<div dir="ltr">On 27 August 2013 00:04, Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@google.com" target="_blank">chandlerc@google.com</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div><div><br><div class="gmail_quote">On Mon, Aug 26, 2013 at 11:40 PM, Nick Lewycky <span dir="ltr"><<a href="mailto:nlewycky@google.com" target="_blank">nlewycky@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div>On 26 August 2013 23:22, Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@google.com" target="_blank">chandlerc@google.com</a>></span> wrote:<br>
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<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><div>
<br><div class="gmail_quote">On Mon, Aug 26, 2013 at 11:09 PM, Nick Lewycky <span dir="ltr"><<a href="mailto:nlewycky@google.com" target="_blank">nlewycky@google.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>On 26 August 2013 22:53, Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@google.com" target="_blank">chandlerc@google.com</a>></span> wrote:<br>
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<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">I think this case has more problems than just verbosity...</div>
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<br></div><div class="gmail_extra"><div>On Mon, Aug 26, 2013 at 10:38 PM, Nick Lewycky <span dir="ltr"><<a href="mailto:nlewycky@google.com" target="_blank">nlewycky@google.com</a>></span> wrote:<br>
</div><div class="gmail_quote"><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>a.cc:1:56: error: no template named 'Foox'; did you mean 'Foo'?<br>
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<div><div>template <typename T> class Foo {}; class Bar : public Foox {};</div>
<div>[point at 'Foox' suggest 'Foo']</div></div></blockquote><div><br></div></div><div>Why does it assume Foox is a template?</div></div></div></div></blockquote><div><br></div></div><div>It's already proven that it's not not-a-template.</div>
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<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">
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<div><div>a.cc:1:29: note: 'Foo' declared here<br></div><div>template <typename T> class Foo {}; class Bar : public Foox {};</div><div>[point at 'Foo']</div>
<div>a.cc:1:56: error: expected template argument list after template-id</div><div>template <typename T> class Foo {}; class Bar : public Foox {};</div><div>[point at 'Foox']</div></div></blockquote></div></div>
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And given that we then hit this error, why do we even consider the Foo typo correction? Do we prefer that over a "Fooxie" class due to shorter edit distance? That doesn't seem right. I would intuitively expect the lack of "<..." to be a stronger signal than any edit distance, and thus disqualify template-ids from the typo correction candidate set.</div>
</div></blockquote><div><br></div></div><div>No. We only go down this patch after we've done a lookup and typo correction on non-templates, and found nothing.</div></div></div></blockquote></div><br></div></div>I'm suggesting that a missing header or exceeding the maximum edit distance threshold seems just as plausible as using a template without template arguments. I'm not claiming that I have some strong reason to believe one interpretation or the other to be more likely, only that it doesn't seem clear-cut in either direction to me.</div>
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</blockquote></div><br></div></div></div><div class="gmail_extra">... if it can't find a template, then it doesn't mention templates:</div><div class="gmail_extra"><br></div><div class="gmail_extra"><div class="gmail_extra">
$ echo 'class Bar : public Foo {};' | llvm/Debug+Asserts/bin/clang -x c++ -</div><div class="gmail_extra"><stdin>:1:20: error: expected class name</div><div class="gmail_extra">class Bar : public Foo {};</div>
<div class="gmail_extra"> ^</div><div class="gmail_extra">1 error generated.</div><div class="gmail_extra"><br></div><div><div>$ echo 'template<typename T> class Fooa; class Foob {}; class Bar : public Foo {};' | llvm/Debug+Asserts/bin/clang -x c++ -</div>
<div><stdin>:1:68: error: unknown class name 'Foo'; did you mean 'Foob'?</div><div>template<typename T> class Fooa; class Foob {}; class Bar : public Foo {};</div><div> ^~~</div>
<div> Foob</div><div><stdin>:1:40: note: 'Foob' declared here</div><div>template<typename T> class Fooa; class Foob {}; class Bar : public Foo {};</div>
<div> ^</div><div>1 error generated.</div></div><div><br></div><div>Today, clang emits the exact same diagnostic "expected class name" even when you do have Foo declared as a template. That's the only thing I'm trying to fix, but it has this weird side-effect in that even asking Sema isTemplateName() causes does typo-correction, and when that typo-correction succeeds it issues this "no template" diagnostic.</div>
</div></blockquote></div><br></div></div>I really do understand that, and I don't think your patch is wrong. I just think the problem in typo correction it exposes is severe enough to warrant fixing.</div></div></blockquote>
<div><br></div><div>Ah, okay! Then I'm glad I included it in the email. I was worried that you saw my example of what I thought was a bad diagnostic, and interpreted it as the goal of my patch.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><div class="gmail_extra">Specifically, I don't think we should be typo-correcting to a template-id when we have syntactic indicators that a template-id isn't valid. For example, given "foo->baz", we should only correct to a method name "bar" if we can also correct to "bar()" because it has a zero-argument overload (modulo weird cases where the expression "foo->bar" is valid). There are likely other places (maybe even with methods!) where we get this wrong, but I think all of them are pretty dubious. Here, I think the lack of "<" is a *really* strong signal as there is just no way to use a template-id in that context. If all template parameters had default arguments, perhaps 'Foo<>' would be a good correction, but that's a more clever step.<br>
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</blockquote></div><br></div><div class="gmail_extra">Good catch. Foo could be a template function (or a template variable in C++14 I suppose) instead of a template class. That I know how to fix.</div><div class="gmail_extra">
<br></div><div class="gmail_extra">Unfortunately, the template typo correction is wired into LookupTemplateName. Even if I bypass isTemplateName and create a LookupResult with diagnostics suppressed, we still get the typo corrections. I do not know the design of clang well enough to know how to change that.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">Nick</div></div>