path: root/ebuild-vars.tex

\chapter{Ebuild-defined Variables}
\label{sec:ebuild-vars}

\note This section describes variables that may or must be defined by ebuilds. For
variables that are passed from the package manager to the ebuild, see section~\ref{sec:ebuild-env-vars}.

\section{Metadata invariance}
\label{sec:metadata-invariance}

All ebuild-defined variables discussed in this chapter must be defined independently of
any system, profile or tree dependent data, and must not vary depending upon the ebuild
phase. In particular, ebuild metadata can and will be generated on a different system from that upon
which the ebuild will be used, and the ebuild must generate identical metadata every time it
is used.

Globally defined ebuild variables without a special meaning must similarly not rely upon
variable data.

\section{Mandatory Ebuild-defined Variables}

All ebuilds must define at least the following variables:

\begin{description}
\item[DESCRIPTION] A short human-readable description of the package's purpose. May be defined by an
    eclass. Must not be empty.
\item[HOMEPAGE] The URI or URIs for a package's homepage, including protocols. May be defined by an
    eclass. See section~\ref{sec:dependencies} for full syntax.
\item[IUSE] The \t{USE} flags used by the ebuild. Any eclass that works with \t{USE} flags
    must also set \t{IUSE}, listing only the variables used by that eclass. The package manager is
    responsible for merging these values. See section~\ref{sec:use-iuse-handling} for discussion on
    which values must be listed this variable.

    \featurelabel{iuse-defaults} In EAPIs shown in table~\ref{tab:iuse-defaults-table} as supporting
    \t{IUSE} defaults, any use flag name in \t{IUSE} may be prefixed by at most one of a plus or a
    minus sign. If such a prefix is present, the package manager may use it as a suggestion as to
    the default value of the use flag if no other configuration overrides it.
\item[KEYWORDS] A whitespace separated list of keywords for the ebuild. Each token must be a
    valid keyword name, as per section~\ref{sec:keyword-names}. May include \t{-*}, which
    indicates that the package will only work on explicitly listed archs. May include \t{-arch},
    which indicates that the package will not work on the specified arch. May be empty, which
    indicates uncertain functionality on any architecture. May be defined in an eclass.
\item[LICENSE] The package's license. Each text token must correspond to a tree ``licenses/'' entry
    (see section~\ref{sec:licenses-dir}). See section~\ref{sec:dependencies} for full syntax.
    May be defined by an eclass. \label{ebuild-var-LICENSE}
\item[SLOT] The package's slot. Must be a valid slot name, as per section~\ref{sec:slot-names}. May
    be defined by an eclass. Must not be empty.
\item[SRC\_URI] A list of source URIs for the package. Valid protocols are \t{http://},
    \t{https://}, \t{ftp://} and \t{mirror://} (see section~\ref{sec:thirdpartymirrors} for mirror
    behaviour). Fetch restricted packages may include URL parts consisting of just a filename.
    May be defined by an eclass. See section~\ref{sec:dependencies} for full syntax.
\end{description}

If any of these variables are undefined, or if any of these variables are set to invalid values,
the package manager's behaviour is undefined; ideally, an error in one ebuild should not prevent
operations upon other ebuilds or packages.

\begin{centertable}{EAPIs supporting \t{IUSE} defaults} \label{tab:iuse-defaults-table}
    \begin{tabular}{ l l }
        \toprule
        \multicolumn{1}{c}{\textbf{EAPI}} &
        \multicolumn{1}{c}{\textbf{Supports \t{IUSE} defaults?}} \\
        \midrule
    \t{0} & No \\
    \t{1} & Yes \\
    \t{2} & Yes \\
    \t{3} & Yes \\
    \t{4} & Yes \\
    \bottomrule
    \end{tabular}
\end{centertable}

\section{Optional Ebuild-defined Variables}

Ebuilds may define any of the following variables:

\begin{description}
\item[DEPEND] See section~\ref{sec:dependencies}.
\item[EAPI] The EAPI. See below.
\item[PDEPEND] See section~\ref{sec:dependencies}.
\item[RDEPEND] See section~\ref{sec:dependencies}. For some EAPIs, \t{RDEPEND} has special behaviour
    for its value if unset and when used with an eclass. See section~\ref{sec:rdepend-depend} for
    details.
\item[RESTRICT] Zero or more behaviour restrictions for this package. See section~\ref{sec:restrict}
    for value meanings and section~\ref{sec:dependencies} for full syntax.
\item[PROPERTIES] \featurelabel{properties} Zero or more properties for this package. See
    section~\ref{sec:properties} for value meanings and section~\ref{sec:dependencies} for full
    syntax. For EAPIs listed in table~\ref{tab:optional-vars-table} as having optional support,
    ebuilds must not rely upon the package manager recognising or understanding this variable in
    any way.
\item[REQUIRED\_USE] \featurelabel{required-use} Zero or more assertions that must be met by the
    configuration of \t{USE} flags to be valid for this ebuild. See section~\ref{sec:required-use}
    for description and section~\ref{sec:dependencies} for full syntax. Only in EAPIs listed in
    table~\ref{tab:optional-vars-table} as supporting \t{REQUIRED\_USE}.
\end{description}

\begin{centertable}{EAPIs supporting various ebuild-defined variables}
\label{tab:optional-vars-table}
    \begin{tabular}{ l l l }
        \toprule
        \multicolumn{1}{c}{\textbf{EAPI}} &
        \multicolumn{1}{c}{\textbf{Supports \t{PROPERTIES}?}} &
        \multicolumn{1}{c}{\textbf{Supports \t{REQUIRED\_USE}?}} \\
        \midrule
    \t{0} & Optionally & No \\
    \t{1} & Optionally & No \\
    \t{2} & Optionally & No \\
    \t{3} & Optionally & No \\
    \t{4} & Yes & Yes \\
    \bottomrule
    \end{tabular}
\end{centertable}

\subsection{EAPI}
\label{sec:pre-source-eapi}

An empty or unset \t{EAPI} value is equivalent to \t{0}. Ebuilds must not assume that they will get
a particular one of these two values if they are expecting one of these two values.

The package manager must either pre-set the \t{EAPI} variable to \t{0} or ensure that it is unset
before sourcing the ebuild for metadata generation. When using the ebuild for other purposes, the
package manager must either pre-set \t{EAPI} to the value specified by the ebuild's metadata or
ensure that it is unset.

If any of these variables are set to invalid values, the package manager's behaviour is undefined;
ideally, an error in one ebuild should not prevent operations upon other ebuilds or packages.

If the EAPI is to be specified in an ebuild, the \t{EAPI} variable must be assigned to precisely
once. The assignment must not be preceded by any lines other than blank lines or those that start
with optional whitespace (spaces or tabs) followed by a \t{\#} character, and the line containing
the assignment statement must match the following regular expression:
\begin{verbatim}
^[ \t]*EAPI=(['"]?)([A-Za-z0-9+_.-]*)\1[ \t]*(#.*)?$
\end{verbatim}

The package manager may optionally determine the EAPI of an ebuild by parsing its first non-blank
and non-comment line, using above regular expression. If a recognised EAPI has been determined
such, then the package manager must make sure that the \t{EAPI} value obtained by sourcing the
ebuild with bash is identical to the EAPI obtained by parsing. The ebuild must be treated as
invalid if these values are different.

\subsection{\t{RDEPEND} value}
\label{sec:rdepend-depend}

\featurelabel{rdepend-depend} In EAPIs listed in table~\ref{tab:rdepend-depend-table} as having
\t{RDEPEND=DEPEND}, if \t{RDEPEND} is unset (but not if it is set to an empty string) in an ebuild,
when generating metadata the package manager must treat its value as being equal to the value of
\t{DEPEND}.

When dealing with eclasses, only values set in the ebuild itself are considered for this behaviour;
any \t{DEPEND} or \t{RDEPEND} set in an eclass does not change the implicit \t{RDEPEND=DEPEND} for
the ebuild portion, and any \t{DEPEND} value set in an eclass does not get treated as being part of
\t{RDEPEND}.

\begin{centertable}{EAPIs with \t{RDEPEND=DEPEND} Default} \label{tab:rdepend-depend-table}
    \begin{tabular}{ l l }
        \toprule
        \multicolumn{1}{c}{\textbf{EAPI}} &
        \multicolumn{1}{c}{\textbf{\t{RDEPEND=DEPEND}?}} \\
        \midrule
    \t{0} & Yes \\
    \t{1} & Yes \\
    \t{2} & Yes \\
    \t{3} & Yes \\
    \t{4} & No \\
    \bottomrule
    \end{tabular}
\end{centertable}

\section{Magic Ebuild-defined Variables}

The following variables must be defined by \t{inherit} (see section~\ref{sec:inherit}, and may be
considered to be part of the ebuild's metadata:

\begin{description}
\item[ECLASS] The current eclass, or unset if there is no current eclass. This is handled magically
    by \t{inherit} and must not be modified manually.
\item[INHERITED] List of inherited eclass names. Again, this is handled magically by \t{inherit}.
\end{description}

\note Thus, by extension of section~\ref{sec:metadata-invariance}, \t{inherit} may not be used
    conditionally, except upon constant conditions.

The following are special variables defined by the package manager for internal use and may or may
not be exported to the ebuild environment:

\begin{description}
\item[DEFINED\_PHASES] \featurelabel{defined-phases} A space separated arbitrarily ordered list of
phase names (e.\,g.\ \t{configure setup unpack}) whose phase functions are defined by the ebuild or
an eclass inherited by the ebuild. If no phase functions are defined, a single hyphen is used
instead of an empty string. For EAPIs listed in table~\ref{tab:defined-phases-table} as having
optional \t{DEFINED\_PHASES} support, package managers may not rely upon the metadata cache having
this variable defined, and must treat an empty string as ``this information is not available''.
\end{description}

\note Thus, by extension of section~\ref{sec:metadata-invariance}, phase functions must not be defined
based upon any variant condition.

\begin{centertable}{EAPIs supporting \t{DEFINED\_PHASES}} \label{tab:defined-phases-table}
    \begin{tabular}{ l l }
        \toprule
        \multicolumn{1}{c}{\textbf{EAPI}} &
        \multicolumn{1}{c}{\textbf{Supports \t{DEFINED\_PHASES}?}} \\
        \midrule
    \t{0} & Optionally \\
    \t{1} & Optionally \\
    \t{2} & Optionally \\
    \t{3} & Optionally \\
    \t{4} & Yes \\
    \bottomrule
    \end{tabular}
\end{centertable}

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