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Guarantee compatibility for Qt's extension protocols

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Spell out and formalize the policy that we have been following
since Qt 5.4: We don't break compatibility for our internal
protocols. Otherwise, it would not be safe to use a Qt client
with a Qt-based compositor.

Change-Id: I632e9fbb56095ab07560413977c79777ae9fdcd2
Reviewed-by: Johan Helsing <johan.helsing@qt.io>
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@liri.io>
This commit is contained in:
Paul Olav Tvete 2019-02-28 10:23:16 +01:00
parent ecf297ac72
commit 7f21a684f7
1 changed files with 12 additions and 6 deletions
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18
src/3rdparty/wayland/extensions/README.md vendored
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@ -3,12 +3,10 @@
The protocol extensions in this folder are considered implementation details of The protocol extensions in this folder are considered implementation details of
Qt. I.e. they may removed, renamed or changed without warning. Qt. I.e. they may removed, renamed or changed without warning.
## Suffixed protocols However, starting with Qt 5.4, we promise not to break backwards compatibility
without renaming (or removing) the protocol. I.e., if your client sees a global
For protocols that have a version suffix, however, we will strive to not break from one of these extensions, it can safely bind to it: the existing events
backwards compatibility without bumping the suffix (renaming the protocol). and requests will always take the same number of arguments, regardless of
E.g.: If your client sees a `zqt_key_v1` global, it can safely bind to it:
the key event will always take the same number of arguments, regardless of
compositor version. compositor version.
This is important also within a Qt-only scope if there are multiple versions of This is important also within a Qt-only scope if there are multiple versions of
@ -16,3 +14,11 @@ Qt on the system. Consider for instance an application statically linked to Qt
(such as Qt Creator) running against a Qt compositor installed by the distro). (such as Qt Creator) running against a Qt compositor installed by the distro).
In such cases we don't want the compositor and client to disagree on the In such cases we don't want the compositor and client to disagree on the
protocol definition. protocol definition.
## Protocol versioning.
Protocol extensions in this folder should be versioned (e.g. `zqt_key_v1`).
If it is necessary to break protocol compatibility, they will be renamed by
incrementing the version number. For legacy reasons, there are also unversioned
protocols in this folder. Those protocols should be renamed to be versioned
if compatibility is broken.