================
@@ -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:
Both of these are not constrained to be the span object. You'll probably want
to swap the `callee` and `on` matchers, and add an
`equalsBoundNode("span_object")` check for the `on` and `hasArgument(0,...` in
the matchers of `SizeCall`.
Right now, this would match `span.subspan(other.size() - n)` and turn it into
`span.last(n)`.
https://github.com/llvm/llvm-project/pull/118074
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