[clang-tidy] Add readability-use-span-first-last check

clang-tools-extra/clang-tidy/readability/UseSpanFirstLastCheck.cpp

@@ -7,13 +7,16 @@
 //===----------------------------------------------------------------------===//
 
 #include "UseSpanFirstLastCheck.h"
+#include "../utils/ASTUtils.h"
+#include "../utils/Matchers.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
+using namespace clang::tidy::matchers;
 
 namespace clang::tidy::readability {
 
@@ -32,13 +35,17 @@ void UseSpanFirstLastCheck::registerMatchers(MatchFinder *Finder) {
           .bind("first_subspan"),
       this);
 
-  // Match span.subspan(size() - n) or span.subspan(std::ranges::size(span) - n)
+  // Match span.subspan(span.size() - n) or span.subspan(std::ranges::size(span)
+  // - n)
   // -> last(n)
   const auto SizeCall = anyOf(
       cxxMemberCallExpr(
-          callee(memberExpr(hasDeclaration(cxxMethodDecl(hasName("size")))))),
-      callExpr(callee(
-          functionDecl(hasAnyName("::std::size", "::std::ranges::size")))));
+          callee(memberExpr(hasDeclaration(cxxMethodDecl(hasName("size"))))),
+          on(expr(isStatementIdenticalToBoundNode("span_object")))),
+      callExpr(callee(functionDecl(
+                   hasAnyName("::std::size", "::std::ranges::size"))),
+               hasArgument(
+                   0, expr(isStatementIdenticalToBoundNode("span_object")))));
 
   Finder->addMatcher(
       cxxMemberCallExpr(
@@ -75,6 +82,7 @@ void UseSpanFirstLastCheck::check(const MatchFinder::MatchResult &Result) {
     diag(FirstCall->getBeginLoc(), "prefer 'span::first()' over 'subspan()'")
         << FixItHint::CreateReplacement(FirstCall->getSourceRange(),
                                         Replacement);
+    return;
   }
 
   if (const auto *LastCall =

clang-tools-extra/test/clang-tidy/checkers/readability/use-span-first-last.cpp

@@ -120,3 +120,30 @@ void test_ranges() {
   // 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);
+}