Extra Clang Tools 19.0.0git (In-Progress) Release Notes

Written by the LLVM Team


These are in-progress notes for the upcoming Extra Clang Tools 19 release. Release notes for previous releases can be found on the Download Page.


This document contains the release notes for the Extra Clang Tools, part of the Clang release 19.0.0git. Here we describe the status of the Extra Clang Tools in some detail, including major improvements from the previous release and new feature work. All LLVM releases may be downloaded from the LLVM releases web site.

For more information about Clang or LLVM, including information about the latest release, please see the Clang Web Site or the LLVM Web Site.

Note that if you are reading this file from a Git checkout or the main Clang web page, this document applies to the next release, not the current one. To see the release notes for a specific release, please see the releases page.

What’s New in Extra Clang Tools 19.0.0git?

Some of the major new features and improvements to Extra Clang Tools are listed here. Generic improvements to Extra Clang Tools as a whole or to its underlying infrastructure are described first, followed by tool-specific sections.

Major New Features

Improvements to clangd

  • Introduced exmperimental support for C++20 Modules. The experimental support can be enabled by -experimental-modules-support option. It is in an early development stage and may not perform efficiently in real-world scenarios.

Inlay hints


Semantic Highlighting

Compile flags


Code completion

Code actions

  • The tweak for turning unscoped into scoped enums now removes redundant prefixes from the enum values.

Signature help




  • Added a boolean option AnalyzeAngledIncludes to Includes config section, which allows to enable unused includes detection for all angled (“system”) headers. At this moment umbrella headers are not supported, so enabling this option may result in false-positives.

Improvements to clang-doc

Improvements to clang-query

  • Added the file command to dynamically load a list of commands and matchers from an external file, allowing the cost of reading the compilation database and building the AST to be imposed just once for faster prototyping.

  • Removed support for enable output srcloc. Fixes #GH82591

Improvements to clang-rename

The improvements are…

Improvements to clang-tidy

  • Improved run-clang-tidy.py script. Added argument -source-filter to filter source files from the compilation database, via a RegEx. In a similar fashion to what -header-filter does for header files.

  • Improved check_clang_tidy.py script. Added argument -export-fixes to aid in clang-tidy and test development.

  • Fixed bug where big values for unsigned check options overflowed into negative values when being printed with –dump-config.

  • Fixed –verify-config option not properly parsing checks when using the literal operator in the .clang-tidy config.

  • Added argument –exclude-header-filter and config option ExcludeHeaderFilterRegex to exclude headers from analysis via a RegEx.

  • Added argument –allow-no-checks to suppress “no checks enabled” error when disabling all of the checks by –checks=’-*’.

New checks

  • New boost-use-ranges check.

    Detects calls to standard library iterator algorithms that could be replaced with a Boost ranges version instead.

  • New bugprone-crtp-constructor-accessibility check.

    Detects error-prone Curiously Recurring Template Pattern usage, when the CRTP can be constructed outside itself and the derived class.

  • New bugprone-pointer-arithmetic-on-polymorphic-object check.

    Finds pointer arithmetic performed on classes that contain a virtual function.

  • New bugprone-return-const-ref-from-parameter check.

    Detects return statements that return a constant reference parameter as constant reference. This may cause use-after-free errors if the caller uses xvalues as arguments.

  • New bugprone-suspicious-stringview-data-usage check.

    Identifies suspicious usages of std::string_view::data() that could lead to reading out-of-bounds data due to inadequate or incorrect string null termination.

  • New misc-use-internal-linkage check.

    Detects variables and functions that can be marked as static or moved into an anonymous namespace to enforce internal linkage.

  • New modernize-min-max-use-initializer-list check.

    Replaces nested std::min and std::max calls with an initializer list where applicable.

  • New modernize-use-designated-initializers check.

    Finds initializer lists for aggregate types that could be written as designated initializers instead.

  • New modernize-use-ranges check.

    Detects calls to standard library iterator algorithms that could be replaced with a ranges version instead.

  • New modernize-use-std-format check.

    Converts calls to absl::StrFormat, or other functions via configuration options, to C++20’s std::format, or another function via a configuration option, modifying the format string appropriately and removing now-unnecessary calls to std::string::c_str() and std::string::data().

  • New readability-enum-initial-value check.

    Enforces consistent style for enumerators’ initialization, covering three styles: none, first only, or all initialized explicitly.

  • New readability-math-missing-parentheses check.

    Check for missing parentheses in mathematical expressions that involve operators of different priorities.

  • New readability-use-std-min-max check.

    Replaces certain conditional statements with equivalent calls to std::min or std::max.

New check aliases

Changes in existing checks

  • Improved bugprone-assert-side-effect check by detecting side effect from calling a method with non-const reference parameters.

  • Improved bugprone-assignment-in-if-condition check by ignoring assignments in the C++20 requires clause.

  • Improved bugprone-casting-through-void check by ignoring casts where source is already a void` pointer, making middle void pointer casts bug-free.

  • Improved bugprone-forwarding-reference-overload check to ignore deleted constructors which won’t hide other overloads.

  • Improved bugprone-implicit-widening-of-multiplication-result check by adding an option to ignore constant expressions of signed integer types that fit in the source expression type.

  • Improved bugprone-inc-dec-in-conditions check to ignore code within unevaluated contexts, such as decltype.

  • Improved bugprone-lambda-function-name check by ignoring __func__ macro in lambda captures, initializers of default parameters and nested function declarations.

  • Improved bugprone-multi-level-implicit-pointer-conversion check by ignoring implicit pointer conversions that are part of a cast expression.

  • Improved bugprone-non-zero-enum-to-bool-conversion check by eliminating false positives resulting from direct usage of bitwise operators within parentheses.

  • Improved bugprone-optional-value-conversion check by eliminating false positives resulting from use of optionals in unevaluated context.

  • Improved bugprone-sizeof-expression check by clarifying the diagnostics, eliminating some false positives and adding a new (off-by-default) option WarnOnSizeOfPointer that reports all sizeof(pointer) expressions (except for a few that are idiomatic).

  • Improved bugprone-suspicious-include check by replacing the local options HeaderFileExtensions and ImplementationFileExtensions by the global options of the same name.

  • Improved bugprone-too-small-loop-variable check by incorporating better support for const loop boundaries.

  • Improved bugprone-unused-local-non-trivial-variable check by ignoring local variable with [maybe_unused] attribute.

  • Improved bugprone-unused-return-value check by updating the parameter CheckedFunctions to support regexp, avoiding false positive for function with the same prefix as the default argument, e.g. std::unique_ptr and std::unique, avoiding false positive for assignment operator overloading.

  • Improved bugprone-use-after-move check to also handle calls to std::forward. Fixed sequencing of designated initializers. Fixed sequencing of callees: In C++17 and later, the callee of a function is guaranteed to be sequenced before the arguments, so don’t warn if the use happens in the callee and the move happens in one of the arguments.

  • Improved cppcoreguidelines-avoid-non-const-global-variables check with a new option AllowInternalLinkage to disable the warning for variables with internal linkage.

  • Improved cppcoreguidelines-macro-usage check by ignoring macro with hash preprocessing token.

  • Improved cppcoreguidelines-missing-std-forward check by no longer giving false positives for deleted functions, by fixing false negatives when only a few parameters are forwarded and by ignoring parameters without a name (unused arguments).

  • Improved cppcoreguidelines-owning-memory check to properly handle return type in lambdas and in nested functions.

  • Improved cppcoreguidelines-prefer-member-initializer check by removing enforcement of rule C.48, which was deprecated since clang-tidy 17. This rule is now covered by cppcoreguidelines-use-default-member-init. Fixed incorrect hints when using list-initialization.

  • Improved cppcoreguidelines-special-member-functions check with a new option AllowImplicitlyDeletedCopyOrMove, which removes the requirement for explicit copy or move special member functions when they are already implicitly deleted.

  • Improved google-build-namespaces check by replacing the local option HeaderFileExtensions by the global option of the same name.

  • Improved google-explicit-constructor check to better handle C++20 explicit(bool).

  • Improved google-global-names-in-headers check by replacing the local option HeaderFileExtensions by the global option of the same name.

  • Improved google-runtime-int check performance through optimizations.

  • Improved hicpp-signed-bitwise check by ignoring false positives involving positive integer literals behind implicit casts when IgnorePositiveIntegerLiterals is enabled.

  • Improved hicpp-ignored-remove-result check by ignoring other functions with same prefixes as the target specific functions.

  • Improved linuxkernel-must-check-errs check documentation to consistently use the check’s proper name.

  • Improved llvm-header-guard check by replacing the local option HeaderFileExtensions by the global option of the same name.

  • Improved misc-const-correctness check by avoiding infinite recursion for recursive functions with forwarding reference parameters and reference variables which refer to themselves.

  • Improved misc-definitions-in-headers check by replacing the local option HeaderFileExtensions by the global option of the same name. Additionally, the option UseHeaderFileExtensions is removed, so that the check uses the HeaderFileExtensions option unconditionally.

  • Improved misc-header-include-cycle check by avoiding crash for self include cycles.

  • Improved misc-unused-using-decls check by replacing the local option HeaderFileExtensions by the global option of the same name.

  • Improved misc-use-anonymous-namespace check by replacing the local option HeaderFileExtensions by the global option of the same name.

  • Improved modernize-avoid-c-arrays check by introducing the new AllowStringArrays option, enabling the exclusion of array types with deduced length initialized from string literals.

  • Improved modernize-loop-convert check by ensuring that fix-its don’t remove parentheses used in sizeof calls when they have array index accesses as arguments.

  • Improved modernize-use-constraints check by fixing a crash that occurred in some scenarios and excluding system headers from analysis.

  • Improved modernize-use-nullptr check to include support for C23, which also has introduced the nullptr keyword.

  • Improved modernize-use-override check to also remove any trailing whitespace when deleting the virtual keyword.

  • Improved modernize-use-starts-ends-with check to also handle calls to compare method.

  • Improved modernize-use-std-print check to not crash if the format string parameter of the function to be replaced is not of the expected type.

  • Improved modernize-use-using check by adding support for detection of typedefs declared on function level.

  • Improved performance-inefficient-vector-operation fixing false negatives caused by different variable definition type and variable initial value type in loop initialization expression.

  • Improved performance-move-const-arg check by ignoring std::move() calls when their target is used as an rvalue.

  • Improved performance-unnecessary-copy-initialization check by detecting more cases of constant access. In particular, pointers can be analyzed, so the check now handles the common patterns const auto e = (*vector_ptr)[i] and const auto e = vector_ptr->at(i);. Calls to mutable function where there exists a const overload are also handled. Fix crash in the case of a non-member operator call.

  • Improved performance-unnecessary-value-param check detecting more cases for template functions including lambdas with auto. E.g., std::sort(a.begin(), a.end(), [](auto x, auto y) { return a > b; }); will be detected for expensive to copy types. Fixed false positives for dependent call expressions.

  • Improved readability-avoid-return-with-void-value check by adding fix-its.

  • Improved readability-const-return-type check to eliminate false positives when returning types with const not at the top level.

  • Improved readability-container-size-empty check to prevent false positives when utilizing size or length methods that accept parameter. Fixed crash when facing template user defined literals.

  • Improved readability-duplicate-include check by excluding include directives that form the filename using macro.

  • Improved readability-else-after-return check to ignore if consteval statements, for which the else branch must not be removed.

  • Improved readability-identifier-naming check in GetConfigPerFile mode by resolving symbolic links to header files. Fixed handling of Hungarian Prefix when configured to LowerCase. Added support for renaming designated initializers. Added support for renaming macro arguments. Fixed renaming conflicts arising from out-of-line member function template definitions.

  • Improved readability-implicit-bool-conversion check to provide valid fix suggestions for static_cast without a preceding space and fixed problem with duplicate parentheses in double implicit casts. Corrected the fix suggestions for C23 and later by using C-style casts instead of static_cast. Fixed false positives in C++20 spaceship operator by ignoring casts in implicit and defaulted functions.

  • Improved readability-redundant-inline-specifier check to properly emit warnings for static data member with an in-class initializer.

  • Improved readability-redundant-member-init check to avoid false-positives when type of the member does not match the type of the initializer.

  • Improved readability-static-accessed-through-instance check to support calls to overloaded operators as base expression and provide fixes to expressions with side-effects.

  • Improved readability-simplify-boolean-expr check to avoid to emit warning for macro when IgnoreMacro option is enabled and improve messages when auto-fix does not work.

  • Improved readability-static-definition-in-anonymous-namespace check by resolving fix-it overlaps in template code by disregarding implicit instances.

  • Improved readability-string-compare check to also detect usages of std::string_view::compare. Added a StringLikeClasses option to detect usages of compare method in custom string-like classes.

Removed checks

  • Removed cert-dcl21-cpp, which was deprecated since clang-tidy 17, since the rule DCL21-CPP has been removed from the CERT guidelines.


  • Fixed incorrect formatting in clang-apply-replacements when no –format option is specified. Now clang-apply-replacements applies formatting only with the option.

Improvements to include-fixer

The improvements are…

Improvements to clang-include-fixer

The improvements are…

Improvements to modularize

The improvements are…

Improvements to pp-trace

Clang-tidy Visual Studio plugin