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

[Congcong Cai via cfe-commits]

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@@ -0,0 +1,94 @@
+//===--- 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) -> last(n)
+  const auto SizeCall = cxxMemberCallExpr(
+      callee(memberExpr(hasDeclaration(cxxMethodDecl(hasName("size"))))));
+
+  Finder->addMatcher(
+      cxxMemberCallExpr(
+          callee(memberExpr(hasDeclaration(cxxMethodDecl(hasName("subspan"))))),
+          on(expr(HasSpanType).bind("span_object")),
+          hasArgument(0, binaryOperator(hasOperatorName("-"), hasLHS(SizeCall),
+                                        hasRHS(expr().bind("count")))),
+          argumentCountIs(1))
+          .bind("last_subspan"),
+      this);
+}
+
+void UseSpanFirstLastCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *SpanObj = Result.Nodes.getNodeAs<Expr>("span_object");
+  if (!SpanObj)
+    return;
+
+  StringRef SpanText = Lexer::getSourceText(
+      CharSourceRange::getTokenRange(SpanObj->getSourceRange()),
+      *Result.SourceManager, Result.Context->getLangOpts());
+
+  if (const auto *FirstCall =
+          Result.Nodes.getNodeAs<CXXMemberCallExpr>("first_subspan")) {
+    const auto *Count = Result.Nodes.getNodeAs<Expr>("count");
+    if (!Count)
+      return;
+
+    StringRef CountText = Lexer::getSourceText(
+        CharSourceRange::getTokenRange(Count->getSourceRange()),
+        *Result.SourceManager, Result.Context->getLangOpts());
+
+    std::string Replacement =
+        SpanText.str() + ".first(" + CountText.str() + ")";
+
+    diag(FirstCall->getBeginLoc(), "prefer 'span::first()' over 'subspan()'")
+        << FixItHint::CreateReplacement(FirstCall->getSourceRange(),
+                                        Replacement);
+  }
+
+  if (const auto *LastCall =
+          Result.Nodes.getNodeAs<CXXMemberCallExpr>("last_subspan")) {
+    const auto *Count = Result.Nodes.getNodeAs<Expr>("count");
+    if (!Count)
+      return;
----------------
HerrCai0907 wrote:

can be assert

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