feat: Add shim to allow wrapped access to CLOCK_REALTIME struct from WASILibc.

Author: scottmarchant

Package.swift

@@ -35,6 +35,7 @@ let package = Package(
             dependencies: [
                 .product(name: "ServiceContextModule", package: "swift-service-context"),
                 .target(name: "Instrumentation"),
+                .target(name: "_CWASI", condition: .when(platforms: [.wasi])),
             ]
         ),
         .testTarget(
@@ -43,6 +44,16 @@ let package = Package(
                 .target(name: "Tracing")
             ]
         ),
+
+        // ==== --------------------------------------------------------------------------------------------------------
+        // MARK: Wasm Support
+
+        // Provides C shims for compiling to wasm
+        .target(
+            name: "_CWASI",
+            dependencies: []
+        ),
+
     ]
 )
 

Sources/Tracing/TracingTime.swift

@@ -90,7 +90,11 @@ public struct DefaultTracerClock {
 
     public var now: Self.Instant {
         var ts = timespec()
-        clock_gettime(CLOCK_REALTIME, &ts)
+        #if os(WASI)
+            CWASI_clock_gettime_realtime(&ts)
+        #else
+            clock_gettime(CLOCK_REALTIME, &ts)
+        #endif
         /// We use unsafe arithmetic here because `UInt64.max` nanoseconds is more than 580 years,
         /// and the odds that this code will still be running 530 years from now is very, very low,
         /// so as a practical matter this will never overflow.

Sources/_CWASI/_CWASI.c

@@ -0,0 +1,13 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Distributed Tracing open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift Distributed Tracing project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift Distributed Tracing project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//

Sources/_CWASI/include/_CWASI.h

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Distributed Tracing open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift Distributed Tracing project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift Distributed Tracing project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#if __wasi__
+
+#include <fcntl.h>
+#include <time.h>
+
+static inline void CWASI_clock_gettime_realtime(struct timespec *tv) {
+    // ClangImporter doesn't support `CLOCK_REALTIME` declaration in WASILibc, thus we have to define a bridge manually
+    clock_gettime(CLOCK_REALTIME, tv);
+}
+
+#endif // __wasi__