21.11.1 Source File Tag Syntax

Here is how tag syntax is defined for the most popular languages:

• In C code, any C function or typedef is a tag, and so are definitions of struct, union and enum. You can tag function declarations and external variables in addition to function definitions by giving the ‘--declarations’ option to etags. #define macro definitions and enum constants are also tags, unless you specify ‘--no-defines’ when making the tags table. Similarly, global variables are tags, unless you specify ‘--no-globals’. Use of ‘--no-globals’ and ‘--no-defines’ can make the tags table file much smaller.
• In C++ code, in addition to all the tag constructs of C code, member functions are also recognized, and optionally member variables if you use the ‘--members’ option. Tags for variables and functions in classes are named ‘class::variable’ and ‘class::function’. operator functions tags are named, for example ‘operator+’.
• In Java code, tags include all the constructs recognized in C++, plus the interface, extends and implements constructs. Tags for variables and functions in classes are named ‘class.variable’ and ‘class.function’.
• In LaTeX text, the argument of any of the commands \chapter, \section, \subsection, \subsubsection, \eqno, \label, \ref, \cite, \bibitem, \part, \appendix, \entry, or \index, is a tag.

  Other commands can make tags as well, if you specify them in the environment variable TEXTAGS before invoking etags. The value of this environment variable should be a colon-separated list of command names. For example,

  TEXTAGS="def:newcommand:newenvironment"
  export TEXTAGS
  

  specifies (using Bourne shell syntax) that the commands ‘\def’, ‘\newcommand’ and ‘\newenvironment’ also define tags.

• In Lisp code, any function defined with defun, any variable defined with defvar or defconst, and in general the first argument of any expression that starts with ‘(def’ in column zero, is a tag.
• In Scheme code, tags include anything defined with def or with a construct whose name starts with ‘def’. They also include variables set with set! at top level in the file.

Several other languages are also supported:

• In Ada code, functions, procedures, packages, tasks, and types are tags. Use the ‘--packages-only’ option to create tags for packages only.

  With Ada, it is possible to have the same name used for different entity kinds (e.g. the same name for a procedure and a function). Also, for things like packages, procedures and functions, there is the spec (i.e. the interface) and the body (i.e. the implementation). To facilitate the choice to the user, a tag value is appended with a qualifier:

  function

  /f

  procedure

  /p

  package spec

  /s

  package body

  /b

  type

  /t

  task

  /k

  So, as an example, M-x find-tag bidule/b will go directly to the body of the package bidule while M-x find-tag bidule will just search for any tag bidule.

• In assembler code, labels appearing at the beginning of a line, followed by a colon, are tags.
• In Bison or Yacc input files, each rule defines as a tag the nonterminal it constructs. The portions of the file that contain C code are parsed as C code.
• In Cobol code, tags are paragraph names; that is, any word starting in column 8 and followed by a period.
• In Erlang code, the tags are the functions, records, and macros defined in the file.
• In Fortran code, functions, subroutines and blockdata are tags.
• In makefiles, targets are tags.
• In Objective C code, tags include Objective C definitions for classes, class categories, methods, and protocols.
• In Pascal code, the tags are the functions and procedures defined in the file.
• In Perl code, the tags are the procedures defined by the sub, my and local keywords. Use ‘--globals’ if you want to tag global variables.
• In PostScript code, the tags are the functions.
• In Prolog code, a tag name appears at the left margin.
• In Python code, def or class at the beginning of a line generate a tag.

You can also generate tags based on regexp matching (see Etags Regexps) to handle other formats and languages.