From 26c420723b27273c9c7e4c06b98f7af57032a877 Mon Sep 17 00:00:00 2001
From: Artem Chikin <achikin@apple.com>
Date: Thu, 23 Jan 2025 14:11:16 -0800
Subject: [PATCH] [ModuleInterface] Determine package-only resolution need
 based on input mode

Instead of requested action. In implicit builds, implicit interface build sub-invocations inherit their parent invocation's requested action, which the code was failing to detect that we were building an interface, not source, and erroneously resulted in enabling in-package module dependency resolution.

Resolves rdar://143505814
---
 lib/Frontend/CompilerInvocation.cpp           |  5 +--
 ...es-on-non-package-interface-implicit.swift | 35 +++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 test/ModuleInterface/no-package-dependencies-on-non-package-interface-implicit.swift

diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index a7112d069300a..7cbc2df7ea748 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -2297,9 +2297,10 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts, ArgList &Args,
   Opts.ScannerModuleValidation |= Args.hasFlag(OPT_scanner_module_validation,
                                                OPT_no_scanner_module_validation,
                                                CASOpts.EnableCaching);
+
   bool buildingFromInterface =
-      FrontendOptions::doesActionBuildModuleFromInterface(
-          FrontendOpts.RequestedAction);
+      FrontendOpts.InputMode ==
+      FrontendOptions::ParseInputMode::SwiftModuleInterface;
   auto firstInputPath =
       FrontendOpts.InputsAndOutputs.hasInputs()
           ? FrontendOpts.InputsAndOutputs.getFilenameOfFirstInput()
diff --git a/test/ModuleInterface/no-package-dependencies-on-non-package-interface-implicit.swift b/test/ModuleInterface/no-package-dependencies-on-non-package-interface-implicit.swift
new file mode 100644
index 0000000000000..85724913b7554
--- /dev/null
+++ b/test/ModuleInterface/no-package-dependencies-on-non-package-interface-implicit.swift
@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/module-cache)
+// RUN: %empty-directory(%t/Swift)
+// RUN: %empty-directory(%t/OtherSwift)
+// RUN: split-file %s %t
+
+// Build in-package ModuleC
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/OtherSwift/ModuleC.swiftmodule -module-name ModuleC -package-name TestPak %t/C.swift
+
+// Build in-package ModuleB
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/Swift/ModuleB.swiftmodule -enable-library-evolution -emit-module-interface-path %t/Swift/ModuleB.swiftinterface  -module-name ModuleB -package-name TestPak %t/B.swift -I%t/OtherSwift
+
+// Build in-package ModuleA
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/Swift/ModuleA.swiftmodule -enable-library-evolution -emit-module-interface-path %t/Swift/ModuleA.swiftinterface -module-name ModuleA -package-name TestPak %t/A.swift -I%t/Swift -I%t/OtherSwift
+
+// Remove binary module for A to make sure an implicit interface compile gets triggered
+// RUN: rm %t/Swift/ModuleA.swiftmodule
+// Remove in-package-only dependency of B to ensure that if the compiler looks for it, compilation will fail
+// RUN: rm %t/OtherSwift/ModuleC.swiftmodule
+
+// Build out-of-package client source
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/Swift/Client.swiftmodule -module-name Client %t/Client.swift -I%t/Swift
+
+//--- C.swift
+public func c() {}
+
+//--- B.swift
+package import ModuleC
+
+//--- A.swift
+@_exported public import ModuleB
+
+//--- Client.swift
+import ModuleA
+