Don't wrap line comments that start with /// .

Until we have full support for Markdown Javadoc, this at least prevents us from misguidedly destroying it by using only `// ` for the continuation lines.

PiperOrigin-RevId: 885030098

Author: eamonnmcmanus

core/src/main/java/com/google/googlejavaformat/java/JavaCommentsHelper.java

@@ -108,6 +108,9 @@ private String indentLineComments(List<String> lines, int column0) {
     return builder.toString();
   }
 
+  /** Probably a markdown comment, so don't try to wrap it. */
+  private static final Pattern MARKDOWN_JAVADOC_PREFIX = Pattern.compile("^///(\\s|$)");
+
   // Preserve special `//noinspection` and `//$NON-NLS-x$` comments used by IDEs, which cannot
   // contain leading spaces.
   private static final Pattern LINE_COMMENT_MISSING_SPACE_PREFIX =
@@ -116,6 +119,13 @@ private String indentLineComments(List<String> lines, int column0) {
   private List<String> wrapLineComments(List<String> lines, int column0) {
     List<String> result = new ArrayList<>();
     for (String line : lines) {
+      if (MARKDOWN_JAVADOC_PREFIX.matcher(line).find()) {
+        // Don't try to wrap comments that might be markdown javadoc.
+        // This is fairly approximate: a /// comment is only javadoc if it precedes a javadocable
+        // program element. But even if this isn't javadoc, it's not a disaster if we don't wrap it.
+        result.add(line);
+        continue;
+      }
       // Add missing leading spaces to line comments: `//foo` -> `// foo`.
       Matcher matcher = LINE_COMMENT_MISSING_SPACE_PREFIX.matcher(line);
       if (matcher.find()) {

core/src/test/java/com/google/googlejavaformat/java/JavadocFormattingTest.java

@@ -1507,21 +1507,18 @@ public void simpleMarkdown() {
       "  }",
       "}",
     };
-    // TODO(emcmanus): Fix the formatter so it doesn't produce this nonsense:
-    // - wrapped lines should start with /// not //
-    // - blank line before @param
+    // TODO(emcmanus): Actually format the javadoc. For now, we just leave `///` lines alone, unlike
+    // `//` lines which get wrapped.
     String[] expected = {
       "package com.example;",
       "",
       "/// # Heading",
       "///",
       "/// A very long line of text, long enough that it will need to be wrapped to fit within the"
-          + " maximum",
-      "// line length.",
+          + " maximum line length.",
       "class Test {",
       "  /// Another very long line of text, also long enough that it will need to be wrapped to"
-          + " fit within",
-      "  // the maximum line length.",
+          + " fit within the maximum line length.",
       "  /// @param <T> a generic type",
       "  <T> T method() {",
       "    return null;",