| CTAGS-UNIVERSAL(7) | Universal-ctags | CTAGS-UNIVERSAL(7) |
ctags-universal - Universal-ctags parser definition language
ctags-universal [options] [file(s)] etags [options] [file(s)]
Exuberant-ctags, the ancestor of Universal-ctags, has provided the way to define a new parser from command line. Universal-ctags extends and refines this feature. optlib parser is the name for such parser in Universal-ctags. "opt" intents a parser is defined with combination of command line options. "lib" intents an optlib parser can be more than ad-hoc personal configuration.
This man page is for people who wants to define an optlib parser. The reader should read ctags(1) of Universal-ctags first. Following options are for defining (or customizing) a parser:
Following options are for controlling loading parser definition:
The design of options and notations for defining a parser in Exuberant-ctags may focus on reducing the number of typing by user. Reducing the number of typing is important for users who want to define (or customize) a parser quickly.
On the other hand, the design in Universal-ctags focuses on maintainability. The notation of Universal-ctags is redundant than that of Exuberant-ctags; the newly introduced kind should be declared explicitly, (long) names are approved than single letter flags specifying kinds, and naming rules are stricter.
This man page explains only stable options and flags. Universal-ctags also introduces experimental options and flags which have names starting with _. For documentation on these options and flags, visit Universal-ctags web site at https://ctags.io/.
Though it is possible to define a parser from command line, you don't want to type the same command line each time when you need the parser. You can store options for defining a parser into a file.
ctags-universal loads files (preload files) listed in "FILES" section of ctags(1) at program starting up. You can put your parser definition needed usually to the files.
--options=pathname, --options-maybe=pathname, and --optlib-dir=[+]directory are for loading optlib files you need occasionally. See "COMMAND LINE INTERFACE" section of ctags(1) for these options.
As explained in FILES section of ctags(1), options for defining a parser listed line by line in an optlib file. Prefixed white spaces are ignored. A line starting with '#' is treated as a comment. Escaping shell meta character is not needed.
Use ".ctags" as file extension for optlib file. You can define multiple parsers in an optlib file but it is better to make a file for each parser definition.
--_echo=msg and --_force-quit=[num] options are for debugging optlib parser.
You need know both the target language and the ctags' concepts (definition, reference, kind, role, field, extra). About the concepts, ctags(1) of Universal-ctags may help you.
Use --langdef=name option. NAME is referred as <LANG> in the later steps.
Use --map-<LANG>=[+|-]extension|pattern.
Use --kinddef-<LANG>=letter,name,description option. Universal-ctags introduces this option. Exuberant-ctags doesn't have. In Exuberant-ctags, a kind is defined as a side effect of specifying --regex-<LANG>= option. So user doesn't have a chance to recognize how important the definition of kind.
Use --regex-<LANG>=/regexp/replacement/[kind-spec/][flags] option.
As KIND-SPEC, you can use the letter defined with --kinddef-<LANG>=letter,name,description option.
This is the definition (pod.ctags) used in ctags for parsing pod (https://perldoc.perl.org/perlpod.html) file.
--langdef=pod --map-pod=+.pod --kinddef-pod=c,chapter,chapters --kinddef-pod=s,section,sections --kinddef-pod=S,subsection,subsections --kinddef-pod=t,subsubsection,subsubsections --regex-pod=/^=head1[ \t]+(.+)/\1/c/ --regex-pod=/^=head2[ \t]+(.+)/\1/s/ --regex-pod=/^=head3[ \t]+(.+)/\1/S/ --regex-pod=/^=head4[ \t]+(.+)/\1/t/
The names of built-in parsers are capitalized. When ctags-universal evaluates an option in a command line, and chooses a parser, ctags-universal uses the names of parsers in a case-insensitive way. Therefore, giving a name started from a lowercase character doesn't help you to avoid the parser name confliction. However, in a tags file, ctags-universal prints parser names in a case-sensitive way; it prints a parser name as specified in --langdef= option. Therefore, we recommend you to give a name started from a lowercase character to your private optlib parser. With this convention, people can know where a tag entry in a tag file comes from a built-in parser or a private optlib parser.
letter must be an alphabetical character ('[0-9a-zA-EG-Z]') other than "F". "F" has been reserved for representing a file since Exuberant-ctags.
name also must come from alphabetical characters ('[0-9a-zA-Z]+'). Do not use "file" as name. It has been reserved for representing a file since Exuberant-ctags.
description comes from any printable ASCII characters. The exception is "{" and "". "{" is reserved for adding flags this option in the future. So put "" before "{" to include "{" to a description. To include "" itself to a description, put "" before "".
Both letter, name and their combination must be unique in a <LANG>.
This option is newly introduced in Universal-ctags. This option reduces the typing defining a regex pattern with --regex-<LANG>=, and keeps the consistency of kind definitions in a language.
The letter can be used as an argument for --kinds-<LANG> option to enable or disable the kind. Unless K field is enabled, the letter is used as value in the "kind" extension field in tags output.
The name surrounded by braces can be used as an argument for --kind-<LANG> option. If K field is enabled, the name is used as value in the "kind" extension field in tags output.
The description and letter are listed in --list-kinds output. All three elements of kind-spec are listed in --list-kinds-full output. Don't use braces in the description. They will be used meta characters in the future.
Unless modified by flags, regexp is interpreted as a Posix extended regular expression. The replacement should expand for all matching lines to a non-empty string of characters, or a warning message will be reported unless {placeholder} regex flag is specified. An optional kind specifier for tags matching regexp may follow replacement, which will determine what kind of tag is reported in the "kind" extension field (see ctags-tags(5)).
kind-spec has two forms: letter only form and full form. The letter form assumes using --regex-<LANG> option with --kinddef-<LANG> option. The kind-spec in --regex-<LANG> option just refers a letter defined with --kinddef-<LANG>. This form is recommended in Universal-ctags.
The full form of kind-spec is in the form of a single letter, a comma, a name (only out of alphabetical characters), a comma, a description. See the description of --kinddef-<LANG>=letter,name,description option about how the elements are used.
Either the kind name and/or the description can be omitted. However, unless the letter is not defined with --kinddef-<LANG> option, omitting is not recommended in in Universal-ctags. The omitting form is supported only for keeping the compatibility with Exuberant-ctags. Supporting the omitting form will be removed from Universal-ctags in the future. If kind-spec is omitted, it defaults to "r,regex".
About flag, see "Flags for --regex-<LANG> option".
For more information on the regular expressions used by ctags-universal, see either the regex(5,7) man page, or the GNU info documentation for regex (e.g. "info regex").
You can specify more than one flag at the end of --regex-<LANG> to control how Universal-ctags uses the pattern.
Exuberant-ctags uses a letter to represent a flag. In Universal-ctags, a name surrounded by braces (name form) can be used in addition to letter. The name form makes a user reading an optlib file easier. The most of all flags newly added in Universal-ctags don't have the letter representation. All of them have only the name representation. --list-regex-flags lists all the flags.
scope=ref|push|pop|clear|set
A parser programmed with --regex-<LANG> has a stack (scope stack) internally. You can use it for tracking scope information. The scope=... flag is for manipulating and utilizing the scope stack.
If {scope=push} is specified, a tag captured with --regex-<LANG> is pushed to the stack. {scope=push} implies {scope=ref}.
You can fill the scope field of captured tag with {scope=ref}. If {scope=ref} flag is given, ctags-universal attaches the tag at the top to the tag captured with --regex-<LANG> as the value for the scope: field.
ctags-universal pops the tag at the top of the stack when --regex-<LANG> with {scope=pop} is matched to the input line.
Specifying {scope=clear} removes all the tags in the scope. Specifying {scope=set} removes all the tags in the scope, and then pushes the captured tag as {scope=push} does.
In some cases, you may want to use --regex-<LANG> only for its side effects: using it only to manipulate the stack but not for capturing a tag. In such a case, make replacement component of --regex-<LANG> option empty while specifying {placeholder} as a regex flag. For example, a non-named tag can be put on the stack by giving a regex flag {scope=push}{placeholder}.
You may wonder what happens if a regex pattern with {scope=ref} flag matches an input line but the stack is empty, or a non-named tag is at the top. If the regex pattern contains a {scope=ref} flag and the stack is empty, the {scope=ref} flag is ignored and nothing is attached to the scope: field.
If the top of the stack contains an unnamed tag, ctags-universal searches deeper into the stack to find the top-most named tag. If it reaches the bottom of the stack without finding a named tag, the {scope=ref} flag is ignored and nothing is attached to the scope: field.
When a named tag on the stack is popped or cleared as the side effect of a pattern matching, ctags-universal attaches the line number of the match to the end: field of the named tag.
ctags-universal clears all of the tags on the stack when it reaches the end of the input source file. The line number of the end is attached to the end: field of the cleared tags.
Four things, an input source file, an optlib file, a command line invoking ctags, and output makes an example.
Let's think about writing a parser for a very small subset of the Ruby language.
input source file ("input.srb"):
class Example
def methodA
puts "in class_method"
end
def methodB
puts "in class_method"
end end
The parser for the input should capture "Example" with class kind, "methodA", and "methodB" with method kind. "methodA" and "methodB" should have "Example" as their scope. end: fields of each tag should have proper values.
optlib file ("sub-ruby.ctags"):
--langdef=subRuby
--map-subRuby=.srb
--kinddef-subRuby=c,class,classes
--kinddef-subRuby=m,method,methods
--regex-subRuby=/^class[ \t]+([a-zA-Z][a-zA-Z0-9]+)/\1/c/{scope=push}
--regex-subRuby=/^end///{scope=pop}{placeholder}
--regex-subRuby=/^[ \t]+def[ \t]+([a-zA-Z][a-zA-Z0-9_]+)/\1/m/{scope=push}
--regex-subRuby=/^[ \t]+end///{scope=pop}{placeholder}
command line and output:
$ ctags --quiet --options=NONE --fields=+eK \ --options=./sub-ruby.ctags -o - input.srb Example input.srb /^class Example$/;" class end:8 methodA input.srb /^ def methodA$/;" method class:Example end:4 methodB input.srb /^ def methodB$/;" method class:Example end:7
The official Universal-ctags web site at:
https://ctags.io/
Universal-ctags project https://ctags.io (This man page partially derived from ctags(1) of Executable-ctags)
Darren Hiebert <dhiebert@users.sourceforge.net> http://DarrenHiebert.com/
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