[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
Fri Nov 15 14:12:15 PST 2024
https://github.com/hjanuschka updated https://github.com/llvm/llvm-project/pull/116033
>From 8a48d6be0b0cf28ab8e98b3a5e7f45628ceadb52 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 1/5] [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 | 65 ++++++++++++++++++-
clang-tools-extra/docs/ReleaseNotes.rst | 5 +-
.../checks/modernize/use-starts-ends-with.rst | 45 ++++++++-----
.../clang-tidy/checkers/Inputs/Headers/string | 1 +
.../modernize/use-starts-ends-with.cpp | 34 ++++++++++
5 files changed, 131 insertions(+), 19 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
index 1231f954298adc..bcfb7227be722b 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp
@@ -171,10 +171,24 @@ void UseStartsEndsWithCheck::registerMatchers(MatchFinder *Finder) {
hasRHS(lengthExprForStringNode("needle")))))
.bind("expr"),
this);
+ Finder->addMatcher(
+ cxxOperatorCallExpr(
+ hasAnyOperatorName("==", "!="),
+ hasOperands(
+ expr().bind("needle"),
+ cxxMemberCallExpr(
+ argumentCountIs(2), hasArgument(0, ZeroLiteral),
+ hasArgument(1, lengthExprForStringNode("needle")),
+ callee(cxxMethodDecl(hasName("substr"),
+ ofClass(OnClassWithStartsWithFunction))
+ .bind("find_fun")))
+ .bind("find_expr")))
+ .bind("expr"),
+ this);
}
void UseStartsEndsWithCheck::check(const MatchFinder::MatchResult &Result) {
- const auto *ComparisonExpr = Result.Nodes.getNodeAs<BinaryOperator>("expr");
+ const auto *ComparisonExpr = Result.Nodes.getNodeAs<Expr>("expr");
const auto *FindExpr = Result.Nodes.getNodeAs<CXXMemberCallExpr>("find_expr");
const auto *FindFun = Result.Nodes.getNodeAs<CXXMethodDecl>("find_fun");
const auto *SearchExpr = Result.Nodes.getNodeAs<Expr>("needle");
@@ -189,7 +203,54 @@ void UseStartsEndsWithCheck::check(const MatchFinder::MatchResult &Result) {
if (ComparisonExpr->getBeginLoc().isMacroID())
return;
- const bool Neg = ComparisonExpr->getOpcode() == BO_NE;
+ bool Neg;
+ if (const auto *BO = llvm::dyn_cast<BinaryOperator>(ComparisonExpr)) {
+ Neg = BO->getOpcode() == BO_NE;
+ } else {
+ assert(llvm::isa<CXXOperatorCallExpr>(ComparisonExpr));
+ Neg = llvm::cast<CXXOperatorCallExpr>(ComparisonExpr)->getOperator() ==
+ OO_ExclaimEqual;
+ }
+
+ // Check if this is a substr case
+ bool IsSubstr = FindFun->getName() == "substr";
+
+ if (IsSubstr) {
+ const auto *SubstrCall = cast<CXXMemberCallExpr>(FindExpr);
+ const Expr *Object = SubstrCall->getImplicitObjectArgument();
+
+ std::string ObjectStr;
+ std::string SearchStr;
+ bool Invalid = false;
+
+ auto &SM = *Result.SourceManager;
+
+ CharSourceRange ObjectRange = CharSourceRange::getTokenRange(
+ Object->getBeginLoc(), Object->getEndLoc());
+ ObjectStr = Lexer::getSourceText(ObjectRange, SM, getLangOpts(), &Invalid).str();
+ if (Invalid)
+ return;
+
+ CharSourceRange SearchRange = CharSourceRange::getTokenRange(
+ SearchExpr->getBeginLoc(), SearchExpr->getEndLoc());
+ SearchStr = Lexer::getSourceText(SearchRange, SM, getLangOpts(), &Invalid).str();
+ if (Invalid)
+ return;
+
+ // Build the new expression: [!]Object.starts_with(SearchExpr)
+ std::string NewExpr =
+ (llvm::Twine(Neg ? "!" : "") + ObjectStr + "." +
+ ReplacementFunction->getName() + "(" + SearchStr + ")").str();
+ // Replace the entire comparison expression
+ auto Diag = diag(ComparisonExpr->getBeginLoc(),
+ "use %0 instead of substr() %select{==|!=}1")
+ << ReplacementFunction->getName() << Neg;
+ Diag << FixItHint::CreateReplacement(
+ CharSourceRange::getTokenRange(ComparisonExpr->getSourceRange()),
+ NewExpr);
+ return;
+ }
+
auto Diagnostic =
diag(FindExpr->getExprLoc(), "use %0 instead of %1() %select{==|!=}2 0")
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index db971f08ca3dbc..62dbc7646740bc 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -244,7 +244,10 @@ Changes in existing checks
- Improved :doc:`modernize-use-starts-ends-with
<clang-tidy/checks/modernize/use-starts-ends-with>` check to handle two cases
- that can be replaced with ``ends_with``
+ that can be replaced with ``ends_with`` and detect 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:`modernize-use-std-format
<clang-tidy/checks/modernize/use-std-format>` check to support replacing
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..41e49e19fa03fd 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 follow ing 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 Replacement
+------------------------------------------------------ ---------------------
+``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..bd797cac0dbe0d 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
+++ b/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
@@ -59,6 +59,7 @@ 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(C ch) const noexcept;
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..cfc773b769d2bb 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
@@ -266,3 +266,37 @@ 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() == [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() == [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() != [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, strlen("hello")) == "hello";
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead of substr() == [modernize-use-starts-ends-with]
+ // CHECK-FIXES: str.starts_with("hello");
+
+}
>From 87444a7331f48f9620f7e2c5bdc851e9f5085e3d Mon Sep 17 00:00:00 2001
From: Helmut Januschka <helmut at januschka.com>
Date: Fri, 15 Nov 2024 23:05:24 +0100
Subject: [PATCH 2/5] Update
clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst
Co-authored-by: Nicolas van Kempen <nvankemp at gmail.com>
---
.../docs/clang-tidy/checks/modernize/use-starts-ends-with.rst | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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 41e49e19fa03fd..e1dd8c47f01d57 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
@@ -7,7 +7,7 @@ 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``.
-The check handles the follow ing expressions:
+The check handles the following expressions:
====================================================== =====================
Expression Replacement
>From b90d6d98605c44f34fa156082034ef26ba450a2b Mon Sep 17 00:00:00 2001
From: Helmut Januschka <helmut at januschka.com>
Date: Fri, 15 Nov 2024 23:05:35 +0100
Subject: [PATCH 3/5] Update
clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst
Co-authored-by: Nicolas van Kempen <nvankemp at gmail.com>
---
.../checks/modernize/use-starts-ends-with.rst | 23 +++++++++----------
1 file changed, 11 insertions(+), 12 deletions(-)
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 e1dd8c47f01d57..2fdd118beefaa2 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
@@ -9,18 +9,17 @@ this will work with ``std::string`` and ``std::string_view``.
The check handles the following expressions:
-====================================================== =====================
-Expression Replacement
------------------------------------------------------- ---------------------
-``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)``
-====================================================== =====================
+==================================================== =====================
+Expression Replacement
+---------------------------------------------------- ---------------------
+``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.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:
>From 005d0dd81a673f7dd30e79a8d825d176fb15f4a9 Mon Sep 17 00:00:00 2001
From: Helmut Januschka <helmut at januschka.com>
Date: Fri, 15 Nov 2024 23:10:07 +0100
Subject: [PATCH 4/5] Update
clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
Co-authored-by: Nicolas van Kempen <nvankemp at gmail.com>
---
clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string | 1 +
1 file changed, 1 insertion(+)
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 bd797cac0dbe0d..51f68174169067 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
+++ b/clang-tools-extra/test/clang-tidy/checkers/Inputs/Headers/string
@@ -59,6 +59,7 @@ 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;
>From 8b4b0a9dcf13d06537fae28130c71dca8d13f0e0 Mon Sep 17 00:00:00 2001
From: Helmut Januschka <helmut at januschka.com>
Date: Fri, 15 Nov 2024 23:12:05 +0100
Subject: [PATCH 5/5] Update
clang-tools-extra/test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp
Co-authored-by: Nicolas van Kempen <nvankemp at gmail.com>
---
.../test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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 cfc773b769d2bb..906cd9f4c3c55f 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
@@ -274,7 +274,7 @@ void test_substr() {
// Basic pattern
str.substr(0, 5) == "hello";
- // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead of substr() == [modernize-use-starts-ends-with]
+ // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead of substr
// CHECK-FIXES: str.starts_with("hello");
// With string literal on left side
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