https://github.com/hjanuschka created
https://github.com/llvm/llvm-project/pull/118074
Add new clang-tidy check that suggests using std::span's more expressive
first() and last() member functions instead of equivalent subspan() calls.
The check modernizes code by replacing:
- subspan(0, n) -> first(n)
- subspan(n) -> last(size() - n)
These dedicated methods were added to the standard to provide clearer
alternatives to common subspan operations. They improve readability by better
expressing intent and are less error-prone by eliminating manual offset
calculations.
For example:
```cpp
std::span<int> s = ...;
auto sub1 = s.subspan(0, n); // transforms to: auto sub1 = s.first(n);
auto sub2 = s.subspan(n); // transforms to: auto sub2 = s.last(s.size()
- n);
auto sub3 = s.subspan(1, n); // not transformed, no direct equivalent
```
not sure if this is a readability or a modernize check ❓
>From cb748c34d35b8c0c9ca93a67b111dcf5d7665b34 Mon Sep 17 00:00:00 2001
From: Helmut Januschka <hel...@januschka.com>
Date: Fri, 29 Nov 2024 10:17:49 +0100
Subject: [PATCH 1/2] [clang-tidy] Add modernize-use-span-first-last check
Add new check that modernizes std::span::subspan() calls to use the more
expressive first() and last() member functions where applicable.
---
.../clang-tidy/modernize/CMakeLists.txt | 1 +
.../modernize/ModernizeTidyModule.cpp | 3 +
.../modernize/UseSpanFirstLastCheck.cpp | 97 +++++++++++++++++++
.../modernize/UseSpanFirstLastCheck.h | 40 ++++++++
clang-tools-extra/docs/ReleaseNotes.rst | 4 +
.../checks/modernize/use-span-first-last.rst | 19 ++++
.../modernize-subspan-conversion.cpp | 50 ++++++++++
7 files changed, 214 insertions(+)
create mode 100644
clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
create mode 100644
clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
create mode 100644
clang-tools-extra/docs/clang-tidy/checks/modernize/use-span-first-last.rst
create mode 100644
clang-tools-extra/test/clang-tidy/checkers/modernize/modernize-subspan-conversion.cpp
diff --git a/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
b/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
index c919d49b42873a..47dd12a2640b6c 100644
--- a/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
@@ -49,6 +49,7 @@ add_clang_library(clangTidyModernizeModule STATIC
UseTransparentFunctorsCheck.cpp
UseUncaughtExceptionsCheck.cpp
UseUsingCheck.cpp
+ UseSpanFirstLastCheck.cpp
LINK_LIBS
clangTidy
diff --git a/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
b/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
index 18607593320635..6fc5de5aad20b7 100644
--- a/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
@@ -42,6 +42,7 @@
#include "UseNullptrCheck.h"
#include "UseOverrideCheck.h"
#include "UseRangesCheck.h"
+#include "UseSpanFirstLastCheck.h"
#include "UseStartsEndsWithCheck.h"
#include "UseStdFormatCheck.h"
#include "UseStdNumbersCheck.h"
@@ -122,6 +123,8 @@ class ModernizeModule : public ClangTidyModule {
CheckFactories.registerCheck<UseUncaughtExceptionsCheck>(
"modernize-use-uncaught-exceptions");
CheckFactories.registerCheck<UseUsingCheck>("modernize-use-using");
+
CheckFactories.registerCheck<UseSpanFirstLastCheck>("modernize-use-span-first-last");
+
}
};
diff --git a/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
new file mode 100644
index 00000000000000..f57571f2aa7c86
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
@@ -0,0 +1,97 @@
+//===--- 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/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+void UseSpanFirstLastCheck::registerMatchers(MatchFinder *Finder) {
+ // Match span::subspan calls
+ const auto HasSpanType = hasType(hasUnqualifiedDesugaredType(
+ recordType(hasDeclaration(classTemplateSpecializationDecl(
+ hasName("::std::span"))))));
+
+ Finder->addMatcher(
+ cxxMemberCallExpr(
+ callee(memberExpr(hasDeclaration(
+ cxxMethodDecl(hasName("subspan"))))),
+ on(expr(HasSpanType)))
+ .bind("subspan"),
+ this);
+}
+
+void UseSpanFirstLastCheck::check(const MatchFinder::MatchResult &Result) {
+ const auto *Call = Result.Nodes.getNodeAs<CXXMemberCallExpr>("subspan");
+ if (!Call)
+ return;
+
+ handleSubspanCall(Result, Call);
+}
+
+void UseSpanFirstLastCheck::handleSubspanCall(
+ const MatchFinder::MatchResult &Result, const CXXMemberCallExpr *Call) {
+ // Get arguments
+ unsigned NumArgs = Call->getNumArgs();
+ if (NumArgs == 0 || NumArgs > 2)
+ return;
+
+ const Expr *Offset = Call->getArg(0);
+ const Expr *Count = NumArgs > 1 ? Call->getArg(1) : nullptr;
+ auto &Context = *Result.Context;
+ bool IsZeroOffset = false;
+
+ // Check if offset is zero through any implicit casts
+ const Expr* OffsetE = Offset->IgnoreImpCasts();
+ if (const auto *IL = dyn_cast<IntegerLiteral>(OffsetE)) {
+ IsZeroOffset = IL->getValue() == 0;
+ }
+
+ // Build replacement text
+ std::string Replacement;
+ if (IsZeroOffset && Count) {
+ // subspan(0, count) -> first(count)
+ auto CountStr = Lexer::getSourceText(
+ CharSourceRange::getTokenRange(Count->getSourceRange()),
+ Context.getSourceManager(), Context.getLangOpts());
+ const auto *Base =
cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
+ auto BaseStr = Lexer::getSourceText(
+ CharSourceRange::getTokenRange(Base->getSourceRange()),
+ Context.getSourceManager(), Context.getLangOpts());
+ Replacement = BaseStr.str() + ".first(" + CountStr.str() + ")";
+ } else if (NumArgs == 1) {
+ // subspan(n) -> last(size() - n)
+ auto OffsetStr = Lexer::getSourceText(
+ CharSourceRange::getTokenRange(Offset->getSourceRange()),
+ Context.getSourceManager(), Context.getLangOpts());
+
+ const auto *Base =
cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
+ auto BaseStr = Lexer::getSourceText(
+ CharSourceRange::getTokenRange(Base->getSourceRange()),
+ Context.getSourceManager(), Context.getLangOpts());
+
+ Replacement = BaseStr.str() + ".last(" + BaseStr.str() + ".size() - " +
OffsetStr.str() + ")";
+ }
+
+ if (!Replacement.empty()) {
+ if (IsZeroOffset && Count) {
+ diag(Call->getBeginLoc(), "prefer span::first() over subspan()")
+ << FixItHint::CreateReplacement(Call->getSourceRange(),
Replacement);
+ } else {
+ diag(Call->getBeginLoc(), "prefer span::last() over subspan()")
+ << FixItHint::CreateReplacement(Call->getSourceRange(),
Replacement);
+ }
+ }
+}
+
+} // namespace clang::tidy::modernize
\ No newline at end of file
diff --git a/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
new file mode 100644
index 00000000000000..141b848be9abbb
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
@@ -0,0 +1,40 @@
+//===--- UseSpanFirstLastCheck.h - 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USESPANFIRSTLASTCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USESPANFIRSTLASTCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::modernize {
+
+/// Converts std::span::subspan() calls to the more modern first()/last()
methods
+/// where applicable.
+///
+/// For example:
+/// \code
+/// std::span<int> s = ...;
+/// auto sub = s.subspan(0, n); // -> auto sub = s.first(n);
+/// auto sub2 = s.subspan(n); // -> auto sub2 = s.last(s.size() - n);
+/// \endcode
+class UseSpanFirstLastCheck : public ClangTidyCheck {
+public:
+ UseSpanFirstLastCheck(StringRef Name, ClangTidyContext *Context)
+ : ClangTidyCheck(Name, Context) {}
+
+ void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+ void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+private:
+ void handleSubspanCall(const ast_matchers::MatchFinder::MatchResult &Result,
+ const CXXMemberCallExpr *Call);
+};
+
+} // namespace clang::tidy::modernize
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USESPANFIRSTLASTCHECK_H
\ No newline at end of file
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst
b/clang-tools-extra/docs/ReleaseNotes.rst
index f050391110385e..04a45d002c0d1d 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -145,6 +145,10 @@ New checks
New check aliases
^^^^^^^^^^^^^^^^^
+- New check `modernize-use-span-first-last` has been added that suggests using
+ ``std::span::first()`` and ``std::span::last()`` member functions instead of
+ equivalent ``subspan()``.
+
- New alias :doc:`cert-arr39-c <clang-tidy/checks/cert/arr39-c>` to
:doc:`bugprone-sizeof-expression
<clang-tidy/checks/bugprone/sizeof-expression>` was added.
diff --git
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-span-first-last.rst
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-span-first-last.rst
new file mode 100644
index 00000000000000..e8aad59bb2264f
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-span-first-last.rst
@@ -0,0 +1,19 @@
+.. title:: clang-tidy - modernize-use-span-first-last
+
+modernize-use-span-first-last
+============================
+
+Checks for uses of ``std::span::subspan()`` that can be replaced with clearer
+``first()`` or ``last()`` member functions.
+
+Covered scenarios:
+
+==================================== ==================================
+Expression Replacement
+------------------------------------ ----------------------------------
+``s.subspan(0, n)`` ``s.first(n)``
+``s.subspan(n)`` ``s.last(s.size() - n)``
+==================================== ==================================
+
+Non-zero offset with count (like ``subspan(1, n)``) has no direct equivalent
+using ``first()`` or ``last()``, so these cases are not transformed.
\ No newline at end of file
diff --git
a/clang-tools-extra/test/clang-tidy/checkers/modernize/modernize-subspan-conversion.cpp
b/clang-tools-extra/test/clang-tidy/checkers/modernize/modernize-subspan-conversion.cpp
new file mode 100644
index 00000000000000..cb78bc02f22d4f
--- /dev/null
+++
b/clang-tools-extra/test/clang-tidy/checkers/modernize/modernize-subspan-conversion.cpp
@@ -0,0 +1,50 @@
+// RUN: %check_clang_tidy %s modernize-use-span-first-last %t
+
+namespace std {
+template <typename T>
+class span {
+ T* ptr;
+ __SIZE_TYPE__ len;
+
+public:
+ span(T* p, __SIZE_TYPE__ l) : ptr(p), len(l) {}
+
+ span<T> subspan(__SIZE_TYPE__ offset) const {
+ return span(ptr + offset, len - offset);
+ }
+
+ span<T> subspan(__SIZE_TYPE__ offset, __SIZE_TYPE__ count) const {
+ return span(ptr + offset, count);
+ }
+
+ span<T> first(__SIZE_TYPE__ count) const {
+ return span(ptr, count);
+ }
+
+ span<T> last(__SIZE_TYPE__ count) const {
+ return span(ptr + (len - count), count);
+ }
+
+ __SIZE_TYPE__ size() const { return len; }
+};
+} // namespace std
+
+void test() {
+ int arr[] = {1, 2, 3, 4, 5};
+ std::span<int> s(arr, 5);
+
+ auto sub1 = s.subspan(0, 3);
+ // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer span::first() over
subspan()
+ // CHECK-FIXES: auto sub1 = s.first(3);
+
+ auto sub2 = s.subspan(2);
+ // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer span::last() over
subspan()
+ // CHECK-FIXES: auto sub2 = s.last(s.size() - 2);
+
+ __SIZE_TYPE__ n = 2;
+ auto sub3 = s.subspan(0, n);
+ // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: prefer span::first() over
subspan()
+ // CHECK-FIXES: auto sub3 = s.first(n);
+
+ auto sub4 = s.subspan(1, 2); // No warning
+}
\ No newline at end of file
>From ec5a6b0ceb0fbbf03ea36a38fb627b25ab4e62de Mon Sep 17 00:00:00 2001
From: Helmut Januschka <hel...@januschka.com>
Date: Fri, 29 Nov 2024 10:19:21 +0100
Subject: [PATCH 2/2] format
---
.../modernize/UseSpanFirstLastCheck.cpp | 41 ++++++++++---------
.../modernize/UseSpanFirstLastCheck.h | 6 +--
2 files changed, 24 insertions(+), 23 deletions(-)
diff --git a/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
index f57571f2aa7c86..6cf01386b0c3fb 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.cpp
@@ -18,17 +18,15 @@ namespace clang::tidy::modernize {
void UseSpanFirstLastCheck::registerMatchers(MatchFinder *Finder) {
// Match span::subspan calls
- const auto HasSpanType = hasType(hasUnqualifiedDesugaredType(
- recordType(hasDeclaration(classTemplateSpecializationDecl(
- hasName("::std::span"))))));
+ const auto HasSpanType =
+ hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
+ classTemplateSpecializationDecl(hasName("::std::span"))))));
- Finder->addMatcher(
- cxxMemberCallExpr(
- callee(memberExpr(hasDeclaration(
- cxxMethodDecl(hasName("subspan"))))),
- on(expr(HasSpanType)))
- .bind("subspan"),
- this);
+ Finder->addMatcher(cxxMemberCallExpr(callee(memberExpr(hasDeclaration(
+
cxxMethodDecl(hasName("subspan"))))),
+ on(expr(HasSpanType)))
+ .bind("subspan"),
+ this);
}
void UseSpanFirstLastCheck::check(const MatchFinder::MatchResult &Result) {
@@ -52,7 +50,7 @@ void UseSpanFirstLastCheck::handleSubspanCall(
bool IsZeroOffset = false;
// Check if offset is zero through any implicit casts
- const Expr* OffsetE = Offset->IgnoreImpCasts();
+ const Expr *OffsetE = Offset->IgnoreImpCasts();
if (const auto *IL = dyn_cast<IntegerLiteral>(OffsetE)) {
IsZeroOffset = IL->getValue() == 0;
}
@@ -64,7 +62,8 @@ void UseSpanFirstLastCheck::handleSubspanCall(
auto CountStr = Lexer::getSourceText(
CharSourceRange::getTokenRange(Count->getSourceRange()),
Context.getSourceManager(), Context.getLangOpts());
- const auto *Base =
cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
+ const auto *Base =
+ cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
auto BaseStr = Lexer::getSourceText(
CharSourceRange::getTokenRange(Base->getSourceRange()),
Context.getSourceManager(), Context.getLangOpts());
@@ -74,22 +73,24 @@ void UseSpanFirstLastCheck::handleSubspanCall(
auto OffsetStr = Lexer::getSourceText(
CharSourceRange::getTokenRange(Offset->getSourceRange()),
Context.getSourceManager(), Context.getLangOpts());
-
- const auto *Base =
cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
+
+ const auto *Base =
+ cast<CXXMemberCallExpr>(Call)->getImplicitObjectArgument();
auto BaseStr = Lexer::getSourceText(
CharSourceRange::getTokenRange(Base->getSourceRange()),
Context.getSourceManager(), Context.getLangOpts());
-
- Replacement = BaseStr.str() + ".last(" + BaseStr.str() + ".size() - " +
OffsetStr.str() + ")";
+
+ Replacement = BaseStr.str() + ".last(" + BaseStr.str() + ".size() - " +
+ OffsetStr.str() + ")";
}
if (!Replacement.empty()) {
if (IsZeroOffset && Count) {
- diag(Call->getBeginLoc(), "prefer span::first() over subspan()")
- << FixItHint::CreateReplacement(Call->getSourceRange(),
Replacement);
+ diag(Call->getBeginLoc(), "prefer span::first() over subspan()")
+ << FixItHint::CreateReplacement(Call->getSourceRange(), Replacement);
} else {
- diag(Call->getBeginLoc(), "prefer span::last() over subspan()")
- << FixItHint::CreateReplacement(Call->getSourceRange(),
Replacement);
+ diag(Call->getBeginLoc(), "prefer span::last() over subspan()")
+ << FixItHint::CreateReplacement(Call->getSourceRange(), Replacement);
}
}
}
diff --git a/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
index 141b848be9abbb..8d4c6035f7ec76 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseSpanFirstLastCheck.h
@@ -13,8 +13,8 @@
namespace clang::tidy::modernize {
-/// Converts std::span::subspan() calls to the more modern first()/last()
methods
-/// where applicable.
+/// Converts std::span::subspan() calls to the more modern first()/last()
+/// methods where applicable.
///
/// For example:
/// \code
@@ -32,7 +32,7 @@ class UseSpanFirstLastCheck : public ClangTidyCheck {
private:
void handleSubspanCall(const ast_matchers::MatchFinder::MatchResult &Result,
- const CXXMemberCallExpr *Call);
+ const CXXMemberCallExpr *Call);
};
} // namespace clang::tidy::modernize
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