Ensure leading space is present in line comments

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=156080131

Author: cushon

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

@@ -722,6 +722,9 @@ float computeWidth() {
       if (tok.isComment()) {
         if (idx > 0) {
           return idx;
+        } else if (tok.isSlashSlashComment() && !tok.getOriginalText().startsWith("// ")) {
+          // Account for line comments with missing spaces, see computeFlat.
+          return tok.length() + 1;
         } else {
           return tok.length();
         }
@@ -731,6 +734,12 @@ float computeWidth() {
 
     @Override
     String computeFlat() {
+      // TODO(cushon): commentsHelper.rewrite doesn't get called for spans that fit in a single
+      // line. That's fine for multi-line comment reflowing, but problematic for adding missing
+      // spaces in line comments.
+      if (tok.isSlashSlashComment() && !tok.getOriginalText().startsWith("// ")) {
+        return "// " + tok.getOriginalText().substring("//".length());
+      }
       return tok.getOriginalText();
     }
 

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

@@ -104,6 +104,10 @@ private List<String> wrapLineComments(
       List<String> lines, int column0, JavaFormatterOptions options) {
     List<String> result = new ArrayList<>();
     for (String line : lines) {
+      // Add missing leading spaces to line comments: `//foo` -> `// foo`
+      if (!line.startsWith("// ")) {
+        line = "// " + line.substring("//".length());
+      }
       while (line.length() + column0 > options.maxLineLength()) {
         int idx = options.maxLineLength() - column0;
         // only break on whitespace characters, and ignore the leading `// `

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

@@ -383,7 +383,7 @@ public void onlyWrapLineCommentOnWhitespace_noLeadingWhitespace() throws Excepti
             "class T {\n"
                 + "  public static void main(\n"
                 + "      String[]\n"
-                + "          args) { //one_long_incredibly"
+                + "          args) { // one_long_incredibly"
                 + "_unbroken_sentence_moving_from_topic_to_topic_so_that_no-one_had_a"
                 + "_chance_to_interrupt;\n"
                 + "  }\n"

core/src/test/resources/com/google/googlejavaformat/java/testdata/B20844369.output

@@ -11,23 +11,23 @@ public class B20844369 {
           + "(?<tokenHash>[0-9a-fA-F]{8})" // subtype's token hash
           + ")?"; // end optional subtype
 
-  int x = //foo
-      42 + //bar
+  int x = // foo
+      42 + // bar
           1;
 
   int x =
-      //foo
+      // foo
       42
-          + //bar
+          + // bar
           1;
 
   int x = /*foo*/
-      42 + //bar
+      42 + // bar
           1;
 
   int x =
       /*foo*/
       42
-          + //bar
+          + // bar
           1;
 }

core/src/test/resources/com/google/googlejavaformat/java/testdata/B38241237.input

@@ -0,0 +1,5 @@
+class B38241237 {
+  //foo
+  //bar
+  //one long incredibly unbroken sentence moving from topic to topic so that no-one had a chance to interrupt
+}

core/src/test/resources/com/google/googlejavaformat/java/testdata/B38241237.output

@@ -0,0 +1,6 @@
+class B38241237 {
+  // foo
+  // bar
+  // one long incredibly unbroken sentence moving from topic to topic so that no-one had a chance to
+  // interrupt
+}