Masatake YAMATO <>

You are welcome.

Supporting many parsers with few developers is impossible. We invite the person who contributes a parser to u-ctags team, especially if the target language is updated frequently. TypeScript is a typical frequently updated language.

This is what we would like potential contributors to know. In this section “you” means a contributor, and “we” means reviewers. “I” means Masatake YAMATO, the author of this section.

This page gathers random notes for newly joined members.

Basic rules

You are the maintainer of your parser, of course.

You may update your parser as you want under the rules described later.

You may review pull requests changing your parser.

A parser exists and is maintained independently form other parsers. However, considering the consistency between parsers are not bad.

You can put your name to docs/developers.rst.


Before You Start

When working on ctags I take into account the following uses for tags:

  1. inserting the name with completion,

  2. jumping to the definition of the name (in an editor or similar tool),

  3. navigating the source code tree,

  4. summarizing the source code tree, and

  5. answering a query about the source code tree.

When I review new parser code, I expect the parser to contribute to these purposes.

What should be tagged?

There are two classes of tags. The primary class is a definition tag. If a name is defined in a file, the name and the line and the file where the name is defined should be tagged (recorded). However, in some languages answering, “What is a definition?” is not so obvious. You may have to decide what is tagged in your parser thoughtfully. The purposes listed at the top of this subsection should help you decide.

The secondary class is a reference tag. This is newly introduced in Universal Ctags and is not available in Exuberant Ctags. If a name is used (or referenced) in a file, it can be tagged as a reference tag.

Don’t be confused by the two tag classes.

Defining kinds and roles

Defining kinds is the most important task in writing a new parser. Once a kind is introduced, we cannot change it because it breaks tags file compatibility.

See TAG ENTRIES in ctags(1) for more details of kinds and roles.

Scope information and full qualified tags

Optional. TBW.

Developing a parser

Origin of changes and license

Make clear where the patches come from and who wrote them.

If you backport patches from Geany or some other project, their commit IDs should be logged, too.

Include a copyright notice when adding a new {parsers,main}/*.[ch] file. A new file also requires a license notice at the head of the file.

We expect your change (or new code) to be provided under the terms of the General Public License version 2 or any later version. We would like you to express “version 2 or any later version”.


In the comment at the head of your source file, include a URL for a web page that explains the language your parser deals with. Especially if the language is not well known.

Here is an example.

*   Copyright (c) 2016, Masatake YAMATO
*   Copyright (c) 2016, Red Hat, K.K.
*   This source code is released for free distribution under the terms of the
*   GNU General Public License version 2 or (at your option) any later version.
*   This module contains functions for generating tags for property list defined
*   in

C language

Don’t forget to use static modifiers. Don’t introduce unnecessary global variables.

Remove unused variables and types. If you want to keep them in your source code, include a descriptive comment.

Use the available facilities provided by the ctags core. If the facilities are not enough for writing a parser, consider extending the core first.

Use underscores in names only in file scope objects. Don’t use them in function declarations, variable declarations or macro names in header files.

Basic whitespace settings are specified in the EditorConfig configuration file (.editorconfig). There are plugins available for most popular editors to automatically configure these settings.

Style guidelines are largely captured in the Uncrustify configuration file (.uncrustify.cfg). Formatting can be checked with:

$ uncrustify -c .uncrustify.cfg -f parsers/awk.c | diff -u parsers/awk.c -

Don’t mix whitespace cleanup fixes and other improvements in one commit when changing the existing code. Style fixes, including whitespace cleanup, should be in a separate commit. Mixing functional changes with style fixes makes reviewing harder.

If possible, don’t use file static variables. Find an alternative way that uses parameters.

Notes for GNU emacs users

If you use GNU emacs, utilize the .editorconfig configuration based on non-GNU C style. Here non-GNU C style means “align a keyword for control flow and { of the block start”.

GNU style:

if (...)

non-GNU style:

if (...)

For combining the style and .editorconfig configuration, put following code snippet to your .emacs:

(add-hook 'hack-local-variables-hook
        (lambda () (editorconfig-apply)))

.dir-locals.el in ctags source tree applies “linux” style of cc-mode. Above code snippet applies the .editorconfig configuration AFTER installing the “linux” style to the current buffer.

I like GNU style, but for keeping consistency in existing code of Exuberant Ctags, the origin of Universal Ctags, I introduced the style and configuration to my .emacs. Please, do the same.


We are trying to maintain compatibility with Exuberant-ctags in the following two areas.

  • Command line option

  • Tag file compatibility

Command line options

Don’t introduce --<LANG>-foo=… style options. They are less suitable for command-line completion by the zsh/bash completion engines. Instead, introduce --foo-<LANG>=… style options.

Add an entry to docs/news.rst if you change the behavior of an option or introduce a new option. If you think the option is stable enough, add it to, too.

Use underscore as a prefix for experimental options. Once an option is introduced, it must be maintained. We don’t want to remove it later. If you are not sure of the usefulness of the option, use an underscore at the start of a long option name like: --_echo.

Write a test case for Tmain or Units.

Don’t remove an option, especially if it exists in Exuberant Ctags.

Writing parser

There are two ways to write a parser, writing in C and using optlib parser.

Universal Ctags extends the optlib parser feature so extensively that it can implement most of functions of a parser. optlib parser is also suitable for prototyping.

See ctags-optlib(7) and Extending ctags with Regex parser (optlib) for details. See Translating an option file into C source code (optlib2c) how to add a optlib parser on ctags.

For writing a parser in C see Writing a parser in C.

Build script

To add your optlib parser, foo.ctags, into ctags do the following steps;

  • put foo.ctags file on optlib/ directory

  • add foo.ctags on OPTLIB2C_INPUT variable in source.mak

  • add fooParser on PARSER_LIST macro variable in main/parser_p.h

  • add foo on the list in the section “New parsers” in docs/news.rst

  • add "..\optlib\foo.c" in win32/ctags_vs2013.vcxproj

  • add "..\optlib\foo.c" in win32/ctags_vs2013.vcxproj.filters

Translated C code is also committed to our git repository. The translated code is useful for building ctags on the platforms where optlib2c doesn’t run.

To add your parser file, foo.c, into ctags do the following steps;

  • put foo.c file on parsers/ directory

  • add foo.c on PARSER_SRCS variable in sources.mak

  • add foo on the list in the section “New parsers” in docs/news.rst

  • add "..\parsers\foo.c" in win32/ctags_vs2013.vcxproj

  • add "..\parsers\foo.c" in win32/ctags_vs2013.vcxproj.filters

If you have GNU make, make -C win32 updates the win32 files described above from makefile.mak. Without updating win32 files our CI process run on Appveyor will fail.

See this pull request for the Meson parser as an example of optlib parser.


Add test cases, and run both existing cases and your new cases.

If you add a new parser or modify an existing parser, add new test cases to “Units”. If you modify the core, add new test cases to “Tmain”. The way to write and run test cases is described in Testing ctags and Testing a parser section of this guide.

With the exception of the tmain test harness, you can specify VG=1 for running test cases under the Valgrind memory debugger.

A parse should not enter an infinite loop for bad input. A parse should not crash for bad input. A parse should return control to its caller for bad input.

Describe what kind of tests are passed in the commit message. e.g.

make units LANGUAGES=TTCN VG=1 is passed.
make fuzz LANGUAGES=TTCN VG=1  is passed.
make chop LANGUAGES=TTCN VG=1  is passed.

Test cases

Add a test case to Unit when creating or modifying a parser.

Add a test case to Tmain when modifying the core.

Add a test case to Tinst when modifying the install target in the Makefile.

Testing your parser

If possible, prepare a simple test and a complex one. The simple one for helping us, the maintainers, understand the intent of the modification.

If there are more than 3 test cases for a parser, a parser specific test case directory should be prepared like Units/parser-c.r.

Add realistic examples for you parser to codebase

At codebase, we collect realistic examples that can be used for evaluating your parser especially about its performance aspect. Consider contributing to the repository when adding a new parser to Universal Ctags.

Writing Documents

  • man/*.rst files are the source files of our man pages. The man pages are for users. See “How to add a new man page for your parser”.

  • docs/*.rst files explain experimental new features. The files are for developers. The parts of contents of docs/*.rst should be moved to man/*.rst in the future.

  • Update docs/news.rst especially if you add a new parser.

  • Write docs/parser-<NAME-OF-YOUR-PARSER>.rst as you want. A FAQ and the design or your parser are common topics. Consider the maintenance of your parser after you left the project for some reason.

How to add a new man page for your parser

  1. write what the users of your parser may want to (or should) know to man/

  2. add man/ctags-lang-LANGUAGE.7 to GEN_IN_MAN_FILES of man/

  3. run make -C man update-docs. This step generates the rst file at docs/man/ctags-lang-LANGUAGE.7.rst.

  4. add ctags-lang-LANGUAGE(7) to (toctree of) docs/man-pages.rst.

  5. do git add for
    • man/

    • docs/man/ctags-lang-LANGUAGE.7.rst

  6. git commit with a log header: “docs(man): add a man page for LANGUAGE”.

  7. make a pull request

Committing and submitting a pull request

  • Make a pull request even if the change is small enough.

  • Wait for one day till merging even if the change is small enough.

  • Wait for 3 days at least for non-small change to your parser.

  • Wait for 7 days at least and get an LGTM (Looks Good To Me) comment from a member of the team if your commit changes the other parts than your parser and the changes are not obvious.

  • Add a test case to your pull request. To make git-bisect happy, don’t add a test case for a feature or a bugfix before adding the code for the feature or the bugfix.

  • Even if a pull request includes multiple commits, each commit must be semantically well separated. Sometimes you may want to adjust whitespaces in the code. Adjusting whitespaces is o.k., but don’t mix the other change with it. Make a commit just for the whitespaces adjustment.

Title of commit log and pull request

  • “Misc Fixes” is allowed as far as each commit in a pull request is semantically well separated. Sometimes, you may fix various minor things randomly. Making pull requests for each of them is boring. You may want to make “mix fixes” pull request especially if your code is young.

  • Use [WIP] (Work In Progress) prefix as the title of your pull request, if you don’t want people to take time for reviewing your code. Removing [WIP] implies “ready to be reviewed.”

  • Use [FYI] (For Your Information) prefix as the title to show your idea or sketch represented in C language.

  • Use the name of your parser as the prefix of a commit log.

    C++: record template type parameters to detect the end of template prefix
    If we know Foo is a name of type, it becomes easier to detect whether
    ">>" in "Foo>>" is a shift operator or the end marker of the template

    In the above example, “C++: “ is the prefix.

  • Use the name of your parser as the prefix of a pull request if your change is about a parser.

  • Use following prefixes for the changes other than parsers.


    Changes for files under main/ directory


    Changes for the test cases under Units/ directory


    Changes for the test cases under Tmain/ directory


    Changes for the test harness (misc/ itself


    Changes for the docs/*.rst


    Changes for the man/*.rst


    Changes operators that can be used in optscript command


    Changes operators that can be used in optlib {{}} blocks


    Changes optlib procedures defined in main/

    CXX (or Cxx)

    Changes affecting all parsers defined in parsers/cxx

    See also the output of git log command.

  • Combine prefixes with a comma if a change modifies multiple parts of our source tree

    Here is an example.

    commit 64a05963c108af4b7832a2215006ff5cafcaaebb
    Author: Masatake YAMATO <>
    Date:   Tue Mar 19 12:19:37 2019 +0900
    main,Flex,JavaScript,SQL,refactor: introduce a helper function to skip two character sequence
  • Use following prefixes if the change as no run-time impact.

    • Remove whitespaces at the end of lines

    • Adjust indentation

    • Remove an empty line

    • Rename symbol names

    • Code transformation that doesn’t intent changing run-time behavior

    These prefixes reduce the load of reviewers.

  • Use [INCOMPATIBLE] as a prefix for both pull request and commit log if the change breaks the compatibility with Exuberant Ctags. Write an explanation in man/ about the detail of breakage.

  • Use [SELF-INCOMPATIBLE] as a prefix for both pull request and commit log if the change breaks the compatibility with Universal Ctags itself.

Commit log

(For new parsers the following criteria is not applicable.)

Make clear the original motivation for the change and/or the impact on the tags file.

If you fix a bug reported somewhere on the web, its URL should be logged, too.

If the bug is reported in the Exuberant Ctags tracker on the SourceForge web site, log it as sf-bugs:N, sf-patches:N, sf-support-requests:N, or sf-feature-requests:N. docs/tracking.rst also should be updated.

Squashing commits

When you submit a pull request you might receive some comments from a reviewer and, in response, update your patches. After updating, we would like you to squash your patches into logical units of work before we merge them to keep the repository history as simple as possible.

  • Use git rebase -i and git push --force to refine your change in the meaning of “semantically well separated.” “semantically well separated” is important than “recording the history of your try and error.”

Quoted from @steveno in #393 :

You can check out this page for a good example of how to squash commits

Once you’ve squashed all your commits, simply do a git push -f to your fork, and GitHub will update the pull request for you automatically.

Rules for reviewing a pull request

  • Put your rough schedule as a comment if you don’t have time, but you want to review.

Testing a PR locally before being merged

You may want to test a PR locally before it is merged into the master repository.

If you want to test a PR #2234 on a repository upstream as branch name BRANCHNAME;:

$ git fetch upstream pull/2234/head:BRANCHNAME
$ git checkout BRANCHNAME

This creates a branch BRANCHNAME, and pulls the PR into the branch, and switches to the branch. The branch name BRANCHNAME does not have to be the same as the branch name of the PR.

Alternatively suppose you want to test USERNAME’s PR with branch name main-fix-foo;:

git checkout -b tmp-main-fix-foo master
git pull main-fix-foo

This creates a branch tmp-main-fix-fix-foo from a branch master and switches to it, then pulls the branch main-fix-foo from