[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 +1,125 @@
+//===--- 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) {
+  // Match span::subspan calls
+  const auto HasSpanType =
+      hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
+          classTemplateSpecializationDecl(hasName("::std::span"))))));
+
+  Finder->addMatcher(cxxMemberCallExpr(callee(memberExpr(hasDeclaration(
+                                           cxxMethodDecl(hasName("subspan"))))),
+                                       on(expr(HasSpanType)))
+                         .bind("subspan"),
+                     this);
+}
+
+void UseSpanFirstLastCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Call = Result.Nodes.getNodeAs<CXXMemberCallExpr>("subspan");
+  if (!Call)
+    return;
+
+  handleSubspanCall(Result, Call);
+}
+
+void UseSpanFirstLastCheck::handleSubspanCall(
+    const MatchFinder::MatchResult &Result, const CXXMemberCallExpr *Call) {
+  unsigned NumArgs = Call->getNumArgs();
+  if (NumArgs == 0 || NumArgs > 2)
+    return;
+
+  const Expr *Offset = Call->getArg(0);
+  const Expr *Count = NumArgs > 1 ? Call->getArg(1) : nullptr;
+  auto &Context = *Result.Context;
+
+  class SubspanVisitor : public RecursiveASTVisitor<SubspanVisitor> {
+  public:
+    SubspanVisitor(const ASTContext &Context) : Context(Context) {}
+
+    TraversalKind getTraversalKind() const {
+      return TK_IgnoreUnlessSpelledInSource;
+    }
+
+    bool VisitIntegerLiteral(IntegerLiteral *IL) {
+      if (IL->getValue() == 0)
+        IsZeroOffset = true;
+      return true;
+    }
+
+    bool VisitBinaryOperator(BinaryOperator *BO) {
+      if (BO->getOpcode() == BO_Sub) {
+        if (const auto *SizeCall = dyn_cast<CXXMemberCallExpr>(BO->getLHS())) {
+          if (SizeCall->getMethodDecl()->getName() == "size") {
+            IsSizeMinusN = true;
+            SizeMinusArg = BO->getRHS();
+          }
+        }
+      }
+      return true;
+    }
+
+    bool IsZeroOffset = false;
+    bool IsSizeMinusN = false;
+    const Expr *SizeMinusArg = nullptr;
+
+  private:
+    const ASTContext &Context;
+  };
+
+  SubspanVisitor Visitor(Context);
+  Visitor.TraverseStmt(const_cast<Expr *>(Offset->IgnoreImpCasts()));
+
+  // Build replacement text
+  std::string Replacement;
+  if (Visitor.IsZeroOffset && Count) {
+    // subspan(0, count) -> first(count)
+    const StringRef CountStr = Lexer::getSourceText(
+        CharSourceRange::getTokenRange(Count->getSourceRange()),
+        Context.getSourceManager(), Context.getLangOpts());
+    const auto *Base =
+        cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
----------------
5chmidti wrote:

`Call` is already a `CXXMemberCallExpr`

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