<div dir="auto"><br><br><div class="gmail_quote" dir="auto"><div dir="ltr" class="gmail_attr">On Wed 27 May 2020, 11:01 Sam McCall, <<a href="mailto:sammccall@google.com">sammccall@google.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div dir="ltr"><br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>Unfortunately this is causing widespread problems in downstream tools that are difficult to track:<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">Sorry this is causing problems in downstream tools.</div><div dir="auto"><br></div><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> - this is a prominent API that is used in many places<br> - the semantics have changed subtly but pervasively, so all usage sites need to be audited, but because there was no API syntax change (e.g. build break), it's not trivial to find all the affected locations to audit<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">Is it trivial to set the TraversalKind presumptively on the ParentMapContext early in the runtime of the downstream tool? The ParentMapContext is available via your ASTContext. </div><div dir="auto"><br></div><div dir="auto">I ask because reading your email it doesn't look like you considered this option? If you did consider it and rejected it, please say more about why it is not an option. </div><div dir="auto"><br></div><div dir="auto">That way you don't have to try to audit any matchers yet. You would just set the TraversalKind to AsIs in the entire tool. </div></div></blockquote><div>Right, I should have addressed this.</div><div>The first problem is that we don't have a really solid way of identifying all the downstream tools that are affected. </div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">Can you just change the setting for all of your downstream tools? (Excepting that clang-tidy might be a different beast in which you have to set it for each downstream check)</div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>There are certainly hundreds of these.</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">Are all of these hundreds of tools independent? Or do they share some abstraction or common setup code or initialization code which lives in a library?<br></div><div dir="auto"><br></div><div dir="auto">I'm trying to find out whether the number of places in your code which need to be adjusted can be reduced from hundreds to a handful. Any early-enough place in the code which you own and which affects all or most of your tools would be a good start. </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>Another problem is tools that mix matchers defined upstream with those defined downstream, such as clang-tidy, where there are large numbers of checks defined with various owners.</div><div><br></div><div>For this reason I'd been assuming the right workaround was to wrap the matchers in traverse() everywhere. Maybe we should consider clang-tidy and other tools as separate problems -</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">I also suspect that would be helpful. </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> if it's *just* clang-tidy then wrapping all of the matchers might be manageable (with the bug fixed).</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">I have a proof of concept patch which adds a virtual method to ClangTidyCheck which returns an overriding optional<TraversalKind> to use for the check. If you reimplement that method in your downstream checks to return AsIs then you don't have to change individual matchers yet. </div><div dir="auto"><br></div><div dir="auto">What do you think?</div><div dir="auto"><br></div><div dir="auto">I have the patch on a computer I will have access to in about 2 hours. </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> And for other tools I think we can probably flip the mode, if we can find all the tools and find an appropriate place in the code to do so.</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">Yes. </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> - the differences between old and new only occur when running against certain code patterns that often aren't covered by tests, therefore each audit is a lot of work<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">If that audit can be deferred, does the situation change?</div></div></blockquote><div>Yes - for a start it's now safe to upgrade LLVM again :-)</div><div>We usually integrate LLVM head daily, and when this process gets blocked it affects a large number of developers in unrelated areas (say, MLIR).</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">Sorry for the disruption. At least the issue is getting visibility here and feedback already indicates that the release notes could be more informative. </div><div dir="auto"><br></div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> - because the default was flipped globally, all usage sites must be dealt with at once<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">Does this become manageable if you flip the setting locally in your tool in your ParentMapContext?</div><div dir="auto"><br></div><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> - the "revert-to-old-behaviour" is invasive at all usage sites (hurts readability a lot) and apparently has bugs (D80606)<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">If changing the TraversalKind in the ParentMapContext in your tool is a potential solution, then I can look into the above issue this morning.</div><div dir="auto"><br></div><div dir="auto">Please let me know. </div></div></blockquote><div>+yitzhakm<br></div><div>Yitzhak was also looking into a fix here and may have ideas already.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>In summary: it requires changes in consuming tools that are numerous, hard to find, hard to analyze, must all be done at once, and the changes aren't mechanically reliable.<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">Hmm, the location to call setTraversalKind on the ParentMapContext in each external tool should be easy to find? Should be easy to analyze too. There is presumably fewer places <span style="font-family:sans-serif">in your tool</span> (or just one place in the entire tool) where ASTContexts are created, so "all" is either "1" or close to it?</div><div dir="auto"><br></div><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>I expect this to bite people building tools against release versions to hit the same problems in a few months.<br></div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">Perhaps the solution of changing the setting in the ParentMapContext needs to be spelled out better in the release notes. It would also be good to know whether doing so makes the impact on your tools manageable. Can you look into that?</div></div></blockquote><div>I think putting the solution in the release notes will hurt people not paying attention in the same way I didn't spot this early enough on cfe-dev (well, Dmitri did).</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">I'd think that at least if someone upgrades to a new release and their code breaks, the they would check the release notes. I realize that doesn't scale so we'll for those that "live at HEAD". </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>It certainly helps to have good documentation but subtly changing the meaning of existing code is still dangerous.</div><div>I don't know the matcher API details well enough yet to have a concrete suggestion, but I'm trying to get a better grasp on this.</div></div></div></blockquote></div><div dir="auto"><br></div><div dir="auto">I agree that compile failures are better than runtime failures. We couldn't come up with a better solution.</div><div dir="auto"><br></div><div dir="auto">At least this runtime failure is likely to be "loud" where it occurs. </div><div dir="auto"><br></div><div dir="auto"><br></div><div dir="auto">Thanks,</div><div dir="auto"><br></div><div dir="auto">Stephen. </div><div dir="auto"><br></div><div class="gmail_quote" dir="auto"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto"><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div>We should consider reverting this and finding a less-silent way to roll out the change (like adding it with different syntax, or having no default for a transition period covering a stable release).</div></div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">Before doing that I'd like to find out more about whether the above solution works. </div><div dir="auto"><br></div><div dir="auto">Thanks,</div><div dir="auto"><br></div><div dir="auto">Stephen. </div><div dir="auto"><br></div><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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