path: root/src/solver.c

/* solver.c - Alpine Package Keeper (APK)
 * Up- and down-propagating, forwarding checking, deductive dependency solver.
 *
 * Copyright (C) 2008-2013 Timo Teräs <timo.teras@iki.fi>
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation. See http://www.gnu.org/ for details.
 */

#include <stdint.h>
#include <unistd.h>
#include "apk_defines.h"
#include "apk_database.h"
#include "apk_package.h"
#include "apk_solver.h"

#include "apk_print.h"

//#define DEBUG_PRINT

#ifdef DEBUG_PRINT
#include <stdio.h>
#define dbg_printf(args...) fprintf(stderr, args)
#else
#define dbg_printf(args...)
#endif

#define ASSERT(cond, fmt...)	if (!(cond)) { apk_error(fmt); *(char*)NULL = 0; }

struct apk_solver_state {
	struct apk_database *db;
	struct apk_changeset *changeset;
	struct list_head dirty_head;
	struct list_head unresolved_head;
	unsigned int errors;
	unsigned int num_selections, num_solution_entries;
	unsigned int solver_flags_inherit;
	unsigned int pinning_inherit;
	unsigned int default_repos;
	unsigned prefer_pinning : 1;
};

static struct apk_provider provider_none = {
	.pkg = NULL,
	.version = &apk_null_blob
};

void apk_solver_set_name_flags(struct apk_name *name,
			       unsigned short solver_flags,
			       unsigned short solver_flags_inheritable)
{
	struct apk_provider *p;

	foreach_array_item(p, name->providers) {
		struct apk_package *pkg = p->pkg;
		pkg->ss.solver_flags |= solver_flags;
		pkg->ss.solver_flags_inheritable |= solver_flags_inheritable;
	}
}

static int get_tag(struct apk_database *db, unsigned int pinning_mask, unsigned int repos)
{
	int i;

	for (i = 0; i < db->num_repo_tags; i++) {
		if (!(BIT(i) & pinning_mask))
			continue;
		if (db->repo_tags[i].allowed_repos & repos)
			return i;
	}
	return APK_DEFAULT_REPOSITORY_TAG;
}

static unsigned int get_pkg_repos(struct apk_database *db, struct apk_package *pkg)
{
	return pkg->repos | (pkg->ipkg ? db->repo_tags[pkg->ipkg->repository_tag].allowed_repos : 0);
}

static void foreach_rinstall_if_pkg(
	struct apk_solver_state *ss, struct apk_package *pkg,
	void (*cb)(struct apk_solver_state *ss, struct apk_package *rinstall_if, struct apk_package *parent_pkg))
{
	struct apk_name *name = pkg->name, *name0, **pname0;
	struct apk_dependency *dep;
	struct apk_provider *p0;

	foreach_array_item(pname0, pkg->name->rinstall_if) {
		name0 = *pname0;
		dbg_printf(PKG_VER_FMT ": rinstall_if %s\n", PKG_VER_PRINTF(pkg), name0->name);
		foreach_array_item(p0, name0->providers) {
			foreach_array_item(dep, p0->pkg->install_if) {
				if (dep->name == name && apk_dep_is_provided(dep, p0)) {
					/* pkg depends (via install_if) on pkg0 */
					cb(ss, p0->pkg, pkg);
					break;
				}
			}
		}
	}
}

static void mark_error(struct apk_solver_state *ss, struct apk_package *pkg)
{
	if (pkg == NULL || pkg->ss.error)
		return;
	pkg->ss.error = 1;
	ss->errors++;
}

static void queue_dirty(struct apk_solver_state *ss, struct apk_name *name)
{
	if (list_hashed(&name->ss.dirty_list) || name->ss.locked ||
	    (name->ss.requirers == 0 && !name->ss.reevaluate_iif))
		return;

	dbg_printf("queue_dirty: %s\n", name->name);
	list_add_tail(&name->ss.dirty_list, &ss->dirty_head);
}

static void queue_unresolved(struct apk_solver_state *ss, struct apk_name *name)
{
	int want;

	if (name->ss.locked)
		return;

	want = (name->ss.requirers > 0) || (name->ss.has_iif);
	dbg_printf("queue_unresolved: %s, want=%d\n", name->name, want);
	if (want && !list_hashed(&name->ss.unresolved_list))
		list_add(&name->ss.unresolved_list, &ss->unresolved_head);
	else if (!want && list_hashed(&name->ss.unresolved_list))
		list_del_init(&name->ss.unresolved_list);
}

static void reevaluate_reverse_deps(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_name **pname0, *name0;

	foreach_array_item(pname0, name->rdepends) {
		name0 = *pname0;
		if (!name0->ss.seen)
			continue;
		name0->ss.reevaluate_deps = 1;
		queue_dirty(ss, name0);
	}
}

static void reevaluate_reverse_installif(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_name **pname0, *name0;

	foreach_array_item(pname0, name->rinstall_if) {
		name0 = *pname0;
		if (!name0->ss.seen)
			continue;
		name0->ss.reevaluate_iif = 1;
		queue_dirty(ss, name0);
	}
}

static void disqualify_package(struct apk_solver_state *ss, struct apk_package *pkg, const char *reason)
{
	struct apk_dependency *p;

	dbg_printf("disqualify_package: " PKG_VER_FMT " (%s)\n", PKG_VER_PRINTF(pkg), reason);
	pkg->ss.available = 0;
	reevaluate_reverse_deps(ss, pkg->name);
	foreach_array_item(p, pkg->provides)
		reevaluate_reverse_deps(ss, p->name);
	reevaluate_reverse_installif(ss, pkg->name);
}

static int dependency_satisfiable(struct apk_solver_state *ss, struct apk_dependency *dep)
{
	struct apk_name *name = dep->name;
	struct apk_provider *p;

	if (name->ss.locked)
		return apk_dep_is_provided(dep, &name->ss.chosen);

	if (name->ss.requirers == 0 && apk_dep_is_provided(dep, &provider_none))
		return TRUE;

	foreach_array_item(p, name->providers)
		if (p->pkg->ss.available && apk_dep_is_provided(dep, p))
			return TRUE;

	return FALSE;
}

static void discover_name(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_database *db = ss->db;
	struct apk_name **pname0;
	struct apk_provider *p;
	struct apk_dependency *dep;
	unsigned int repos;

	if (name->ss.seen)
		return;

	name->ss.seen = 1;
	foreach_array_item(p, name->providers) {
		struct apk_package *pkg = p->pkg;
		if (pkg->ss.seen)
			continue;
		pkg->ss.seen = 1;
		pkg->ss.available = pkg->ipkg || (pkg->repos & db->available_repos);
		pkg->ss.pinning_allowed = APK_DEFAULT_PINNING_MASK;
		pkg->ss.pinning_preferred = APK_DEFAULT_PINNING_MASK;

		repos = get_pkg_repos(db, pkg);
		pkg->ss.tag_ok = !!(repos & ss->default_repos);
		pkg->ss.tag_preferred = !!(repos & ss->default_repos);

		foreach_array_item(dep, pkg->depends) {
			discover_name(ss, dep->name);
			pkg->ss.max_dep_chain = max(pkg->ss.max_dep_chain,
						    dep->name->ss.max_dep_chain+1);
		}
		name->ss.max_dep_chain = max(name->ss.max_dep_chain, pkg->ss.max_dep_chain);

		dbg_printf("discover " PKG_VER_FMT ": tag_ok=%d, tag_pref=%d max_dep_chain=%d available=%d\n",
			PKG_VER_PRINTF(pkg),
			pkg->ss.tag_ok,
			pkg->ss.tag_preferred,
			pkg->ss.max_dep_chain,
			pkg->ss.available);
	}
	foreach_array_item(pname0, name->rinstall_if)
		discover_name(ss, *pname0);
}

static void name_requirers_changed(struct apk_solver_state *ss, struct apk_name *name)
{
	queue_unresolved(ss, name);
	reevaluate_reverse_installif(ss, name);
	queue_dirty(ss, name);
}

static void inherit_pinning(struct apk_solver_state *ss, struct apk_package *pkg, unsigned int pinning, int prefer)
{
	unsigned int repo_mask = apk_db_get_pinning_mask_repos(ss->db, pinning);
	unsigned int repos = get_pkg_repos(ss->db, pkg);

	pkg->ss.pinning_allowed |= pinning;
	pkg->ss.tag_ok |= !!(repos & repo_mask);
	if (prefer) {
		pkg->ss.pinning_preferred |= pinning;
		pkg->ss.tag_preferred = !!(repos & apk_db_get_pinning_mask_repos(ss->db, pkg->ss.pinning_preferred));
	}
}

static void apply_constraint(struct apk_solver_state *ss, struct apk_package *ppkg, struct apk_dependency *dep)
{
	struct apk_name *name = dep->name;
	struct apk_provider *p0;
	unsigned int solver_flags_inherit = ss->solver_flags_inherit;
	int is_provided;

	dbg_printf("apply_constraint: %s%s%s" BLOB_FMT "\n",
		dep->conflict ? "!" : "",
		name->name,
		apk_version_op_string(dep->result_mask),
		BLOB_PRINTF(*dep->version));

	name->ss.requirers += !dep->conflict;
	if (name->ss.requirers == 1 && !dep->conflict)
		name_requirers_changed(ss, name);

	foreach_array_item(p0, name->providers) {
		struct apk_package *pkg0 = p0->pkg;

		is_provided = apk_dep_is_provided(dep, p0);
		dbg_printf("apply_constraint: provider: %s-" BLOB_FMT ": %d\n",
			pkg0->name->name, BLOB_PRINTF(*p0->version), is_provided);

		pkg0->ss.conflicts += !is_provided;
		if (unlikely(pkg0->ss.available && pkg0->ss.conflicts))
			disqualify_package(ss, pkg0, "conflicting dependency");

		if (is_provided) {
			pkg0->ss.solver_flags |= solver_flags_inherit;
			pkg0->ss.solver_flags_inheritable |= solver_flags_inherit;
			inherit_pinning(ss, pkg0, ss->pinning_inherit, ss->prefer_pinning);

			dbg_printf(PKG_VER_FMT ": tag_ok=%d, tag_pref=%d\n",
				PKG_VER_PRINTF(pkg0),
				pkg0->ss.tag_ok,
				pkg0->ss.tag_preferred);
		}
	}
}

static void reconsider_name(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_name *name0, **pname0;
	struct apk_dependency *dep;
	struct apk_package *first_candidate = NULL;
	struct apk_provider *p;
	int reevaluate_deps, reevaluate_iif;
	int num_options = 0, num_tag_not_ok = 0, has_iif = 0;

	dbg_printf("reconsider_name: %s\n", name->name);

	reevaluate_deps = name->ss.reevaluate_deps;
	reevaluate_iif = name->ss.reevaluate_iif;
	name->ss.reevaluate_deps = 0;
	name->ss.reevaluate_iif = 0;

	/* propagate down by merging common dependencies and
	 * applying new constraints */
	foreach_array_item(p, name->providers) {
		struct apk_package *pkg = p->pkg;

		/* check if this pkg's dependencies have become unsatisfiable */
		pkg->ss.dependencies_merged = 0;
		if (reevaluate_deps) {
			if (!pkg->ss.available)
				continue;
			foreach_array_item(dep, pkg->depends) {
				if (!dependency_satisfiable(ss, dep)) {
					disqualify_package(ss, pkg, "dependency no longer satisfiable");
					break;
				}
			}
		}
		if (!pkg->ss.available)
			continue;

		if (reevaluate_iif) {
			pkg->ss.iif_triggered = 1;
			foreach_array_item(dep, pkg->install_if) {
				if (!dependency_satisfiable(ss, dep)) {
					pkg->ss.iif_triggered = 0;
					break;
				}
			}
			has_iif |= pkg->ss.iif_triggered;
		}

		if (name->ss.requirers == 0 && !pkg->ss.iif_triggered)
			continue;

		/* merge common dependencies */
		pkg->ss.dependencies_merged = 1;
		if (first_candidate == NULL)
			first_candidate = pkg;
		foreach_array_item(dep, pkg->depends) {
			/* FIXME: can merge also conflicts */
			if (dep->conflict)
				continue;
			name0 = dep->name;
			if (name0->ss.merge_index == num_options)
				name0->ss.merge_index = num_options + 1;
		}

		num_tag_not_ok += !pkg->ss.tag_ok;
		num_options++;
	}
	name->ss.has_options = (num_options > 1 || num_tag_not_ok > 0);
	name->ss.has_iif = has_iif;
	queue_unresolved(ss, name);

	if (first_candidate != NULL) {
		foreach_array_item(p, name->providers)
			p->pkg->ss.dependencies_used = p->pkg->ss.dependencies_merged;

		/* propagate down common dependencies */
		if (num_options == 1) {
			/* FIXME: keeps increasing counts, use bit fields instead? */
			foreach_array_item(dep, first_candidate->depends)
				apply_constraint(ss, first_candidate, dep);
		} else {
			/* FIXME: could merge versioning bits too */
			foreach_array_item(dep, first_candidate->depends) {
				if (dep->conflict)
					continue;
				name0 = dep->name;
				if (name0->ss.merge_index == num_options) {
					/* common dependency name with all */
					if (name0->ss.requirers == 0) {
						dbg_printf("%s common dependency: %s\n",
							   name->name, name0->name);
						name0->ss.requirers++;
						name_requirers_changed(ss, name0);
					}
				}
				name0->ss.merge_index = 0;
			}
		}
	}
	name->ss.reverse_deps_done = 1;
	foreach_array_item(pname0, name->rdepends) {
		name0 = *pname0;
		if (name0->ss.seen && !name0->ss.locked) {
			name->ss.reverse_deps_done = 0;
			break;
		}
	}

	dbg_printf("reconsider_name: %s [finished], has_options=%d, reverse_deps_done=%d\n",
		name->name, name->ss.has_options, name->ss.reverse_deps_done);
}

static int compare_providers(struct apk_solver_state *ss,
			     struct apk_provider *pA, struct apk_provider *pB)
{
	struct apk_database *db = ss->db;
	struct apk_package *pkgA = pA->pkg, *pkgB = pB->pkg;
	unsigned int solver_flags;
	int r;

	/* Prefer existing package */
	if (pkgA == NULL || pkgB == NULL)
		return (pkgA != NULL) - (pkgB != NULL);

	/* Latest version required? */
	solver_flags = pkgA->ss.solver_flags | pkgB->ss.solver_flags;
	if ((solver_flags & APK_SOLVERF_LATEST) &&
	    (pkgA->ss.pinning_allowed == APK_DEFAULT_PINNING_MASK) &&
	    (pkgB->ss.pinning_allowed == APK_DEFAULT_PINNING_MASK)) {
		/* Prefer allowed pinning */
		r = (int)pkgA->ss.tag_ok - (int)pkgB->ss.tag_ok;
		if (r)
			return r;

		/* Prefer available */
		if (solver_flags & (APK_SOLVERF_AVAILABLE | APK_SOLVERF_REINSTALL)) {
			r = !!(pkgA->repos & db->available_repos) - !!(pkgB->repos & db->available_repos);
			if (r)
				return r;
		}
	} else {
		/* Prefer without errors */
		r = (int)pkgA->ss.available - (int)pkgB->ss.available;
		if (r)
			return r;

		/* Prefer those that were in last dependency merging group */
		r = (int)pkgA->ss.dependencies_used - (int)pkgB->ss.dependencies_used;
		if (r)
			return r;
		r = pkgB->ss.conflicts - pkgA->ss.conflicts;
		if (r)
			return r;

		/* Prefer installed on self-upgrade */
		if (db->performing_self_update && !(solver_flags & APK_SOLVERF_UPGRADE)) {
			r = (pkgA->ipkg != NULL) - (pkgB->ipkg != NULL);
			if (r)
				return r;
		}

		/* Prefer allowed pinning */
		r = (int)pkgA->ss.tag_ok - (int)pkgB->ss.tag_ok;
		if (r)
			return r;

		/* Prefer available */
		if (solver_flags & (APK_SOLVERF_AVAILABLE | APK_SOLVERF_REINSTALL)) {
			r = !!(pkgA->repos & db->available_repos) - !!(pkgB->repos & db->available_repos);
			if (r)
				return r;
		}

		/* Prefer preferred pinning */
		r = (int)pkgA->ss.tag_preferred - (int)pkgB->ss.tag_preferred;
		if (r)
			return r;

		/* Prefer installed */
		if (!(solver_flags & APK_SOLVERF_UPGRADE)) {
			r = (pkgA->ipkg != NULL) - (pkgB->ipkg != NULL);
			if (r)
				return r;
		}
	}

	/* Select latest by requested name */
	switch (apk_version_compare_blob(*pA->version, *pB->version)) {
	case APK_VERSION_LESS:
		return -1;
	case APK_VERSION_GREATER:
		return 1;
	}

	/* Select latest by principal name */
	if (pkgA->name == pkgB->name) {
		switch (apk_version_compare_blob(*pkgA->version, *pkgB->version)) {
		case APK_VERSION_LESS:
			return -1;
		case APK_VERSION_GREATER:
			return 1;
		}
	}

	/* Prefer installed (matches here if upgrading) */
	r = (pkgA->ipkg != NULL) - (pkgB->ipkg != NULL);
	if (r)
		return r;

	/* Prefer lowest available repository */
	return ffsl(pkgB->repos) - ffsl(pkgA->repos);
}

static void inherit_pinning_from_pkg(struct apk_solver_state *ss, struct apk_package *rinstall_if, struct apk_package *parent_pkg)
{
	inherit_pinning(ss, rinstall_if, parent_pkg->ss.pinning_allowed, 0);
}

static void assign_name(struct apk_solver_state *ss, struct apk_name *name, struct apk_provider p)
{
	struct apk_provider *p0;

	if (name->ss.locked) {
		/* If both are providing this name without version, it's ok */
		if (p.version == &apk_null_blob &&
		    name->ss.chosen.version == &apk_null_blob)
			return;
		/* Conflict: providing same name */
		mark_error(ss, p.pkg);
		mark_error(ss, name->ss.chosen.pkg);
		return;
	}

	if (p.pkg)
		dbg_printf("assign %s to "PKG_VER_FMT"\n", name->name, PKG_VER_PRINTF(p.pkg));

	name->ss.locked = 1;
	name->ss.chosen = p;
	if (list_hashed(&name->ss.unresolved_list))
		list_del(&name->ss.unresolved_list);
	if (list_hashed(&name->ss.dirty_list))
		list_del(&name->ss.dirty_list);

	/* propagate pinning to install_if candidates */
	if (p.pkg)
		foreach_rinstall_if_pkg(ss, p.pkg, inherit_pinning_from_pkg);

	/* disqualify all conflicting packages */
	foreach_array_item(p0, name->providers) {
		if (p0->pkg == p.pkg)
			continue;
		if (p.version == &apk_null_blob &&
		    p0->version == &apk_null_blob)
			continue;
		disqualify_package(ss, p0->pkg, "conflicting provides");
	}
	reevaluate_reverse_deps(ss, name);
}

static void select_package(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_provider chosen = { NULL, &apk_null_blob }, *p;
	struct apk_package *pkg = NULL;
	struct apk_dependency *d;

	dbg_printf("select_package: %s\n", name->name);

	if (name->ss.requirers || name->ss.has_iif) {
		foreach_array_item(p, name->providers) {
			/* Ensure valid pinning and install-if trigger */
			if (name->ss.requirers == 0 &&
			    (!p->pkg->ss.iif_triggered ||
			     !p->pkg->ss.tag_ok))
				continue;
			/* Virtual packages cannot be autoselected */
			if (p->version == &apk_null_blob && p->pkg->name->ss.requirers == 0)
				continue;
			if (compare_providers(ss, p, &chosen) > 0)
				chosen = *p;
		}
	}

	pkg = chosen.pkg;
	if (pkg) {
		if (!pkg->ss.available || !pkg->ss.tag_ok) {
			/* Selecting broken or unallowed package */
			mark_error(ss, pkg);
		}
		dbg_printf("selecting: " PKG_VER_FMT ", available: %d\n", PKG_VER_PRINTF(pkg), pkg->ss.available);

		assign_name(ss, pkg->name, APK_PROVIDER_FROM_PACKAGE(pkg));
		foreach_array_item(d, pkg->provides)
			assign_name(ss, d->name, APK_PROVIDER_FROM_PROVIDES(pkg, d));

		ss->solver_flags_inherit = pkg->ss.solver_flags_inheritable;
		ss->pinning_inherit = pkg->ss.pinning_allowed;
		foreach_array_item(d, pkg->depends)
			apply_constraint(ss, pkg, d);
		ss->solver_flags_inherit = 0;
		ss->pinning_inherit = 0;

		ss->num_selections++;
	} else {
		dbg_printf("selecting: %s [unassigned]\n", name->name);
		assign_name(ss, name, provider_none);
		ss->errors += (name->ss.requirers > 0);
	}
}

static void generate_change_dep(struct apk_solver_state *ss, struct apk_package *ppkg, struct apk_dependency *dep);
static void generate_change_iif(struct apk_solver_state *ss, struct apk_name *name);

static void generate_change(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_name **pname;
	struct apk_package *pkg = name->ss.chosen.pkg, *opkg;
	struct apk_changeset *changeset = ss->changeset;
	struct apk_change *change;
	struct apk_dependency *d;

	if (pkg == NULL)
		return;

	if (pkg->ss.in_changeset)
		return;
	pkg->ss.in_changeset = 1;
	pkg->name->ss.in_changeset = 1;

	foreach_array_item(d, pkg->depends)
		generate_change_dep(ss, pkg, d);

	change = &changeset->changes->item[ss->num_solution_entries++];
	dbg_printf("Selecting: "PKG_VER_FMT"%s\n", PKG_VER_PRINTF(pkg), pkg->ss.available ? "" : " [NOT AVAILABLE]");
	opkg = apk_pkg_get_installed(pkg->name);
	*change = (struct apk_change) {
		.old_pkg = opkg,
		.old_repository_tag = opkg ? opkg->ipkg->repository_tag : 0,
		.new_pkg = pkg,
		.new_repository_tag = get_tag(ss->db, pkg->ss.pinning_allowed, get_pkg_repos(ss->db, pkg)),
		.reinstall = !!(pkg->ss.solver_flags & APK_SOLVERF_REINSTALL),
	};
	if (change->new_pkg == NULL)
		changeset->num_remove++;
	else if (change->old_pkg == NULL)
		changeset->num_install++;
	else if (change->new_pkg != change->old_pkg || change->reinstall ||
		 change->new_repository_tag != change->old_repository_tag)
		changeset->num_adjust++;

	foreach_array_item(pname, pkg->name->rinstall_if)
		generate_change_iif(ss, *pname);
}

static void generate_change_iif(struct apk_solver_state *ss, struct apk_name *name)
{
	struct apk_package *pkg = name->ss.chosen.pkg;
	struct apk_dependency *dep0;

	if (pkg == NULL || !name->ss.seen)
		return;

	foreach_array_item(dep0, pkg->install_if) {
		struct apk_name *name0 = dep0->name;
		if (!name0->ss.in_changeset)
			return;
		if (!apk_dep_is_provided(dep0, &name0->ss.chosen))
			return;
	}

	generate_change(ss, name);
}

static void generate_change_dep(struct apk_solver_state *ss, struct apk_package *ppkg, struct apk_dependency *dep)
{
	struct apk_name *name = dep->name;
	struct apk_package *pkg = name->ss.chosen.pkg;

	if (!apk_dep_is_provided(dep, &name->ss.chosen))
		mark_error(ss, ppkg);

	generate_change(ss, name);

	if (pkg && pkg->ss.error)
		mark_error(ss, ppkg);
}

static void generate_changeset(struct apk_solver_state *ss, struct apk_dependency_array *world)
{
	struct apk_changeset *changeset = ss->changeset;
	struct apk_installed_package *ipkg;
	struct apk_dependency *d;

	list_for_each_entry(ipkg, &ss->db->installed.packages, installed_pkgs_list) {
		struct apk_name *name = ipkg->pkg->name;
		if (name->ss.chosen.pkg == NULL && !name->ss.locked)
			ss->num_selections++;
	}

	apk_change_array_resize(&ss->changeset->changes, ss->num_selections);
	foreach_array_item(d, world)
		generate_change_dep(ss, NULL, d);

	/* FIXME: could order better the removals of unneeded packages */
	list_for_each_entry(ipkg, &ss->db->installed.packages, installed_pkgs_list) {
		struct apk_name *name = ipkg->pkg->name;
		if (name->ss.chosen.pkg == NULL && !name->ss.in_changeset) {
			struct apk_change *change = &changeset->changes->item[ss->num_solution_entries++];
			*change = (struct apk_change) {
				.old_pkg = ipkg->pkg,
				.new_pkg = NULL,
			};
			changeset->num_remove++;
		}
	}

	changeset->num_total_changes = changeset->num_install + changeset->num_remove + changeset->num_adjust;

#if 1
	/* FIXME: calculate num_solution_entries correctly */
	ASSERT(ss->num_solution_entries <= changeset->changes->num,
		"Got %d changes, but expected %d\n",
		ss->num_solution_entries, changeset->changes->num);
	apk_change_array_resize(&ss->changeset->changes, ss->num_solution_entries);
#else
	ASSERT(ss->num_solution_entries == changeset->changes->num,
		"Got %d changes, but expected %d\n",
		ss->num_solution_entries, changeset->changes->num);
#endif
}

static int free_state(apk_hash_item item, void *ctx)
{
	struct apk_name *name = (struct apk_name *) item;
	memset(&name->ss, 0, sizeof(name->ss));
	return 0;
}

static int free_package(apk_hash_item item, void *ctx)
{
	struct apk_package *pkg = (struct apk_package *) item;
	memset(&pkg->ss, 0, sizeof(pkg->ss));
	return 0;
}

int apk_solver_solve(struct apk_database *db,
		     unsigned short solver_flags,
		     struct apk_dependency_array *world,
		     struct apk_changeset *changeset)
{
	struct apk_name *name, *name0;
	struct apk_package *pkg;
	struct apk_solver_state ss_data, *ss = &ss_data;
	struct apk_dependency *d;

restart:
	memset(ss, 0, sizeof(*ss));
	ss->db = db;
	ss->changeset = changeset;
	ss->default_repos = apk_db_get_pinning_mask_repos(db, APK_DEFAULT_PINNING_MASK);
	list_init(&ss->dirty_head);
	list_init(&ss->unresolved_head);

	dbg_printf("applying world\n");
	ss->prefer_pinning = 1;
	ss->solver_flags_inherit = solver_flags;
	foreach_array_item(d, world) {
		if (d->broken)
			continue;
		name = d->name;
		name->ss.in_world_dependency = 1;
		discover_name(ss, d->name);
		ss->pinning_inherit = BIT(d->repository_tag);
		apply_constraint(ss, NULL, d);
	}
	ss->solver_flags_inherit = 0;
	ss->pinning_inherit = 0;
	ss->prefer_pinning = 0;
	dbg_printf("applying world [finished]\n");

	do {
		while (!list_empty(&ss->dirty_head)) {
			name = list_pop(&ss->dirty_head, struct apk_name, ss.dirty_list);
			reconsider_name(ss, name);
		}

		name = NULL;
		list_for_each_entry(name0, &ss->unresolved_head, ss.unresolved_list) {
			if (name0->ss.reverse_deps_done && name0->ss.requirers && !name0->ss.has_options) {
				name = name0;
				break;
			}
			if (name == NULL)
				goto prefer;
			if ((!!name0->ss.requirers) - (!!name->ss.requirers) < 0)
				continue;
			if (name0->ss.max_dep_chain - name->ss.max_dep_chain < 0)
				continue;
		prefer:
			name = name0;
		}
		if (name == NULL)
			break;

		select_package(ss, name);
	} while (1);

	generate_changeset(ss, world);

	if (ss->errors && (apk_flags & APK_FORCE)) {
		foreach_array_item(d, world) {
			name = d->name;
			pkg = name->ss.chosen.pkg;
			if (pkg == NULL || pkg->ss.error) {
				d->broken = 1;
				dbg_printf("disabling broken world dep: %s", name->name);
			}
		}
		apk_hash_foreach(&db->available.names, free_state, NULL);
		apk_hash_foreach(&db->available.packages, free_package, NULL);
		goto restart;
	}

	apk_hash_foreach(&db->available.names, free_state, NULL);
	apk_hash_foreach(&db->available.packages, free_package, NULL);
	dbg_printf("solver done, errors=%d\n", ss->errors);

	return ss->errors;
}