DPM Conflict Resolutions

Dependency Resolution

Dependency resolution in DPM is fairly straight forward. DPM reads the DEPENDENCIES file from the package’s metadata and then checks if a file whose NAME, PROVIDES, or REPLACES entries name a package with a version met by that named dependency.

The DON repository metadata provides larger dependency chains for larger package transactions, such as in the event of system updates are large framework installations, and this will be discussed more in the specification for DON.

In DPM, the behaviour is very simple if a dependency is not found: it will fail, unless an override switch to force the transaction is supplied.

Dependency Version Comparison Resolution

Version comparison will be an implementation of the behaviour documented in the public Semantic Versioning 2.0 (SemVer) specification, with a default patch number of 0 that increments with every official package created for that package version. So, if a typo is identified or some other change is made to the package, it increments by 1. If a backwards compatible patch is applied, it increments by 1 if it hasn’t already. The patch here is used to indicate package versions of the same software version, and not necessarily patching state.

If a software’s versioning scheme does not align with SemVer, it will be converted to a form that is, and this will be noted in the package description.

File Conflict Resolution

While undesired, it is possible for package creators to create more than one package that provides a file.

1. For instance, if PackageA is installed and provides a file at $file_path, and PackageB is being attempted to be installed and provides a different (or even the same) file at the same $file_path, this will create a file conflict.
   
   In this installation file conflict, DPM detects that $file_path is already owned by PackageA. DPM will then fail with an error that names the conflicting file, and which package (PackageA) owns it. It will identify the package (PackageB) that is trying to additionally provide it.
   
   
2. There are exceptions. In the event that PackageB lists PackageA in its REPLACES metadata, then it will replace the file along with any other files in PackageA and PackageA will be removed. This handles legitimate cases where one package is meant to replace another.
   
   
3. Another exception is if the user supplies a commandline option to force installation of PackageB:
   
   If PackageA lists the file as non-controlled and PackageB lists the file as non-controlled, it will place the file from PackageB at ${file_path}.dpmnew.
   
   If PackageA lists the file as controlled, and PackageB lists the file as non-controlled, the original file will be preserved and PackageB will place the file at ${file_path}.dpmnew.
   
   If PackageA lists the file as non-controlled, and PackageB lists the file as controlled, the original file at ${file_path} will be renamed to ${file_path}.dpmbackup and PackageB‘s version will take ownership priority of the file at the conflicting path.
   
   If both packages list the file as controlled, the transaction will fail as described in (1). The user must uninstall PackageA and install PackageB or one of the packages must be modified and (re)installed to allow installation without a package conflict.