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

[Julian Schmidt via cfe-commits]

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@@ -0,0 +1,96 @@
+//===--- UseSpanFirstLastCheck.cpp - clang-tidy -----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseSpanFirstLastCheck.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;
+
+namespace clang::tidy::readability {
+
+void UseSpanFirstLastCheck::registerMatchers(MatchFinder *Finder) {
+  const auto HasSpanType =
+      hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
+          classTemplateSpecializationDecl(hasName("::std::span"))))));
+
+  // Match span.subspan(0, n) -> first(n)
+  Finder->addMatcher(
+      cxxMemberCallExpr(
+          callee(memberExpr(hasDeclaration(cxxMethodDecl(hasName("subspan"))))),
+          on(expr(HasSpanType).bind("span_object")),
+          hasArgument(0, integerLiteral(equals(0))),
+          hasArgument(1, expr().bind("count")), argumentCountIs(2))
+          .bind("first_subspan"),
+      this);
+
+  // Match span.subspan(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")))));
----------------
5chmidti wrote:

This has generally been done with `utils::areStatementsIdentical` or its matcher equivalent, which is not 

See https://github.com/llvm/llvm-project/blob/3c464d23682b0f9e6f70965e8f8f3861c9ba5417/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp#L73-L75

https://github.com/llvm/llvm-project/blob/3c464d23682b0f9e6f70965e8f8f3861c9ba5417/clang-tools-extra/clang-tidy/modernize/MinMaxUseInitializerListCheck.cpp#L151-L152

https://github.com/llvm/llvm-project/blob/3c464d23682b0f9e6f70965e8f8f3861c9ba5417/clang-tools-extra/clang-tidy/utils/Matchers.h#L164-L168

https://github.com/llvm/llvm-project/blob/3c464d23682b0f9e6f70965e8f8f3861c9ba5417/clang-tools-extra/clang-tidy/utils/ASTUtils.h#L40-L41

You can add `isStatementIdenticalToBoundNode` to your `SizeCall` matcher, checking the argument or object to be equivalent to `span_object`, e.g., `on(expr(isStatementIdenticalToBoundNode("span_object")))`

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