Avoid BlockHound NoSuchTypeException when context propagation depende…

…ncy is unavailable (#3337)

When the context-propagation jar is unavailable (which can happen since the dependency is optional), then BlockHound reports the following ERROR log:

reactor.blockhound.shaded.net.bytebuddy.pool.TypePool$Resolution$NoSuchTypeException: Cannot resolve type description for io.micrometer.context.ContextRegistry

This log does not break anything, it is only about logging, but it can be avoided using this patch.
In a nutshell, Byte Buddy requires all type information for a transformed type to be available, else the above error log may be displayed. The log may happen occasionally with very rare byte code combinations
when the class is being defined (initial classloading).

To avoid this problem, the proposed patch is refactoring the ContextPropagation static initializer in order to not use a lambda when capturing the context snapshot.

reactor-core/src/main/java/reactor/core/publisher/ContextPropagation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022 VMware Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2022-2023 VMware Inc. or its affiliates, All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -53,9 +53,9 @@ final class ContextPropagation {
 		Function<Context, Context> contextCaptureFunction;
 		boolean contextPropagation;
 		try {
+			// The following line will throw a LinkageError (NoClassDefFoundError) in case context propagation is not available
 			ContextRegistry globalRegistry = ContextRegistry.getInstance();
-			contextCaptureFunction = target -> ContextSnapshot.captureAllUsing(PREDICATE_TRUE, globalRegistry)
-				.updateContext(target);
+			contextCaptureFunction = new ContextCaptureNoPredicate(globalRegistry);
 			contextPropagation = true;
 		}
 		catch (LinkageError t) {
@@ -280,4 +280,17 @@ public Context addToContext(Context originalContext) {
 			}
 		}
 	}
+
+	static final class ContextCaptureNoPredicate implements Function<Context, Context> {
+		final ContextRegistry globalRegistry;
+
+		ContextCaptureNoPredicate(ContextRegistry globalRegistry) {
+			this.globalRegistry = globalRegistry;
+		}
+		@Override
+		public Context apply(Context context) {
+			return ContextSnapshot.captureAllUsing(PREDICATE_TRUE, globalRegistry)
+					.updateContext(context);
+		}
+	}
 }