[clang] [clang] Disable missing definition warning on pure virtual functions (PR #74510)

[Charalampos Mitrodimas via cfe-commits]

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@@ -4952,7 +4952,8 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
         std::make_pair(Function, PointOfInstantiation));
     } else if (TSK == TSK_ImplicitInstantiation) {
       if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
-          !getSourceManager().isInSystemHeader(PatternDecl->getBeginLoc())) {
+          !getSourceManager().isInSystemHeader(PatternDecl->getBeginLoc()) &&
+          !Function->isVirtualAsWritten() && !Function->isPure()) {
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charmitro wrote:

After double-checking this, I think we should just check for `isPure()` and don't bother checking for `isVirtualAsWritten()` at all since non-virtual functions cannot be pure. Also, for reference,

https://github.com/llvm/llvm-project/blob/d6fbd96e5eaf3e8acbf1b43dce7a311352907567/clang/include/clang/AST/Decl.h#L2293-L2295

Code updated to match this. Also a test-case added to verify that non-pure virtual functions still get diagnosed.

https://github.com/llvm/llvm-project/pull/74510