Drop trailing tabs from comments instead of writing them out

A line comment that ended in tabs, "// comment\t\t\t", kept them in
the output, so the formatted file had trailing whitespace where the
same comment ending in spaces had none. JavaOutput collected pending
spaces in a counter and wrote them only in front of the next non-blank
character, which is what drops trailing spaces; a tab fell through to
the default case and was written straight away.

This ports google/google-java-format#423 by Alexander Eckert (upstream
commit 05f57ec9, fixing google/google-java-format#422): pending
whitespace is kept as text, tabs included, and written out only when
something follows it on the line, so a tab inside a comment stays and a
tab at the end of one goes. The removeTrailingTabsInComments test comes
from upstream, in this project's style.

The 15,747 files of the JDK 21 sources format exactly as before.

Author: Eckaaaaaat

open-java-format/src/main/java/com/palantir/javaformat/java/JavaOutput.java

@@ -50,9 +50,11 @@ public final class JavaOutput extends Output {
     private final InputMetadata inputMetadata;
     private int iLine = 0; // Closest corresponding line number on input.
     private int lastK = -1; // Last {@link Tok} index output.
-    private int spacesPending = 0;
     private int newlinesPending = 0;
     private StringBuilder lineBuilder = new StringBuilder();
+    // Spaces and tabs seen since the last non-blank character. Written out in front of the next one, so that a line
+    // never ends in whitespace: trailing tabs inside a comment were kept before, and only a second run removed them.
+    private StringBuilder spacesPending = new StringBuilder();
 
     /**
      * {@code JavaOutput} constructor.
@@ -99,23 +101,26 @@ public void append(State state, String text, Range<Integer> range) {
             if (newlinesPending == 0) {
                 ++newlinesPending;
             }
-            spacesPending = 0;
+            spacesPending = new StringBuilder();
         } else {
             boolean rangesSet = false;
             int textN = text.length();
             for (int i = 0; i < textN; i++) {
                 char c = text.charAt(i);
                 switch (c) {
                     case ' ':
-                        ++spacesPending;
+                        spacesPending.append(' ');
+                        break;
+                    case '\t':
+                        spacesPending.append('\t');
                         break;
                     case '\r':
                         if (i + 1 < text.length() && text.charAt(i + 1) == '\n') {
                             i++;
                         }
                     // falls through
                     case '\n':
-                        spacesPending = 0;
+                        spacesPending = new StringBuilder();
                         ++newlinesPending;
                         break;
                     default:
@@ -128,9 +133,9 @@ public void append(State state, String text, Range<Integer> range) {
                             rangesSet = false;
                             --newlinesPending;
                         }
-                        while (spacesPending > 0) {
-                            lineBuilder.append(' ');
-                            --spacesPending;
+                        if (spacesPending.length() > 0) {
+                            lineBuilder.append(spacesPending);
+                            spacesPending = new StringBuilder();
                         }
                         lineBuilder.append(c);
                         if (!range.isEmpty()) {
@@ -152,7 +157,7 @@ public void append(State state, String text, Range<Integer> range) {
 
     @Override
     public void indent(int indent) {
-        spacesPending = indent;
+        spacesPending.append(" ".repeat(indent));
     }
 
     /** Flush any incomplete last line, then add the EOF token into our data structures. */
@@ -354,7 +359,7 @@ public String toString() {
         return MoreObjects.toStringHelper(this)
                 .add("iLine", iLine)
                 .add("lastK", lastK)
-                .add("spacesPending", spacesPending)
+                .add("spacesPending", spacesPending.toString().replace("\t", "\\t"))
                 .add("newlinesPending", newlinesPending)
                 .add("inputMetadata", inputMetadata)
                 .add("super", super.toString())

open-java-format/src/test/java/com/palantir/javaformat/java/FormatterTest.java

@@ -508,4 +508,14 @@ void indentsCommentsThatShareALineLinearly() throws FormatterException {
 
         assertThat(formatter.formatSource(input.toString()).length()).isLessThan(10_000);
     }
+
+    @Test
+    public void removeTrailingTabsInComments() throws FormatterException {
+        String input = "class Foo {\n    void f() {\n        int x = 0; // comment\t\t\t\n        return;\n    }\n}\n";
+        String expected = "class Foo {\n    void f() {\n        int x = 0; // comment\n        return;\n    }\n}\n";
+        Formatter formatter = Formatter.createFormatter(
+                JavaFormatterOptions.builder().style(Style.OJF).build());
+
+        assertThat(formatter.formatSource(input)).isEqualTo(expected);
+    }
 }