[clang-format] comment reflow: add last line's penalty when ending broken

[krasimir]

Summary

This fixes a bug in clang-format where the last line's penalty is not
taken into account when its ending is broken. Usually the last line's penalty
is handled by addNextStateToQueue, but in cases where the trailing */ is put
on a newline, the contents of the last line have to be considered for penalizing.

lib/Format/ContinuationIndenter.cpp

while (ContentStartColumn + RemainingTokenColumns > ColumnLimit) {
       // compress whitespace within a line.
       BreakableToken::Split Split =
           Token->getSplit(LineIndex, TailOffset, ColumnLimit,
                           ContentStartColumn, CommentPragmasRegex);
       if (Split.first == StringRef::npos) {
         // No break opportunity - update the penalty and continue with the next
         // logical line.
         if (LineIndex < EndIndex - 1)
-          // The last line's penalty is handled in addNextStateToQueue().
+          // The last line's penalty is handled in addNextStateToQueue() or when
+          // calling replaceWhitespaceAfterLastLine below.
           Penalty += Style.PenaltyExcessCharacter *
                      (ContentStartColumn + RemainingTokenColumns - ColumnLimit);
         LLVM_DEBUG(llvm::dbgs() << "    No break opportunity.\n");
         break;
       }
       assert(Split.first != 0);
 
       if (Token->supportsReflow()) {
if (LineIndex + 1 != EndIndex) {
       }
     }
   }
 
   BreakableToken::Split SplitAfterLastLine =
       Token->getSplitAfterLastLine(TailOffset);
   if (SplitAfterLastLine.first != StringRef::npos) {
     LLVM_DEBUG(llvm::dbgs() << "Replacing whitespace after last line.\n");
+
+    // We add the last line's penalty here, since that line is going to be split
+    // now.
+    Penalty += Style.PenaltyExcessCharacter *
+               (ContentStartColumn + RemainingTokenColumns - ColumnLimit);
+
     if (!DryRun)
       Token->replaceWhitespaceAfterLastLine(TailOffset, SplitAfterLastLine,
                                             Whitespaces);
     ContentStartColumn =
         Token->getContentStartColumn(Token->getLineCount() - 1, /*Break=*/true);
     RemainingTokenColumns = Token->getRemainingLength(
         Token->getLineCount() - 1,
         TailOffset + SplitAfterLastLine.first + SplitAfterLastLine.second,

unittests/Format/FormatTestJS.cpp

verifyFormat("// st \\ art\\\n"
                "// continue \\\n"
                "formatMe();\n",
                "// st \\ art\\\n"
                "// comment"
                "// continue \\\n"
                "formatMe( );\n");
 }
 
+TEST_F(FormatTestJS, AddsLastLinePenaltyIfEndingIsBroken) {
+  EXPECT_EQ(
+      "a = function() {\n"
+      "  b = function() {\n"
+      "    this.aaaaaaaaaaaaaaaaaaa[aaaaaaaaaaa] = aaaa.aaaaaa ?\n"
+      "        aaaa.aaaaaa : /** @type "
+      "{aaaa.aaaa.aaaaaaaaa.aaaaaaaaaaaaaaaaaaa} */\n"
+      "        (aaaa.aaaa.aaaaaaaaa.aaaaaaaaaaaaa.aaaaaaaaaaaaaaaaa);\n"
+      "  };\n"
+      "};",
+      format("a = function() {\n"
+             "  b = function() {\n"
+             "    this.aaaaaaaaaaaaaaaaaaa[aaaaaaaaaaa] = aaaa.aaaaaa ? "
+             "aaaa.aaaaaa : /** @type "
+             "{aaaa.aaaa.aaaaaaaaa.aaaaaaaaaaaaaaaaaaa} */\n"
+             "        (aaaa.aaaa.aaaaaaaaa.aaaaaaaaaaaaa.aaaaaaaaaaaaaaaaa);\n"
+             "  };\n"
+             "};"));
+}
+
 } // end namespace tooling
 } // end namespace clang