Filter codesign messages

Fixtures/Miscellaneous/DoNotFilterLinkerDiagnostics/Package.swift

@@ -0,0 +1,17 @@
+// swift-tools-version: 5.11
+
+import PackageDescription
+
+let package = Package(
+    name: "DoNotFilterLinkerDiagnostics",
+    targets: [
+        .executableTarget(
+            name: "DoNotFilterLinkerDiagnostics",
+            linkerSettings: [
+                .linkedLibrary("z"),
+                .unsafeFlags(["-lz"]),
+                // should produce: ld: warning: ignoring duplicate libraries: '-lz'
+            ]
+        ),
+    ]
+)

Fixtures/Miscellaneous/DoNotFilterLinkerDiagnostics/Sources/DoNotFilterLinkerDiagnostics/main.swift

@@ -0,0 +1,4 @@
+// The Swift Programming Language
+// https://docs.swift.org/swift-book
+
+print("Hello, world!")

Sources/Build/BuildOperationBuildSystemDelegateHandler.swift

@@ -826,8 +826,10 @@ final class BuildOperationBuildSystemDelegateHandler: LLBuildBuildSystemDelegate
         process: ProcessHandle,
         result: CommandExtendedResult
     ) {
+        // FIXME: This should really happen at the command-level and is just a stopgap measure.
+        let shouldFilterOutput = !self.logLevel.isVerbose && command.verboseDescription.hasPrefix("codesign ") && result.result != .failed
         queue.async {
-            if let buffer = self.nonSwiftMessageBuffers[command.name] {
+            if let buffer = self.nonSwiftMessageBuffers[command.name], !shouldFilterOutput {
                 self.progressAnimation.clear()
                 self.outputStream.send(buffer)
                 self.outputStream.flush()

Tests/BuildTests/BuildSystemDelegateTests.swift

@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SPMTestSupport
+import XCTest
+
+import var TSCBasic.localFileSystem
+
+final class BuildSystemDelegateTests: XCTestCase {
+    func testDoNotFilterLinkerDiagnostics() throws {
+        try fixture(name: "Miscellaneous/DoNotFilterLinkerDiagnostics") { fixturePath in
+            #if !os(macOS)
+            // These linker diagnostics are only produced on macOS.
+            try XCTSkipIf(true, "test is only supported on macOS")
+            #endif
+            let (fullLog, _) = try executeSwiftBuild(fixturePath)
+            XCTAssertTrue(fullLog.contains("ld: warning: ignoring duplicate libraries: '-lz'"), "log didn't contain expected linker diagnostics")
+        }
+    }
+
+    func testFilterNonFatalCodesignMessages() throws {
+        // Note: we can re-use the `TestableExe` fixture here since we just need an executable.
+        try fixture(name: "Miscellaneous/TestableExe") { fixturePath in
+            _ = try executeSwiftBuild(fixturePath)
+            let execPath = fixturePath.appending(components: ".build", "debug", "TestableExe1")
+            XCTAssertTrue(localFileSystem.exists(execPath), "executable not found at '\(execPath)'")
+            try localFileSystem.removeFileTree(execPath)
+            let (fullLog, _) = try executeSwiftBuild(fixturePath)
+            XCTAssertFalse(fullLog.contains("replacing existing signature"), "log contained non-fatal codesigning messages")
+        }
+    }
+}