Fix HtmlUnitRequestBuilder merge

Previously invoking HtmlUnitRequestBuilder merge caused the pathInfo of
the parent to be corrupted. This could additional invocations with the
same parent.

This fix ensures that the parent is no longer directly used. Instead,
we create a copy of the parent by merging the parent that was passed in
with the copy.

Fixes SPR-14584

spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java

@@ -45,6 +45,8 @@ import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.mock.web.MockHttpSession;
 import org.springframework.test.web.servlet.RequestBuilder;
 import org.springframework.test.web.servlet.SmartRequestBuilder;
+import org.springframework.test.web.servlet.request.MockHttpServletRequestBuilder;
+import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
 import org.springframework.test.web.servlet.request.RequestPostProcessor;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
@@ -435,7 +437,11 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		if (parent == null) {
 			return this;
 		}
-		if (parent instanceof RequestBuilder) {
+		if (parent instanceof MockHttpServletRequestBuilder) {
+			MockHttpServletRequestBuilder copiedParent = MockMvcRequestBuilders.get("/");
+			copiedParent.merge(parent);
+			this.parentBuilder = copiedParent;
+		} else if (parent instanceof RequestBuilder) {
 			this.parentBuilder = (RequestBuilder) parent;
 		}
 		if (parent instanceof SmartRequestBuilder) {

spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilderTests.java

@@ -895,6 +895,20 @@ public class HtmlUnitRequestBuilderTests {
 		assertThat(mockMvc.perform(requestBuilder).andReturn().getRequest().getAttribute(attrName), equalTo(attrValue));
 	}
 
+	@Test // SPR-14584
+	public void mergeDoesNotCorruptPathInfoOnParent() throws Exception {
+		String pathInfo = "/foo/bar";
+		MockMvc mockMvc = MockMvcBuilders.standaloneSetup(new HelloController())
+				.defaultRequest(get("/"))
+				.build();
+
+		assertThat(mockMvc.perform(get(pathInfo)).andReturn().getRequest().getPathInfo(), equalTo(pathInfo));
+
+		mockMvc.perform(requestBuilder);
+
+		assertThat(mockMvc.perform(get(pathInfo)).andReturn().getRequest().getPathInfo(), equalTo(pathInfo));
+	}
+
 
 	private void assertSingleSessionCookie(String expected) {
 		com.gargoylesoftware.htmlunit.util.Cookie jsessionidCookie = webClient.getCookieManager().getCookie("JSESSIONID");