================
@@ -0,0 +1,152 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "StringViewConversionsCheck.h"
+#include "clang/AST/Expr.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::performance {
+
+static auto getStringTypeMatcher(StringRef CharType) {
+ return hasCanonicalType(hasDeclaration(cxxRecordDecl(hasName(CharType))));
+}
+
+void StringViewConversionsCheck::registerMatchers(MatchFinder *Finder) {
+ // Matchers for std::basic_[w|u8|u16|u32]string and
+ // std::basic_[w|u8|u16|u32]string_view families.
+ const auto IsStdString = getStringTypeMatcher("::std::basic_string");
+ const auto IsStdStringView =
getStringTypeMatcher("::std::basic_string_view");
+
+ // Matches pointer to any character type (char*, const char*, wchar_t*, etc.)
+ // or array of any character type (char[], char[N], const char[N], etc.).
+ const auto IsCharPointerOrArray =
+ anyOf(hasType(pointerType(pointee(isAnyCharacter()))),
+ hasType(arrayType(hasElementType(isAnyCharacter()))));
+
+ // Matches expressions that can be implicitly converted to string_view
+ // without going through std::string:
+ // - string_view itself (no conversion needed)
+ // - string literals ("hello", L"wide", u8"utf8", etc.)
+ // - character pointers (const char*, char*)
+ // - character arrays (char arr[], char arr[N])
+ // These are the expressions we want to preserve after removing
+ // the redundant std::string conversion.
+ const auto ImplicitlyConvertibleToStringView =
+ expr(anyOf(hasType(IsStdStringView), stringLiteral(),
+ IsCharPointerOrArray))
+ .bind("originalStringView");
+
+ // Matches direct std::string construction from a string_view-convertible
+ // expression. This handles cases like:
+ // - Implicit construction in certain contexts
+ // - Brace initialization: std::string{sv}
+ // Excludes copy/move constructors to avoid false positives when
+ // an existing std::string is being copied or moved.
+ const auto RedundantStringConstruction = cxxConstructExpr(
+ hasType(IsStdString),
+ hasArgument(0, ignoringImplicit(ImplicitlyConvertibleToStringView)),
+ unless(hasDeclaration(cxxConstructorDecl(isCopyConstructor()))),
+ unless(hasDeclaration(cxxConstructorDecl(isMoveConstructor()))));
----------------
localspook wrote:
If a `std::string` is being copy or move constructed, that means its first
argument has type `std::string`, which wouldn't be matched by
`ImplicitlyConvertibleToStringView` anyway, so is explicitly excluding copy and
move constructors needed?
```suggestion
const auto RedundantStringConstruction = cxxConstructExpr(
hasType(IsStdString),
hasArgument(0, ignoringImplicit(ImplicitlyConvertibleToStringView)));
```
https://github.com/llvm/llvm-project/pull/174288
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