Java 25 parser: don't merge /// blocks across blank lines

Per JEP 467, a blank line terminates a markdown doc comment, so two
`///` blocks separated by an empty line are distinct doc comments.
The merging code in `formatWithMarkdownJavaDoc` previously walked
backward across all consecutive `///` lines without checking the
inter-comment suffix, which interleaved their characters when re-printed.

Found while running `FindParseFailures` against `JabRef/jabref` for
#7554.

Author: timtebeek

rewrite-java-25/src/main/java/org/openrewrite/java/isolated/ReloadableJava25ParserVisitor.java

@@ -1999,6 +1999,16 @@ private static int findFirstNonWhitespaceChar(String s) {
         return -1;
     }
 
+    private static int countNewlines(String s) {
+        int count = 0;
+        for (int i = 0; i < s.length(); i++) {
+            if (s.charAt(i) == '\n') {
+                count++;
+            }
+        }
+        return count;
+    }
+
     private long lineNumber(Tree tree) {
         return source.substring(0, ((JCTree) tree).getStartPosition()).chars().filter(c -> c == '\n').count() + 1;
     }
@@ -2606,6 +2616,11 @@ private Space formatWithMarkdownJavaDoc(JCTree tree, DocCommentTree commentTree,
         for (int k = last - 1; k >= 0; k--) {
             Comment c = comments.get(k);
             if (!c.isMultiline() && c instanceof TextComment tc && tc.getText().startsWith("/")) {
+                // A blank line between two `///` blocks separates them into distinct
+                // doc comments per JEP 467; only merge when the suffix contains a single line break.
+                if (countNewlines(c.getSuffix()) > 1) {
+                    break;
+                }
                 first = k;
             } else {
                 break;

rewrite-java-tck/src/main/java/org/openrewrite/java/tree/JavadocTest.java

@@ -2989,5 +2989,20 @@ class Test {
               )
             );
         }
+
+        @Issue("https://github.com/openrewrite/rewrite/issues/7554")
+        @Test
+        void twoTripleSlashBlocksSeparatedByBlankLine() {
+            rewriteRun(
+              java(
+                """
+                  /// First doc-comment block.
+
+                  /// Second doc-comment block.
+                  class Test {}
+                  """
+              )
+            );
+        }
     }
 }