[clang-tools-extra] [clang-tidy] Add readability-use-span-first-last check (PR #118074)

[via cfe-commits]

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@@ -0,0 +1,51 @@
+// RUN: %check_clang_tidy -std=c++20 %s readability-use-span-first-last %t
+
+namespace std {
+template <typename T>
+class span {
+  T* ptr;
+  __SIZE_TYPE__ len;
+
+public:
+  span(T* p, __SIZE_TYPE__ l) : ptr(p), len(l) {}
+  
+  span<T> subspan(__SIZE_TYPE__ offset) const {
+    return span(ptr + offset, len - offset);
+  }
+  
+  span<T> subspan(__SIZE_TYPE__ offset, __SIZE_TYPE__ count) const {
+    return span(ptr + offset, count);
+  }
+
+  span<T> first(__SIZE_TYPE__ count) const {
+    return span(ptr, count);
+  }
+
+  span<T> last(__SIZE_TYPE__ count) const {
+    return span(ptr + (len - count), count);
+  }
+
+  __SIZE_TYPE__ size() const { return len; }
+};
+} // namespace std
+
+void test() {
+  int arr[] = {1, 2, 3, 4, 5};
+  std::span<int> s(arr, 5);
+
+  auto sub1 = s.subspan(0, 3);
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer span::first() over subspan()
+  // CHECK-FIXES: auto sub1 = s.first(3);
+
+  auto sub2 = s.subspan(s.size() - 2);
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer span::last() over subspan()
+  // CHECK-FIXES: auto sub2 = s.last(2);
+
+  __SIZE_TYPE__ n = 2;
+  auto sub3 = s.subspan(0, n);
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer span::first() over subspan()
+  // CHECK-FIXES: auto sub3 = s.first(n);
+
+  auto sub4 = s.subspan(1, 2);  // No warning
+  auto sub5 = s.subspan(2);     // No warning
+}
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EugeneZelenko wrote:

Missing newline.

https://github.com/llvm/llvm-project/pull/118074