================
@@ -0,0 +1,194 @@
+// RUN: %check_clang_tidy -std=c++20 %s readability-use-span-first-last %t
+
+namespace std {
+
+enum class byte : unsigned char {};
+
+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; }
+ __SIZE_TYPE__ size_bytes() const { return len * sizeof(T); }
+};
+} // namespace std
+
+// Add here, right after the std namespace closes:
+namespace std::ranges {
+ template<typename T>
+ __SIZE_TYPE__ size(const span<T>& s) { return s.size(); }
+}
+
+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
+
+
+#define ZERO 0
+#define TWO 2
+#define SIZE_MINUS(s, n) s.size() - n
+#define MAKE_SUBSPAN(obj, n) obj.subspan(0, n)
+#define MAKE_LAST_N(obj, n) obj.subspan(obj.size() - n)
+
+ auto sub_zero = s.subspan(ZERO, 3);
+ // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: prefer 'span::first()' over
'subspan()'
+ // CHECK-FIXES: auto sub_zero = s.first(3);
+
+ auto sub_two = s.subspan(s.size() - TWO);
+ // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto sub_two = s.last(TWO);
+
+ auto sub6 = s.subspan(SIZE_MINUS(s, 2));
+ // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto sub6 = s.last(2);
+
+ auto sub7 = MAKE_SUBSPAN(s, 3);
+ // CHECK-MESSAGES: :[[@LINE-1]]:28: warning: prefer 'span::first()' over
'subspan()'
+ // CHECK-FIXES: auto sub7 = s.first(3);
+
+ auto sub8 = MAKE_LAST_N(s, 2);
+ // CHECK-MESSAGES: :[[@LINE-1]]:27: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto sub8 = s.last(2);
+
+}
+
+template <typename T>
+void testTemplate() {
+ T arr[] = {1, 2, 3, 4, 5};
+ std::span<T> 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
+
+ auto complex = s.subspan(0 + (s.size() - 2), 3); // No warning
+
+ auto complex2 = s.subspan(100 + (s.size() - 2)); // No warning
+}
+
+// Test instantiation
+void testInt() {
+ testTemplate<int>();
+}
+
+void test_ranges() {
+ int arr[] = {1, 2, 3, 4, 5};
+ std::span<int> s(arr, 5);
+
+ auto sub1 = s.subspan(std::ranges::size(s) - 2);
+ // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto sub1 = s.last(2);
+
+ __SIZE_TYPE__ n = 2;
+ auto sub2 = s.subspan(std::ranges::size(s) - n);
+ // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto sub2 = s.last(n);
+}
+
+void test_different_spans() {
+ int arr1[] = {1, 2, 3, 4, 5};
+ int arr2[] = {6, 7, 8, 9, 10};
+ std::span<int> s1(arr1, 5);
+ std::span<int> s2(arr2, 5);
+
+ // These should NOT trigger warnings as they use size() from a different span
+ auto sub1 = s1.subspan(s2.size() - 2); // No warning
+ auto sub2 = s2.subspan(s1.size() - 3); // No warning
+
+ // Also check with std::ranges::size
+ auto sub3 = s1.subspan(std::ranges::size(s2) - 2); // No warning
+ auto sub4 = s2.subspan(std::ranges::size(s1) - 3); // No warning
+
+ // Mixed usage should also not trigger
+ auto sub5 = s1.subspan(s2.size() - s1.size()); // No warning
+
+ // Verify that correct usage still triggers warnings
+ auto good1 = s1.subspan(s1.size() - 2);
+ // CHECK-MESSAGES: :[[@LINE-1]]:16: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto good1 = s1.last(2);
+
+ auto good2 = s2.subspan(std::ranges::size(s2) - 3);
+ // CHECK-MESSAGES: :[[@LINE-1]]:16: warning: prefer 'span::last()' over
'subspan()'
+ // CHECK-FIXES: auto good2 = s2.last(3);
+}
+
+void test_span_of_bytes() {
+ std::byte arr[] = {std::byte{0x1}, std::byte{0x2}, std::byte{0x3},
+ std::byte{0x4}, std::byte{0x5}};
+ std::span<std::byte> 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_bytes() is not the same as size() in general, so should not trigger
+ auto sub3 = s.subspan(s.size_bytes() - 2); // No warning
+}
+
+// Test uninstantiated template -- should still warn on dependent code
+template <typename T>
+void uninstantiated_template(std::span<T> s) {
+ 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);
+
+ auto sub3 = s.subspan(1, 2); // No warning
+ auto sub4 = s.subspan(2); // No warning
+}
+
----------------
EugeneZelenko wrote:
```suggestion
```
https://github.com/llvm/llvm-project/pull/118074
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