Optional path and req param descriptors should count as documented

Previously, optional path and request parameter descriptors were
ignored when checking that all of the parameters that are present
had been documented. This lead to a false negative if a request
or path parameter was present and was documented with an optional
descriptor.

This commit uses all of the descriptors, not just those that are not
optional, when checking for undocumented parameters.

Closes gh-228

spring-restdocs-core/src/main/java/org/springframework/restdocs/request/AbstractParametersSnippet.java

@@ -124,7 +124,7 @@ public abstract class AbstractParametersSnippet extends TemplatedSnippet {
 		}
 		else {
 			undocumentedParameters = new HashSet<>(actualParameters);
-			undocumentedParameters.removeAll(expectedParameters);
+			undocumentedParameters.removeAll(this.descriptorsByName.keySet());
 		}
 		Set<String> missingParameters = new HashSet<>(expectedParameters);
 		missingParameters.removeAll(actualParameters);

spring-restdocs-core/src/test/java/org/springframework/restdocs/request/PathParametersSnippetTests.java

@@ -99,6 +99,24 @@ public class PathParametersSnippetTests extends AbstractSnippetTests {
 								"/{a}").build());
 	}
 
+	@Test
+	public void presentOptionalPathParameter() throws IOException {
+		this.snippet
+				.expectPathParameters(
+						"present-optional-path-parameter")
+				.withContents(tableWithTitleAndHeader(
+						this.templateFormat == TemplateFormats.asciidoctor() ? "/{a}"
+								: "`/{a}`",
+						"Parameter", "Description").row("a", "one"));
+		new PathParametersSnippet(
+				Arrays.asList(parameterWithName("a").description("one").optional()))
+						.document(operationBuilder("present-optional-path-parameter")
+								.attribute(
+										RestDocumentationGenerator.ATTRIBUTE_NAME_URL_TEMPLATE,
+										"/{a}")
+								.build());
+	}
+
 	@Test
 	public void pathParametersWithQueryString() throws IOException {
 		this.snippet.expectPathParameters("path-parameters-with-query-string")

spring-restdocs-core/src/test/java/org/springframework/restdocs/request/RequestParametersSnippetTests.java

@@ -104,6 +104,17 @@ public class RequestParametersSnippetTests extends AbstractSnippetTests {
 										.build());
 	}
 
+	@Test
+	public void presentOptionalRequestParameter() throws IOException {
+		this.snippet.expectRequestParameters("present-optional-request-parameter")
+				.withContents(
+						tableWithHeader("Parameter", "Description").row("a", "one"));
+		new RequestParametersSnippet(
+				Arrays.asList(parameterWithName("a").description("one").optional()))
+						.document(operationBuilder("present-optional-request-parameter")
+								.request("http://localhost").param("a", "one").build());
+	}
+
 	@Test
 	public void requestParametersWithCustomAttributes() throws IOException {
 		TemplateResourceResolver resolver = mock(TemplateResourceResolver.class);