[PATCH] D78100: [AST] Suppress the spammy "attempt to use a deleted fucntion" diagnostic.

[Sam McCall via Phabricator via cfe-commits]

sammccall added a comment.

In D78100#1981729 <https://reviews.llvm.org/D78100#1981729>, @rsmith wrote:

> In D78100#1981620 <https://reviews.llvm.org/D78100#1981620>, @sammccall wrote:
>
> > Sorry to go back and forth on this, but I'm not sure whether these diagnostics are actually spam to be suppressed. I think @adamcz mentioned these today as reasonable diagnostics we're enabling.
> >
> > @rsmith do you have an opinion here?
>
>
> My initial reaction was certainly that it wasn't obvious why an initialization error would necessarily have anything to do with a destruction error. But this line of thinking helped me: suppose we would encounter both an (unrecoverable) initialization error *and* an error during destruction. How likely is it that they have a common cause? My guess would be way more than half the time. Given that we know we're on an error recovery path, and that we've already produced an unrecoverable error during initialization, skipping the destruction checks is probably the better choice. Even if we're wrong, the worst case is that the programmer fixes the initialization error and is then presented with a destruction error that they didn't see before, which doesn't seem all that bad of an outcome.
>
> (Generally I don't think we need to be sure that errors would be correlated to suppress latter errors as being follow-on diagnostics from earlier errors, and should lean towards suppressing diagnostics in order to make the second and subsequent diagnostic as likely as possible to be meaningful and useful.)


Thanks, that's useful. The common cause was our original intuition but I wasn't sure if that was an appropriate reason to suppress.



================
Comment at: clang/lib/Sema/SemaDecl.cpp:11998-12001
     if (Result.isInvalid()) {
       VDecl->setInvalidDecl();
       return;
     }
----------------
rsmith wrote:
> Should we attach a `RecoveryExpr` initializer in this case?
This is D78116 (which should probably handle the case above, too)


================
Comment at: clang/lib/Sema/SemaDecl.cpp:12268
 /// of sanity.
 void Sema::ActOnInitializerError(Decl *D) {
   // Our main concern here is re-establishing invariants like "a
----------------
rsmith wrote:
> Should we attach a `RecoveryExpr` initializer in this case too?
Now we're really slipping into a different set of use-cases for RecoveryExpr... 
I assume we're talking about a RecoveryExpr that has no children, at least in the short term, as parsing failures don't return the likely subexpressions found. So it's a pure error marker in the form of an AST node. Quite a lot of ExprError()s could become these...

Actually there's another virtue here: even without subexpressions, the RecoveryExpr can capture the token range. So VarDecl::getSourceRange() will include the malformed initializer, so tools can at least attribute these tokens to the right part of the AST.


================
Comment at: clang/test/CXX/class.access/p4.cpp:1
-// RUN: %clang_cc1 -triple %itanium_abi_triple -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++98 %s
-// RUN: %clang_cc1 -triple %itanium_abi_triple -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++11 %s
-// RUN: %clang_cc1 -triple %itanium_abi_triple -fcxx-exceptions -fexceptions -fsyntax-only -verify %s
-// RUN: %clang_cc1 -triple x86_64-windows-msvc -fms-compatibility-version=19 -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++98 %s
-// RUN: %clang_cc1 -triple x86_64-windows-msvc -fms-compatibility-version=19 -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++11 %s
-// RUN: %clang_cc1 -triple x86_64-windows-msvc -fms-compatibility-version=19 -fcxx-exceptions -fexceptions -fsyntax-only -verify %s
+// RUN: %clang_cc1 -frecovery-ast -triple %itanium_abi_triple -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++98 %s
+// RUN: %clang_cc1 -frecovery-ast -triple %itanium_abi_triple -fcxx-exceptions -fexceptions -fsyntax-only -verify -std=c++11 %s
----------------
rsmith wrote:
> I'm not really happy about improving our quality of diagnostics only under `-frecovery-ast`. Do we really need that flag? The way I see it, we can divide the users of Clang up into:
> 
>  * We want valid code (eg, as a compiler): if we hit an error, it doesn't matter too much whether we build `RecoveryExpr`s or not, since we're on a path to bailing out anyway. If `RecoveryExpr`s allow us to improve our diagnostics, we should build them. (Exception: if we want valid code or to get a simple pass/fail as early as possible, maybe not.)
>  * We want to accept invalid code (eg, tooling): if we hit an error, we probably want to retain as much information as we reasonably can about the non-erroneous parts of the program.
> 
> So I think at least the default should be to build `RecoveryExpr`s, and maybe we can remove the flag entirely?
Agree that want to flip the default to true, and maybe eventually get rid of it. But:
 - we're still fighting quite a lot of new crash-on-invalids, and can't fix them all in one big patch. We plan to find more by rolling this out to a subset of google-internal IDE users (where we have good monitoring), the flag is needed for this.
 - we expect this to be stable for C++ long before it can be enabled for C, because that requires making the C codepaths safe handle (at least error-)dependence. So there'll be a similar testing/improvement period later.

However I don't like adding -frecovery-ast to big existing tests, we lose coverage of today's production behavior. I think we may need to create new tests to show the effect of these changes, and clean them up after flipping the default.


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https://reviews.llvm.org/D78100