This is an experimental feature subject to breaking changes in future releases.
The goal of the revisions feature is to achieve package immutability, the packages in a server are never overwritten.
This is the first piece to achieve reproducibility: Recreate the exact dependency graph by using some mechanism like a “graph lock” file. For example, if we store a “graph lock” file for the different releases of our project, we can install the same dependencies just by using the graph lock.
IMPORTANT: The reproducibility is in the Conan roadmap and currently under development.
How it works¶
In the client
When a recipe is exported, Conan calculates a unique ID (revision). For every change, a new recipe revision (RREV) will be calculated. By default it will use the checksum hash of the recipe manifest.
Nevertheless, the recipe creator can explicitly declare the revision mode, it can be either
scm(uses version control system or raises) or
hash(use manifest hash).
When a package is created (by running conan create or conan export-pkg) a new package revision (PREV) will be calculated always using the hash of the package contents. The packages and their revisions (PREVs) belongs to a concrete recipe revision (RREV). The same package ID (for example for Linux/GCC5/Debug), can have multiple revisions (PREVs) that belong to a concrete RREV.
If a client requests a reference like
lib/1.0@conan/stable, Conan will retrieve automatically the latest revision.
In the client cache there will be only one revision installed at the same time.
The revisions can be pinned when you write a reference (in the recipe requires, or in a reference in a conan install command…) but if you don’t specify a revision the server will retrieve the latest one.
You can specify the references in the following formats:
|lib/1.0@conan/stable||Latest RREV for lib/1.0@conan/stable|
|lib/1.0@conan/stable#RREV||Specific RREV for lib/1.0@conan/stable|
|lib/1.0@conan/stable#RREV:PACKAGE_ID||A binary package belonging to the specific RREV|
|lib/1.0@conan/stable#RREV:PACKAGE_ID#PREV||A binary package revision PREV belonging to the specific RREV|
In the server
By using a new folder layout and protocol it is able to store multiple revisions, both for recipes and binary packages.
How to activate the revisions¶
You have to explicitly activate the feature by:
[general]section of your conan.conf file.
- Setting the
Take into account that it changes the default Conan behavior. e.g:
- A client with revisions enabled will only find binary packages that belongs to the installed recipe revision. For example, If you create a recipe and run conan create . user/channel and then you modify the recipe and export it conan export . user/channel, the binary package generated in the conan create command doesn’t belong to the new exported recipe, so it won’t be located unless the previous recipe is recovered.
- If you generate and upload N binary packages for a recipe revision, if you upload the revision you need to generate and upload again the N binaries if you want them to be used with the new recipe.