Upgrade to Reactor 2020.0.18

Closes gh-28329

Author: snicoll

build.gradle

@@ -29,7 +29,7 @@ configure(allprojects) { project ->
 		imports {
 			mavenBom "com.fasterxml.jackson:jackson-bom:2.12.6"
 			mavenBom "io.netty:netty-bom:4.1.75.Final"
-			mavenBom "io.projectreactor:reactor-bom:2020.0.17"
+			mavenBom "io.projectreactor:reactor-bom:2020.0.18"
 			mavenBom "io.r2dbc:r2dbc-bom:Arabba-SR13"
 			mavenBom "io.rsocket:rsocket-bom:1.1.2"
 			mavenBom "org.eclipse.jetty:jetty-bom:9.4.46.v20220331"

spring-core/src/main/java/org/springframework/core/io/buffer/DataBufferUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -1061,7 +1061,7 @@ protected void hookOnComplete() {
 
 		@Override
 		public Context currentContext() {
-			return this.sink.currentContext();
+			return Context.of(this.sink.contextView());
 		}
 
 	}
@@ -1158,7 +1158,7 @@ private void sinkDataBuffer() {
 
 		@Override
 		public Context currentContext() {
-			return this.sink.currentContext();
+			return Context.of(this.sink.contextView());
 		}
 
 	}

spring-web/src/main/java/org/springframework/http/codec/multipart/MultipartParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -105,7 +105,7 @@ public static Flux<Token> parse(Flux<DataBuffer> buffers, byte[] boundary, int m
 
 	@Override
 	public Context currentContext() {
-		return this.sink.currentContext();
+		return Context.of(this.sink.contextView());
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/codec/multipart/PartGenerator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -116,7 +116,7 @@ public static Flux<Part> createParts(Flux<MultipartParser.Token> tokens, int max
 
 	@Override
 	public Context currentContext() {
-		return this.sink.currentContext();
+		return Context.of(this.sink.contextView());
 	}
 
 	@Override