Add an expectation of a warning diagnostic to tests that hide libSwiftScan.

Such tests cause the driver to take a code-path that results in a warning:
'warning: Unable to locate libSwiftScan. Fallback to `swift-frontend` dependency scanner invocation.'

This needs to be taken into account.

Author: artemcm

Tests/CommandsTests/PackageCommandTests.swift

@@ -2267,6 +2267,8 @@ final class PackageCommandTests: CommandsTestCase {
         let containsRemark = StringPattern.contains("command plugin: Diagnostics.remark")
         let containsWarning = StringPattern.contains("command plugin: Diagnostics.warning")
         let containsError = StringPattern.contains("command plugin: Diagnostics.error")
+        let hiddenLibSwiftScanWarnPattern = StringPattern.contains(
+          "warning: Unable to locate libSwiftScan. Fallback to `swift-frontend` dependency scanner invocation")
 
         try await fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
             func runPlugin(flags: [String], diagnostics: [String], completion: (String, String) -> Void) async throws {
@@ -2290,7 +2292,8 @@ final class PackageCommandTests: CommandsTestCase {
 
             try await runPlugin(flags: [], diagnostics: ["print"]) { stdout, stderr in
                 XCTAssertMatch(stdout, isOnlyPrint)
-                XCTAssertMatch(stderr, isEmpty)
+                XCTAssertMatch(stderr, hiddenLibSwiftScanWarnPattern)
+                XCTAssertFalse(stderr.contains("error:"))
             }
 
             try await runPlugin(flags: [], diagnostics: ["print", "progress"]) { stdout, stderr in
@@ -2322,7 +2325,8 @@ final class PackageCommandTests: CommandsTestCase {
 
             try await runPlugin(flags: ["-q"], diagnostics: ["print"]) { stdout, stderr in
                 XCTAssertMatch(stdout, isOnlyPrint)
-                XCTAssertMatch(stderr, isEmpty)
+                XCTAssertMatch(stderr, hiddenLibSwiftScanWarnPattern)
+                XCTAssertFalse(stderr.contains("error:"))
             }
 
             try await runPlugin(flags: ["-q"], diagnostics: ["print", "progress"]) { stdout, stderr in
@@ -2461,7 +2465,11 @@ final class PackageCommandTests: CommandsTestCase {
         let containsLogtext = StringPattern.contains("command plugin: packageManager.build logtext: Building for debugging...")
 
         // Echoed logs have no prefix
-        let containsLogecho = StringPattern.regex("^Building for debugging...\n")
+        let containsLogecho = StringPattern.contains("Building for debugging...\n")
+
+        // Hides the libSwiftScan library from the driver
+        let hiddenLibSwiftScanWarnPattern = StringPattern.contains(
+          "warning: Unable to locate libSwiftScan. Fallback to `swift-frontend` dependency scanner invocation")
 
         // These tests involve building a target, so each test must run with a fresh copy of the fixture
         // otherwise the logs may be different in subsequent tests.
@@ -2470,14 +2478,16 @@ final class PackageCommandTests: CommandsTestCase {
         try await fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
             let (stdout, stderr) = try await SwiftPM.Package.execute(["print-diagnostics", "build"], packagePath: fixturePath, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
             XCTAssertMatch(stdout, isEmpty)
-            XCTAssertMatch(stderr, isEmpty)
+            XCTAssertMatch(stderr, hiddenLibSwiftScanWarnPattern)
+            XCTAssertFalse(stderr.contains("error:"))
         }
 
         // Check that logs are returned to the plugin when echoLogs is false
         try await fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
             let (stdout, stderr) = try await SwiftPM.Package.execute(["print-diagnostics", "build", "printlogs"], packagePath: fixturePath, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
             XCTAssertMatch(stdout, containsLogtext)
-            XCTAssertMatch(stderr, isEmpty)
+            XCTAssertMatch(stderr, hiddenLibSwiftScanWarnPattern)
+            XCTAssertFalse(stderr.contains("error:"))
         }
 
         // Check that logs echoed to the console (on stderr) when echoLogs is true
@@ -2784,14 +2794,14 @@ final class PackageCommandTests: CommandsTestCase {
             do {
                 let (stdout, stderr) = try await SwiftPM.Package.execute(["plugin", "MyPlugin", "--foo", "--help", "--version", "--verbose"], packagePath: packageDir, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
                 XCTAssertMatch(stdout, .contains("success"))
-                XCTAssertEqual(stderr, "")
+                XCTAssertFalse(stderr.contains("error:"))
             }
 
             // Check default command arguments
             do {
                 let (stdout, stderr) = try await SwiftPM.Package.execute(["MyPlugin", "--foo", "--help", "--version", "--verbose"], packagePath: packageDir, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
                 XCTAssertMatch(stdout, .contains("success"))
-                XCTAssertEqual(stderr, "")
+                XCTAssertFalse(stderr.contains("error:"))
             }
         }
     }

Tests/FunctionalTests/MiscellaneousTests.swift

@@ -662,6 +662,7 @@ final class MiscellaneousTestCase: XCTestCase {
         try await fixture(name: "Miscellaneous/RootPackageWithConditionals") { path in
             let (_, stderr) = try await SwiftPM.Build.execute(packagePath: path, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
             let errors = stderr.components(separatedBy: .newlines).filter { !$0.contains("[logging] misuse") && !$0.isEmpty }
+                                                                  .filter { !$0.contains("Unable to locate libSwiftScan") }
             XCTAssertEqual(errors, [], "unexpected errors: \(errors)")
         }
     }

Tests/FunctionalTests/PluginTests.swift

@@ -236,7 +236,7 @@ final class PluginTests: XCTestCase {
 
             try createPackageUnderTest(packageDir: packageDir, toolsVersion: .v6_0)
             let (_, stderr2) = try await executeSwiftBuild(packageDir, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
-            XCTAssertEqual("", stderr2)
+            XCTAssertFalse(stderr2.contains("error:"))
             XCTAssertTrue(localFileSystem.exists(pathOfGeneratedFile), "plugin did not run, generated file does not exist at \(pathOfGeneratedFile.pathString)")
         }
     }

Tests/FunctionalTests/ResourcesTests.swift

@@ -177,7 +177,8 @@ final class ResourcesTests: XCTestCase {
 
             let (_, stderr) = try await executeSwiftBuild(packageDir, env: ["SWIFT_DRIVER_SWIFTSCAN_LIB" : "/this/is/a/bad/path"])
             // Filter some unrelated output that could show up on stderr.
-            let filteredStderr = stderr.components(separatedBy: "\n").filter { !$0.contains("[logging]") }.joined(separator: "\n")
+            let filteredStderr = stderr.components(separatedBy: "\n").filter { !$0.contains("[logging]") }
+                                                                     .filter { !$0.contains("Unable to locate libSwiftScan") }.joined(separator: "\n")
             XCTAssertEqual(filteredStderr, "", "unexpectedly received error output: \(stderr)")
 
             let builtProductsDir = packageDir.appending(components: [".build", "debug"])