diff --git a/Package.swift b/Package.swift
index b8da017f322..7189908a617 100644
--- a/Package.swift
+++ b/Package.swift
@@ -184,7 +184,8 @@ let package = Package(
 
     .target(
       name: "SwiftLexicalLookup",
-      dependencies: ["SwiftSyntax", "SwiftIfConfig"]
+      dependencies: ["SwiftSyntax", "SwiftIfConfig"],
+      exclude: ["CMakeLists.txt"]
     ),
 
     .testTarget(
diff --git a/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift b/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift
index c4aa143c7fc..077aec6a646 100644
--- a/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift
+++ b/Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift
@@ -10,11 +10,19 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if compiler(>=6)
+#if compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly private import _SwiftSyntaxCShims
+#elseif compiler(>=6) && !RESILIENT_LIBRARIES
+private import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && RESILIENT_LIBRARIES
+@_implementationOnly import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && !RESILIENT_LIBRARIES
+import _SwiftSyntaxCShims
+#endif
+
+#if compiler(>=6)
 public import SwiftSyntaxMacros
 #else
-@_implementationOnly import _SwiftSyntaxCShims
 import SwiftSyntaxMacros
 #endif
 
diff --git a/Sources/SwiftCompilerPluginMessageHandling/JSON/JSONDecoding.swift b/Sources/SwiftCompilerPluginMessageHandling/JSON/JSONDecoding.swift
index 79c77910871..20a56a633c6 100644
--- a/Sources/SwiftCompilerPluginMessageHandling/JSON/JSONDecoding.swift
+++ b/Sources/SwiftCompilerPluginMessageHandling/JSON/JSONDecoding.swift
@@ -10,10 +10,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if compiler(>=6)
+#if compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly private import _SwiftSyntaxCShims
-#else
+#elseif compiler(>=6) && !RESILIENT_LIBRARIES
+private import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && !RESILIENT_LIBRARIES
+import _SwiftSyntaxCShims
 #endif
 
 func decodeFromJSON<T: Decodable>(json: UnsafeBufferPointer<UInt8>) throws -> T {
diff --git a/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift b/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift
index 8f89ac125c9..750ce3b72dd 100644
--- a/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift
+++ b/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift
@@ -10,10 +10,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if compiler(>=6)
+#if compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly private import _SwiftSyntaxCShims
-#else
+#elseif compiler(>=6) && !RESILIENT_LIBRARIES
+private import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && !RESILIENT_LIBRARIES
+import _SwiftSyntaxCShims
 #endif
 
 #if canImport(ucrt)
@@ -173,6 +177,17 @@ private enum IOError: Error, CustomStringConvertible {
 
 // Private function to construct an error message from an `errno` code.
 private func describe(errno: CInt) -> String {
-  if let cStr = strerror(errno) { return String(cString: cStr) }
-  return String(describing: errno)
+  // We can't tell how long the error message will be but 1024 characters should be enough to hold most, if not all,
+  // error messages.
+  return withUnsafeTemporaryAllocation(of: CChar.self, capacity: 1024) { buffer in
+    guard let baseAddress = buffer.baseAddress else {
+      return ""
+    }
+    #if os(Windows)
+    strerror_s(baseAddress, buffer.count, errno)
+    #else
+    strerror_r(errno, baseAddress, buffer.count)
+    #endif
+    return String(cString: baseAddress)
+  }
 }
diff --git a/Sources/SwiftLibraryPluginProvider/LibraryPluginProvider.swift b/Sources/SwiftLibraryPluginProvider/LibraryPluginProvider.swift
index 1f156f380a2..7cb686a0622 100644
--- a/Sources/SwiftLibraryPluginProvider/LibraryPluginProvider.swift
+++ b/Sources/SwiftLibraryPluginProvider/LibraryPluginProvider.swift
@@ -14,6 +14,7 @@
 public import SwiftSyntaxMacros
 @_spi(PluginMessage) public import SwiftCompilerPluginMessageHandling
 private import _SwiftLibraryPluginProviderCShims
+
 // NOTE: Do not use '_SwiftSyntaxCShims' for 'dlopen' and 'LoadLibraryW' (Windows)
 // because we don't want other modules depend on 'WinSDK'.
 #if canImport(Darwin)
@@ -24,10 +25,15 @@ private import Glibc
 private import Musl
 #elseif canImport(Android)
 private import Android
-#endif
-#else
+#endif  // canImport
+
+#else  // compiler(>=6)
+
 import SwiftSyntaxMacros
 @_spi(PluginMessage) import SwiftCompilerPluginMessageHandling
+
+#if RESILIENT_LIBRARIES
+
 @_implementationOnly import _SwiftLibraryPluginProviderCShims
 #if canImport(Darwin)
 @_implementationOnly import Darwin
@@ -35,8 +41,22 @@ import SwiftSyntaxMacros
 @_implementationOnly import Glibc
 #elseif canImport(Musl)
 @_implementationOnly import Musl
-#endif
-#endif
+#endif  // canImport
+
+#else  // RESILIENT_LIBRARIES
+
+import _SwiftLibraryPluginProviderCShims
+#if canImport(Darwin)
+import Darwin
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(Musl)
+import Musl
+#endif  // canImport
+
+#endif  // RESILIENT_LIBRARIES
+
+#endif  // compiler(>=6)
 
 /// Singleton 'PluginProvider' that can serve shared library plugins.
 @_spi(PluginMessage)
diff --git a/Sources/SwiftSyntax/CMakeLists.txt b/Sources/SwiftSyntax/CMakeLists.txt
index 4d2457f6cbb..cfb8d888622 100644
--- a/Sources/SwiftSyntax/CMakeLists.txt
+++ b/Sources/SwiftSyntax/CMakeLists.txt
@@ -83,5 +83,12 @@ add_swift_syntax_library(SwiftSyntax
   generated/syntaxNodes/SyntaxNodesTUVWXYZ.swift
 )
 
-target_link_swift_syntax_libraries(SwiftSyntax PRIVATE
-  _SwiftSyntaxCShims)
+if (SWIFTSYNTAX_EMIT_MODULE)
+  target_link_swift_syntax_libraries(SwiftSyntax PRIVATE
+    _SwiftSyntaxCShims)
+else()
+  # We can't use @_implementationOnly if we don't enable library evolution, so we need
+  # to link _SwiftSyntaxCShims publicly.
+  target_link_swift_syntax_libraries(SwiftSyntax PUBLIC
+    _SwiftSyntaxCShims)
+endif()
diff --git a/Sources/SwiftSyntax/Raw/RawSyntaxArena.swift b/Sources/SwiftSyntax/Raw/RawSyntaxArena.swift
index 3d57003ace4..f5566e831b2 100644
--- a/Sources/SwiftSyntax/Raw/RawSyntaxArena.swift
+++ b/Sources/SwiftSyntax/Raw/RawSyntaxArena.swift
@@ -10,10 +10,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if compiler(>=6)
+#if compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly private import _SwiftSyntaxCShims
-#else
+#elseif compiler(>=6) && !RESILIENT_LIBRARIES
+private import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && !RESILIENT_LIBRARIES
+import _SwiftSyntaxCShims
 #endif
 
 /// A syntax arena owns the memory for all syntax nodes within it.
diff --git a/Sources/SwiftSyntax/Syntax.swift b/Sources/SwiftSyntax/Syntax.swift
index c214c41d5f4..407febff7ca 100644
--- a/Sources/SwiftSyntax/Syntax.swift
+++ b/Sources/SwiftSyntax/Syntax.swift
@@ -10,10 +10,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if compiler(>=6)
+#if compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly private import _SwiftSyntaxCShims
-#else
+#elseif compiler(>=6) && !RESILIENT_LIBRARIES
+private import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && RESILIENT_LIBRARIES
 @_implementationOnly import _SwiftSyntaxCShims
+#elseif !compiler(>=6) && !RESILIENT_LIBRARIES
+import _SwiftSyntaxCShims
 #endif
 
 // `Syntax` is a user facing tree wrapping `RawSyntax` tree. A value is a pair