only use the last file component when deciding decoding strategy (#665)

rdar://112664398

Author: QuietMisdreavus

Sources/SwiftDocC/Infrastructure/Symbol Graph/SymbolGraphLoader.swift

@@ -113,7 +113,7 @@ struct SymbolGraphLoader {
         // This strategy benchmarks better when we have multiple
         // "larger" symbol graphs.
         #if os(macOS) || os(iOS)
-        if bundle.symbolGraphURLs.filter({ !$0.path.contains("@") }).count > 1 {
+        if bundle.symbolGraphURLs.filter({ !$0.lastPathComponent.contains("@") }).count > 1 {
             // There are multiple main symbol graphs, better parallelize all files decoding.
             decodingStrategy = .concurrentlyAllFiles
         }

Tests/SwiftDocCTests/Infrastructure/SymbolGraph/SymbolGraphLoaderTests.swift

@@ -309,7 +309,27 @@ class SymbolGraphLoaderTests: XCTestCase {
             XCTAssertTrue(foundMainAsyncMethodsGraph, "AsyncMethods graph wasn't found")
         }
     }
-    
+
+    /// Ensure that loading symbol graphs from a directory with an at-sign properly selects the
+    /// `concurrentlyAllFiles` decoding strategy on macOS and iOS.
+    func testLoadingSymbolsInAtSignDirectory() throws {
+        let tempURL = try createTemporaryDirectory(pathComponents: "MyTempDir@2")
+        let originalSymbolGraphs = [
+            CopyOfFile(original: Bundle.module.url(forResource: "Asides.symbols", withExtension: "json", subdirectory: "Test Resources")!),
+            CopyOfFile(original: Bundle.module.url(forResource: "WithCompletionHandler.symbols", withExtension: "json", subdirectory: "Test Resources")!)
+        ]
+        let symbolGraphURLs = try originalSymbolGraphs.map({ try $0.write(inside: tempURL) })
+
+        var loader = try makeSymbolGraphLoader(symbolGraphURLs: symbolGraphURLs)
+        try loader.loadAll()
+
+        #if os(macOS) || os(iOS)
+        XCTAssertEqual(loader.decodingStrategy, .concurrentlyAllFiles)
+        #else
+        XCTAssertEqual(loader.decodingStrategy, .concurrentlyEachFileInBatches)
+        #endif
+    }
+
     func testInputWithMixedGraphFormats() throws {
         let tempURL = try createTemporaryDirectory()