[Fixes #972] 1-arg lambdas with explicit typing on the argument did not pretty print correctly.

doc/changelog.markdown

@@ -6,6 +6,7 @@ Lombok Changelog
 * FEATURE: `@Builder` updates: The annotation can now be put on instance methods. [Issue #63](https://github.com/rzwitserloot/lombok/issues/63).
 * FEATURE: `@Builder` updates: `@Singular` now supports guava's ImmutableTable [Issue #937](https://github.com/rzwitserloot/lombok/issues/937).
 * FEATURE: A `lombok.config` key can now be used to make your fields `final` and/or `private`... __everywhere__. We'll be monitoring the performance impact of this for a while. We'll touch every source file if you turn these on, and even if you don't, we have to call into the lombok config system for every file.
+* BUGFIX: lambdas with 1 argument that has an explicit type did not pretty print correctly. [Issue #972](https://github.com/rzwitserloot/lombok/issues/972).
 * BUGFIX: `@Value` and `@FieldDefaults` no longer make uninitialized static fields final. [Issue #928](https://github.com/rzwitserloot/lombok/issues/928).
 * BUGFIX: When using delombok, a source file with only `@NonNull` annotations on parameters as lombok feature would not get properly delomboked.  [Issue #950](https://github.com/rzwitserloot/lombok/issues/950).
 * ENHANCEMENT: Putting `@NonNull` on a parameter of an abstract method no longer generates a warning, to allow you to use this annotation to document intended behaviour [Issue #807](https://github.com/rzwitserloot/lombok/issues/807).

src/delombok/lombok/delombok/PrettyPrinter.java

@@ -1438,10 +1438,11 @@ public class PrettyPrinter extends JCTree.Visitor {
 		List<JCVariableDecl> params = readObject(tree, "params", List.<JCVariableDecl>nil());
 		boolean explicit = true;
 		int paramLength = params.size();
-		if (paramLength != 1) print("(");
 		try {
 			explicit = readObject(tree, "paramKind", new Object()).toString().equals("EXPLICIT");
 		} catch (Exception e) {}
+		boolean useParens = paramLength != 1 || explicit;
+		if (useParens) print("(");
 		if (explicit) {
 			boolean first = true;
 			for (JCVariableDecl vd : params) {
@@ -1457,7 +1458,7 @@ public class PrettyPrinter extends JCTree.Visitor {
 				sep = ", ";
 			}
 		}
-		if (paramLength != 1) print(")");
+		if (useParens) print(")");
 		print(" -> ");
 		JCTree body = readObject(tree, "body", (JCTree) null);
 		if (body instanceof JCBlock) {

test/pretty/resource/after/Lambda.java

@@ -4,4 +4,15 @@ public class Lambda {
 	java.util.Comparator<Integer> c2 = (Integer a, Integer b) -> {
 		return a - b;
 	};
-}
+	java.util.function.Function<String, String> fnc = (String c) -> c;
+	void testLambdaInArgsList(String name, java.util.function.Function<String, String> f) {
+	}
+	void testLambdaInArgsList2(java.util.function.Function<String, String> f, String name) {
+	}
+	void test() {
+		testLambdaInArgsList("hello", (String c) -> c);
+		testLambdaInArgsList("hello", c -> c);
+		testLambdaInArgsList2((String c) -> c, "hello");
+		testLambdaInArgsList2(c -> c, "hello");
+	}
+}

test/pretty/resource/before/Lambda.java

@@ -5,4 +5,20 @@ public class Lambda {
 	java.util.Comparator<Integer> c2 = (Integer a, Integer b) -> {
 		return a - b;
 	};
-}
+	java.util.function.Function<String, String> fnc = (String c) -> c;
+	
+	void testLambdaInArgsList(String name, java.util.function.Function<String, String> f) {
+		
+	}
+	
+	void testLambdaInArgsList2(java.util.function.Function<String, String> f, String name) {
+		
+	}
+	
+	void test() {
+		testLambdaInArgsList("hello", (String c) -> c);
+		testLambdaInArgsList("hello", c -> c);
+		testLambdaInArgsList2((String c) -> c, "hello");
+		testLambdaInArgsList2(c -> c, "hello");
+	}
+}