@node VCS To ChangeLog
@section VCS To ChangeLog

@c Copyright (C) 2020--2021 Free Software Foundation, Inc.

@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.

@cindex VCS To ChangeLog
@findex vcs-to-changelog

Gnulib provides the @samp{vcs-to-changelog} module to generate an output
similar to the GNU ChangeLog format from metadata of source control software
such as git.  Here's an example of using @samp{vcs-to-changelog}:

@example
build-aux/vcs-to-changelog.py <from_ref> <to_ref>
@end example

where @code{<from_ref>} and @code{<to_ref>} refer to the range of commits to
generate the output.

VCS To ChangeLog currently recognises changes in C source code and can traverse
commits in git.  Additional source frontends and source control backends may be
added to the module. @samp{vcs-to-changelog} takes the following optional
arguments:

@itemize
@item @code{-d}: Run the parser debugger, used for debugging
@samp{vcs-to-changelog}
@item @code{-q filename}: Load @var{filename} as the quirks file for the
project.
@end itemize

The quirks file is a python module that must minimally implement a
@code{get_project_quirks} function that returns an object of type
@code{ProjectQuirks} or its subclass.  The subclass may override the following
members of @code{ProjectQuirks}:

@itemize @bullet
@item @code{repo}: Specify the project repo source control.  The default value
is @code{git}.

@item @code{IGNORE_LIST}: A list of files to ignore in the changesets, either
because they are not needed (such as the ChangeLog) or because they are
not parseable.  For example, the GNU C Library has a header file that is only
assembly code, which breaks the C parser.

@item @code{MACRO_QUIRKS}: A list of dictionary entries with indexes as
@code{orig} and @code{sub} where @code{orig} is a Python regular expression
pattern to match and @code{sub} is the substitution.  These substitutions are
used to work around C/C++ macros that are known to break parsing of C programs.

@item @code{C_MACROS}: This is a list of C preprocessor macro definitions that
are extensively used and are known to break parsing due to some characteristic,
mainly the lack of a semicolon at the end.

@end itemize
