The type of variables that play a role in the solver. Note that the tree currently does not use this type directly, and rather has separate tree nodes for the different types of variables. This fits better with the fact that in most cases, these have to be treated differently.

Extract the package name from a Var

The set of variables involved in a solver conflict, each paired with details about the conflict.

Constrained instance. It represents the allowed instances for a package, which can be either a fixed instance or a version range.

Flagged dependencies

FlaggedDeps is the modular solver's view of a packages dependencies: rather than having the dependencies indexed by component, each dependency defines what component it is in.

Note that each dependency is associated with a Component. We must know what component the dependencies belong to, or else we won't be able to construct fine-grained reverse dependencies.

Flagged dependencies can either be plain dependency constraints, or flag-dependent dependency trees.

A Dep labeled with the reason it was introduced.

LDep intentionally has no Functor instance because the type variable is used both to record the dependencies as well as who's doing the depending; having a Functor instance makes bugs where we don't distinguish these two far too likely. (By rights LDep ought to have two type variables.)

A dependency (constraint) associates a package name with a constrained instance. It can also represent other types of dependencies, such as dependencies on language extensions.

An exposed component within a package. This type is used to represent build-depends and build-tool-depends dependencies.

A component that can be depended upon by another package, i.e., a library or an executable.

The reason that a dependency is active. It identifies the package and any flag and stanza choices that introduced the dependency. It contains everything needed for creating ConflictSets or describing conflicts in solver log messages.

Print the reason that a dependency was introduced.

Conservatively flatten out flagged dependencies

NOTE: We do not filter out duplicates.

Options for goal qualification (used in qualifyDeps)

See also defaultQualifyOptions

Apply built-in rules for package qualifiers

Although the behaviour of qualifyDeps depends on the QualifyOptions, it is important that these QualifyOptions are _static_. Qualification does NOT depend on flag assignment; in other words, it behaves the same no matter which choices the solver makes (modulo the global QualifyOptions); we rely on this in linkDeps (see comment there).

NOTE: It's the _dependencies_ of a package that may or may not be independent from the package itself. Package flag choices must of course be consistent.

Remove qualifiers from set of dependencies

This is used during link validation: when we link package Q.A to Q'.A, then all dependencies Q.B need to be linked to Q'.B. In order to compute what to link these dependencies to, we need to requalify Q.B to become Q'.B; we do this by first removing all qualifiers and then calling qualifyDeps again.

A map containing reverse dependencies between qualified package names.

A goal is just a solver variable paired with a reason. The reason is only used for tracing.

Reason why a goal is being added to a goal set.

Compute a singleton conflict set from a Var

Convert a GoalReason to a ConflictSet that can be used when the goal leads to a conflict.

Convert a GoalReason to a ConflictSet containing the reason that the conflict occurred, namely the conflict set variables caused a conflict by introducing the given package goal. See the documentation for GoalConflict.

This function currently only specifies the reason for the conflict in the simple case where the GoalReason does not involve any flags or stanzas. Otherwise, it falls back to calling goalReasonToConflictSet.

This function returns the solver variables responsible for the dependency. It drops the values chosen for flag and stanza variables, which are only needed for log messages.

Convert a DependencyReason to a ConflictSet specifying that the conflict occurred because the conflict set variables introduced a problematic version constraint. See the documentation for VersionConstraintConflict.

This function currently only specifies the reason for the conflict in the simple case where the DependencyReason does not involve any flags or stanzas. Otherwise, it falls back to calling dependencyReasonToConflictSet.

Convert a DependencyReason to a ConflictSet specifying that the conflict occurred because the conflict set variables introduced a version of a package that was excluded by a version constraint. See the documentation for VersionConflict.

This function currently only specifies the reason for the conflict in the simple case where the DependencyReason does not involve any flags or stanzas. Otherwise, it falls back to calling dependencyReasonToConflictSet.