline + (last.firstToken(viewMode: .sourceAccurate)?.indentationOfLine ?? Trivia())
+      } else {
+        leadingTrivia = last.leadingTrivia.indentation(isOnNewline: false) ?? Trivia()
+      }
 
       // Add a trailing comma to the last element if it isn't already
       // there.

Tests/SwiftRefactorTest/ManifestEditTests.swift

@@ -97,6 +97,72 @@ final class ManifestEditTests: XCTestCase {
         )
       )
     )
+
+    try assertManifestRefactor(
+      """
+      // swift-tools-version: 5.5
+      let package = Package(
+          name: "packages",
+          dependencies: [
+            /* test */ .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "510.0.1")
+          ]
+      )
+      """,
+      expectedManifest: """
+        // swift-tools-version: 5.5
+        let package = Package(
+            name: "packages",
+            dependencies: [
+              /* test */ .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "510.0.1"),
+              .package(url: "https://github.com/apple/swift-system.git", exact: "510.0.0"),
+            ]
+        )
+        """,
+      provider: AddPackageDependency.self,
+      context: .init(
+        dependency: .sourceControl(
+          .init(
+            identity: PackageIdentity("swift-system"),
+            location: .remote(Self.swiftSystemURL),
+            requirement: .exact(SemanticVersion("510.0.0"))
+          )
+        )
+      )
+    )
+
+    try assertManifestRefactor(
+      """
+      // swift-tools-version: 5.5
+      let package = Package(
+          name: "packages",
+          dependencies: [
+            /* test */
+            .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "510.0.1")
+          ]
+      )
+      """,
+      expectedManifest: """
+        // swift-tools-version: 5.5
+        let package = Package(
+            name: "packages",
+            dependencies: [
+              /* test */
+              .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "510.0.1"),
+              .package(url: "https://github.com/apple/swift-system.git", exact: "510.0.0"),
+            ]
+        )
+        """,
+      provider: AddPackageDependency.self,
+      context: .init(
+        dependency: .sourceControl(
+          .init(
+            identity: PackageIdentity("swift-system"),
+            location: .remote(Self.swiftSystemURL),
+            requirement: .exact(SemanticVersion("510.0.0"))
+          )
+        )
+      )
+    )
   }
 
   func testAddPackageDependencyExistingAppended() throws {
@@ -160,6 +226,33 @@ final class ManifestEditTests: XCTestCase {
         )
       )
     )
+
+    try assertManifestRefactor(
+      """
+      // swift-tools-version: 5.5
+      let package = Package(
+          name: "packages",
+          dependencies: [ /*test*/ .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "510.0.1") ]
+      )
+      """,
+      expectedManifest: """
+        // swift-tools-version: 5.5
+        let package = Package(
+            name: "packages",
+            dependencies: [ /*test*/ .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "510.0.1"), .package(url: "https://github.com/apple/swift-system.git", from: "510.0.0"),]
+        )
+        """,
+      provider: AddPackageDependency.self,
+      context: .init(
+        dependency: .sourceControl(
+          .init(
+            identity: PackageIdentity("swift-system"),
+            location: .remote(Self.swiftSystemURL),
+            requirement: .rangeFrom(SemanticVersion("510.0.0"))
+          )
+        )
+      )
+    )
   }
 
   func testAddPackageDependencyExistingEmpty() throws {
@@ -450,7 +543,7 @@ final class ManifestEditTests: XCTestCase {
             .target(name: "TargetLib"),
             .byName(name: "MyLib"),
           ]
-        ),
+        )
       )
     )
   }