[clangd] Round WorkDoneProgressBegin.percentage down

[kbobyrev]

Summary

When showing job progression in the text editors, it is hard to read
"precise" percentage numbers. This patch rounds
WorkDoneProgressBegin.percentage to 2 decimal places to improve readability.
While plugins might have different heuristics on how to display those numbers,
many of them will just show the value server provided and therefore it's easier
to do "formatting" on our side.

[kbobyrev]

%s/ceil/floor/g

[sammccall]

clang-tools-extra/clangd/ClangdLSPServer.cpp

1409

Yikes, rounding a float value in the protocol is pretty weird and would deserve more of a comment.

Also this seems like a fairly... improbable bug, in that it's trivial to fix in the editor and would usually be visible if the implementer tried the feature even once.

Which editors specifically are you seeing bad display in? Can we just send them a PR?

[kbobyrev]

clang-tools-extra/clangd/ClangdLSPServer.cpp

1409

Okay, makes sense. I saw this in coc.nvim and I can just fix it there, but I thought it might also happen in other editors. I also thought we do not care too much about precision here, but I'm OK with fixing it on the editor side.

clang-tools-extra/clangd/ClangdLSPServer.cpp

if (BackgroundIndexProgressState != BackgroundIndexProgress::Live) {
       BackgroundIndexProgressState = BackgroundIndexProgress::Live;
     }
 
     if (Stats.Completed < Stats.Enqueued) {
       assert(Stats.Enqueued > Stats.LastIdle);
       WorkDoneProgressReport Report;
       Report.percentage = 100.0 * (Stats.Completed - Stats.LastIdle) /
                           (Stats.Enqueued - Stats.LastIdle);
+      // Round down to 2 decimal places for readability.
+      Report.percentage = std::floor(*Report.percentage * 100.0) / 100.0;
       Report.message =
           llvm::formatv("{0}/{1}", Stats.Completed - Stats.LastIdle,
                         Stats.Enqueued - Stats.LastIdle);
       progress(ProgressToken, std::move(Report));
     } else {
       assert(Stats.Completed == Stats.Enqueued);
       progress(ProgressToken, WorkDoneProgressEnd());
       BackgroundIndexProgressState = BackgroundIndexProgress::Empty;