[Explicit Module Builds] Enable incremental dependency scanning\nWith an opt-out build setting SWIFT_DISABLE_INCREMENTAL_SCAN in case early adoption shows any troubles

Author: artemcm

Sources/SWBCore/Settings/BuiltinMacros.swift

@@ -1003,6 +1003,7 @@ public final class BuiltinMacros {
     public static let SWIFT_EMIT_MODULE_INTERFACE = BuiltinMacros.declareBooleanMacro("SWIFT_EMIT_MODULE_INTERFACE")
     public static let SWIFT_ENABLE_BATCH_MODE = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_BATCH_MODE")
     public static let SWIFT_ENABLE_INCREMENTAL_COMPILATION = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_INCREMENTAL_COMPILATION")
+    public static let SWIFT_DISABLE_INCREMENTAL_SCAN = BuiltinMacros.declareBooleanMacro("SWIFT_DISABLE_INCREMENTAL_SCAN")
     public static let SWIFT_ENABLE_LAYOUT_STRING_VALUE_WITNESSES = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_LAYOUT_STRING_VALUE_WITNESSES")
     public static let SWIFT_ENABLE_LIBRARY_EVOLUTION = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_LIBRARY_EVOLUTION")
     public static let SWIFT_ENABLE_BARE_SLASH_REGEX = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_BARE_SLASH_REGEX")
@@ -2164,6 +2165,7 @@ public final class BuiltinMacros {
         SWIFT_EMIT_MODULE_INTERFACE,
         SWIFT_ENABLE_BATCH_MODE,
         SWIFT_ENABLE_INCREMENTAL_COMPILATION,
+        SWIFT_DISABLE_INCREMENTAL_SCAN,
         SWIFT_ENABLE_LAYOUT_STRING_VALUE_WITNESSES,
         SWIFT_ENABLE_LIBRARY_EVOLUTION,
         SWIFT_USE_INTEGRATED_DRIVER,

Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift

@@ -1743,6 +1743,10 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
 
                 if cbc.scope.evaluate(BuiltinMacros.SWIFT_ENABLE_INCREMENTAL_COMPILATION) {
                     args.append("-incremental")
+                    if LibSwiftDriver.supportsDriverFlag(spelled: "-incremental-dependency-scan"),
+                       !cbc.scope.evaluate(BuiltinMacros.SWIFT_DISABLE_INCREMENTAL_SCAN) {
+                        args.append("-incremental-dependency-scan")
+                    }
                 }
             }
 

Tests/SWBTaskConstructionTests/SwiftTaskConstructionTests.swift

@@ -1530,6 +1530,64 @@ fileprivate struct SwiftTaskConstructionTests: CoreBasedTests {
         }
     }
 
+    @Test(.requireSDKs(.macOS), .enabled(if: LibSwiftDriver.supportsDriverFlag(spelled: "-incremental-dependency-scan")))
+    func optOutIncrementalScanning() async throws {
+        let testProject = try await TestProject(
+            "aProject",
+            groupTree: TestGroup(
+                "SomeFiles", path: "Sources",
+                children: [
+                    TestFile("main.swift"),
+                ]),
+            buildConfigurations: [
+                TestBuildConfiguration(
+                    "Debug",
+                    buildSettings: [
+                        "PRODUCT_NAME": "$(TARGET_NAME)",
+                        "SWIFT_ENABLE_EXPLICIT_MODULES": "YES",
+                    ]),
+            ],
+            targets: [
+                TestStandardTarget(
+                    "Exec", type: .commandLineTool,
+                    buildConfigurations: [
+                        TestBuildConfiguration("Debug",
+                                               buildSettings: [
+                                                "SWIFT_EXEC": swiftCompilerPath.str,
+                                                "SWIFT_VERSION": swiftVersion,
+                                               ]),
+                    ],
+                    buildPhases: [
+                        TestSourcesBuildPhase([
+                            "main.swift",
+                        ]),
+                    ])
+            ])
+        let tester = try await TaskConstructionTester(getCore(), testProject)
+
+        await tester.checkBuild(runDestination: .macOS) { results in
+            results.checkTarget("Exec") { target in
+                results.checkTask(.matchTarget(target), .matchRuleType("SwiftDriver Compilation Requirements")) { task in
+                    task.checkCommandLineContains(["-explicit-module-build"])
+                    task.checkCommandLineContains(["-incremental"])
+                    task.checkCommandLineContains(["-incremental-dependency-scan"])
+                }
+            }
+            results.checkNoDiagnostics()
+        }
+
+        await tester.checkBuild(BuildParameters(configuration: "Debug", overrides: ["SWIFT_DISABLE_INCREMENTAL_SCAN": "YES"]), runDestination: .macOS) { results in
+            results.checkTarget("Exec") { target in
+                results.checkTask(.matchTarget(target), .matchRuleType("SwiftDriver Compilation Requirements")) { task in
+                    task.checkCommandLineContains(["-explicit-module-build"])
+                    task.checkCommandLineContains(["-incremental"])
+                    task.checkCommandLineDoesNotContain("-incremental-dependency-scan")
+                }
+            }
+            results.checkNoDiagnostics()
+        }
+    }
+
     @Test(.requireSDKs(.macOS))
     func swift4DisablesExplicitModules() async throws {
         let testProject = try await TestProject(