Add a Test Demonstrating Superfluous Cascading Across Module Boundaries

test/Incremental/Inputs/superfluous-cascade-across-modules/doesNotUseLib.swift

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+extension Map {
+  func pin() {}
+}

test/Incremental/Inputs/superfluous-cascade-across-modules/main.swift

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+

test/Incremental/Inputs/superfluous-cascade-across-modules/ofm.json

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+{
+  "main.swift": {
+    "object": "./main.o",
+    "swift-dependencies": "./main.swiftdeps"
+  },
+  "usesLib.swift": {
+    "object": "./usesLib.o",
+    "swift-dependencies": "./usesLib.swiftdeps"
+  },
+  "usesLibTransitively.swift": {
+    "object": "./usesLib.o",
+    "swift-dependencies": "./usesLib.swiftdeps"
+  },
+  "doesNotUseLib.swift": {
+    "object": "./doesNotUseLib.o",
+    "swift-dependencies": "./doesNotUseLib.swiftdeps"
+  },
+  "": {
+    "swift-dependencies": "./main~buildrecord.swiftdeps"
+  }
+}
+

test/Incremental/Inputs/superfluous-cascade-across-modules/submodule/lib-after.swift

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+public struct Library {
+  var catalog: [Book]
+}
+
+public struct Book {
+  var title: String
+  var checkOutCount: Int
+}

test/Incremental/Inputs/superfluous-cascade-across-modules/submodule/lib-before.swift

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+public struct Library {
+  var catalog: [Book]
+}
+
+public struct Book {
+  var title: String
+}

test/Incremental/Inputs/superfluous-cascade-across-modules/submodule/ofm.json

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+{
+  "lib.swift": {
+    "object": "./lib.o",
+    "swift-dependencies": "./lib.swiftdeps"
+  },
+  "": {
+    "swift-dependencies": "./submodule~buildrecord.swiftdeps"
+  }
+}
+

test/Incremental/Inputs/superfluous-cascade-across-modules/usesLib.swift

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+import Lib
+
+public struct District {
+  var libraries: [Library]
+}
+
+struct Map {}

test/Incremental/Inputs/superfluous-cascade-across-modules/usesLibTransitively.swift

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+struct County {
+  var districts: [District]
+}

test/Incremental/superfluous-cascade-across-modules.swift

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+// =============================================================================
+// Without private dependencies
+// =============================================================================
+
+// First, build a submodule
+
+// RUN: %empty-directory(%t)
+// RUN: cp %S/Inputs/superfluous-cascade-across-modules/*.swift %t
+// RUN: cp %S/Inputs/superfluous-cascade-across-modules/*.json %t
+
+// RUN: %target-build-swift %S/Inputs/superfluous-cascade-across-modules/submodule/lib-before.swift -emit-module -emit-library -module-name Lib -module-link-name Lib -emit-module-path %t/Lib.swiftmodule -o %t/%target-library-name(Lib)
+
+// Build the main executable that depends on the submodule we just built
+
+// RUN: cd %t && %swiftc_driver -emit-module -enable-batch-mode -j2 -incremental -driver-show-incremental -I %t -L %t -lLib -module-name main \
+// RUN:   -output-file-map ofm.json \
+// RUN:   main.swift \
+// RUN:   doesNotUseLib.swift \
+// RUN:   usesLib.swift \
+// RUN:   usesLibTransitively.swift >&output1
+
+// Rebuild the submodule
+
+// RUN: %target-build-swift %S/Inputs/superfluous-cascade-across-modules/submodule/lib-after.swift -emit-module -emit-library -module-name Lib -module-link-name Lib -emit-module-path %t/Lib.swiftmodule -o %t/%target-library-name(Lib)
+
+// Rebuild the main executable
+
+// RUN: cd %t && %swiftc_driver -emit-module -enable-batch-mode -j2 -incremental -driver-show-incremental -I %t -L %t -lLib -module-name main \
+// RUN:   -output-file-map ofm.json \
+// RUN:   main.swift \
+// RUN:   doesNotUseLib.swift \
+// RUN:   usesLib.swift \
+// RUN:   usesLibTransitively.swift >&output2
+
+// RUN: %FileCheck -check-prefix=CHECK-STATUS-QUO-RECOMPILED %s < %t/output2
+
+// CHECK-STATUS-QUO-RECOMPILED-DAG: Queuing because of external dependencies: {compile: main
+// CHECK-STATUS-QUO-RECOMPILED-DAG: Queuing because of external dependencies: {compile: usesLib
+// CHECK-STATUS-QUO-RECOMPILED-DAG: Queuing because of external dependencies: {compile: doesNotUseLib