SwiftFixIt: Skip duplicate insertion fix-its

There are various scenarios — most notably involving protocol
compositions — where multiple different sites are diagnosed the same
insertion fix-it, as in

```swift
protocol P {
  associatedtype A
}
protocol Q {
  associatedtype A
}
// two errors, two fix-its to prepend `any` to the composition.
func foo(_: P & Q) {}
```

Applying these duplicate fix-its will produce invalid code:
`func foo(_: any any P & Q) {}`.

Author: AnthonyLatsis

Fixtures/SwiftMigrate/ExistentialAnyMigration/Sources/Fixed/Test.swift

@@ -1,5 +1,7 @@
 protocol P {
 }
+protocol Q {
+}
 
 func test1(_: any P) {
 }
@@ -14,3 +16,6 @@ func test3() {
 func test4() {
     var x = 42
 }
+
+func test5(_: any P & Q) {
+}

Fixtures/SwiftMigrate/ExistentialAnyMigration/Sources/Test.swift

@@ -1,5 +1,7 @@
 protocol P {
 }
+protocol Q {
+}
 
 func test1(_: P) {
 }
@@ -14,3 +16,6 @@ func test3() {
 func test4() {
     var x = 42
 }
+
+func test5(_: P & Q) {
+}

Fixtures/SwiftMigrate/InferIsolatedConformancesMigration/Sources/Fixed/Test.swift

@@ -6,3 +6,9 @@ class C: nonisolated Equatable {
     lhs.name == rhs.name
   }
 }
+
+protocol P {}
+protocol Q {}
+
+@MainActor
+struct S: nonisolated P & Q {}

Fixtures/SwiftMigrate/InferIsolatedConformancesMigration/Sources/Test.swift

@@ -6,3 +6,9 @@ class C: Equatable {
     lhs.name == rhs.name
   }
 }
+
+protocol P {}
+protocol Q {}
+
+@MainActor
+struct S: P & Q {}

Sources/SwiftFixIt/SwiftFixIt.swift

@@ -301,7 +301,11 @@ extension SwiftFixIt {
                 }
             }
 
-            let result = SwiftIDEUtils.FixItApplier.apply(edits: consume edits, to: sourceFile.syntax)
+            let result = SwiftIDEUtils.FixItApplier.apply(
+                edits: consume edits,
+                to: sourceFile.syntax,
+                allowDuplicateInsertions: false
+            )
 
             try self.fileSystem.writeFileContents(sourceFile.path, string: consume result)
         }

Tests/CommandsTests/PackageCommandTests.swift

@@ -2151,9 +2151,9 @@ class PackageCommandTestCase: CommandsBuildProviderTestCase {
             }
         }
 
-        try await doMigration(featureName: "ExistentialAny", expectedSummary: "Applied 3 fix-its in 1 file")
+        try await doMigration(featureName: "ExistentialAny", expectedSummary: "Applied 4 fix-its in 1 file")
         try await doMigration(featureName: "StrictMemorySafety", expectedSummary: "Applied 1 fix-it in 1 file")
-        try await doMigration(featureName: "InferIsolatedConformances", expectedSummary: "Applied 1 fix-it in 1 file")
+        try await doMigration(featureName: "InferIsolatedConformances", expectedSummary: "Applied 2 fix-its in 1 file")
     }
 
     func testBuildToolPlugin() async throws {

Tests/SwiftFixItTests/BasicTests.swift

@@ -278,6 +278,61 @@ struct BasicTests {
         }
     }
 
+    @Test
+    func testOverlappingFixIts2() throws {
+        try testAPI1File { path in
+            .init(
+                edits: .init(input: "var x = 1", result: "_ == 1"),
+                summary: .init(
+                    // 2 because skipped by SwiftIDEUtils.FixItApplier, not SwiftFixIt.
+                    numberOfFixItsApplied: 3 /**/,
+                    numberOfFilesChanged: 1
+                ),
+                diagnostics: [
+                    PrimaryDiagnostic(
+                        level: .error,
+                        text: "error1",
+                        location: .init(path: path, line: 1, column: 1),
+                        fixIts: [
+                            // Applied.
+                            .init(
+                                start: .init(path: path, line: 1, column: 1),
+                                end: .init(path: path, line: 1, column: 6),
+                                text: "_"
+                            ),
+                        ]
+                    ),
+                    PrimaryDiagnostic(
+                        level: .error,
+                        text: "error2",
+                        location: .init(path: path, line: 1, column: 1),
+                        fixIts: [
+                            // Skipped, overlaps with previous fix-it.
+                            .init(
+                                start: .init(path: path, line: 1, column: 7),
+                                end: .init(path: path, line: 1, column: 8),
+                                text: "=="
+                            ),
+                        ]
+                    ),
+                    PrimaryDiagnostic(
+                        level: .error,
+                        text: "error3",
+                        location: .init(path: path, line: 1, column: 1),
+                        fixIts: [
+                            // Skipped, overlaps with previous fix-it.
+                            .init(
+                                start: .init(path: path, line: 1, column: 1),
+                                end: .init(path: path, line: 1, column: 4),
+                                text: "let"
+                            ),
+                        ]
+                    ),
+                ]
+            )
+        }
+    }
+
     @Test
     func testFixItsMultipleFiles() throws {
         try testAPI2Files { path1, path2 in

Tests/SwiftFixItTests/FilteringTests.swift

@@ -412,19 +412,12 @@ struct FilteringTests {
         }
     }
 
-    @Test
     func testDuplicateInsertionFixIts() throws {
-        withKnownIssue("FIXME: Filter out duplicate insertion fix-its") {
-            try self._testDuplicateInsertionFixIts()
-        }
-    }
-
-    func _testDuplicateInsertionFixIts() throws {
         try testAPI1File { path in
             .init(
                 edits: .init(input: "var x = 1", result: "@W var yx = 21"),
                 summary: .init(
-                    // 4 because skipped by SwiftIDEUtils.FixItApplier, not SwiftFixIt.
+                    // 6 because skipped by SwiftIDEUtils.FixItApplier, not SwiftFixIt.
                     numberOfFixItsApplied: 6,
                     numberOfFilesChanged: 1
                 ),
@@ -470,7 +463,7 @@ struct FilteringTests {
                         text: "error3_fixit1",
                         location: .init(path: path, line: 1, column: 3),
                         fixIts: [
-                            // FIXME: Should be skipped.
+                            // Skipped, duplicate insertion.
                             .init(
                                 start: .init(path: path, line: 1, column: 1),
                                 end: .init(path: path, line: 1, column: 1),
@@ -500,7 +493,7 @@ struct FilteringTests {
                                 text: "error5_note1",
                                 location: .init(path: path, line: 1, column: 9),
                                 fixIts: [
-                                    // FIXME: Should be skipped.
+                                    // Skipped, duplicate insertion.
                                     .init(
                                         start: .init(path: path, line: 1, column: 9),
                                         end: .init(path: path, line: 1, column: 9),
@@ -519,7 +512,7 @@ struct FilteringTests {
                                 text: "error6_note1",
                                 location: .init(path: path, line: 1, column: 5),
                                 fixIts: [
-                                    // FIXME: Should be skipped.
+                                    // Skipped, duplicate insertion.
                                     .init(
                                         start: .init(path: path, line: 1, column: 5),
                                         end: .init(path: path, line: 1, column: 5),