<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Jun 4, 2015 at 1:27 PM, Richard Smith <span dir="ltr"><<a href="mailto:richard@metafoo.co.uk" target="_blank">richard@metafoo.co.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div><div class="h5">On Wed, Jun 3, 2015 at 6:24 PM, Sean Silva <span dir="ltr"><<a href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div><div>On Wed, Jun 3, 2015 at 8:40 AM, Ben Langmuir <span dir="ltr"><<a href="mailto:blangmuir@apple.com" target="_blank">blangmuir@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><br><div><span><blockquote type="cite"><div>On Jun 2, 2015, at 7:57 PM, Sean Silva <<a href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>> wrote:</div><br><div><div dir="ltr">Hi all,<div><br></div><div>Currently we do not seem to issue any form of diagnostic when there are missing headers named in a module map. See the attached test case. Even worse, we will just treat all headers in the module as textual. Hilarity ensues.</div></div></div></blockquote><div><br></div></span><div>Yep, this is <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_PR20507&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=CnzuN65ENJ1H9py9XLiRvC_UQz6u3oG6GUNn7_wosSM&m=SZsuwK7NbouG4WN-Ya3nj5-_IjPX8Bw-435WPI-nsFw&s=8bxz2STldcDlBD7ex1LrFXHtqvr7EEuU5T6jKA2XkyU&e=" target="_blank">llvm.org/PR20507</a></div><span><div><br></div><blockquote type="cite"><div><div dir="ltr"><div><br></div><div>Some prior art in this area:<div>Daniel - r197485</div><div>Ben - r206664</div></div><div><br></div><div>Based on these commits, it ostensibly seems that clang does *some* sort of checking for missing files in a module map, but I can't seem to coax clang into doing this in C++ language mode.</div><div><br></div><div>Looking at the source code, it seems like we end up conflating "unavailable" due to a failed `requires` with "a header is missing". It sounds like we essentially need two notions "unsatisfied `requires`" and "necessary header is missing" (a header guarded by an unsatisfied `requires` does not count as "necessary"). Haven't dug in deep yet, but my hypothesis is that somewhere along the way we silently treat a module with missing headers as though it had an unsatisfied `requires`, leading to us silently neglecting that it was ever in a module at all.</div></div></div></blockquote><div><br></div></span><div>Yes, they both come out as the module being “unvavailable”, which is why we don’t import it. I think the right answer is that attempting to import any unavailable module (even via an auto-import) should be an error. That is:</div><div><br></div><div><div>module MissingHeader {</div><div> header “exists.h"</div><div> header “doesnt_exist.h”</div><div>}</div><div><br></div><div>#include <exists.h> // error, this would import MissingHeader, which is unavailable because we're missing header “doesnt_exist.h"</div></div><div><br></div><div>module Top {</div><div> header “Top.h”</div><div> module A {</div><div> requires non_existent</div><div> header “A.h”</div><div> }</div><div> module B {</div><div> header “B.h”</div><div> }</div><div>}</div><div><br></div><div>#include <Top.h> // OK</div><div>#include <A.h> // error, this would import Top.A, which is unavailable because of the missing requirment</div><div>#include <B.h> // OK</div><div><br></div><div>But handling the first case is more important I think.</div><span><br><blockquote type="cite"><div><div dir="ltr"><div><br></div><div>I'm glad to put some effort into fixing this; I spent a good part of today with a bizarre error that I traced back to this and I don't want my users to have to deal with the same. Any pointers would be appreciated.</div></div></div></blockquote><div><br></div></span><div>That would be great! I was coincidentally hoping to fix this myself in the next few weeks, but if you beat me to it even better.</div><br></div></div></blockquote><div><br></div></div></div><div>I'm still acclimating myself to the modules code, do you have any concrete thoughts on how to do this? I was just planning on looking through for everywhere we use "unavailable" happens and figure out a pattern, but if you already have an idea, it might save me some time.</div></div></div></div></blockquote><div><br></div></div></div><div>Something like:</div><div> * make ModuleMap::findModuleForHeader able to produce an unavailable module, but treat it as being worse than any available module</div><div> * make Preprocessor::HandleIncludeDirective issue an error if its call to LookupFile produces a SuggestedModule that is unavailable</div></div></div></div></blockquote><div><br></div><div>I ran into a bit of a snag when doing this. It looks like diag::err_module_header_missing (and diag::err_module_unavailable) are considered to be frontend diagnostics, so we can't issue them from Lex. Any ideas on how to proceed? It doesn't feel right to duplicate a diagnostic, it suggests we're missing a single point of truth for this.</div><div><br></div><div>Doing `git grep 'isAvailable([^)]'` suggests to me that we are checking the availability way too "deep" in the frontend code. It seems the only centralized place to check this would be in the module map parser, so maybe we can reinstate this check in the module map parser like it was before r197485 (the commit that regressed our diagnosing missing headers)? It seems like that commit removed this functionality as work towards not stating headers while reading the module map, but nothing seems to have come of that.</div><div><br></div><div>-- Sean Silva</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div><br></div><div>This should probably happen even if modules is disabled (that is, when we are parsing module maps but not actually building / using precompiled module files).</div><span class=""><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div>Also, any preferred bikeshed for the names for "unvailable because of unsatisfied requires" and "necessary header is missing" concepts in the source?</div></div></div></div></blockquote><div><br></div></span><div>If the response to both is the same (as Ben suggested, and I agree) then I'm not sure that we need to distinguish them anywhere other than the place where we produce the diagnostic.</div><span class=""><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div>-- Sean Silva</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><div><blockquote type="cite"><div><div dir="ltr"><div><br></div><div>-- Sean Silva</div></div>
<span><testmoduledepbuildfail.tar></span></div></blockquote></div><br></div></blockquote></div><br></div></div>
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