Issue checkstyle#12486: NoWhitespaceAfter shouldn't check synchronize…

…d method

src/main/java/com/puppycrawl/tools/checkstyle/checks/whitespace/NoWhitespaceAfterCheck.java

@@ -55,6 +55,24 @@
  * <pre>
  * public void foo(final char @NotNull [] param) {} // No violation
  * </pre>
+ * <p>
+ * Note: This check processes the
+ * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LITERAL_SYNCHRONIZED">
+ * LITERAL_SYNCHRONIZED</a> token only when it appears as a part of a
+ * <a href="https://docs.oracle.com/javase/specs/jls/se19/html/jls-14.html#jls-14.19">
+ * synchronized statement</a>.
+ * </p>
+ * <p>
+ * Example:
+ * </p>
+ * <pre>
+ * void m1() {
+ *     synchronized(this) {} // ok
+ *     synchronized (this) {} // violation
+ * }
+ * synchronized &lt;T&gt; void m2() {} // ok
+ * synchronized&lt;T&gt; void m3() {} // ok
+ * </pre>
  * <ul>
  * <li>
  * Property {@code allowLineBreaks} - Control whether whitespace is allowed
@@ -284,7 +302,10 @@ private static DetailAST getWhitespaceFollowedNode(DetailAST ast) {
      */
     private static boolean shouldCheckWhitespaceAfter(DetailAST ast) {
         final DetailAST previousSibling = ast.getPreviousSibling();
-        return previousSibling == null || previousSibling.getType() != TokenTypes.ANNOTATIONS;
+        final boolean isSynchronizedMethod = ast.getType() == TokenTypes.LITERAL_SYNCHRONIZED
+                        && ast.getFirstChild() == null;
+        return !isSynchronizedMethod
+                && (previousSibling == null || previousSibling.getType() != TokenTypes.ANNOTATIONS);
     }
 
     /**

src/main/resources/com/puppycrawl/tools/checkstyle/meta/checks/whitespace/NoWhitespaceAfterCheck.xml

@@ -30,6 +30,24 @@
  </p>
  <pre>
  public void foo(final char @NotNull [] param) {} // No violation
+ </pre>
+ <p>
+ This check processes the
+ <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LITERAL_SYNCHRONIZED">
+ LITERAL_SYNCHRONIZED</a> token only when it appears as a part of a
+ <a href="https://docs.oracle.com/javase/specs/jls/se19/html/jls-14.html#jls-14.19">
+ synchronized statement</a>.
+ </p>
+ <p>
+ Example:
+ </p>
+ <pre>
+ void m1() {
+     synchronized(this) {} // ok
+     synchronized (this) {} // violation
+ }
+ synchronized <T> void m2() {} // ok
+ synchronized<T> void m3() {} // ok
  &lt;/pre&gt;</description>
          <properties>
             <property default-value="true" name="allowLineBreaks" type="boolean">

src/test/java/com/puppycrawl/tools/checkstyle/checks/whitespace/NoWhitespaceAfterCheckTest.java

@@ -354,6 +354,17 @@ public void testNoWhitespaceAfterWithEmoji() throws Exception {
                 getPath("InputNoWhitespaceAfterWithEmoji.java"), expected);
     }
 
+    @Test
+    public void testNoWhitespaceAfterSynchronized() throws Exception {
+        final String[] expected = {
+            "18:9: " + getCheckMessage(MSG_KEY, "synchronized"),
+        };
+
+        verifyWithInlineConfigParser(
+                getPath("InputNoWhitespaceAfterSynchronized.java"),
+                expected);
+    }
+
     /**
      * Creates MOCK lexical token and returns AST node for this token.
      *

src/test/resources/com/puppycrawl/tools/checkstyle/checks/whitespace/nowhitespaceafter/InputNoWhitespaceAfterSynchronized.java

@@ -0,0 +1,59 @@
+/*
+NoWhitespaceAfter
+allowLineBreaks = (default)true
+tokens = LITERAL_SYNCHRONIZED
+
+
+*/
+package com.puppycrawl.tools.checkstyle.checks.whitespace.nowhitespaceafter;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+public class InputNoWhitespaceAfterSynchronized<T> {
+
+    private final Object lock = new Object();
+
+    void m1() {
+        synchronized (lock) {} // violation
+        synchronized(lock) {} // ok
+    }
+
+    synchronized int m2() { // ok
+        return 2;
+    }
+
+    synchronized private int[] m3() { // ok
+        return new int[]{2};
+    }
+
+    synchronized int[] m4() { // ok
+        return new int[]{2};
+    }
+
+    private final synchronized int m5() { // ok
+        return 2;
+    }
+
+    synchronized T m6() { // ok
+        return null;
+    }
+
+    @SyncAnno synchronized T m7() { // ok
+        return null;
+    }
+
+    @SyncAnno private synchronized T m8() { // ok
+        return null;
+    }
+
+    // Note that we do not check 'synchronized' as a modifier,
+    // convention is to have type parameters of a generic method
+    // be surrounded by whitespace.
+    synchronized <T2> void m9() {} // ok
+    synchronized<T2> void m10() {} // ok
+}
+
+@Target(ElementType.METHOD)
+@interface SyncAnno {
+}

src/xdocs/config_whitespace.xml

@@ -1353,6 +1353,23 @@ import static java.math.BigInteger.ZERO;
         <source>
 public void foo(final char @NotNull [] param) {} // No violation
         </source>
+        <p>
+          Note: This check processes the <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LITERAL_SYNCHRONIZED">
+          LITERAL_SYNCHRONIZED</a> token only when it appears as a part of a
+          <a href="https://docs.oracle.com/javase/specs/jls/se19/html/jls-14.html#jls-14.19">
+          synchronized statement</a>.
+        </p>
+        <p>
+          Example:
+        </p>
+        <source>
+void m1() {
+  synchronized(this) {} // ok
+  synchronized (this) {} // violation
+}
+synchronized &lt;T&gt; void m2() {} // ok
+synchronized&lt;T&gt; void m3() {} // ok
+        </source>
       </subsection>
 
       <subsection name="Properties" id="NoWhitespaceAfter_Properties">