Extend DependencyResolver to properly handle optional dependencies.

Mention version for invalid root package dependencies.

Fix warnings on DMD master. See #541.

Fix detection of unknown root dependencies and the resulting error message. Fixes #418.

Eliminate dependency versions that are known to not match the root package. See #405. ...

This change eliminates all dependency versions that are known to violate the dependency specification of the root package or of uniquely defined dependencies thereof. This can greatly reduce the search space for valid combinations later on in the algorithm.

Add missing recursion during dependency resolution. See #405.

Add an early out for invalid child configurations in the dependency resolver. Fixes #405. ...

Previous behavior could cause exponential run time.

Fix using an invalid configuration in DependencyResolver when validating dependencies. ...

This was caused by the fix for #359.

Fix DependencyResolver's unit test.

Fix optional dependencies being always downloaded with the new dependency resolver. Fixes #359.

Remove redundant try-catch

Fix detection of root package references during dependency resolution. See #334. ...

- References to and from sub packages of the root package are now also recognized as coming from the root package
 - Any dependency reference within a certain package "family"* (including path based ones) is now mapped to the same base package (circumventing the lookup of all possible matches)

* "family" == base package and all of its sub packages

Fix detection of invalid dependencies in sub packages of the root package. See #334.

Avoid probing all versions of the root package when resolving its own sub packages. ...

This avoids downloading all versions of the root package whenever it contains references to sub packages of itself. See #334.

Print a proper error message for unknown dependency versions of the root package.

Removed trailing whitespace

Fix detection of already visited nodes in DependencyResolver. See #280. ...

Fixes a stack overflow for package graphs with cycles.

Emit better error messages for unresolvable dependency trees.

Fix dependency resolution. ...

The "if (parent == root) return pidx;" line needed to be inside the "if(!matches" block.

Optimize dependency version resolution when root dependencies fail.

Fix an error in the dependency resolution due to a signed/unsigned comparison. See #285. ...

Also added some diagnostic output to the dependency resolution algorithm.

Avoid exponential run time in the dependency resolution algorithm if possible. ...

When going through all combinations of package versions, all sub trees of the search space are now skipped for a conflicting node, as those are guaranteed to conflict anyway.

Fix path based dependencies to be ignored for version selections.

Fix unit tests of DependencyResolver.

Fix resolution of optional and path based dependencies.

Correct copyright notices.

Fix handling of overriding selections and let printUpgradesOnly fail gracefully.

Fix dependency resolution for outdated invalid dependencies. ...

Now the invalid dependency is simply ignored as long as it isn't actually chosen.

Move DependencyResolver to its own module and reorder Version<->Dependency.