Define memmem using a header file

On Ubuntu 20.04, you need to define `_GNU_SOURCE` before importing `<string.h>` to get `memmem`. It is thus not available when importing `Glibc`.

Author: ahoppen

Package.swift

@@ -111,17 +111,22 @@ var targets: [Target] = [
     dependencies: []
   ),
 
+  .target(
+    name: "CCompletionScoring",
+    dependencies: []
+  ),
+
   // MARK: CompletionScoring
 
   .target(
     name: "CompletionScoring",
-    dependencies: [],
+    dependencies: ["CCompletionScoring"],
     swiftSettings: globalSwiftSettings
   ),
 
   .target(
     name: "CompletionScoringForPlugin",
-    dependencies: [],
+    dependencies: ["CCompletionScoring"],
     swiftSettings: globalSwiftSettings
   ),
 

Sources/CCompletionScoring/include/CCompletionScoring.h

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SOURCEKITLSP_CCOMPLETIONSCORING_H
+#define SOURCEKITLSP_CCOMPLETIONSCORING_H
+
+#define _GNU_SOURCE
+#include <string.h>
+
+static inline void *sourcekitlsp_memmem(const void *haystack, size_t haystacklen, const void *needle, size_t needlelen) {
+  return memmem(haystack, haystacklen, needle, needlelen);
+}
+
+#endif // SOURCEKITLSP_CCOMPLETIONSCORING_H

Sources/CompletionScoring/Utilities/SwiftExtensions.swift

@@ -10,20 +10,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+import CCompletionScoring
 import Foundation
 
-#if canImport(Darwin)
-import Darwin
-#elseif canImport(Glibc)
-import Glibc
-#elseif canImport(Musl)
-import Musl
-#elseif canImport(CRT)
-import CRT
-#elseif canImport(Bionic)
-import Bionic
-#endif
-
 extension Range where Bound: Numeric {
   init(from: Bound, length: Bound) {
     self = from..<(from + length)
@@ -447,7 +436,9 @@ extension UnsafeBufferPointer<UInt8> {
     guard needle.count > 0, let needleBaseAddress = needle.baseAddress else {
       return nil
     }
-    guard let match = memmem(baseAddress + startOffset, count - startOffset, needleBaseAddress, needle.count) else {
+    guard
+      let match = sourcekitlsp_memmem(baseAddress + startOffset, count - startOffset, needleBaseAddress, needle.count)
+    else {
       return nil
     }
     let start = baseAddress.distance(to: match.assumingMemoryBound(to: UInt8.self))