[clang-tools-extra] [clang-tidy] Enhance modernize-use-starts-ends-with to handle substr patterns (PR #116033)
Helmut Januschka via cfe-commits
cfe-commits at lists.llvm.org
Thu Nov 14 12:50:14 PST 2024
https://github.com/hjanuschka updated https://github.com/llvm/llvm-project/pull/116033
>From caddb82d73d49b59dff71547d8ab986039895696 Mon Sep 17 00:00:00 2001
From: Helmut Januschka <helmut at januschka.com>
Date: Wed, 13 Nov 2024 12:52:36 +0100
Subject: [PATCH] [clang-tidy] Enhance modernize-use-starts-ends-with with
substr detection
Enhances the modernize-use-starts-ends-with check to detect substr-based
patterns that can be replaced with starts_with() (C++20). This improves code
readability and efficiency by avoiding temporary string creation.
New patterns detected:
str.substr(0, n) == "foo" -> str.starts_with("foo")
"foo" == str.substr(0, n) -> str.starts_with("foo")
str.substr(0, n) != "foo" -> !str.starts_with("foo")
str.substr(0, strlen("foo")) == "foo" -> str.starts_with("foo")
str.substr(0, prefix.size()) == "foo" -> str.starts_with("foo")
The enhancement:
- Integrates with existing starts_with patterns
- Handles substr with zero first argument
- Supports length via literals, strlen(), and size()/length()
- Validates string literal length matches
- Handles both == and != operators
Part of modernize-use-starts-ends-with check.
---
.../modernize/UseStartsEndsWithCheck.cpp | 185 ++++++++++++++++--
.../modernize/UseStartsEndsWithCheck.h | 4 +
clang-tools-extra/docs/ReleaseNotes.rst | 7 +
.../checks/modernize/use-starts-ends-with.rst | 45 +++--
.../clang-tidy/checkers/Inputs/Headers/string | 5 +-
.../modernize/use-starts-ends-with.cpp | 42 +++-
6 files changed, 257 insertions(+), 31 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
index 1231f954298adc..e7da45198df6c1 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
@@ -22,28 +22,46 @@ struct NotLengthExprForStringNode {
NotLengthExprForStringNode(std::string ID, DynTypedNode Node,
ASTContext *Context)
: ID(std::move(ID)), Node(std::move(Node)), Context(Context) {}
+
bool operator()(const internal::BoundNodesMap &Nodes) const {
- // Match a string literal and an integer size or strlen() call.
if (const auto *StringLiteralNode = Nodes.getNodeAs<StringLiteral>(ID)) {
+ // Match direct integer literals
if (const auto *IntegerLiteralSizeNode = Node.get<IntegerLiteral>()) {
return StringLiteralNode->getLength() !=
IntegerLiteralSizeNode->getValue().getZExtValue();
}
- if (const auto *StrlenNode = Node.get<CallExpr>()) {
- if (StrlenNode->getDirectCallee()->getName() != "strlen" ||
- StrlenNode->getNumArgs() != 1) {
- return true;
+ // Match strlen() calls
+ if (const auto *CallNode = Node.get<CallExpr>()) {
+ if (const auto *FD = CallNode->getDirectCallee()) {
+ if (FD->getName() == "strlen" && CallNode->getNumArgs() == 1) {
+ if (const auto *StrArg = CallNode->getArg(0)->IgnoreParenImpCasts()) {
+ // Handle both string literals and string variables in strlen
+ if (const auto *StrLit = dyn_cast<StringLiteral>(StrArg)) {
+ return StrLit->getLength() != StringLiteralNode->getLength();
+ } else if (const auto *StrVar = dyn_cast<Expr>(StrArg)) {
+ return !utils::areStatementsIdentical(StrVar, StringLiteralNode, *Context);
+ }
+ }
+ }
}
-
- if (const auto *StrlenArgNode = dyn_cast<StringLiteral>(
- StrlenNode->getArg(0)->IgnoreParenImpCasts())) {
- return StrlenArgNode->getLength() != StringLiteralNode->getLength();
+ }
+
+ // Match size()/length() member calls
+ if (const auto *MemberCall = Node.get<CXXMemberCallExpr>()) {
+ if (const auto *Method = MemberCall->getMethodDecl()) {
+ StringRef Name = Method->getName();
+ if (Method->isConst() && Method->getNumParams() == 0 &&
+ (Name == "size" || Name == "length")) {
+ // For string literals used in comparison, allow size/length calls
+ // on any string variable
+ return false;
+ }
}
}
}
- // Match a string variable and a call to length() or size().
+ // Match member function calls on string variables
if (const auto *ExprNode = Nodes.getNodeAs<Expr>(ID)) {
if (const auto *MemberCallNode = Node.get<CXXMemberCallExpr>()) {
const CXXMethodDecl *MethodDeclNode = MemberCallNode->getMethodDecl();
@@ -53,8 +71,8 @@ struct NotLengthExprForStringNode {
return true;
}
- if (const auto *OnNode =
- dyn_cast<Expr>(MemberCallNode->getImplicitObjectArgument())) {
+ if (const auto *OnNode = dyn_cast<Expr>(
+ MemberCallNode->getImplicitObjectArgument())) {
return !utils::areStatementsIdentical(OnNode->IgnoreParenImpCasts(),
ExprNode->IgnoreParenImpCasts(),
*Context);
@@ -83,6 +101,55 @@ UseStartsEndsWithCheck::UseStartsEndsWithCheck(StringRef Name,
void UseStartsEndsWithCheck::registerMatchers(MatchFinder *Finder) {
const auto ZeroLiteral = integerLiteral(equals(0));
+ // Match the substring call
+ const auto SubstrCall = cxxMemberCallExpr(
+ callee(cxxMethodDecl(hasName("substr"))),
+ hasArgument(0, ZeroLiteral),
+ hasArgument(1, expr().bind("length")),
+ on(expr().bind("str")))
+ .bind("substr_fun");
+
+ // Match string literals
+ const auto Literal = stringLiteral().bind("literal");
+
+ // Helper for matching comparison operators
+ auto AddSubstrMatcher = [&](auto Matcher) {
+ Finder->addMatcher(
+ traverse(TK_IgnoreUnlessSpelledInSource, std::move(Matcher)), this);
+ };
+
+ // Match str.substr(0,n) == "literal"
+ AddSubstrMatcher(
+ binaryOperation(
+ hasOperatorName("=="),
+ hasLHS(SubstrCall),
+ hasRHS(Literal))
+ .bind("positiveComparison"));
+
+ // Also match "literal" == str.substr(0,n)
+ AddSubstrMatcher(
+ binaryOperation(
+ hasOperatorName("=="),
+ hasLHS(Literal),
+ hasRHS(SubstrCall))
+ .bind("positiveComparison"));
+
+ // Match str.substr(0,n) != "literal"
+ AddSubstrMatcher(
+ binaryOperation(
+ hasOperatorName("!="),
+ hasLHS(SubstrCall),
+ hasRHS(Literal))
+ .bind("negativeComparison"));
+
+ // Also match "literal" != str.substr(0,n)
+ AddSubstrMatcher(
+ binaryOperation(
+ hasOperatorName("!="),
+ hasLHS(Literal),
+ hasRHS(SubstrCall))
+ .bind("negativeComparison"));
+
const auto ClassTypeWithMethod = [](const StringRef MethodBoundName,
const auto... Methods) {
return cxxRecordDecl(anyOf(
@@ -173,7 +240,101 @@ void UseStartsEndsWithCheck::registerMatchers(MatchFinder *Finder) {
this);
}
+void UseStartsEndsWithCheck::handleSubstrMatch(const MatchFinder::MatchResult &Result) {
+ const auto *SubstrCall = Result.Nodes.getNodeAs<CXXMemberCallExpr>("substr_fun");
+ const auto *PositiveComparison = Result.Nodes.getNodeAs<Expr>("positiveComparison");
+ const auto *NegativeComparison = Result.Nodes.getNodeAs<Expr>("negativeComparison");
+
+ if (!SubstrCall || (!PositiveComparison && !NegativeComparison))
+ return;
+
+ const bool Negated = NegativeComparison != nullptr;
+ const auto *Comparison = Negated ? NegativeComparison : PositiveComparison;
+
+ if (SubstrCall->getBeginLoc().isMacroID())
+ return;
+
+ const auto *Str = Result.Nodes.getNodeAs<Expr>("str");
+ const auto *Literal = Result.Nodes.getNodeAs<StringLiteral>("literal");
+ const auto *Length = Result.Nodes.getNodeAs<Expr>("length");
+
+ if (!Str || !Literal || !Length)
+ return;
+
+ // Special handling for strlen and size/length member calls
+ const bool IsValidLength = [&]() {
+ if (const auto *LengthInt = dyn_cast<IntegerLiteral>(Length)) {
+ return LengthInt->getValue().getZExtValue() == Literal->getLength();
+ }
+
+ if (const auto *Call = dyn_cast<CallExpr>(Length)) {
+ if (const auto *FD = Call->getDirectCallee()) {
+ if (FD->getName() == "strlen" && Call->getNumArgs() == 1) {
+ if (const auto *StrArg = dyn_cast<StringLiteral>(
+ Call->getArg(0)->IgnoreParenImpCasts())) {
+ return StrArg->getLength() == Literal->getLength();
+ }
+ }
+ }
+ }
+
+ if (const auto *MemberCall = dyn_cast<CXXMemberCallExpr>(Length)) {
+ if (const auto *Method = MemberCall->getMethodDecl()) {
+ StringRef Name = Method->getName();
+ if (Method->isConst() && Method->getNumParams() == 0 &&
+ (Name == "size" || Name == "length")) {
+ // For string literals in comparison, we'll trust that size()/length()
+ // calls are valid
+ return true;
+ }
+ }
+ }
+
+ return false;
+ }();
+
+ if (!IsValidLength) {
+ return;
+ }
+
+ // Get the string expression and literal text for the replacement
+ const std::string StrText = Lexer::getSourceText(
+ CharSourceRange::getTokenRange(Str->getSourceRange()),
+ *Result.SourceManager, getLangOpts()).str();
+
+ const std::string LiteralText = Lexer::getSourceText(
+ CharSourceRange::getTokenRange(Literal->getSourceRange()),
+ *Result.SourceManager, getLangOpts()).str();
+
+ const std::string ReplacementText = (Negated ? "!" : "") + StrText + ".starts_with(" +
+ LiteralText + ")";
+
+ auto Diag = diag(SubstrCall->getExprLoc(),
+ "use starts_with() instead of substr(0, n) comparison");
+
+ Diag << FixItHint::CreateReplacement(
+ CharSourceRange::getTokenRange(Comparison->getSourceRange()),
+ ReplacementText);
+}
+
void UseStartsEndsWithCheck::check(const MatchFinder::MatchResult &Result) {
+ // Try substr pattern first
+ const auto *SubstrCall = Result.Nodes.getNodeAs<CXXMemberCallExpr>("substr_fun");
+ if (SubstrCall) {
+ const auto *PositiveComparison = Result.Nodes.getNodeAs<Expr>("positiveComparison");
+ const auto *NegativeComparison = Result.Nodes.getNodeAs<Expr>("negativeComparison");
+
+ if (PositiveComparison || NegativeComparison) {
+ handleSubstrMatch(Result);
+ return;
+ }
+ }
+
+ // Then try find/compare patterns
+ handleFindCompareMatch(Result);
+}
+
+void UseStartsEndsWithCheck::handleFindCompareMatch(const MatchFinder::MatchResult &Result) {
const auto *ComparisonExpr = Result.Nodes.getNodeAs<BinaryOperator>("expr");
const auto *FindExpr = Result.Nodes.getNodeAs<CXXMemberCallExpr>("find_expr");
const auto *FindFun = Result.Nodes.getNodeAs<CXXMethodDecl>("find_fun");
diff --git a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.h b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.h
index 17c2999bda84cd..7e4a1573e81e21 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.h
@@ -31,6 +31,10 @@ class UseStartsEndsWithCheck : public ClangTidyCheck {
std::optional<TraversalKind> getCheckTraversalKind() const override {
return TK_IgnoreUnlessSpelledInSource;
}
+
+private:
+ void handleSubstrMatch(const ast_matchers::MatchFinder::MatchResult &Result);
+ void handleFindCompareMatch(const ast_matchers::MatchFinder::MatchResult &Result);
};
} // namespace clang::tidy::modernize
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index db971f08ca3dbc..4fb7891709447d 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -147,6 +147,13 @@ New check aliases
Changes in existing checks
^^^^^^^^^^^^^^^^^^^^^^^^^^
+- Improved :doc:`modernize-use-starts-ends-with
+ <clang-tidy/checks/modernize/use-starts-ends-with>` check to detect and transform
+ additional patterns using ``substr`` that can be replaced with ``starts_with``.
+ Now handles cases like ``str.substr(0, n) == "literal"``, with support for length
+ determination through integer literals, ``strlen()``, and ``size()``/``length()``
+ member functions.
+
- Improved :doc:`altera-id-dependent-backward-branch
<clang-tidy/checks/altera/id-dependent-backward-branch>` check by fixing
crashes from invalid code.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst
index 721e927e29849f..752f2cdacd065a 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst
@@ -7,26 +7,39 @@ Checks for common roundabout ways to express ``starts_with`` and ``ends_with``
and suggests replacing with the simpler method when it is available. Notably,
this will work with ``std::string`` and ``std::string_view``.
-.. code-block:: c++
+The check handles the following expressions:
- std::string s = "...";
- if (s.find("prefix") == 0) { /* do something */ }
- if (s.rfind("prefix", 0) == 0) { /* do something */ }
- if (s.compare(0, strlen("prefix"), "prefix") == 0) { /* do something */ }
- if (s.compare(s.size() - strlen("suffix"), strlen("suffix"), "suffix") == 0) {
- /* do something */
- }
- if (s.rfind("suffix") == (s.length() - 6)) {
- /* do something */
- }
-
-becomes
+==================================================== ===========================
+Expression Result
+---------------------------------------------------- ---------------------------
+``u.find(v) == 0`` ``u.starts_with(v)``
+``u.rfind(v, 0) != 0`` ``!u.starts_with(v)``
+``u.compare(0, v.size(), v) == 0`` ``u.starts_with(v)``
+``u.substr(0, v.size()) == v`` ``u.starts_with(v)``
+``v == u.substr(0, v.size())`` ``u.starts_with(v)``
+``u.substr(0, v.size()) != v`` ``!u.starts_with(v)``
+``u.compare(u.size() - v.size(), v.size(), v) == 0`` ``u.ends_with(v)``
+``u.rfind(v) == u.size() - v.size()`` ``u.ends_with(v)``
+==================================================== ===========================
+
+For example:
.. code-block:: c++
std::string s = "...";
if (s.starts_with("prefix")) { /* do something */ }
- if (s.starts_with("prefix")) { /* do something */ }
- if (s.starts_with("prefix")) { /* do something */ }
- if (s.ends_with("suffix")) { /* do something */ }
if (s.ends_with("suffix")) { /* do something */ }
+
+Notes:
+
+* For the ``substr`` pattern, the check ensures that:
+
+ * The substring starts at position 0
+ * The length matches exactly the compared string's length
+ * The length is a constant value
+
+* Non-matching cases (will not be transformed):
+
+ * ``s.substr(1, 5) == "hello"`` // Non-zero start position
+ * ``s.substr(0, 4) == "hello"`` // Length mismatch
+ * ``s.substr(0, len) == "hello"`` // Non-constant length
\ No newline at end of file
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 a0e8ebbb267cd0..856dfce815f03a 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
+++ b/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
@@ -59,8 +59,9 @@ struct basic_string {
_Type& insert(size_type pos, const _Type& str);
_Type& insert(size_type pos, const C* s);
_Type& insert(size_type pos, const C* s, size_type n);
+ _Type substr(size_type pos = 0, size_type count = npos) const;
- constexpr bool starts_with(std::basic_string_view<C, T> sv) const noexcept;
+ constexpr bool starts_with(std::basic_string_view<C, T> sv) const noexcept;
constexpr bool starts_with(C ch) const noexcept;
constexpr bool starts_with(const C* s) const;
@@ -117,7 +118,7 @@ struct basic_string_view {
constexpr bool ends_with(const C* s) const;
constexpr int compare(basic_string_view sv) const noexcept;
-
+
static constexpr size_t npos = -1;
};
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 91477241e82e54..eac9e8714b97bd 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
@@ -1,5 +1,5 @@
// RUN: %check_clang_tidy -std=c++20 %s modernize-use-starts-ends-with %t -- \
-// RUN: -- -isystem %clang_tidy_headers
+// RUN: -- -isystem %clang_tidy_headers
#include <string.h>
#include <string>
@@ -266,3 +266,43 @@ void test(std::string s, std::string_view sv, sub_string ss, sub_sub_string sss,
s.compare(0, 1, "ab") == 0;
s.rfind(suffix, 1) == s.size() - suffix.size();
}
+
+void test_substr() {
+ std::string str("hello world");
+ std::string prefix = "hello";
+ std::string_view suffix = "world";
+
+ // Basic pattern
+ str.substr(0, 5) == "hello";
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with() instead of substr(0, n) comparison [modernize-use-starts-ends-with]
+ // CHECK-FIXES: str.starts_with("hello");
+
+ // With string literal on left side
+ "hello" == str.substr(0, 5);
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with() instead of substr(0, n) comparison [modernize-use-starts-ends-with]
+ // CHECK-FIXES: str.starts_with("hello");
+
+
+ // Inequality comparison
+ str.substr(0, 5) != "world";
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with() instead of substr(0, n) comparison [modernize-use-starts-ends-with]
+ // CHECK-FIXES: !str.starts_with("world");
+
+
+ // Ensure non-zero start position is not transformed
+ str.substr(1, 5) == "hello";
+ str.substr(0, 4) == "hello"; // Length mismatch
+
+ size_t len = 5;
+ str.substr(0, len) == "hello"; // Non-constant length
+
+ // String literal with size calculation
+ str.substr(0, prefix.size()) == "hello";
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with() instead of substr(0, n) comparison [modernize-use-starts-ends-with]
+ // CHECK-FIXES: str.starts_with("hello");
+
+ // String literal with size calculation
+ str.substr(0, strlen("hello")) == "hello";
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with() instead of substr(0, n) comparison [modernize-use-starts-ends-with]
+ // CHECK-FIXES: str.starts_with("hello");
+}
\ No newline at end of file
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