[Tests] swift fixit: Add test against fixture package

Author: AnthonyLatsis

Fixtures/SwiftFixIt/SwiftFixItPackage/Package.swift

@@ -0,0 +1,10 @@
+// swift-tools-version:5.9
+
+import PackageDescription
+
+let package = Package(
+    name: "SwiftFixItPackage",
+    targets: [
+        .target(name: "Diagnostics", path: "Sources", exclude: ["Fixed"]),
+    ]
+)

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/Fixed/first.swift

@@ -0,0 +1,12 @@
+func foo(_: any P, _: any P) {}
+
+func throwing() throws -> Int {}
+
+func foo() throws {
+    do {
+        _ = 0
+    }
+    do {
+        _ = try throwing()
+    }
+}

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/Fixed/second.swift

@@ -0,0 +1,5 @@
+protocol P {
+    associatedtype A
+}
+
+func bar(_: any P) {}

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/first.swift

@@ -0,0 +1,12 @@
+func foo(_: P, _: P) {}
+
+func throwing() throws -> Int {}
+
+func foo() throws {
+    do {
+        var x = 0
+    }
+    do {
+        let x = throwing()
+    }
+}

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/second.swift

@@ -0,0 +1,5 @@
+protocol P {
+    associatedtype A
+}
+
+func bar(_: P) {}

Tests/CommandsTests/SwiftFixItCommandTests.swift

@@ -11,8 +11,11 @@
 //===----------------------------------------------------------------------===//
 
 import _InternalTestSupport
+import struct Basics.AbsolutePath
+import var Basics.localFileSystem
 @testable
 import Commands
+import class PackageModel.UserToolchain
 import XCTest
 
 final class FixItCommandTests: CommandsTestCase {
@@ -22,4 +25,58 @@ final class FixItCommandTests: CommandsTestCase {
         XCTAssert(stdout.contains("USAGE: swift fixit"), stdout)
         XCTAssert(stdout.contains("-h, -help, --help"), stdout)
     }
+
+    func testApplyFixIts() async throws {
+        try await fixture(name: "SwiftFixIt/SwiftFixItPackage") { fixturePath in
+            let sourcePaths: [AbsolutePath]
+            let fixedSourcePaths: [AbsolutePath]
+            do {
+                let sourcesPath = fixturePath.appending(components: "Sources")
+                let fixedSourcesPath = sourcesPath.appending("Fixed")
+
+                sourcePaths = try localFileSystem.getDirectoryContents(sourcesPath).filter { filename in
+                    filename.hasSuffix(".swift")
+                }.sorted().map { filename in
+                    sourcesPath.appending(filename)
+                }
+                fixedSourcePaths = try localFileSystem.getDirectoryContents(fixedSourcesPath).filter { filename in
+                    filename.hasSuffix(".swift")
+                }.sorted().map { filename in
+                    fixedSourcesPath.appending(filename)
+                }
+            }
+
+            XCTAssertEqual(sourcePaths.count, fixedSourcePaths.count)
+
+            let targetName = "Diagnostics"
+
+            _ = try? await executeSwiftBuild(fixturePath, extraArgs: ["--target", targetName])
+
+            do {
+                let artifactsPath = try fixturePath.appending(
+                    components: ".build",
+                    UserToolchain.default.targetTriple.platformBuildPathComponent,
+                    "debug",
+                    "\(targetName).build"
+                )
+                let diaFilePaths = try localFileSystem.getDirectoryContents(artifactsPath).filter { filename in
+                    // Ignore "*.emit-module.dia".
+                    filename.split(".").1 == "dia"
+                }.map { filename in
+                    artifactsPath.appending(component: filename).pathString
+                }
+
+                XCTAssertEqual(sourcePaths.count, diaFilePaths.count)
+
+                _ = try await SwiftPM.fixit.execute(diaFilePaths)
+            }
+
+            for (sourcePath, fixedSourcePath) in zip(sourcePaths, fixedSourcePaths) {
+                try XCTAssertEqual(
+                    localFileSystem.readFileContents(sourcePath),
+                    localFileSystem.readFileContents(fixedSourcePath)
+                )
+            }
+        }
+    }
 }