[clang-format] Fix a bug that indents else-comment-if incorrectly

[owenpan]

Summary

If there is a comment between "else" and "if", the "if" statement including its body is indented incorrectly.

See https://bugs.llvm.org/show_bug.cgi?id=50809 for an example.

[MyDeveloperDay]

LGTM

[owenpan]

Thanks!

[HazardyKnusperkeks]

That was fast. I personally like it better to give others a chance to look at. ;)

[MyDeveloperDay]

@HazardyKnusperkek Its probably my "bad" I should said "LGTM but maybe wait for the others to comment", but I'm fundamentally ok I think with the change. (we'll just revert if it breaks stuff! ;-))

We are free to add review comments after the fact, @owenpan has been providing us with fixes and contributions to clang-format for a some time (years) so I pretty much trust them. I'm less sceptical in the review of those that contribute either on a regular basis (like yourself) or those who have done multiple features (like @owenpan). I did actually download the patch, apply it and run all the unit tests too, (because I was slightly questioning in my mind the use of "Previous" and if it could be null), but it all seemed to check out (and I tried some combinations to try and break it))

I don't think we need to wait multiple accepts (although between us I think we do this from time to time), I think the LLVM rules specify that if you have an accept then its ok, But I do feel its perfectly acceptable to review after the fact and expect the author to change it again.

I was the one that added you and @curdeius as reviewers (as I normally do out of respect for your efforts), but perhaps only we know that we are the ones doing the lion share of clang-format reviewing (others might not know that).

[HazardyKnusperkeks]

In D104774#2838287, @MyDeveloperDay wrote:

@HazardyKnusperkek Its probably my "bad" I should said "LGTM but maybe wait for the others to comment", but I'm fundamentally ok I think with the change. (we'll just revert if it breaks stuff! ;-))

We are free to add review comments after the fact, @owenpan has been providing us with fixes and contributions to clang-format for a some time (years) so I pretty much trust them. I'm less sceptical in the review of those that contribute either on a regular basis (like yourself) or those who have done multiple features (like @owenpan). I did actually download the patch, apply it and run all the unit tests too, (because I was slightly questioning in my mind the use of "Previous" and if it could be null), but it all seemed to check out (and I tried some combinations to try and break it))

I don't think we need to wait multiple accepts (although between us I think we do this from time to time), I think the LLVM rules specify that if you have an accept then its ok, But I do feel its perfectly acceptable to review after the fact and expect the author to change it again.

I was the one that added you and @curdeius as reviewers (as I normally do out of respect for your efforts), but perhaps only we know that we are the ones doing the lion share of clang-format reviewing (others might not know that).

No problem here. :) I think the change is small enough and the fix obvious. It was just a small comment.

clang/lib/Format/UnwrappedLineParser.cpp

if (FormatTok->Tok.is(tok::kw_else)) {
     // handle [[likely]] / [[unlikely]]
     if (FormatTok->Tok.is(tok::l_square) && tryToParseSimpleAttribute())
       parseSquare();
     if (FormatTok->Tok.is(tok::l_brace)) {
       CompoundStatementIndenter Indenter(this, Style, Line->Level);
       parseBlock(/*MustBeDeclaration=*/false);
       addUnwrappedLine();
     } else if (FormatTok->Tok.is(tok::kw_if)) {
+      FormatToken *Previous = AllTokens[Tokens->getPosition() - 1];
+      bool PrecededByComment = Previous->is(tok::comment);
+      if (PrecededByComment) {
+        addUnwrappedLine();
+        ++Line->Level;
+      }
       parseIfThenElse();
+      if (PrecededByComment)
+        --Line->Level;
     } else {
       addUnwrappedLine();
       ++Line->Level;
       parseStructuralElement();
       if (FormatTok->is(tok::eof))
         addUnwrappedLine();
       --Line->Level;
     }

clang/unittests/Format/FormatTest.cpp

 TEST_F(FormatTest, ElseIf) {
   verifyFormat("if (a) {\n} else if (b) {\n}");
   verifyFormat("if (a)\n"
                "  f();\n"
                "else if (b)\n"
                "  g();\n"
                "else\n"
                "  h();");
+  verifyFormat("if (a)\n"
+               "  f();\n"
+               "else // comment\n"
+               "  if (b) {\n"
+               "    g();\n"
+               "    h();\n"
+               "  }");
   verifyFormat("if constexpr (a)\n"
                "  f();\n"
                "else if constexpr (b)\n"
                "  g();\n"
                "else\n"
                "  h();");
   verifyFormat("if CONSTEXPR (a)\n"
                "  f();\n"