https://github.com/nicovank created
https://github.com/llvm/llvm-project/pull/117837
In C++20, `operator!=` can be rewritten by negating `operator==`. This is the
case for `std::string`, where `operator!=` is not provided hence relying on
this rewriting.
Cover this case by matching `binaryOperation` and adding one case to
`isNegativeComparison`.
This is only relevant in the newly added `substr` case, previous cases used a
simple BinaryOperator. Release notes already mention adding this new case so I
don't think further comments there are necessary.
Testing on non-mock:
```
> cat tmp.cpp
#include <string>
void f(std::string u, std::string v) { u.substr(0, v.size()) != v; }
# Before change, no warning.
> ./build/bin/clang-tidy -checks="-*,modernize-use-starts-ends-with" tmp.cpp --
> -std=c++20
# After change.
> ./build/bin/clang-tidy -checks="-*,modernize-use-starts-ends-with" tmp.cpp --
> -std=c++20
tmp.cpp:2:42: warning: use starts_with instead of substr
[modernize-use-starts-ends-with]
2 | void f(std::string u, std::string v) { u.substr(0, v.size()) != v; }
| ^~~~~~ ~~~~~~~~~~~~~~~~~
| ! starts_with v)
```
>From 65400949047a15424bcbb8bb2a1e1f515e886cf8 Mon Sep 17 00:00:00 2001
From: Nicolas van Kempen <nvank...@gmail.com>
Date: Tue, 26 Nov 2024 22:26:20 -0500
Subject: [PATCH] [clang-tidy][modernize-use-starts-ends-with] Fix operator
rewriting false negative
In C++20, `operator!=` can be rewritten by negating `operator==`. This is the
case for `std::string`, where `operator!=` is not provided hence relying on
this rewriting.
Cover this case by matching `binaryOperation` and adding one case to
`isNegativeComparison`.
This is only relevant in the newly added `substr` case, previous cases used a
simple BinaryOperator. Release notes already mention adding this new case so I
don't think further comments there are necessary.
Testing on non-mock:
```
> cat tmp.cpp
#include <string>
void f(std::string u, std::string v) { u.substr(0, v.size()) != v; }
# Before change, no warning.
> ./build/bin/clang-tidy -checks="-*,modernize-use-starts-ends-with" tmp.cpp --
> -std=c++20
# After change.
> ./build/bin/clang-tidy -checks="-*,modernize-use-starts-ends-with" tmp.cpp --
> -std=c++20
tmp.cpp:2:42: warning: use starts_with instead of substr
[modernize-use-starts-ends-with]
2 | void f(std::string u, std::string v) { u.substr(0, v.size()) != v; }
| ^~~~~~ ~~~~~~~~~~~~~~~~~
| ! starts_with v)
```
---
.../clang-tidy/modernize/UseStartsEndsWithCheck.cpp | 10 +++++++---
.../test/clang-tidy/checkers/Inputs/Headers/string | 10 ++++++----
.../checkers/modernize/use-starts-ends-with.cpp | 10 ++++++++++
3 files changed, 23 insertions(+), 7 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
index 234f6790a7ed9b..ab72c6796bb4cd 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
@@ -20,12 +20,16 @@ using namespace clang::ast_matchers;
namespace clang::tidy::modernize {
static bool isNegativeComparison(const Expr *ComparisonExpr) {
- if (const auto *BO = llvm::dyn_cast<BinaryOperator>(ComparisonExpr))
- return BO->getOpcode() == BO_NE;
+ if (const auto *Op = llvm::dyn_cast<BinaryOperator>(ComparisonExpr))
+ return Op->getOpcode() == BO_NE;
if (const auto *Op = llvm::dyn_cast<CXXOperatorCallExpr>(ComparisonExpr))
return Op->getOperator() == OO_ExclaimEqual;
+ if (const auto *Op =
+ llvm::dyn_cast<CXXRewrittenBinaryOperator>(ComparisonExpr))
+ return Op->getOperator() == BO_NE;
+
return false;
}
@@ -185,7 +189,7 @@ void UseStartsEndsWithCheck::registerMatchers(MatchFinder
*Finder) {
// Case 6: X.substr(0, LEN(Y)) [!=]= Y -> starts_with.
Finder->addMatcher(
- cxxOperatorCallExpr(
+ binaryOperation(
hasAnyOperatorName("==", "!="),
hasOperands(
expr().bind("needle"),
diff --git a/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
b/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
index 51f68174169067..7e579e5319752a 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
+++ b/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
@@ -136,10 +136,6 @@ bool operator==(const std::string&, const std::string&);
bool operator==(const std::string&, const char*);
bool operator==(const char*, const std::string&);
-bool operator!=(const std::string&, const std::string&);
-bool operator!=(const std::string&, const char*);
-bool operator!=(const char*, const std::string&);
-
bool operator==(const std::wstring&, const std::wstring&);
bool operator==(const std::wstring&, const wchar_t*);
bool operator==(const wchar_t*, const std::wstring&);
@@ -148,9 +144,15 @@ bool operator==(const std::string_view&, const
std::string_view&);
bool operator==(const std::string_view&, const char*);
bool operator==(const char*, const std::string_view&);
+#if __cplusplus < 202002L
+bool operator!=(const std::string&, const std::string&);
+bool operator!=(const std::string&, const char*);
+bool operator!=(const char*, const std::string&);
+
bool operator!=(const std::string_view&, const std::string_view&);
bool operator!=(const std::string_view&, const char*);
bool operator!=(const char*, const std::string_view&);
+#endif
size_t strlen(const char* str);
}
diff --git
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp
index 18a65f7f1cf260..8699ca03ba3313 100644
---
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp
+++
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp
@@ -320,3 +320,13 @@ void test_substr() {
str.substr(0, strlen("hello123")) == "hello";
}
+
+void test_operator_rewriting(std::string str, std::string prefix) {
+ str.substr(0, prefix.size()) == prefix;
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead
of substr
+ // CHECK-FIXES: str.starts_with(prefix);
+
+ str.substr(0, prefix.size()) != prefix;
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead
of substr
+ // CHECK-FIXES: !str.starts_with(prefix);
+}
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