[ADT] Allow std::next to work on BitVector's set_bits_iterator

[jayfoad]

Without this I would hit errors with libstdc++-12 like:

/usr/include/c++/12/bits/stl_iterator_base_funcs.h:230:5: note: candidate template ignored: substitution failure [with _InputIterator = llvm::const_set_bits_iterator_implllvm::BitVector]: argument may not have 'void' type
next(_InputIterator __x, typename
^

[llvmbot]

@llvm/pr-subscribers-llvm-adt

Author: Jay Foad (jayfoad)

Changes

Without this I would hit errors with libstdc++-12 like:

/usr/include/c++/12/bits/stl_iterator_base_funcs.h:230:5: note: candidate template ignored: substitution failure [with _InputIterator = llvm::const_set_bits_iterator_impl<llvm::BitVector>]: argument may not have 'void' type
next(_InputIterator __x, typename
^

---

Full diff: https://github.com/llvm/llvm-project/pull/80830.diff

2 Files Affected:

• (modified) llvm/include/llvm/ADT/BitVector.h (+1-1)
• (modified) llvm/unittests/ADT/BitVectorTest.cpp (+3)

diff --git a/llvm/include/llvm/ADT/BitVector.h b/llvm/include/llvm/ADT/BitVector.h
index e0de1afcc94182..0eaa77b6dd81ce 100644
--- a/llvm/include/llvm/ADT/BitVector.h
+++ b/llvm/include/llvm/ADT/BitVector.h
@@ -42,7 +42,7 @@ template <typename BitVectorT> class const_set_bits_iterator_impl {
 
 public:
   using iterator_category = std::forward_iterator_tag;
-  using difference_type   = void;
+  using difference_type   = std::ptrdiff_t;
   using value_type        = int;
   using pointer           = value_type*;
   using reference         = value_type&;
diff --git a/llvm/unittests/ADT/BitVectorTest.cpp b/llvm/unittests/ADT/BitVectorTest.cpp
index e00e11e4655aa0..79d5dee5ad30fd 100644
--- a/llvm/unittests/ADT/BitVectorTest.cpp
+++ b/llvm/unittests/ADT/BitVectorTest.cpp
@@ -1143,6 +1143,9 @@ TYPED_TEST(BitVectorTest, EmptyVectorGetData) {
 }
 
 TYPED_TEST(BitVectorTest, Iterators) {
+  TypeParam Singleton(1);
+  EXPECT_EQ(std::next(Singleton.set_bits_begin()), Singleton.set_bits_end());
+
   TypeParam Filled(10, true);
   EXPECT_NE(Filled.set_bits_begin(), Filled.set_bits_end());
   unsigned Counter = 0;

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 42b5b720caf62e0710b9c1e32e894d8606106a19 b9860fd2fb692899bc0222a273d1109f948f13a6 -- llvm/include/llvm/ADT/BitVector.h llvm/unittests/ADT/BitVectorTest.cpp

View the diff from clang-format here.

diff --git a/llvm/include/llvm/ADT/BitVector.h b/llvm/include/llvm/ADT/BitVector.h
index 0eaa77b6dd..0d8ebc46d8 100644
--- a/llvm/include/llvm/ADT/BitVector.h
+++ b/llvm/include/llvm/ADT/BitVector.h
@@ -42,7 +42,7 @@ template <typename BitVectorT> class const_set_bits_iterator_impl {
 
 public:
   using iterator_category = std::forward_iterator_tag;
-  using difference_type   = std::ptrdiff_t;
+  using difference_type = std::ptrdiff_t;
   using value_type        = int;
   using pointer           = value_type*;
   using reference         = value_type&;

[dwblaikie]

It's OK (I have mixed feelings about the more integration-y test of using std::next rather than only testing the interface of BitVector.h to check the type traits directly, or whatever other features we should have - rather than whatever features std::next (on some implementation) happens to use - but it'll be OK as-is)