Bug#761219: debian-policy: document versioned Provides
On Wed, Jan 02, 2019 at 11:53:50AM +0000, Sean Whitton wrote:
> Hello Dominic,
>
> Thank you for coming back to this.
>
> On Tue 01 Jan 2019 at 06:41pm GMT, Dominic Hargreaves wrote:
>
> > -If a relationship field has a version number attached, only real
> > -packages will be considered to see whether the relationship is satisfied
> > -(or the prohibition violated, for a conflict or breakage). In other
> > -words, if a version number is specified, this is a request to ignore all
> > -``Provides`` for that package name and consider only real packages. The
> > -package manager will assume that a package providing that virtual
> > -package is not of the "right" version. A ``Provides`` field may not
> > -contain version numbers, and the version number of the concrete package
> > -which provides a particular virtual package will not be considered when
> > -considering a dependency on or conflict with the virtual package name.
> > -[#]_
> > +A ``Provides`` field may contain version numbers, and the version number
> > +of the concrete package which provides a particular virtual package will
> > +be considered when considering a dependency on or conflict with the
> > +virtual package name. [#]_
>
> It might be useful to have an example here to explain the sense in which
> the version number of the concrete package will be considered.
>
> As someone who has not had to think through a case of versioned Provides
> for any of his packages, it is hard for me to understand how versioned
> Provides works in even very general terms from this text. By contrast,
> the text you are replacing has a lot more details and is easy to
> understand.
This is a fair comment. The wording was potentially misleading. How about
the attached instead?
Dominic.
>From ea67fb0cee5ad789f3036ec7c937d7a236672483 Mon Sep 17 00:00:00 2001
From: Dominic Hargreaves <dom@earth.li>
Date: Tue, 1 Jan 2019 18:36:54 +0000
Subject: [PATCH] Remove restrictions on versioned Provides
Closes: #761219
---
policy/ch-relationships.rst | 47 +++++++++++++++++++++++++--------------------
1 file changed, 26 insertions(+), 21 deletions(-)
diff --git a/policy/ch-relationships.rst b/policy/ch-relationships.rst
index 1d790e8..469a808 100644
--- a/policy/ch-relationships.rst
+++ b/policy/ch-relationships.rst
@@ -17,15 +17,16 @@ package names, separated by vertical bar (pipe) symbols ``|``. In such a
case, that part of the dependency can be satisfied by any one of the
alternative packages. [#]_
-All of the fields except for ``Provides`` may restrict their
-applicability to particular versions of each named package. This is done
-in parentheses after each individual package name; the parentheses
-should contain a relation from the list below followed by a version
-number, in the format described in :ref:`s-f-Version`.
+All of the fields may restrict their applicability to particular versions
+of each named package. This is done in parentheses after each individual
+package name; the parentheses should contain a relation from the list
+below followed by a version number, in the format described in
+:ref:`s-f-Version`.
The relations allowed are ``<<``, ``<=``, ``=``, ``>=`` and ``>>`` for
strictly earlier, earlier or equal, exactly equal, later or equal and
-strictly later, respectively. [#]_
+strictly later, respectively. The exception is the Provides field, for
+which only ``=`` is allowed. [#]_
Whitespace may appear at any point in the version specification subject
to the rules in :ref:`s-controlsyntax`, and must appear
@@ -446,17 +447,23 @@ they can say:
and the ``bar-plus`` package will now also satisfy the dependency for
the ``foo`` package.
-If a relationship field has a version number attached, only real
-packages will be considered to see whether the relationship is satisfied
-(or the prohibition violated, for a conflict or breakage). In other
-words, if a version number is specified, this is a request to ignore all
-``Provides`` for that package name and consider only real packages. The
-package manager will assume that a package providing that virtual
-package is not of the "right" version. A ``Provides`` field may not
-contain version numbers, and the version number of the concrete package
-which provides a particular virtual package will not be considered when
-considering a dependency on or conflict with the virtual package name.
-[#]_
+A ``Provides`` field may contain version numbers, and such a version number
+will be considered when considering a dependency on or conflict with the
+virtual package name. [#]_ For example, given the following packages:
+
+::
+
+ Package: foo
+ Depends: bar (>= 1.0)
+
+ Package: bar
+ Version: 0.9
+
+ Package: bar-plus
+ Provides: bar (= 1.0)
+
+the ``bar-plus`` package will again satisfy the dependency for
+the ``foo`` package.
To specify which of a set of real packages should be the default to
satisfy a particular dependency on a virtual package, list the real
@@ -670,10 +677,8 @@ dependencies.
together and then configured in their dependency order.
.. [#]
- It is possible that a future release of ``dpkg`` may add the ability
- to specify a version number for each virtual package it provides.
- This feature is not yet present, however, and is expected to be used
- only infrequently.
+ This functionality was introduced in dpkg 1.17.11 and newer and
+ full support has been provided in the Debian archive since 2018.
.. [#]
To see why ``Breaks`` is normally needed in addition to ``Replaces``,
--
2.11.0
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