Issue checkstyle#3486: clear childCount field cache in DetailAST

src/main/java/com/puppycrawl/tools/checkstyle/api/DetailAST.java

@@ -80,8 +80,8 @@ public void initialize(AST ast) {
 
     @Override
     public void setFirstChild(AST ast) {
-        clearBranchTokenTypesCache();
-        childCount = NOT_INITIALIZED;
+        clearBranchTokenTypes();
+        clearChildCountCache(this);
         super.setFirstChild(ast);
         if (ast != null) {
             ((DetailAST) ast).setParent(this);
@@ -90,7 +90,8 @@ public void setFirstChild(AST ast) {
 
     @Override
     public void setNextSibling(AST ast) {
-        clearBranchTokenTypesCache();
+        clearBranchTokenTypes();
+        clearChildCountCache(parent);
         super.setNextSibling(ast);
         if (ast != null && parent != null) {
             ((DetailAST) ast).setParent(parent);
@@ -106,7 +107,8 @@ public void setNextSibling(AST ast) {
      *        DetailAST object.
      */
     public void addPreviousSibling(DetailAST ast) {
-        clearBranchTokenTypesCache();
+        clearBranchTokenTypes();
+        clearChildCountCache(parent);
         if (ast != null) {
             ast.setParent(parent);
             final DetailAST previousSiblingNode = previousSibling;
@@ -130,7 +132,8 @@ else if (parent != null) {
      *        DetailAST object.
      */
     public void addNextSibling(DetailAST ast) {
-        clearBranchTokenTypesCache();
+        clearBranchTokenTypes();
+        clearChildCountCache(parent);
         if (ast != null) {
             ast.setParent(parent);
             final DetailAST nextSibling = getNextSibling();
@@ -147,7 +150,8 @@ public void addNextSibling(DetailAST ast) {
 
     @Override
     public void addChild(AST ast) {
-        clearBranchTokenTypesCache();
+        clearBranchTokenTypes();
+        clearChildCountCache(this);
         super.addChild(ast);
         if (ast != null) {
             ((DetailAST) ast).setParent(this);
@@ -194,7 +198,7 @@ public int getChildCount(int type) {
      * @param parent the parent token
      */
     private void setParent(DetailAST parent) {
-        clearBranchTokenTypesCache();
+        clearBranchTokenTypes();
         this.parent = parent;
         final DetailAST nextSibling = getNextSibling();
         if (nextSibling != null) {
@@ -402,9 +406,20 @@ public DetailAST getFirstChild() {
     }
 
     /**
-     * Clears branchTokenTypes cache for all parents of the current DetailAST instance.
+     * Clears the child count for the ast instance.
+     * @param ast The ast to clear.
      */
-    private void clearBranchTokenTypesCache() {
+    private static void clearChildCountCache(DetailAST ast) {
+        if (ast != null) {
+            ast.childCount = NOT_INITIALIZED;
+        }
+    }
+
+    /**
+     * Clears branchTokenTypes cache for all parents of the current DetailAST instance, and the
+     * child count for the current DetailAST instance.
+     */
+    private void clearBranchTokenTypes() {
         DetailAST prevParent = getParent();
         while (prevParent != null) {
             prevParent.branchTokenTypes = null;

src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java

@@ -818,10 +818,25 @@ public void visitToken(DetailAST ast) {
             final int childCount = ast.getChildCount();
             if (childCount != METHOD_DEF_CHILD_COUNT) {
                 final String msg = String.format(Locale.getDefault(),
-                    "AST node has wrong number of children. Expected is %d but was %d",
+                    "AST node in no comment tree has wrong number of children. "
+                            + "Expected is %d but was %d",
                     METHOD_DEF_CHILD_COUNT, childCount);
                 log(ast, msg);
             }
+            // count children where comment lives
+            int actualChildCount = 0;
+            for (DetailAST child = ast.getFirstChild().getFirstChild(); child != null; child =
+                    child.getNextSibling()) {
+                actualChildCount++;
+            }
+            final int cacheChildCount = ast.getFirstChild().getChildCount();
+            if (cacheChildCount != actualChildCount) {
+                final String msg = String.format(Locale.getDefault(),
+                        "AST node with no comment has wrong number of children. "
+                                + "Expected is %d but was %d",
+                        cacheChildCount, actualChildCount);
+                log(ast, msg);
+            }
         }
     }
 
@@ -858,10 +873,25 @@ public void visitToken(DetailAST ast) {
             final int childCount = ast.getChildCount();
             if (childCount != METHOD_DEF_CHILD_COUNT) {
                 final String msg = String.format(Locale.getDefault(),
-                    "AST node has wrong number of children. Expected is %d but was %d",
+                    "AST node in comment tree has wrong number of children. "
+                            + "Expected is %d but was %d",
                     METHOD_DEF_CHILD_COUNT, childCount);
                 log(ast, msg);
             }
+            // count children where comment lives
+            int actualChildCount = 0;
+            for (DetailAST child = ast.getFirstChild().getFirstChild(); child != null; child =
+                    child.getNextSibling()) {
+                actualChildCount++;
+            }
+            final int cacheChildCount = ast.getFirstChild().getChildCount();
+            if (cacheChildCount != actualChildCount) {
+                final String msg = String.format(Locale.getDefault(),
+                        "AST node with comment has wrong number of children. "
+                                + "Expected is %d but was %d",
+                        cacheChildCount, actualChildCount);
+                log(ast, msg);
+            }
         }
     }
 }

src/test/resources/com/puppycrawl/tools/checkstyle/api/InputClearDetailAstLazyLoadCache.java

@@ -2,10 +2,11 @@
 
 public class InputClearDetailAstLazyLoadCache {
 
-    /**
+    public
+    /*
      * Javadoc comment
      */
-    public void foo() {
+    static void foo() {
         return;
     }
 }