This is an archive of the discontinued LLVM Phabricator instance.

I like the overview, maybe a link to clangd here might help, as there is currently a lot of effort of integrating clang-tidy into it. (@sammccall WDYT?)

docs/clang-tidy/index.rst
23 ↗	(On Diff #175452)	I think a blank line here would not hurt.
274 ↗	(On Diff #175452)	Could you please align the elements in the columns, some are off by one.

Should this chapter be a separate page linked from index.md?

In D54945#1309467, @JonasToth wrote:

I like the overview, maybe a link to clangd here might help, as there is currently a lot of effort of integrating clang-tidy into it. (@sammccall WDYT?)

This would be great! The integration is not yet complete, so I'm not sure if it's best to add now or later.

For the table:

on-the-fly inspection: yes (I think - this means showing fixes overlaid on the code as you edit, right?)
check list configuration (GUI): no
options to checks (GUI): no
configuration via .clang-tidy file: this will be the supported mechanism. Not done yet.
custom clang-tidy binary: no

The behavior today is that three hard-coded checks are always enabled, as a proof-of-concept. Configuration via .clang-tidy is the main missing piece.
Clang-tidy diagnostics are shown along with others, as-you-type. Fixes can be applied.
Static analyzer checks will probably never be supported.

Eugene.Zelenko added a subscriber: Eugene.Zelenko.Nov 28 2018, 4:55 PM

Eugene.Zelenko added inline comments.

docs/clang-tidy/index.rst
304 ↗	(On Diff #175452)	Please limit line width to 80 characters. Same in other places.
327 ↗	(On Diff #175452)	Will be good idea to mention native plugin, clang-tidy-vs.

Fixes:

empty line before 'Standalone tool'
table columns with '+/-' aligned
line width limited to 80 (except for the table)

Additions:

clang-tidy-vs plugin
Clangd in the intro, the table, and CLion's paragraph

In D54945#1316251, @MarinaKalashina wrote:

Fixes:

empty line before 'Standalone tool'

table columns with '+/-' aligned

line width limited to 80 (except for the table)

Additions:

clang-tidy-vs plugin

Clangd in the intro, the table, and CLion's paragraph

Did you forget to add a new file to the patch?

Please also include full context into the diff. See https://llvm.org/docs/Phabricator.html

In D54945#1318278, @alexfh wrote:

In D54945#1316251, @MarinaKalashina wrote:

Fixes:

empty line before 'Standalone tool'

table columns with '+/-' aligned

line width limited to 80 (except for the table)

Additions:

clang-tidy-vs plugin

Clangd in the intro, the table, and CLion's paragraph

Did you forget to add a new file to the patch?

Please also include full context into the diff. See https://llvm.org/docs/Phabricator.html

Sorry but the new diff was included to the patch.. I can see the updates as Diff 176328. Could you please check and let me know if it does not work? Thank you.

In D54945#1318283, @MarinaKalashina wrote:

In D54945#1318278, @alexfh wrote:

In D54945#1316251, @MarinaKalashina wrote:

Fixes:

empty line before 'Standalone tool'

table columns with '+/-' aligned

line width limited to 80 (except for the table)

Additions:

clang-tidy-vs plugin

Clangd in the intro, the table, and CLion's paragraph

Did you forget to add a new file to the patch?

Please also include full context into the diff. See https://llvm.org/docs/Phabricator.html

Sorry but the new diff was included to the patch.. I can see the updates as Diff 176328. Could you please check and let me know if it does not work? Thank you.

Please see the screenshot. The diff might be reversed (new vs. old) or just wrong. And there's no context (not overly important in this particular patch, but still makes it more convenient to review).

Full-context patch for the changes introduced in the previous commit.

@alexfh Thanks a lot for your patience and help. I've made another revision, now with the diff made by 'git show HEAD -U999999' to have the full context availlable.

In D54945#1318343, @MarinaKalashina wrote:

@alexfh Thanks a lot for your patience and help. I've made another revision, now with the diff made by 'git show HEAD -U999999' to have the full context availlable.

I don't know how this happened, but the diff is still almost empty. This is what I get when I click on the "Download raw diff":

Index: docs/clang-tidy/index.rst
===================================================================
--- docs/clang-tidy/index.rst
+++ docs/clang-tidy/index.rst
@@ -403,7 +403,7 @@
 
     // Silent only the specified diagnostics for the next line
     // NOLINTNEXTLINE(google-explicit-constructor, google-runtime-int)
-    Foo(bool param);
+    Foo(bool param); 
   };
 
 The formal syntax of ``NOLINT``/``NOLINTNEXTLINE`` is the following:

It's definitely not a common problem, since there are other patches in review, which are displayed just fine.

In D54945#1321301, @alexfh wrote:

In D54945#1318343, @MarinaKalashina wrote:

@alexfh Thanks a lot for your patience and help. I've made another revision, now with the diff made by 'git show HEAD -U999999' to have the full context availlable.

I don't know how this happened, but the diff is still almost empty.

A correction: it's now empty (and it was broken in a different way last time).

Could you verify that you're correctly following one of the processed described in the documentation (https://llvm.org/docs/Phabricator.html)? It looks like you're uploading only one commit from the whole branch.

alexfh edited reviewers, added: ilya-biryukov; removed: asl.Dec 6 2018, 6:12 AM

Maybe try to use Arcanist for uploading diffs?
The web interface can be confusing at times, Arcanist is more reliable (LLVM docs have pointers to the Arcanist documentation to get started)

Another attempt to update the patch with the following fixes:

empty line before 'Standalone tool'
table columns with '+/-' aligned
line width limited to 80 (except for the table)
clang-tidy-vs plugin added
Clangd added to the intro, the table, and the CLion's paragraph

Thanks for the update! We still need to solve the technicality here: could you please upload the diff with full context? See LLVM docs for an example on how this can be done with various version controls (the -U99999 args are important, they are the ones that produce diffs with enough lines around it)

Full-context patch

@ilya-biryukov Thank you for a quick response and sorry for so many iterations. I uploaded a full-context version; hopefully this time it's alright - on my side, it finally looks like a proper full-context diff.

Please run script from D55523 over your changes.

alexfh added inline comments.Dec 18 2018, 8:23 AM

docs/clang-tidy/index.rst
262 ↗	(On Diff #178647)	So how about moving this chapter to a separate page and adding a link to it at the top of this document? While certainly useful, the information in this section has a different focus from the rest of the documentation. Given that the document has grown significantly, I suggest to split out this section and the "Getting involved" section. (The latter can be done separately)

@alexfh Just for me to be sure, should there be the following structure in http://clang.llvm.org/extra/index.html:
Clang-Tidy

The list of clang-tidy checks
Using clang-tidy
Suppressing Undesired Diagnostics
Clang-tidy Integrated (separate page)
Getting Involved (separate page)

And should the latter two pages be linked from 'Clang-Tidy' index.rs like 'The list of clang-tidy checks', which is placed in 'See also'?
Thank you.

docs/clang-tidy/index.rst
262 ↗	(On Diff #178647)	Just for me to be sure, should there be the following structure in http://clang.llvm.org/extra/index.html: Clang-Tidy The list of clang-tidy checks Using clang-tidy Suppressing Undesired Diagnostics Clang-tidy Integrated (separate page) Getting Involved (separate page) And should the latter two pages be linked from 'Clang-Tidy' index.rs like 'The list of clang-tidy checks', which is placed in 'See also'? Thank you.

In D54945#1340528, @MarinaKalashina wrote:

@alexfh Just for me to be sure, should there be the following structure in http://clang.llvm.org/extra/index.html: ...

Roughly like that. More specifically, I'd suggest to modify the See also section of clang-tidy/index.rst as follows:

See also:

.. toctree::
   :maxdepth: 1

   The list of clang-tidy checks <checks/list>
   Clang-tidy IDE/Editor Integrations <integrations>
   Getting Involved <contribution>

The order of TOC items in http://clang.llvm.org/extra/index.html will be slightly weird (the three external docs will be placed before the headings of the main document), but that doesn't seem like a huge problem (and may be fixable).

Extracting 'Getting Involved' and 'Clang-tidy integrations' to separate pages linked in See Also.

@alexfh Thank you, please see the updated structure.
@Eugene.Zelenko Done, the only warnings I got were about the table rows width.

Eugene.Zelenko added inline comments.Jan 10 2019, 11:44 AM

docs/clang-tidy/integrations.rst
118 ↗	(On Diff #181018)	Please add newline.

integrations.rst - end of file new line

restoring full content

Awesome! Thanks a lot ! LG

This revision is now accepted and ready to land.Jan 11 2019, 2:50 PM

I would suggest to rename contribution to Contributing (see LLVM documentation) and integrations to Integrations.

Will be also good idea to fix D55523 script warnings.

files renamed: contribution.rst to Contributing.rst, integrations.rst to Integrations.rst

@Eugene.Zelenko

I would suggest to rename contribution to Contributing (see LLVM documentation) and integrations to Integrations.

Sure, done.

Will be also good idea to fix D55523 script warnings.

The script warns about double spaces and line width in the table, for example:

warning: line 39 contains double spaces
warning: line 39 is in excess of 80 characters (196)

These spaces and width are intended since they 'draw' the table layout. Do you think we could ignore such warnings in this particular case?

In D54945#1355920, @MarinaKalashina wrote:
@Eugene.Zelenko

I would suggest to rename contribution to Contributing (see LLVM documentation) and integrations to Integrations.

Sure, done.

Will be also good idea to fix D55523 script warnings.

The script warns about double spaces and line width in the table, for example:
warning: line 39 contains double spaces
warning: line 39 is in excess of 80 characters (196)
These spaces and width are intended since they 'draw' the table layout. Do you think we could ignore such warnings in this particular case?

Sure, it's fine to leave table as it is. Same thing is done in LLDB code where tables are excluded from Clang-format.

@Eugene.Zelenko @alexfh Thank you! How should I proceed with the revision now? Do I get it right from https://llvm.org/docs/Phabricator.html#committing-a-change, that without commit access, I need to ask for committing the changes for me?

Closed by commit rL351463: [Documentation] Add a chapter about Clang-tidy integrations. (authored by eugenezelenko). · Explain WhyJan 17 2019, 10:36 AM

This revision was automatically updated to reflect the committed changes.

Herald added a subscriber: llvm-commits. · View Herald TranscriptJan 17 2019, 10:36 AM

clang-tools-sphinx-docs bot is failing because of:

Warning, treated as error:
/home/buildbot/llvm-build-dir/clang-tools-sphinx-docs/llvm/src/tools/clang/tools/extra/docs/clang-tidy/Contributing.rst:61: ERROR: Unknown target name: "how to setup tooling for llvm".

Frankly I don't know what is proper way to handle cross-module documentation links.

I fixed links.

By the word, I noticed that HTTP was used and replaced it with HTTPS in Contributing.rst. Will be good idea to do the same in other documentation.

I requested merge of updated documentation into 8.0 branch in PR40369.

Revision Contents

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clang-tools-extra/

trunk/

docs/

clang-tidy/

Contributing.rst

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Integrations.rst

117 lines

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clang-tools-extra/trunk/docs/clang-tidy/Contributing.rst

				================
				Getting Involved
				================

				:program:`clang-tidy` has several own checks and can run Clang static analyzer
				checks, but its power is in the ability to easily write custom checks.

				Checks are organized in modules, which can be linked into :program:`clang-tidy`
				with minimal or no code changes in :program:`clang-tidy`.

				Checks can plug into the analysis on the preprocessor level using `PPCallbacks`_
				or on the AST level using `AST Matchers`_. When an error is found, checks can
				report them in a way similar to how Clang diagnostics work. A fix-it hint can be
				attached to a diagnostic message.

				The interface provided by :program:`clang-tidy` makes it easy to write useful
				and precise checks in just a few lines of code. If you have an idea for a good
				check, the rest of this document explains how to do this.

				There are a few tools particularly useful when developing clang-tidy checks:
				* ``add_new_check.py`` is a script to automate the process of adding a new
				check, it will create the check, update the CMake file and create a test;
				* ``rename_check.py`` does what the script name suggests, renames an existing
				check;
				* :program:`clang-query` is invaluable for interactive prototyping of AST
				matchers and exploration of the Clang AST;
				* `clang-check`_ with the ``-ast-dump`` (and optionally ``-ast-dump-filter``)
				provides a convenient way to dump AST of a C++ program.

				If CMake is configured with ``CLANG_ENABLE_STATIC_ANALYZER``,
				:program:`clang-tidy` will not be built with support for the
				``clang-analyzer-`` checks or the ``mpi-`` checks.


				.. _AST Matchers: http://clang.llvm.org/docs/LibASTMatchers.html
				.. _PPCallbacks: http://clang.llvm.org/doxygen/classclang_1_1PPCallbacks.html
				.. _clang-check: http://clang.llvm.org/docs/ClangCheck.html


				Choosing the Right Place for your Check
				---------------------------------------

				If you have an idea of a check, you should decide whether it should be
				implemented as a:

				+ Clang diagnostic: if the check is generic enough, targets code patterns that
				most probably are bugs (rather than style or readability issues), can be
				implemented effectively and with extremely low false positive rate, it may
				make a good Clang diagnostic.

				+ Clang static analyzer check: if the check requires some sort of control flow
				analysis, it should probably be implemented as a static analyzer check.

				+ clang-tidy check is a good choice for linter-style checks, checks that are
				related to a certain coding style, checks that address code readability, etc.


				Preparing your Workspace
				------------------------

				If you are new to LLVM development, you should read the `Getting Started with
				the LLVM System`_, `Using Clang Tools`_ and `How To Setup Tooling For LLVM`_
				documents to check out and build LLVM, Clang and Clang Extra Tools with CMake.

				Once you are done, change to the ``llvm/tools/clang/tools/extra`` directory, and
				let's start!

				.. _Getting Started with the LLVM System: http://llvm.org/docs/GettingStarted.html
				.. _Using Clang Tools: http://clang.llvm.org/docs/ClangTools.html


				The Directory Structure
				-----------------------

				:program:`clang-tidy` source code resides in the
				``llvm/tools/clang/tools/extra`` directory and is structured as follows:

				::

				clang-tidy/ # Clang-tidy core.
				\|-- ClangTidy.h # Interfaces for users and checks.
				\|-- ClangTidyModule.h # Interface for clang-tidy modules.
				\|-- ClangTidyModuleRegistry.h # Interface for registering of modules.
				...
				\|-- google/ # Google clang-tidy module.
				\|-+
				\|-- GoogleTidyModule.cpp
				\|-- GoogleTidyModule.h
				...
				\|-- llvm/ # LLVM clang-tidy module.
				\|-+
				\|-- LLVMTidyModule.cpp
				\|-- LLVMTidyModule.h
				...
				\|-- objc/ # Objective-C clang-tidy module.
				\|-+
				\|-- ObjCTidyModule.cpp
				\|-- ObjCTidyModule.h
				...
				\|-- tool/ # Sources of the clang-tidy binary.
				...
				test/clang-tidy/ # Integration tests.
				...
				unittests/clang-tidy/ # Unit tests.
				\|-- ClangTidyTest.h
				\|-- GoogleModuleTest.cpp
				\|-- LLVMModuleTest.cpp
				\|-- ObjCModuleTest.cpp
				...


				Writing a clang-tidy Check
				--------------------------

				So you have an idea of a useful check for :program:`clang-tidy`.

				First, if you're not familiar with LLVM development, read through the `Getting
				Started with LLVM`_ document for instructions on setting up your workflow and
				the `LLVM Coding Standards`_ document to familiarize yourself with the coding
				style used in the project. For code reviews we mostly use `LLVM Phabricator`_.

				.. _Getting Started with LLVM: http://llvm.org/docs/GettingStarted.html
				.. _LLVM Coding Standards: http://llvm.org/docs/CodingStandards.html
				.. _LLVM Phabricator: http://llvm.org/docs/Phabricator.html

				Next, you need to decide which module the check belongs to. Modules
				are located in subdirectories of `clang-tidy/
				<http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/clang-tidy/>`_
				and contain checks targeting a certain aspect of code quality (performance,
				readability, etc.), certain coding style or standard (Google, LLVM, CERT, etc.)
				or a widely used API (e.g. MPI). Their names are same as user-facing check
				groups names described :ref:`above <checks-groups-table>`.

				After choosing the module and the name for the check, run the
				``clang-tidy/add_new_check.py`` script to create the skeleton of the check and
				plug it to :program:`clang-tidy`. It's the recommended way of adding new checks.

				If we want to create a `readability-awesome-function-names`, we would run:

				.. code-block:: console

				$ clang-tidy/add_new_check.py readability awesome-function-names


				The ``add_new_check.py`` script will:
				* create the class for your check inside the specified module's directory and
				register it in the module and in the build system;
				* create a lit test file in the ``test/clang-tidy/`` directory;
				* create a documentation file and include it into the
				``docs/clang-tidy/checks/list.rst``.

				Let's see in more detail at the check class definition:

				.. code-block:: c++

				...

				#include "../ClangTidy.h"

				namespace clang {
				namespace tidy {
				namespace readability {

				...
				class AwesomeFunctionNamesCheck : public ClangTidyCheck {
				public:
				AwesomeFunctionNamesCheck(StringRef Name, ClangTidyContext *Context)
				: ClangTidyCheck(Name, Context) {}
				void registerMatchers(ast_matchers::MatchFinder *Finder) override;
				void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
				};

				} // namespace readability
				} // namespace tidy
				} // namespace clang

				...

				Constructor of the check receives the ``Name`` and ``Context`` parameters, and
				must forward them to the ``ClangTidyCheck`` constructor.

				In our case the check needs to operate on the AST level and it overrides the
				``registerMatchers`` and ``check`` methods. If we wanted to analyze code on the
				preprocessor level, we'd need instead to override the ``registerPPCallbacks``
				method.

				In the ``registerMatchers`` method we create an AST Matcher (see `AST Matchers`_
				for more information) that will find the pattern in the AST that we want to
				inspect. The results of the matching are passed to the ``check`` method, which
				can further inspect them and report diagnostics.

				.. code-block:: c++

				using namespace ast_matchers;

				void AwesomeFunctionNamesCheck::registerMatchers(MatchFinder *Finder) {
				Finder->addMatcher(functionDecl().bind("x"), this);
				}

				void AwesomeFunctionNamesCheck::check(const MatchFinder::MatchResult &Result) {
				const auto *MatchedDecl = Result.Nodes.getNodeAs<FunctionDecl>("x");
				if (MatchedDecl->getName().startswith("awesome_"))
				return;
				diag(MatchedDecl->getLocation(), "function %0 is insufficiently awesome")
				<< MatchedDecl
				<< FixItHint::CreateInsertion(MatchedDecl->getLocation(), "awesome_");
				}

				(If you want to see an example of a useful check, look at
				`clang-tidy/google/ExplicitConstructorCheck.h
				<http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/clang-tidy/google/ExplicitConstructorCheck.h>`_
				and `clang-tidy/google/ExplicitConstructorCheck.cpp
				<http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/clang-tidy/google/ExplicitConstructorCheck.cpp>`_).


				Registering your Check
				----------------------

				(The ``add_new_check.py`` takes care of registering the check in an existing
				module. If you want to create a new module or know the details, read on.)

				The check should be registered in the corresponding module with a distinct name:

				.. code-block:: c++

				class MyModule : public ClangTidyModule {
				public:
				void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
				CheckFactories.registerCheck<ExplicitConstructorCheck>(
				"my-explicit-constructor");
				}
				};

				Now we need to register the module in the ``ClangTidyModuleRegistry`` using a
				statically initialized variable:

				.. code-block:: c++

				static ClangTidyModuleRegistry::Add<MyModule> X("my-module",
				"Adds my lint checks.");


				When using LLVM build system, we need to use the following hack to ensure the
				module is linked into the :program:`clang-tidy` binary:

				Add this near the ``ClangTidyModuleRegistry::Add<MyModule>`` variable:

				.. code-block:: c++

				// This anchor is used to force the linker to link in the generated object file
				// and thus register the MyModule.
				volatile int MyModuleAnchorSource = 0;

				And this to the main translation unit of the :program:`clang-tidy` binary (or
				the binary you link the ``clang-tidy`` library in)
				``clang-tidy/tool/ClangTidyMain.cpp``:

				.. code-block:: c++

				// This anchor is used to force the linker to link the MyModule.
				extern volatile int MyModuleAnchorSource;
				static int MyModuleAnchorDestination = MyModuleAnchorSource;


				Configuring Checks
				------------------

				If a check needs configuration options, it can access check-specific options
				using the ``Options.get<Type>("SomeOption", DefaultValue)`` call in the check
				constructor. In this case the check should also override the
				``ClangTidyCheck::storeOptions`` method to make the options provided by the
				check discoverable. This method lets :program:`clang-tidy` know which options
				the check implements and what the current values are (e.g. for the
				``-dump-config`` command line option).

				.. code-block:: c++

				class MyCheck : public ClangTidyCheck {
				const unsigned SomeOption1;
				const std::string SomeOption2;

				public:
				MyCheck(StringRef Name, ClangTidyContext *Context)
				: ClangTidyCheck(Name, Context),
				SomeOption(Options.get("SomeOption1", -1U)),
				SomeOption(Options.get("SomeOption2", "some default")) {}

				void storeOptions(ClangTidyOptions::OptionMap &Opts) override {
				Options.store(Opts, "SomeOption1", SomeOption1);
				Options.store(Opts, "SomeOption2", SomeOption2);
				}
				...

				Assuming the check is registered with the name "my-check", the option can then
				be set in a ``.clang-tidy`` file in the following way:

				.. code-block:: yaml

				CheckOptions:
				- key: my-check.SomeOption1
				value: 123
				- key: my-check.SomeOption2
				value: 'some other value'

				If you need to specify check options on a command line, you can use the inline
				YAML format:

				.. code-block:: console

				$ clang-tidy -config="{CheckOptions: [{key: a, value: b}, {key: x, value: y}]}" ...


				Testing Checks
				--------------

				To run tests for :program:`clang-tidy` use the command:

				.. code-block:: console

				$ ninja check-clang-tools

				:program:`clang-tidy` checks can be tested using either unit tests or
				`lit`_ tests. Unit tests may be more convenient to test complex replacements
				with strict checks. `Lit`_ tests allow using partial text matching and regular
				expressions which makes them more suitable for writing compact tests for
				diagnostic messages.

				The ``check_clang_tidy.py`` script provides an easy way to test both
				diagnostic messages and fix-its. It filters out ``CHECK`` lines from the test
				file, runs :program:`clang-tidy` and verifies messages and fixes with two
				separate `FileCheck`_ invocations: once with FileCheck's directive
				prefix set to ``CHECK-MESSAGES``, validating the diagnostic messages,
				and once with the directive prefix set to ``CHECK-FIXES``, running
				against the fixed code (i.e., the code after generated fix-its are
				applied). In particular, ``CHECK-FIXES:`` can be used to check
				that code was not modified by fix-its, by checking that it is present
				unchanged in the fixed code. The full set of `FileCheck`_ directives
				is available (e.g., ``CHECK-MESSAGES-SAME:``, ``CHECK-MESSAGES-NOT:``), though
				typically the basic ``CHECK`` forms (``CHECK-MESSAGES`` and ``CHECK-FIXES``)
				are sufficient for clang-tidy tests. Note that the `FileCheck`_
				documentation mostly assumes the default prefix (``CHECK``), and hence
				describes the directive as ``CHECK:``, ``CHECK-SAME:``, ``CHECK-NOT:``, etc.
				Replace ``CHECK`` by either ``CHECK-FIXES`` or ``CHECK-MESSAGES`` for
				clang-tidy tests.

				An additional check enabled by ``check_clang_tidy.py`` ensures that
				if `CHECK-MESSAGES:` is used in a file then every warning or error
				must have an associated CHECK in that file. Or, you can use ``CHECK-NOTES:``
				instead, if you want to also ensure that all the notes are checked.

				To use the ``check_clang_tidy.py`` script, put a .cpp file with the
				appropriate ``RUN`` line in the ``test/clang-tidy`` directory. Use
				``CHECK-MESSAGES:`` and ``CHECK-FIXES:`` lines to write checks against
				diagnostic messages and fixed code.

				It's advised to make the checks as specific as possible to avoid checks matching
				to incorrect parts of the input. Use ``[[@LINE+X]]``/``[[@LINE-X]]``
				substitutions and distinct function and variable names in the test code.

				Here's an example of a test using the ``check_clang_tidy.py`` script (the full
				source code is at `test/clang-tidy/google-readability-casting.cpp`_):

				.. code-block:: c++

				// RUN: %check_clang_tidy %s google-readability-casting %t

				void f(int a) {
				int b = (int)a;
				// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: redundant cast to the same type [google-readability-casting]
				// CHECK-FIXES: int b = a;
				}

				To check more than one scenario in the same test file use
				``-check-suffix=SUFFIX-NAME`` on ``check_clang_tidy.py`` command line or
				``-check-suffixes=SUFFIX-NAME-1,SUFFIX-NAME-2,...``.
				With ``-check-suffix[es]=SUFFIX-NAME`` you need to replace your ``CHECK-*``
				directives with ``CHECK-MESSAGES-SUFFIX-NAME`` and ``CHECK-FIXES-SUFFIX-NAME``.

				Here's an example:

				.. code-block:: c++

				// RUN: %check_clang_tidy -check-suffix=USING-A %s misc-unused-using-decls %t -- -- -DUSING_A
				// RUN: %check_clang_tidy -check-suffix=USING-B %s misc-unused-using-decls %t -- -- -DUSING_B
				// RUN: %check_clang_tidy %s misc-unused-using-decls %t
				...
				// CHECK-MESSAGES-USING-A: :[[@LINE-8]]:10: warning: using decl 'A' {{.*}}
				// CHECK-MESSAGES-USING-B: :[[@LINE-7]]:10: warning: using decl 'B' {{.*}}
				// CHECK-MESSAGES: :[[@LINE-6]]:10: warning: using decl 'C' {{.*}}
				// CHECK-FIXES-USING-A-NOT: using a::A;$
				// CHECK-FIXES-USING-B-NOT: using a::B;$
				// CHECK-FIXES-NOT: using a::C;$


				There are many dark corners in the C++ language, and it may be difficult to make
				your check work perfectly in all cases, especially if it issues fix-it hints. The
				most frequent pitfalls are macros and templates:

				1. code written in a macro body/template definition may have a different meaning
				depending on the macro expansion/template instantiation;
				2. multiple macro expansions/template instantiations may result in the same code
				being inspected by the check multiple times (possibly, with different
				meanings, see 1), and the same warning (or a slightly different one) may be
				issued by the check multiple times; :program:`clang-tidy` will deduplicate
				_identical_ warnings, but if the warnings are slightly different, all of them
				will be shown to the user (and used for applying fixes, if any);
				3. making replacements to a macro body/template definition may be fine for some
				macro expansions/template instantiations, but easily break some other
				expansions/instantiations.

				.. _lit: http://llvm.org/docs/CommandGuide/lit.html
				.. _FileCheck: http://llvm.org/docs/CommandGuide/FileCheck.html
				.. _test/clang-tidy/google-readability-casting.cpp: http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/test/clang-tidy/google-readability-casting.cpp


				Running clang-tidy on LLVM
				--------------------------

				To test a check it's best to try it out on a larger code base. LLVM and Clang
				are the natural targets as you already have the source code around. The most
				convenient way to run :program:`clang-tidy` is with a compile command database;
				CMake can automatically generate one, for a description of how to enable it see
				`How To Setup Tooling For LLVM`_. Once ``compile_commands.json`` is in place and
				a working version of :program:`clang-tidy` is in ``PATH`` the entire code base
				can be analyzed with ``clang-tidy/tool/run-clang-tidy.py``. The script executes
				:program:`clang-tidy` with the default set of checks on every translation unit
				in the compile command database and displays the resulting warnings and errors.
				The script provides multiple configuration flags.

				* The default set of checks can be overridden using the ``-checks`` argument,
				taking the identical format as :program:`clang-tidy` does. For example
				``-checks=-*,modernize-use-override`` will run the ``modernize-use-override``
				check only.

				* To restrict the files examined you can provide one or more regex arguments
				that the file names are matched against.
				``run-clang-tidy.py clang-tidy/.*Check\.cpp`` will only analyze clang-tidy
				checks. It may also be necessary to restrict the header files warnings are
				displayed from using the ``-header-filter`` flag. It has the same behavior
				as the corresponding :program:`clang-tidy` flag.

				* To apply suggested fixes ``-fix`` can be passed as an argument. This gathers
				all changes in a temporary directory and applies them. Passing ``-format``
				will run clang-format over changed lines.


				On checks profiling
				-------------------

				:program:`clang-tidy` can collect per-check profiling info, and output it
				for each processed source file (translation unit).

				To enable profiling info collection, use the ``-enable-check-profile`` argument.
				The timings will be output to ``stderr`` as a table. Example output:

				.. code-block:: console

				$ clang-tidy -enable-check-profile -checks=-*,readability-function-size source.cpp
				===-------------------------------------------------------------------------===
				clang-tidy checks profiling
				===-------------------------------------------------------------------------===
				Total Execution Time: 1.0282 seconds (1.0258 wall clock)

				---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
				0.9136 (100.0%) 0.1146 (100.0%) 1.0282 (100.0%) 1.0258 (100.0%) readability-function-size
				0.9136 (100.0%) 0.1146 (100.0%) 1.0282 (100.0%) 1.0258 (100.0%) Total

				It can also store that data as JSON files for further processing. Example output:

				.. code-block:: console

				$ clang-tidy -enable-check-profile -store-check-profile=. -checks=-*,readability-function-size source.cpp
				$ # Note that there won't be timings table printed to the console.
				$ ls /tmp/out/
				20180516161318717446360-source.cpp.json
				$ cat 20180516161318717446360-source.cpp.json
				{
				"file": "/path/to/source.cpp",
				"timestamp": "2018-05-16 16:13:18.717446360",
				"profile": {
				"time.clang-tidy.readability-function-size.wall": 1.0421266555786133e+00,
				"time.clang-tidy.readability-function-size.user": 9.2088400000005421e-01,
				"time.clang-tidy.readability-function-size.sys": 1.2418899999999974e-01
				}
				}

				There is only one argument that controls profile storage:

				* ``-store-check-profile=<prefix>``

				By default reports are printed in tabulated format to stderr. When this option
				is passed, these per-TU profiles are instead stored as JSON.
				If the prefix is not an absolute path, it is considered to be relative to the
				directory from where you have run :program:`clang-tidy`. All ``.`` and ``..``
				patterns in the path are collapsed, and symlinks are resolved.

				Example:
				Let's suppose you have a source file named ``example.cpp``, located in the
				``/source`` directory. Only the input filename is used, not the full path
				to the source file. Additionally, it is prefixed with the current timestamp.

				* If you specify ``-store-check-profile=/tmp``, then the profile will be saved
				to ``/tmp/<ISO8601-like timestamp>-example.cpp.json``

				* If you run :program:`clang-tidy` from within ``/foo`` directory, and specify
				``-store-check-profile=.``, then the profile will still be saved to
				``/foo/<ISO8601-like timestamp>-example.cpp.json``

clang-tools-extra/trunk/docs/clang-tidy/Integrations.rst

				==================================
				Clang-tidy IDE/Editor Integrations
				==================================

				.. _Clangd: https://clang.llvm.org/extra/clangd.html

				Apart from being a standalone tool, :program:`clang-tidy` is integrated into
				various IDEs, code analyzers, and editors. Besides, it is currently being
				integrated into Clangd_. The following table shows the most
				well-known :program:`clang-tidy` integrations in detail.

				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\| \| Feature \|
				+======================================+========================+=================================+==========================+=========================================+==========================+
				\| Tool \| On-the-fly inspection \| Check list configuration (GUI) \| Options to checks (GUI) \| Configuration via ``.clang-tidy`` files \| Custom clang-tidy binary \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|A.L.E. for Vim \| \+\ \| \-\ \| \-\ \| \-\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|Clang Power Tools for Visual Studio \| \-\ \| \+\ \| \-\ \| \+\ \| \-\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|Clangd \| \+\ \| \-\ \| \-\ \| \-\ \| \-\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|CLion IDE \| \+\ \| \+\ \| \+\ \| \+\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|CodeChecker \| \-\ \| \-\ \| \-\ \| \-\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|CPPCheck \| \-\ \| \-\ \| \-\ \| \-\ \| \-\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|CPPDepend \| \-\ \| \-\ \| \-\ \| \-\ \| \-\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|Flycheck for Emacs \| \+\ \| \-\ \| \-\ \| \+\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|KDevelop IDE \| \-\ \| \+\ \| \+\ \| \+\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|Qt Creator IDE \| \+\ \| \+\ \| \-\ \| \-\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|ReSharper C++ for Visual Studio \| \+\ \| \+\ \| \-\ \| \+\ \| \-\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|Syntastic for Vim \| \+\ \| \-\ \| \-\ \| \-\ \| \+\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+
				\|Visual Assist for Visual Studio \| \+\ \| \+\ \| \-\ \| \-\ \| \-\ \|
				+--------------------------------------+------------------------+---------------------------------+--------------------------+-----------------------------------------+--------------------------+

				IDEs

				.. _CLion: https://www.jetbrains.com/clion/
				.. _integrates clang-tidy: https://www.jetbrains.com/help/clion/clang-tidy-checks-support.html

				CLion_ 2017.2 and later `integrates clang-tidy`_ as an extension to the
				built-in code analyzer. Starting from 2018.2 EAP, CLion allows using
				:program:`clang-tidy` via Clangd. Inspections and applicable quick-fixes are
				performed on the fly, and checks can be configured in standard command line
				format. In this integration, you can switch to the :program:`clang-tidy`
				binary different from the bundled one, pass the configuration in
				``.clang-tidy`` files instead of using the IDE settings, and configure
				options for particular checks.

				.. _KDevelop: https://www.kdevelop.org/
				.. _kdev-clang-tidy: https://github.com/KDE/kdev-clang-tidy/

				KDevelop_ with the kdev-clang-tidy_ plugin, starting from version 5.1, performs
				static analysis using :program:`clang-tidy`. The plugin launches the
				:program:`clang-tidy` binary from the specified location and parses its
				output to provide a list of issues.

				.. _QtCreator: https://www.qt.io/
				.. _Clang Code Model: http://doc.qt.io/qtcreator/creator-clang-codemodel.html

				QtCreator_ 4.6 integrates :program:`clang-tidy` warnings into the editor
				diagnostics under the `Clang Code Model`_. To employ :program:`clang-tidy`
				inspection in QtCreator, you need to create a copy of one of the presets and
				choose the checks to be performed in the Clang Code Model Warnings menu.

				.. _MS Visual Studio: https://visualstudio.microsoft.com/
				.. _ReSharper C++: https://www.jetbrains.com/help/resharper/Clang_Tidy_Integration.html
				.. _Visual Assist: https://docs.wholetomato.com/default.asp?W761
				.. _Clang Power Tools: https://marketplace.visualstudio.com/items?itemName=caphyon.ClangPowerTools
				.. _clang-tidy-vs: https://github.com/llvm-mirror/clang-tools-extra/tree/master/clang-tidy-vs

				`MS Visual Studio`_ has a native clang-tidy-vs_ plugin and also can integrate
				:program:`clang-tidy` by means of three other tools. The `ReSharper C++`_
				extension, version 2017.3 and later, provides seamless :program:`clang-tidy`
				integration: checks and quick-fixes run alongside native inspections. Apart
				from that, ReSharper C++ incorporates :program:`clang-tidy` as a separate
				step of its code clean-up process. `Visual Assist`_ build 2210 includes a
				subset of :program:`clang-tidy` checklist to inspect the code as you edit.
				Another way to bring :program:`clang-tidy` functionality to Visual Studio is
				the `Clang Power Tools`_ plugin, which includes most of the
				:program:`clang-tidy` checks and runs them during compilation or as a separate
				step of code analysis.

				Editors

				.. _Flycheck: https://github.com/ch1bo/flycheck-clang-tidy
				.. _Syntastic: https://github.com/vim-syntastic/syntastic
				.. _A.L.E.: https://github.com/w0rp/ale
				.. _Emacs24: https://www.gnu.org/s/emacs/
				.. _Vim: https://www.vim.org/

				Emacs24_, when expanded with the Flycheck_ plugin, incorporates the
				:program:`clang-tidy` inspection into the syntax analyzer. For Vim_, you can
				use Syntastic_, which includes :program:`clang-tidy`, or `A.L.E.`_,
				a lint engine that applies :program:`clang-tidy` along with other linters.

				Analyzers

				.. _CPPDepend: https://www.cppdepend.com/cppdependv2018
				.. _CPPCheck: https://sourceforge.net/p/cppcheck/news/
				.. _CodeChecker: https://github.com/Ericsson/codechecker
				.. _plugin: https://github.com/Ericsson/CodeCheckerEclipsePlugin

				:program:`clang-tidy` is integrated in CPPDepend_ starting from version 2018.1
				and CPPCheck_ 1.82. CPPCheck integration lets you import Visual Studio
				solutions and run the :program:`clang-tidy` inspection on them. The
				CodeChecker_ application of version 5.3 or later, which also comes as a plugin_
				for Eclipse, supports :program:`clang-tidy` as a static analysis instrument and
				allows to use a custom :program:`clang-tidy` binary.

clang-tools-extra/trunk/docs/clang-tidy/index.rst

	==========			==========
	Clang-Tidy			Clang-Tidy
	==========			==========

	.. contents::			.. contents::

	See also:			See also:

	.. toctree::			.. toctree::
	:maxdepth: 1			:maxdepth: 1

	The list of clang-tidy checks <checks/list>			The list of clang-tidy checks <checks/list>
				Clang-tidy IDE/Editor Integrations <Integrations>
				Getting Involved <Contributing>

	:program:`clang-tidy` is a clang-based C++ "linter" tool. Its purpose is to			:program:`clang-tidy` is a clang-based C++ "linter" tool. Its purpose is to
	provide an extensible framework for diagnosing and fixing typical programming			provide an extensible framework for diagnosing and fixing typical programming
	errors, like style violations, interface misuse, or bugs that can be deduced via			errors, like style violations, interface misuse, or bugs that can be deduced via
	static analysis. :program:`clang-tidy` is modular and provides a convenient			static analysis. :program:`clang-tidy` is modular and provides a convenient
	interface for writing new checks.			interface for writing new checks.


	▲ Show 20 Lines • Show All 284 Lines • ▼ Show 20 Lines

	Note that whitespaces between ``NOLINT``/``NOLINTNEXTLINE`` and the opening			Note that whitespaces between ``NOLINT``/``NOLINTNEXTLINE`` and the opening
	parenthesis are not allowed (in this case the comment will be treated just as			parenthesis are not allowed (in this case the comment will be treated just as
	``NOLINT``/``NOLINTNEXTLINE``), whereas in check names list (inside			``NOLINT``/``NOLINTNEXTLINE``), whereas in check names list (inside
	the parenthesis) whitespaces can be used and will be ignored.			the parenthesis) whitespaces can be used and will be ignored.

	.. _LibTooling: http://clang.llvm.org/docs/LibTooling.html			.. _LibTooling: http://clang.llvm.org/docs/LibTooling.html
	.. _How To Setup Tooling For LLVM: http://clang.llvm.org/docs/HowToSetupToolingForLLVM.html			.. _How To Setup Tooling For LLVM: http://clang.llvm.org/docs/HowToSetupToolingForLLVM.html


	Getting Involved
	================

	:program:`clang-tidy` has several own checks and can run Clang static analyzer
	checks, but its power is in the ability to easily write custom checks.

	Checks are organized in modules, which can be linked into :program:`clang-tidy`
	with minimal or no code changes in :program:`clang-tidy`.

	Checks can plug into the analysis on the preprocessor level using `PPCallbacks`_
	or on the AST level using `AST Matchers`_. When an error is found, checks can
	report them in a way similar to how Clang diagnostics work. A fix-it hint can be
	attached to a diagnostic message.

	The interface provided by :program:`clang-tidy` makes it easy to write useful
	and precise checks in just a few lines of code. If you have an idea for a good
	check, the rest of this document explains how to do this.

	There are a few tools particularly useful when developing clang-tidy checks:
	* ``add_new_check.py`` is a script to automate the process of adding a new
	check, it will create the check, update the CMake file and create a test;
	* ``rename_check.py`` does what the script name suggests, renames an existing
	check;
	* :program:`clang-query` is invaluable for interactive prototyping of AST
	matchers and exploration of the Clang AST;
	* `clang-check`_ with the ``-ast-dump`` (and optionally ``-ast-dump-filter``)
	provides a convenient way to dump AST of a C++ program.

	If CMake is configured with ``CLANG_ENABLE_STATIC_ANALYZER``,
	:program:`clang-tidy` will not be built with support for the
	``clang-analyzer-`` checks or the ``mpi-`` checks.


	.. _AST Matchers: http://clang.llvm.org/docs/LibASTMatchers.html
	.. _PPCallbacks: http://clang.llvm.org/doxygen/classclang_1_1PPCallbacks.html
	.. _clang-check: http://clang.llvm.org/docs/ClangCheck.html


	Choosing the Right Place for your Check
	---------------------------------------

	If you have an idea of a check, you should decide whether it should be
	implemented as a:

	+ Clang diagnostic: if the check is generic enough, targets code patterns that
	most probably are bugs (rather than style or readability issues), can be
	implemented effectively and with extremely low false positive rate, it may
	make a good Clang diagnostic.

	+ Clang static analyzer check: if the check requires some sort of control flow
	analysis, it should probably be implemented as a static analyzer check.

	+ clang-tidy check is a good choice for linter-style checks, checks that are
	related to a certain coding style, checks that address code readability, etc.


	Preparing your Workspace
	------------------------

	If you are new to LLVM development, you should read the `Getting Started with
	the LLVM System`_, `Using Clang Tools`_ and `How To Setup Tooling For LLVM`_
	documents to check out and build LLVM, Clang and Clang Extra Tools with CMake.

	Once you are done, change to the ``llvm/tools/clang/tools/extra`` directory, and
	let's start!

	.. _Getting Started with the LLVM System: http://llvm.org/docs/GettingStarted.html
	.. _Using Clang Tools: http://clang.llvm.org/docs/ClangTools.html


	The Directory Structure
	-----------------------

	:program:`clang-tidy` source code resides in the
	``llvm/tools/clang/tools/extra`` directory and is structured as follows:

	::

	clang-tidy/ # Clang-tidy core.
	\|-- ClangTidy.h # Interfaces for users and checks.
	\|-- ClangTidyModule.h # Interface for clang-tidy modules.
	\|-- ClangTidyModuleRegistry.h # Interface for registering of modules.
	...
	\|-- google/ # Google clang-tidy module.
	\|-+
	\|-- GoogleTidyModule.cpp
	\|-- GoogleTidyModule.h
	...
	\|-- llvm/ # LLVM clang-tidy module.
	\|-+
	\|-- LLVMTidyModule.cpp
	\|-- LLVMTidyModule.h
	...
	\|-- objc/ # Objective-C clang-tidy module.
	\|-+
	\|-- ObjCTidyModule.cpp
	\|-- ObjCTidyModule.h
	...
	\|-- tool/ # Sources of the clang-tidy binary.
	...
	test/clang-tidy/ # Integration tests.
	...
	unittests/clang-tidy/ # Unit tests.
	\|-- ClangTidyTest.h
	\|-- GoogleModuleTest.cpp
	\|-- LLVMModuleTest.cpp
	\|-- ObjCModuleTest.cpp
	...


	Writing a clang-tidy Check
	--------------------------

	So you have an idea of a useful check for :program:`clang-tidy`.

	First, if you're not familiar with LLVM development, read through the `Getting
	Started with LLVM`_ document for instructions on setting up your workflow and
	the `LLVM Coding Standards`_ document to familiarize yourself with the coding
	style used in the project. For code reviews we mostly use `LLVM Phabricator`_.

	.. _Getting Started with LLVM: http://llvm.org/docs/GettingStarted.html
	.. _LLVM Coding Standards: http://llvm.org/docs/CodingStandards.html
	.. _LLVM Phabricator: http://llvm.org/docs/Phabricator.html

	Next, you need to decide which module the check belongs to. Modules
	are located in subdirectories of `clang-tidy/
	<http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/clang-tidy/>`_
	and contain checks targeting a certain aspect of code quality (performance,
	readability, etc.), certain coding style or standard (Google, LLVM, CERT, etc.)
	or a widely used API (e.g. MPI). Their names are same as user-facing check
	groups names described :ref:`above <checks-groups-table>`.

	After choosing the module and the name for the check, run the
	``clang-tidy/add_new_check.py`` script to create the skeleton of the check and
	plug it to :program:`clang-tidy`. It's the recommended way of adding new checks.

	If we want to create a `readability-awesome-function-names`, we would run:

	.. code-block:: console

	$ clang-tidy/add_new_check.py readability awesome-function-names


	The ``add_new_check.py`` script will:
	* create the class for your check inside the specified module's directory and
	register it in the module and in the build system;
	* create a lit test file in the ``test/clang-tidy/`` directory;
	* create a documentation file and include it into the
	``docs/clang-tidy/checks/list.rst``.

	Let's see in more detail at the check class definition:

	.. code-block:: c++

	...

	#include "../ClangTidy.h"

	namespace clang {
	namespace tidy {
	namespace readability {

	...
	class AwesomeFunctionNamesCheck : public ClangTidyCheck {
	public:
	AwesomeFunctionNamesCheck(StringRef Name, ClangTidyContext *Context)
	: ClangTidyCheck(Name, Context) {}
	void registerMatchers(ast_matchers::MatchFinder *Finder) override;
	void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
	};

	} // namespace readability
	} // namespace tidy
	} // namespace clang

	...

	Constructor of the check receives the ``Name`` and ``Context`` parameters, and
	must forward them to the ``ClangTidyCheck`` constructor.

	In our case the check needs to operate on the AST level and it overrides the
	``registerMatchers`` and ``check`` methods. If we wanted to analyze code on the
	preprocessor level, we'd need instead to override the ``registerPPCallbacks``
	method.

	In the ``registerMatchers`` method we create an AST Matcher (see `AST Matchers`_
	for more information) that will find the pattern in the AST that we want to
	inspect. The results of the matching are passed to the ``check`` method, which
	can further inspect them and report diagnostics.

	.. code-block:: c++

	using namespace ast_matchers;

	void AwesomeFunctionNamesCheck::registerMatchers(MatchFinder *Finder) {
	Finder->addMatcher(functionDecl().bind("x"), this);
	}

	void AwesomeFunctionNamesCheck::check(const MatchFinder::MatchResult &Result) {
	const auto *MatchedDecl = Result.Nodes.getNodeAs<FunctionDecl>("x");
	if (MatchedDecl->getName().startswith("awesome_"))
	return;
	diag(MatchedDecl->getLocation(), "function %0 is insufficiently awesome")
	<< MatchedDecl
	<< FixItHint::CreateInsertion(MatchedDecl->getLocation(), "awesome_");
	}

	(If you want to see an example of a useful check, look at
	`clang-tidy/google/ExplicitConstructorCheck.h
	<http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/clang-tidy/google/ExplicitConstructorCheck.h>`_
	and `clang-tidy/google/ExplicitConstructorCheck.cpp
	<http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/clang-tidy/google/ExplicitConstructorCheck.cpp>`_).


	Registering your Check
	----------------------

	(The ``add_new_check.py`` takes care of registering the check in an existing
	module. If you want to create a new module or know the details, read on.)

	The check should be registered in the corresponding module with a distinct name:

	.. code-block:: c++

	class MyModule : public ClangTidyModule {
	public:
	void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
	CheckFactories.registerCheck<ExplicitConstructorCheck>(
	"my-explicit-constructor");
	}
	};

	Now we need to register the module in the ``ClangTidyModuleRegistry`` using a
	statically initialized variable:

	.. code-block:: c++

	static ClangTidyModuleRegistry::Add<MyModule> X("my-module",
	"Adds my lint checks.");


	When using LLVM build system, we need to use the following hack to ensure the
	module is linked into the :program:`clang-tidy` binary:

	Add this near the ``ClangTidyModuleRegistry::Add<MyModule>`` variable:

	.. code-block:: c++

	// This anchor is used to force the linker to link in the generated object file
	// and thus register the MyModule.
	volatile int MyModuleAnchorSource = 0;

	And this to the main translation unit of the :program:`clang-tidy` binary (or
	the binary you link the ``clang-tidy`` library in)
	``clang-tidy/tool/ClangTidyMain.cpp``:

	.. code-block:: c++

	// This anchor is used to force the linker to link the MyModule.
	extern volatile int MyModuleAnchorSource;
	static int MyModuleAnchorDestination = MyModuleAnchorSource;


	Configuring Checks
	------------------

	If a check needs configuration options, it can access check-specific options
	using the ``Options.get<Type>("SomeOption", DefaultValue)`` call in the check
	constructor. In this case the check should also override the
	``ClangTidyCheck::storeOptions`` method to make the options provided by the
	check discoverable. This method lets :program:`clang-tidy` know which options
	the check implements and what the current values are (e.g. for the
	``-dump-config`` command line option).

	.. code-block:: c++

	class MyCheck : public ClangTidyCheck {
	const unsigned SomeOption1;
	const std::string SomeOption2;

	public:
	MyCheck(StringRef Name, ClangTidyContext *Context)
	: ClangTidyCheck(Name, Context),
	SomeOption(Options.get("SomeOption1", -1U)),
	SomeOption(Options.get("SomeOption2", "some default")) {}

	void storeOptions(ClangTidyOptions::OptionMap &Opts) override {
	Options.store(Opts, "SomeOption1", SomeOption1);
	Options.store(Opts, "SomeOption2", SomeOption2);
	}
	...

	Assuming the check is registered with the name "my-check", the option can then
	be set in a ``.clang-tidy`` file in the following way:

	.. code-block:: yaml

	CheckOptions:
	- key: my-check.SomeOption1
	value: 123
	- key: my-check.SomeOption2
	value: 'some other value'

	If you need to specify check options on a command line, you can use the inline
	YAML format:

	.. code-block:: console

	$ clang-tidy -config="{CheckOptions: [{key: a, value: b}, {key: x, value: y}]}" ...


	Testing Checks
	--------------

	To run tests for :program:`clang-tidy` use the command:

	.. code-block:: console

	$ ninja check-clang-tools

	:program:`clang-tidy` checks can be tested using either unit tests or
	`lit`_ tests. Unit tests may be more convenient to test complex replacements
	with strict checks. `Lit`_ tests allow using partial text matching and regular
	expressions which makes them more suitable for writing compact tests for
	diagnostic messages.

	The ``check_clang_tidy.py`` script provides an easy way to test both
	diagnostic messages and fix-its. It filters out ``CHECK`` lines from the test
	file, runs :program:`clang-tidy` and verifies messages and fixes with two
	separate `FileCheck`_ invocations: once with FileCheck's directive
	prefix set to ``CHECK-MESSAGES``, validating the diagnostic messages,
	and once with the directive prefix set to ``CHECK-FIXES``, running
	against the fixed code (i.e., the code after generated fix-its are
	applied). In particular, ``CHECK-FIXES:`` can be used to check
	that code was not modified by fix-its, by checking that it is present
	unchanged in the fixed code. The full set of `FileCheck`_ directives
	is available (e.g., ``CHECK-MESSAGES-SAME:``, ``CHECK-MESSAGES-NOT:``), though
	typically the basic ``CHECK`` forms (``CHECK-MESSAGES`` and ``CHECK-FIXES``)
	are sufficient for clang-tidy tests. Note that the `FileCheck`_
	documentation mostly assumes the default prefix (``CHECK``), and hence
	describes the directive as ``CHECK:``, ``CHECK-SAME:``, ``CHECK-NOT:``, etc.
	Replace ``CHECK`` by either ``CHECK-FIXES`` or ``CHECK-MESSAGES`` for
	clang-tidy tests.

	An additional check enabled by ``check_clang_tidy.py`` ensures that
	if `CHECK-MESSAGES:` is used in a file then every warning or error
	must have an associated CHECK in that file. Or, you can use ``CHECK-NOTES:``
	instead, if you want to also ensure that all the notes are checked.

	To use the ``check_clang_tidy.py`` script, put a .cpp file with the
	appropriate ``RUN`` line in the ``test/clang-tidy`` directory. Use
	``CHECK-MESSAGES:`` and ``CHECK-FIXES:`` lines to write checks against
	diagnostic messages and fixed code.

	It's advised to make the checks as specific as possible to avoid checks matching
	to incorrect parts of the input. Use ``[[@LINE+X]]``/``[[@LINE-X]]``
	substitutions and distinct function and variable names in the test code.

	Here's an example of a test using the ``check_clang_tidy.py`` script (the full
	source code is at `test/clang-tidy/google-readability-casting.cpp`_):

	.. code-block:: c++

	// RUN: %check_clang_tidy %s google-readability-casting %t

	void f(int a) {
	int b = (int)a;
	// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: redundant cast to the same type [google-readability-casting]
	// CHECK-FIXES: int b = a;
	}

	To check more than one scenario in the same test file use
	``-check-suffix=SUFFIX-NAME`` on ``check_clang_tidy.py`` command line or
	``-check-suffixes=SUFFIX-NAME-1,SUFFIX-NAME-2,...``.
	With ``-check-suffix[es]=SUFFIX-NAME`` you need to replace your ``CHECK-*``
	directives with ``CHECK-MESSAGES-SUFFIX-NAME`` and ``CHECK-FIXES-SUFFIX-NAME``.

	Here's an example:

	.. code-block:: c++

	// RUN: %check_clang_tidy -check-suffix=USING-A %s misc-unused-using-decls %t -- -- -DUSING_A
	// RUN: %check_clang_tidy -check-suffix=USING-B %s misc-unused-using-decls %t -- -- -DUSING_B
	// RUN: %check_clang_tidy %s misc-unused-using-decls %t
	...
	// CHECK-MESSAGES-USING-A: :[[@LINE-8]]:10: warning: using decl 'A' {{.*}}
	// CHECK-MESSAGES-USING-B: :[[@LINE-7]]:10: warning: using decl 'B' {{.*}}
	// CHECK-MESSAGES: :[[@LINE-6]]:10: warning: using decl 'C' {{.*}}
	// CHECK-FIXES-USING-A-NOT: using a::A;$
	// CHECK-FIXES-USING-B-NOT: using a::B;$
	// CHECK-FIXES-NOT: using a::C;$


	There are many dark corners in the C++ language, and it may be difficult to make
	your check work perfectly in all cases, especially if it issues fix-it hints. The
	most frequent pitfalls are macros and templates:

	1. code written in a macro body/template definition may have a different meaning
	depending on the macro expansion/template instantiation;
	2. multiple macro expansions/template instantiations may result in the same code
	being inspected by the check multiple times (possibly, with different
	meanings, see 1), and the same warning (or a slightly different one) may be
	issued by the check multiple times; :program:`clang-tidy` will deduplicate
	_identical_ warnings, but if the warnings are slightly different, all of them
	will be shown to the user (and used for applying fixes, if any);
	3. making replacements to a macro body/template definition may be fine for some
	macro expansions/template instantiations, but easily break some other
	expansions/instantiations.

	.. _lit: http://llvm.org/docs/CommandGuide/lit.html
	.. _FileCheck: http://llvm.org/docs/CommandGuide/FileCheck.html
	.. _test/clang-tidy/google-readability-casting.cpp: http://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/test/clang-tidy/google-readability-casting.cpp


	Running clang-tidy on LLVM
	--------------------------

	To test a check it's best to try it out on a larger code base. LLVM and Clang
	are the natural targets as you already have the source code around. The most
	convenient way to run :program:`clang-tidy` is with a compile command database;
	CMake can automatically generate one, for a description of how to enable it see
	`How To Setup Tooling For LLVM`_. Once ``compile_commands.json`` is in place and
	a working version of :program:`clang-tidy` is in ``PATH`` the entire code base
	can be analyzed with ``clang-tidy/tool/run-clang-tidy.py``. The script executes
	:program:`clang-tidy` with the default set of checks on every translation unit
	in the compile command database and displays the resulting warnings and errors.
	The script provides multiple configuration flags.

	* The default set of checks can be overridden using the ``-checks`` argument,
	taking the identical format as :program:`clang-tidy` does. For example
	``-checks=-*,modernize-use-override`` will run the ``modernize-use-override``
	check only.

	* To restrict the files examined you can provide one or more regex arguments
	that the file names are matched against.
	``run-clang-tidy.py clang-tidy/.*Check\.cpp`` will only analyze clang-tidy
	checks. It may also be necessary to restrict the header files warnings are
	displayed from using the ``-header-filter`` flag. It has the same behavior
	as the corresponding :program:`clang-tidy` flag.

	* To apply suggested fixes ``-fix`` can be passed as an argument. This gathers
	all changes in a temporary directory and applies them. Passing ``-format``
	will run clang-format over changed lines.


	On checks profiling
	-------------------

	:program:`clang-tidy` can collect per-check profiling info, and output it
	for each processed source file (translation unit).

	To enable profiling info collection, use the ``-enable-check-profile`` argument.
	The timings will be output to ``stderr`` as a table. Example output:

	.. code-block:: console

	$ clang-tidy -enable-check-profile -checks=-*,readability-function-size source.cpp
	===-------------------------------------------------------------------------===
	clang-tidy checks profiling
	===-------------------------------------------------------------------------===
	Total Execution Time: 1.0282 seconds (1.0258 wall clock)

	---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name ---
	0.9136 (100.0%) 0.1146 (100.0%) 1.0282 (100.0%) 1.0258 (100.0%) readability-function-size
	0.9136 (100.0%) 0.1146 (100.0%) 1.0282 (100.0%) 1.0258 (100.0%) Total

	It can also store that data as JSON files for further processing. Example output:

	.. code-block:: console

	$ clang-tidy -enable-check-profile -store-check-profile=. -checks=-*,readability-function-size source.cpp
	$ # Note that there won't be timings table printed to the console.
	$ ls /tmp/out/
	20180516161318717446360-source.cpp.json
	$ cat 20180516161318717446360-source.cpp.json
	{
	"file": "/path/to/source.cpp",
	"timestamp": "2018-05-16 16:13:18.717446360",
	"profile": {
	"time.clang-tidy.readability-function-size.wall": 1.0421266555786133e+00,
	"time.clang-tidy.readability-function-size.user": 9.2088400000005421e-01,
	"time.clang-tidy.readability-function-size.sys": 1.2418899999999974e-01
	}
	}

	There is only one argument that controls profile storage:

	* ``-store-check-profile=<prefix>``

	By default reports are printed in tabulated format to stderr. When this option
	is passed, these per-TU profiles are instead stored as JSON.
	If the prefix is not an absolute path, it is considered to be relative to the
	directory from where you have run :program:`clang-tidy`. All ``.`` and ``..``
	patterns in the path are collapsed, and symlinks are resolved.

	Example:
	Let's suppose you have a source file named ``example.cpp``, located in the
	``/source`` directory. Only the input filename is used, not the full path
	to the source file. Additionally, it is prefixed with the current timestamp.

	* If you specify ``-store-check-profile=/tmp``, then the profile will be saved
	to ``/tmp/<ISO8601-like timestamp>-example.cpp.json``

	* If you run :program:`clang-tidy` from within ``/foo`` directory, and specify
	``-store-check-profile=.``, then the profile will still be saved to
	``/foo/<ISO8601-like timestamp>-example.cpp.json``

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