Swift frontend incorrectly searching in SDK_ROOT for .swiftinterface file

[luispadron]

Description

We're hitting a bizarre issue that we've noticed since Xcode 16.0 where swiftc will look for a .swiftinterface in the SDK_ROOT. This obviously fails and thus the -compile-module-from-interface call fails.

Error:

<unknown>:0: error: cannot open file '/Applications/Xcode-16.2.0.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.2.sdk/bazel-out/darwin_arm64-fastbuild/bin/test/fixtures/module_interface/library/toy_outputs/ToyModule.swiftinterface' (No such file or directory)
bazel-out/darwin_arm64-fastbuild/bin/test/fixtures/module_interface/library_consumer/toy_consumer_outputs/ToyModuleConsumer.swiftinterface:4:1: error: failed to build module 'ToyModuleConsumer' for importation due to the errors above; the textual interface may be broken by project issues or a compiler bug
 2 | // swift-compiler-version: Apple Swift version 6.0.3 effective-5.10 (swiftlang-6.0.3.1.10 clang-1600.0.30.1)
 3 | // swift-module-flags: -target arm64-apple-macos13.0 -enable-objc-interop -enable-library-evolution -static -enforce-exclusivity=checked -Onone -enable-experimental-feature AccessLevelOnImport -enable-bare-slash-regex -module-name ToyModuleConsumer
 4 | import Swift
   | `- error: failed to build module 'ToyModuleConsumer' for importation due to the errors above; the textual interface may be broken by project issues or a compiler bug
 5 | import ToyModule
 6 | import _Concurrency

Using the following invocation (on Xcode 16.2):

xcrun swiftc @ToyModuleConsumer.params 

With the following params file:

-frontend
-target
arm64-apple-macos13.0
-sdk
/Applications/Xcode-16.2.0.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.2.sdk
-resource-dir
/Applications/Xcode-16.2.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift
-target-sdk-version
15.2
-Onone
-module-cache-path
bazel-out/darwin_arm64-fastbuild/bin/_swift_module_cache
-Ibazel-out/darwin_arm64-fastbuild/bin/test/fixtures/module_interface
-Xcc
-iquote.
-Xcc
-iquotebazel-out/darwin_arm64-fastbuild/bin
-color-diagnostics
-enable-bare-slash-regex
-Xcc
-O0
-Xcc
-DDEBUG=1
bazel-out/darwin_arm64-fastbuild/bin/test/fixtures/module_interface/library_consumer/toy_consumer_outputs/ToyModuleConsumer.swiftinterface
-enable-library-evolution
-o
bazel-out/darwin_arm64-fastbuild/bin/test/fixtures/module_interface/ToyModuleConsumer.swiftmodule
-compile-module-from-interface

I'm completely lost as to what could be causing swiftc to search in the SDK root here. The ToyModule.swiftinterface in this case is actually in: bazel-out/darwin_arm64-fastbuild/bin/test/fixtures/module_interface/library/toy_outputs/ToyModule.swiftinterface and looks like:

// swift-interface-format-version: 1.0
// swift-compiler-version: Apple Swift version 6.0.3 effective-5.10 (swiftlang-6.0.3.1.10 clang-1600.0.30.1)
// swift-module-flags: -target arm64-apple-macos13.0 -enable-objc-interop -enable-library-evolution -static -enforce-exclusivity=checked -Onone -enable-experimental-feature AccessLevelOnImport -enable-bare-slash-regex -module-name ToyModule
import Swift
import _Concurrency
import _StringProcessing
import _SwiftConcurrencyShims
@frozen public struct ToyValue {
  public var number: Swift.Int
  public var stringValue: Swift.String {
    get
  }
  public init(number: Swift.Int)
  public func squared() -> Swift.Int
}
extension ToyModule.ToyValue : Swift.Sendable {}
extension ToyModule.ToyValue : Swift.BitwiseCopyable {}

Steps to Reproduce

Use the -compile-module-from-interface mode to attempt to compile a .swiftmodule from a .swiftinterface that depends on another .swiftmodule (compiled from a interface).

Reproduction

Use the -compile-module-from-interface mode to attempt to compile a .swiftmodule from a .swiftinterface that depends on another .swiftmodule (compiled from a interface).

Expected behavior

I'd expect swiftc to not look in the SDK root here and to just work at compiling the interface as expected.

Environment

swift-driver version: 1.115.1 Apple Swift version 6.0.3 (swiftlang-6.0.3.1.10 clang-1600.0.30.1)
Target: arm64-apple-macosx15.0

Additional information

No response