# Extra Clang Tools 9 documentation

## Extra Clang Tools 9.0.0 Release Notes

- Introduction

- What’s New in Extra Clang Tools 9.0.0?

  - Improvements to clangd

  - Improvements to clang-tidy

  - Improvements to pp-trace

Written by the LLVM Team

## Introduction

This document contains the release notes for the Extra Clang Tools, part of the Clang release 9.0.0. 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.

## What’s New in Extra Clang Tools 9.0.0?

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.

### Improvements to clangd

- Background indexing is on by default

  When using clangd, it will build an index of your code base (all files listed in your compile database). This index enables go-to-definition, find-references, and even code completion to find symbols across your project.

  This feature can consume a lot of CPU. It can be disabled using the `--background-index=false` flag, and respects `-j` to use fewer threads. The index is written to `.clangd/index` in the project root.

- Contextual code actions

  Extract variable, expand `auto`, expand macro, convert string to raw string. More to come in the future!

- Clang-tidy warnings are available

  These will be produced for projects that have a `.clang-tidy` file in their source tree, as described in the clang-tidy documentation.

- Improved diagnostics

  Errors from headers are now shown (on the #including line). The message now indicates if fixes are available. Navigation between errors and associated notes is improved (for editors that support `Diagnostic.relatedInformation`).

- Suggested includes

  When a class or other name is not found, clangd may suggest to fix this by adding the corresponding `#include` directive.

- Semantic highlighting

  clangd can push syntax information to the editor, allowing it to highlight e.g. member variables differently from locals. (requires editor support)

  This implements the proposed protocol from https://github.com/microsoft/vscode-languageserver-node/pull/367

- Type hierachy

  Navigation to base/derived types is possible in editors that support the proposed protocol from https://github.com/microsoft/vscode-languageserver-node/pull/426

- Improvements to include insertion

  Only headers with `#include`-guards will be inserted, and the feature can be disabled with the `--header-insertion=never` flag.

  Standard library headers should now be inserted more accurately, particularly for C++ other than libstdc++, and for the C standard library.

- Code completion

  Overloads are bundled into a single completion item by default. (for editors that support signature-help).

  Redundant const/non-const overloads are no longer shown.

  Before clangd is warmed up (during preamble build), limited identifier- and index-based code completion is available.

- Format-on-type

  A new implementation of format-on-type is triggered by hitting enter: it attempts to reformat the previous line and reindent the new line. (Requires editor support).

- Toolchain header detection

  Projects that use an embedded gcc toolchain may only work when used with the corresponding standard library. clangd can now query the toolchain to find these headers. The compilation database must correctly specify this toolchain, and the `--query-driver=/path/to/toolchain/bin/*` flag must be passed to clangd.

- Miscellaneous improvements

  Hover now produces richer Markdown-formatted text (for supported editors).

  Rename is safer and more helpful, though is still within one file only.

  Files without extensions (e.g. C++ standard library) are handled better.

  clangd can understand offsets in UTF-8 or UTF-32 through command-line flags or protocol extensions. (Useful with editors/platforms that don’t speak UTF-16).

  Editors that support edits near the cursor in code-completion can set the `textDocument.completion.editsNearCursor` capability to `true`, and clangd will provide completions that correct `.` to `->`, and vice-versa.

### Improvements to clang-tidy

- New OpenMP module.

  For checks specific to OpenMP API.

- New abseil-duration-addition check.

  Checks for cases where addition should be performed in the `absl::Time` domain.

- New abseil-duration-conversion-cast check.

  Checks for casts of `absl::Duration` conversion functions, and recommends the right conversion function instead.

- New abseil-duration-unnecessary-conversion check.

  Finds and fixes cases where `absl::Duration` values are being converted to numeric types and back again.

- New abseil-time-comparison check.

  Prefer comparisons in the `absl::Time` domain instead of the integer domain.

- New abseil-time-subtraction check.

  Finds and fixes `absl::Time` subtraction expressions to do subtraction in the Time domain instead of the numeric domain.

- New android-cloexec-pipe check.

  This check detects usage of `pipe()`.

- New android-cloexec-pipe2 check.

  This checks ensures that `pipe2()` is called with the `O_CLOEXEC` flag.

- New bugprone-branch-clone check.

  Checks for repeated branches in `if/else if/else` chains, consecutive repeated branches in `switch` statements and indentical true and false branches in conditional operators.

- New bugprone-posix-return check.

  Checks if any calls to POSIX functions (except `posix_openpt`) expect negative return values.

- New bugprone-unhandled-self-assignment check.

  Finds user-defined copy assignment operators which do not protect the code against self-assignment either by checking self-assignment explicitly or using the copy-and-swap or the copy-and-move method.

- New fuchsia-default-arguments-calls check.

  Warns if a function or method is called with default arguments. This was previously done by fuchsia-default-arguments check, which has been removed.

- New fuchsia-default-arguments-declarations check.

  Warns if a function or method is declared with default parameters. This was previously done by fuchsia-default-arguments check check, which has been removed.

- New google-objc-avoid-nsobject-new check.

  Checks for calls to `+new` or overrides of it, which are prohibited by the Google Objective-C style guide.

- New google-readability-avoid-underscore-in-googletest-name check.

  Checks whether there are underscores in googletest test and test case names in test macros, which is prohibited by the Googletest FAQ.

- New llvm-prefer-isa-or-dyn-cast-in-conditionals check.

  Looks at conditionals and finds and replaces cases of `cast<>`, which will assert rather than return a null pointer, and `dyn_cast<>` where the return value is not captured. Additionally, finds and replaces cases that match the pattern `var && isa<X>(var)`, where `var` is evaluated twice.

- New modernize-use-trailing-return-type check.

  Rewrites function signatures to use a trailing return type.

- New objc-super-self check.

  Finds invocations of `-self` on super instances in initializers of subclasses of `NSObject` and recommends calling a superclass initializer instead.

- New openmp-exception-escape check.

  Analyzes OpenMP Structured Blocks and checks that no exception escapes out of the Structured Block it was thrown in.

- New openmp-use-default-none check.

  Finds OpenMP directives that are allowed to contain a `default` clause, but either don’t specify it or the clause is specified but with the kind other than `none`, and suggests to use the `default(none)` clause.

- New readability-convert-member-functions-to-static check.

  Finds non-static member functions that can be made `static`.

- New alias cert-oop54-cpp to bugprone-unhandled-self-assignment was added.

- New alias cppcoreguidelines-explicit-virtual-functions to modernize-use-override was added.

- The bugprone-argument-comment now supports CommentBoolLiterals, CommentIntegerLiterals, CommentFloatLiterals, CommentUserDefiniedLiterals, CommentStringLiterals, CommentCharacterLiterals & CommentNullPtrs options.

- The bugprone-too-small-loop-variable now supports MagnitudeBitsUpperLimit option. The default value was set to 16, which greatly reduces warnings related to loops which are unlikely to cause an actual functional bug.

- Added UseAssignment option to cppcoreguidelines-pro-type-member-init

  If set to true, the check will provide fix-its with literal initializers (`int i = 0;`) instead of curly braces (`int i{};`).

- The fuchsia-default-arguments check has been removed.

  Warnings of function or method calls and declarations with default arguments were moved to fuchsia-default-arguments-calls and fuchsia-default-arguments-declarations checks respectively.

- The google-runtime-int check has been disabled in Objective-C++.

- The modernize-use-override now supports OverrideSpelling and FinalSpelling options.

- The misc-throw-by-value-catch-by-reference now supports WarnOnLargeObject and MaxSize options to warn on any large trivial object caught by value.

- The Acronyms and IncludeDefaultAcronyms options for the objc-property-declaration check have been removed.

### Improvements to pp-trace

- Added a new option -callbacks to filter preprocessor callbacks. It replaces the -ignore option.