Fixed build with C++20 standard

[vedranmiletic]

Building LLVM with CMAKE_CXX_STANDARD set to 20 fails since the iterator facade is not fully compatible with C++20. To make it compatible, specific operator overloads have to be constrained.

Overload for operator- in ADT iterator is now constrained with concept BaseT::IsRandomAccess.

Patch by Jonathan Wakely.

Fixes #139072.

[llvmbot]

@llvm/pr-subscribers-llvm-adt

Author: Vedran Miletić (vedranmiletic)

Changes

Overload for operator- in ADT iterator is now constrained with concept BaseT::IsRandomAccess.

Patch by Jonathan Wakely.

Fixes #139072.

---

Full diff: https://github.com/llvm/llvm-project/pull/169772.diff

1 Files Affected:

• (modified) llvm/include/llvm/ADT/iterator.h (+5-1)

diff --git a/llvm/include/llvm/ADT/iterator.h b/llvm/include/llvm/ADT/iterator.h
index 6f0c42fe08bec..f55f9d4a3e7f2 100644
--- a/llvm/include/llvm/ADT/iterator.h
+++ b/llvm/include/llvm/ADT/iterator.h
@@ -267,7 +267,11 @@ class iterator_adaptor_base
     return *static_cast<DerivedT *>(this);
   }
   using BaseT::operator-;
-  difference_type operator-(const DerivedT &RHS) const {
+  difference_type operator-(const DerivedT &RHS) const
+#ifdef __cpp_concepts
+    requires(bool(BaseT::IsRandomAccess))
+#endif
+  {
     static_assert(
         BaseT::IsRandomAccess,
         "The '-' operator is only defined for random access iterators.");

[jwakely]

As noted at #139072 (comment) there are other operators which should really be constrained similarly. So this fixes the immediate issue, but there are still latent bugs that might cause similar errors later.

[jwakely]

but there are still latent bugs that might cause similar errors later.

But they could be fixed later, if needed.

[cor3ntin]

Please update the description of the PR with a description of the problem you are trying to fix, I had to find this comment to understand the context. Thanks
#139072 (comment)

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[vedranmiletic]

Please update the description of the PR with a description of the problem you are trying to fix, I had to find this comment to understand the context. Thanks #139072 (comment)

Hope it is better now.