Only include the platform PrivateFrameworks directory as a runtime, not build-time, search path (#9518)

This constrains a behavior I landed in #8199 so that it only includes
the `PrivateFrameworks` directory from Xcode's platform directory (when
present) as a **runtime** framework search path (via
`DYLD_FRAMEWORK_PATH`) and no longer includes it as a _build-time_
framework search path (via `-F <path>`).

### Motivation:

This is a follow-up to a change I made in #8199. Those changes had an
undesirable side effect of including private frameworks in all builds,
and means that when those frameworks are present at build time, they're
included in client builds and can be `import`'ed or linked. Exposing
those frameworks to clients at _build-time_ was not intended, and can
cause unexpected results or failures if (for example) those private
frameworks themselves contain unresolvable module imports.

However, platform private frameworks directories _should_ continue to be
included in runtime framework search paths, so they can be located and
loaded when referenced by public frameworks/libraries.

### Modifications:

- Introduce separate properties for build-time vs. runtime framework and
library search paths, so the two categories can be differentiated by
callers.
- Omit the private frameworks search path from the new build-time
frameworks property.
- Adopt the relevant new properties at both build and runtime usage
sites.

### Result:

After this change, I validated that:

- a local package build no longer contains the private frameworks search
path entry at build time, using `swift build --build-tests --verbose`,
and
- a local package test operation still includes the search path, using
`env DYLD_PRINT_ENV=1 swift test`.

Author: stmontgomery

Sources/Commands/Utilities/TestingSupport.swift

@@ -242,10 +242,10 @@ enum TestingSupport {
         // Since XCTestHelper targets macOS, we need the macOS platform paths here.
         if let sdkPlatformPaths = try? SwiftSDK.sdkPlatformPaths(for: .macOS) {
             // appending since we prefer the user setting (if set) to the one we inject
-            for frameworkPath in sdkPlatformPaths.frameworks {
+            for frameworkPath in sdkPlatformPaths.runtimeFrameworkSearchPaths {
                 env.appendPath(key: "DYLD_FRAMEWORK_PATH", value: frameworkPath.pathString)
             }
-            for libraryPath in sdkPlatformPaths.libraries {
+            for libraryPath in sdkPlatformPaths.runtimeLibrarySearchPaths {
                 env.appendPath(key: "DYLD_LIBRARY_PATH", value: libraryPath.pathString)
             }
         }

Sources/PackageModel/SwiftSDKs/SwiftSDK.swift

@@ -593,10 +593,10 @@ public struct SwiftSDK: Equatable {
         #if os(macOS)
         do {
             let sdkPaths = try SwiftSDK.sdkPlatformPaths(for: darwinPlatform, environment: environment)
-            extraCCFlags.append(contentsOf: sdkPaths.frameworks.flatMap { ["-F", $0.pathString] })
-            extraSwiftCFlags.append(contentsOf: sdkPaths.frameworks.flatMap { ["-F", $0.pathString] })
-            extraSwiftCFlags.append(contentsOf: sdkPaths.libraries.flatMap { ["-I", $0.pathString] })
-            extraSwiftCFlags.append(contentsOf: sdkPaths.libraries.flatMap { ["-L", $0.pathString] })
+            extraCCFlags.append(contentsOf: sdkPaths.buildTimeFrameworkSearchPaths.flatMap { ["-F", $0.pathString] })
+            extraSwiftCFlags.append(contentsOf: sdkPaths.buildTimeFrameworkSearchPaths.flatMap { ["-F", $0.pathString] })
+            extraSwiftCFlags.append(contentsOf: sdkPaths.buildTimeLibrarySearchPaths.flatMap { ["-I", $0.pathString] })
+            extraSwiftCFlags.append(contentsOf: sdkPaths.buildTimeLibrarySearchPaths.flatMap { ["-L", $0.pathString] })
             xctestSupport = .supported
         } catch {
             xctestSupport = .unsupported(reason: String(describing: error))
@@ -628,11 +628,21 @@ public struct SwiftSDK: Equatable {
     ///
     /// - SeeAlso: ``sdkPlatformPaths(for:environment:)``
     public struct PlatformPaths {
-        /// Paths of directories containing auxiliary platform frameworks.
-        public var frameworks: [Basics.AbsolutePath]
+        /// Paths of directories containing auxiliary platform frameworks which
+        /// should be included as framework search paths at build time.
+        public var buildTimeFrameworkSearchPaths: [Basics.AbsolutePath]
 
-        /// Paths of directories containing auxiliary platform libraries.
-        public var libraries: [Basics.AbsolutePath]
+        /// Paths of directories containing auxiliary platform libraries which
+        /// should be included as library search paths at build time.
+        public var buildTimeLibrarySearchPaths: [Basics.AbsolutePath]
+
+        /// Paths of directories containing auxiliary platform frameworks which
+        /// should be included as framework search paths at runtime.
+        public var runtimeFrameworkSearchPaths: [Basics.AbsolutePath]
+
+        /// Paths of directories containing auxiliary platform libraries which
+        /// should be included as library search paths at runtime.
+        public var runtimeLibrarySearchPaths: [Basics.AbsolutePath]
     }
 
     /// Returns `macosx` sdk platform framework path.
@@ -641,10 +651,10 @@ public struct SwiftSDK: Equatable {
         environment: Environment = .current
     ) throws -> (fwk: Basics.AbsolutePath, lib: Basics.AbsolutePath) {
         let paths = try sdkPlatformPaths(for: .macOS, environment: environment)
-        guard let frameworkPath = paths.frameworks.first else {
+        guard let frameworkPath = paths.buildTimeFrameworkSearchPaths.first else {
             throw StringError("could not determine SDK platform framework path")
         }
-        guard let libraryPath = paths.libraries.first else {
+        guard let libraryPath = paths.buildTimeLibrarySearchPaths.first else {
             throw StringError("could not determine SDK platform library path")
         }
         return (fwk: frameworkPath, lib: libraryPath)
@@ -682,7 +692,12 @@ public struct SwiftSDK: Equatable {
             components: "Developer", "usr", "lib"
         )
 
-        let sdkPlatformFrameworkPath = PlatformPaths(frameworks: [frameworksPath, privateFrameworksPath], libraries: [librariesPath])
+        let sdkPlatformFrameworkPath = PlatformPaths(
+            buildTimeFrameworkSearchPaths: [frameworksPath /* omit privateFrameworksPath */],
+            buildTimeLibrarySearchPaths: [librariesPath],
+            runtimeFrameworkSearchPaths: [frameworksPath, privateFrameworksPath],
+            runtimeLibrarySearchPaths: [librariesPath]
+        )
         _sdkPlatformFrameworkPath[darwinPlatform] = sdkPlatformFrameworkPath
         return sdkPlatformFrameworkPath
     }