Policy: Blockers

Concern: What do soft ! and hard !! blockers mean in the plan?

PMS / Portage:

• Soft !cat/pkg — prefer not to have the blocker installed; may uninstall or avoid selecting it
• Hard !!cat/pkg — forbid co-installation

Versioned forms (!<pkg-ver) restrict which versions are blocked.

Literals:

• Blocker-strength in grouped_package_dependency(weak|strong, …)
• Domain assumption: blocker_assumption (often positive / actionable: unmerge or pick another || arm)
• Ranking interaction: blocked arms demoted or excluded

Owns: resolving.pl grouped dependency clauses, ranking / candidate filters, printer blocker reporting.

Invariants:

• Strong blockers remove or forbid the conflicting selection; soft blockers prefer alternatives and may record an assumption.
• Inside ||, a versioned soft blocker should push ranking toward a non-blocked arm when one exists (see test60 / newest-admitted preference).
• Blocker assumptions are positive when a config / unmerge action restores satisfiability.
• A recorded soft blocker is only reported (blocker section, inline (blocked: soft by …) note, CI exit code) when its atom — operator, version, slot and sub-slot — actually hits a planned merge of the blocked CN, or an installed copy the plan leaves in place. Pass 1 records every soft blocker it walks past because the blocked CN's candidate may be selected later in the proof; relevance is decided post-proof in annotation:collect/2 (annotation:blocker_effective/2), reusing the strong-blocker matching core. !dev-ml/findlib:0/0 against a planned findlib 0/1, or !<dev-util/ragel-7.0.3 against a planned 7.0.4, block nothing and are silent (portage-ng#119 follow-up).

Examples: test26, test27, test60.
See also: Choice, Assumptions.