solver: new package selection logic (which is not yet used)

 * basic code for a backtracking, forward checking dependency satisfier
 * works better when there are tricky dependencies to solve
   (when can't just upgrade everything to most preferred versions)
 * the new code always evaluates all of 'world' constraints
   (old code just does incremental updates based on heuristics)
 * is probably somewhat slower than old code (probably unnoticeable
   difference in most cases)
 * makes easier to write support for provides and repository pinning
 * test applet and a bunch of test cases added which uses the new code
 * from the old feature set install_if is not yet implemented

1 files changed, 563 insertions, 0 deletions

diff --git a/src/solver.c b/src/solver.c
new file mode 100644
index 0000000..71cdccc
--- /dev/null
+++ b/src/solver.c
@@ -0,0 +1,563 @@
+/* solver.c - Alpine Package Keeper (APK)
+ * A backtracking, forward checking dependency graph solver.
+ *
+ * Copyright (C) 2011 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.
+ */
+
+/* FIXME: install-if not supported yet */
+
+#include <stdlib.h>
+#include "apk_defines.h"
+#include "apk_database.h"
+#include "apk_package.h"
+#include "apk_solver.h"
+
+#if 0
+#include <stdio.h>
+#define dbg_printf(args...) fprintf(stderr, args)
+#else
+#define dbg_printf(args...)
+#endif
+
+#define APK_PKGSTF_NOINSTALL		0
+#define APK_PKGSTF_INSTALL		1
+#define APK_PKGSTF_BRANCH		2
+#define APK_PKGSTF_ALT_BRANCH		4
+
+struct apk_package_state {
+	struct apk_package *backtrack;
+	unsigned short flags;
+	unsigned short conflicts;
+};
+
+struct apk_name_state {
+	struct list_head unsolved_list;
+	struct apk_package *chosen;
+	struct apk_package *preferred;
+	unsigned short requirers;
+};
+
+struct apk_solver_state {
+	struct apk_database *db;
+	struct apk_package_state *pkg_state;
+	struct apk_name_state *name_state;
+	struct list_head unsolved_list_head;
+	struct apk_package *latest_decision;
+	unsigned int topology_position;
+	unsigned int assigned_names;
+
+	struct apk_package_array *best_solution;
+	unsigned int best_cost;
+};
+
+static int apply_constraint(struct apk_solver_state *ss, struct apk_dependency *dep);
+static int undo_constraint(struct apk_solver_state *ss, struct apk_dependency *dep);
+static int push_decision(struct apk_solver_state *ss, struct apk_package *pkg,
+			 int flags);
+
+static inline int pkg_available(struct apk_database *db, struct apk_package *pkg)
+{
+	if (pkg->ipkg != NULL)
+		return TRUE;
+	if (pkg->installed_size == 0)
+		return TRUE;
+	if (pkg->filename != NULL)
+		return TRUE;
+	if (apk_db_select_repo(db, pkg) != NULL)
+		return TRUE;
+	return FALSE;
+}
+
+static int foreach_dependency(struct apk_solver_state *ss, struct apk_dependency_array *deps,
+			      int (*func)(struct apk_solver_state *ss, struct apk_dependency *dep))
+{
+	int i, r = 0;
+	for (i = 0; i < deps->num; i++)
+		r += func(ss, &deps->item[i]);
+	return r;
+}
+
+static void calculate_preferred(struct apk_database *db,
+			        struct apk_name *name,
+			        struct apk_name_state *ns)
+{
+	struct apk_package *installed = NULL, *latest = NULL;
+	int i;
+
+	/* Get latest and installed packages */
+	for (i = 0; i < name->pkgs->num; i++) {
+		struct apk_package *pkg = name->pkgs->item[i];
+
+		if (pkg->ipkg != NULL)
+			installed = pkg;
+		else if (!pkg_available(db, pkg))
+			continue;
+		if (latest == NULL) {
+			latest = pkg;
+			continue;
+		}
+
+		if ((apk_flags & APK_PREFER_AVAILABLE) ||
+		    (name->flags & APK_NAME_REINSTALL)) {
+			if (latest->repos != 0 && pkg->repos == 0)
+				continue;
+			if (latest->repos == 0 && pkg->repos != 0) {
+				latest = pkg;
+				continue;
+			}
+			/* Otherwise both are not available, or both are
+			 * available and we just compare the versions then */
+		}
+		if (apk_pkg_version_compare(pkg, latest) == APK_VERSION_GREATER)
+			latest = pkg;
+	}
+
+	/* Choose the best looking candidate. */
+	if (apk_flags & APK_UPGRADE) {
+		ns->preferred = latest;
+	} else {
+		if (installed != NULL &&
+		    (installed->repos != 0 ||
+		     !(name->flags & APK_NAME_REINSTALL)))
+			ns->preferred = installed;
+		else
+			ns->preferred = latest;
+	}
+
+}
+
+static int update_name_state(struct apk_solver_state *ss,
+			     struct apk_name *name, struct apk_name_state *ns)
+{
+	struct apk_package *pkg_best = NULL;
+	int i, options = 0;
+
+	for (i = 0; i < name->pkgs->num; i++) {
+		struct apk_package *pkg0 = name->pkgs->item[i];
+		struct apk_package_state *ps0 = &ss->pkg_state[pkg0->topology_sort];
+
+		if (pkg0->topology_sort >= ss->topology_position ||
+		    ps0->conflicts != 0)
+			continue;
+
+		options++;
+		if (pkg_best == NULL ||
+		    pkg0->topology_sort > pkg_best->topology_sort)
+			pkg_best = pkg0;
+	}
+	ns->chosen = pkg_best;
+	dbg_printf("%s: adjusted preference %d -> %d (options left %d)\n",
+		   name->name, ss->topology_position, ns->chosen->topology_sort,
+		   options);
+	return options;
+}
+
+static int apply_decision(struct apk_solver_state *ss,
+			  struct apk_package *pkg,
+			  struct apk_package_state *ps)
+{
+	struct apk_name_state *ns = &ss->name_state[pkg->name->id];
+
+	dbg_printf("apply_decision: " PKG_VER_FMT " %s\n", PKG_VER_PRINTF(pkg),
+		   (ps->flags & APK_PKGSTF_INSTALL) ? "INSTALL" : "NO_INSTALL");
+
+	if (ps->flags & APK_PKGSTF_INSTALL) {
+		ss->assigned_names++;
+		ns->chosen = pkg;
+		if (list_hashed(&ns->unsolved_list)) {
+			list_del(&ns->unsolved_list);
+			list_init(&ns->unsolved_list);
+			dbg_printf("%s: deleting from unsolved list\n",
+				   pkg->name->name);
+		}
+		return foreach_dependency(ss, pkg->depends, apply_constraint);
+	} else {
+		if (!list_hashed(&ns->unsolved_list)) {
+			ns->chosen = NULL;
+			return 0;
+		}
+		if (update_name_state(ss, pkg->name, ns) != 1)
+			return 0;
+		/* the name is required and we are left with only one candidate
+		 * after deciding to not install pkg; autoselect the last option */
+		return push_decision(ss, ns->chosen, APK_PKGSTF_INSTALL);
+	}
+}
+
+static void undo_decision(struct apk_solver_state *ss,
+			  struct apk_package *pkg,
+			  struct apk_package_state *ps)
+{
+	struct apk_name_state *ns = &ss->name_state[pkg->name->id];
+
+	dbg_printf("undo_decision: " PKG_VER_FMT " %s\n", PKG_VER_PRINTF(pkg),
+		   (ps->flags & APK_PKGSTF_INSTALL) ? "INSTALL" : "NO_INSTALL");
+
+	if (ps->flags & APK_PKGSTF_INSTALL) {
+		ss->assigned_names--;
+		foreach_dependency(ss, pkg->depends, undo_constraint);
+
+		if (ns->requirers) {
+			list_add(&ns->unsolved_list, &ss->unsolved_list_head);
+			dbg_printf("%s: adding back to unsolved list (requirers: %d)\n",
+				pkg->name->name, ns->requirers);
+		} else {
+			ns->chosen = NULL;
+		}
+	}
+}
+
+static int push_decision(struct apk_solver_state *ss, struct apk_package *pkg,
+			 int flags)
+{
+	struct apk_package_state *ps = &ss->pkg_state[pkg->topology_sort];
+
+	ps->backtrack = ss->latest_decision;
+	ps->flags = flags;
+	ss->latest_decision = pkg;
+	if (flags & APK_PKGSTF_BRANCH) {
+		ss->topology_position = pkg->topology_sort;
+		dbg_printf("push_decision: adding new BRANCH at topology_position %d\n",
+			   ss->topology_position);
+	} else
+		ps->flags |= APK_PKGSTF_ALT_BRANCH;
+
+	return apply_decision(ss, pkg, ps);
+}
+
+static int next_branch(struct apk_solver_state *ss)
+{
+	struct apk_package *pkg;
+	struct apk_package_state *ps;
+	int r;
+
+	while (1) {
+		pkg = ss->latest_decision;
+		ps = &ss->pkg_state[pkg->topology_sort];
+		undo_decision(ss, pkg, ps);
+
+		if (ps->flags & APK_PKGSTF_ALT_BRANCH) {
+			pkg = ps->backtrack;
+			ss->latest_decision = pkg;
+			if (pkg == NULL) /* at root, can't back track */
+				return 1;
+			ss->topology_position = pkg->topology_sort;
+			dbg_printf("next_branch: undo decision at topology_position %d\n",
+				   ss->topology_position);
+		} else {
+			dbg_printf("next_branch: swapping BRANCH at topology_position %d\n",
+				   ss->topology_position);
+
+			ps->flags |= APK_PKGSTF_ALT_BRANCH;
+			ps->flags ^= APK_PKGSTF_INSTALL;
+
+			r = apply_decision(ss, pkg, ps);
+			if (r == 0 /*|| report_errors */)
+				return r;
+		}
+	}
+}
+
+static int apply_constraint(struct apk_solver_state *ss, struct apk_dependency *dep)
+{
+	struct apk_name *name = dep->name;
+	struct apk_name_state *ns = &ss->name_state[name->id];
+	struct apk_package *pkg_best = NULL;
+	int i, options = 0;
+
+	for (i = 0; i < name->pkgs->num; i++) {
+		struct apk_package *pkg0 = name->pkgs->item[i];
+		struct apk_package_state *ps0 = &ss->pkg_state[pkg0->topology_sort];
+
+		if (pkg0->topology_sort >= ss->topology_position) {
+			dbg_printf(PKG_VER_FMT ": topology skip %d > %d\n",
+				   PKG_VER_PRINTF(pkg0),
+				   pkg0->topology_sort, ss->topology_position);
+			continue;
+		}
+
+		if (!apk_dep_is_satisfied(dep, pkg0)) {
+			ps0->conflicts++;
+			dbg_printf(PKG_VER_FMT ": conflicts++ -> %d\n",
+				   PKG_VER_PRINTF(pkg0),
+				   ps0->conflicts);
+		}
+		if (ps0->conflicts == 0) {
+			options++;
+			if (pkg_best == NULL ||
+			    pkg0->topology_sort > pkg_best->topology_sort)
+				pkg_best = pkg0;
+		}
+	}
+
+	ns->requirers++;
+	if (!list_hashed(&ns->unsolved_list) && ns->chosen != NULL) {
+		dbg_printf(PKG_VER_FMT " selected already for %s\n",  PKG_VER_PRINTF(ns->chosen),
+			   dep->name->name);
+		return !apk_dep_is_satisfied(dep, ns->chosen);
+	}
+
+	ns->chosen = pkg_best;
+	if (options == 0) {
+		/* we conflicted with all possible options */
+		if (list_hashed(&ns->unsolved_list)) {
+			dbg_printf("%s: deleting unsolved (unable to satisfy)\n",
+				   name->name);
+			list_del(&ns->unsolved_list);
+			list_init(&ns->unsolved_list);
+		}
+		return 1;
+	}
+	if (options == 1) {
+		/* we can short circuit to select the only option
+		 * possible */
+		return push_decision(ss, pkg_best, APK_PKGSTF_INSTALL);
+	}
+	/* multiple ways to satisfy the requirement */
+	if (ns->requirers == 1) {
+		list_init(&ns->unsolved_list);
+		list_add(&ns->unsolved_list, &ss->unsolved_list_head);
+		dbg_printf("%s: adding to unsolved list (%d options)\n",
+			   name->name, options);
+	}
+
+	return 0;
+}
+
+static int undo_constraint(struct apk_solver_state *ss, struct apk_dependency *dep)
+{
+	struct apk_name *name = dep->name;
+	struct apk_name_state *ns = &ss->name_state[name->id];
+	struct apk_package *pkg_best = NULL;
+	int i, had_options = 0, options = 0;
+
+	for (i = 0; i < name->pkgs->num; i++) {
+		struct apk_package *pkg0 = name->pkgs->item[i];
+		struct apk_package_state *ps0 = &ss->pkg_state[pkg0->topology_sort];
+
+		if (pkg0->topology_sort >= ss->topology_position)
+			continue;
+
+		if (ps0->conflicts == 0)
+			had_options++;
+		if (!apk_dep_is_satisfied(dep, pkg0)) {
+			ps0->conflicts--;
+			dbg_printf(PKG_VER_FMT ": conflicts-- -> %d\n",
+				   PKG_VER_PRINTF(pkg0),
+				   ps0->conflicts);
+		}
+		if (ps0->conflicts == 0) {
+			options++;
+			if (pkg_best == NULL ||
+			    pkg0->topology_sort > pkg_best->topology_sort)
+				pkg_best = pkg0;
+		}
+	}
+
+	ns->requirers--;
+
+	if (ns->requirers == 0) {
+		if (list_hashed(&ns->unsolved_list)) {
+			list_del(&ns->unsolved_list);
+			list_init(&ns->unsolved_list);
+			ns->chosen = NULL;
+		}
+	} else {
+		ns->chosen = pkg_best;
+		if (had_options == 0 && options != 0) {
+			if (!list_hashed(&ns->unsolved_list)) {
+				list_add(&ns->unsolved_list, &ss->unsolved_list_head);
+				dbg_printf("%s: adding back to unsolved list (with %d options, %d requirers)\n",
+					   name->name, options, ns->requirers);
+			} else {
+				ns->chosen = NULL;
+			}
+			return 0;
+		}
+	}
+	return 0;
+}
+
+static int expand_branch(struct apk_solver_state *ss)
+{
+	int r;
+
+	while (1) {
+		struct apk_name_state *ns;
+		struct apk_package *pkg0 = NULL;
+
+		/* FIXME: change unsolved_list to a priority queue */
+		list_for_each_entry(ns, &ss->unsolved_list_head, unsolved_list) {
+			if (pkg0 == NULL ||
+			    ns->chosen->topology_sort > pkg0->topology_sort)
+				pkg0 = ns->chosen;
+		}
+		if (pkg0 == NULL) {
+			dbg_printf("expand_branch: list is empty\n");
+			return 0;
+		}
+
+		/* someone needs to provide this name -- find next eligible
+		 * provider candidate */
+		ns = &ss->name_state[pkg0->name->id];
+		dbg_printf("expand_branch: %s %d\n", pkg0->name->name, pkg0->topology_sort);
+
+		/* Is there something we can still use? */
+		if (ns->preferred == NULL)
+			calculate_preferred(ss->db, pkg0->name, ns);
+
+		r = push_decision(ss, pkg0,
+			(pkg0 == ns->preferred) ?
+			 (APK_PKGSTF_INSTALL | APK_PKGSTF_BRANCH) :
+			 (APK_PKGSTF_NOINSTALL | APK_PKGSTF_BRANCH));
+
+		if (/*no_error_reporting &&*/ r)
+			return r;
+	}
+
+	return 0;
+}
+
+static void record_solution(struct apk_solver_state *ss)
+{
+	struct apk_package *pkg;
+	struct apk_package_state *ps;
+	int i;
+
+	apk_package_array_resize(&ss->best_solution, ss->assigned_names);
+
+	i = 0;
+	pkg = ss->latest_decision;
+	while (pkg != NULL) {
+		ps = &ss->pkg_state[pkg->topology_sort];
+		if (ps->flags & APK_PKGSTF_INSTALL)
+			ss->best_solution->item[i++] = pkg;
+
+		dbg_printf("record_solution: " PKG_VER_FMT ": %sINSTALL\n",
+			   PKG_VER_PRINTF(pkg),
+			   (ps->flags & APK_PKGSTF_INSTALL) ? "" : "NO_");
+
+		pkg = ps->backtrack;
+	}
+}
+
+int apk_solver_solve(struct apk_database *db, struct apk_dependency_array *world,
+		     struct apk_package_array **solution)
+{
+	struct apk_solver_state *ss;
+	int r;
+
+	ss = calloc(1, sizeof(struct apk_solver_state));
+	ss->db = db;
+	ss->topology_position = -1;
+	list_init(&ss->unsolved_list_head);
+	ss->pkg_state = calloc(db->available.packages.num_items+1, sizeof(struct apk_package_state));
+	ss->name_state = calloc(db->available.names.num_items+1, sizeof(struct apk_name_state));
+
+	r = foreach_dependency(ss, world, apply_constraint);
+	while (r == 0) {
+		if (expand_branch(ss) == 0) {
+			/* found solution*/
+			/* FIXME: we should check other permutations if they
+			 * have smaller cost to find optimal changeset */
+			break;
+		} else {
+			/* conflicting constraints -- backtrack */
+			r = next_branch(ss);
+		}
+	}
+
+	/* collect packages */
+	if (r == 0) {
+		record_solution(ss);
+		*solution = ss->best_solution;
+	}
+
+	free(ss->name_state);
+	free(ss->pkg_state);
+	free(ss);
+
+	return r;
+}
+
+static int compare_change(const void *p1, const void *p2)
+{
+	const struct apk_change *c1 = (const struct apk_change *) p1;
+	const struct apk_change *c2 = (const struct apk_change *) p2;
+
+	if (c1->newpkg == NULL) {
+		if (c2->newpkg == NULL)
+			/* both deleted - reverse topology order */
+			return c1->oldpkg->topology_sort - c2->oldpkg->topology_sort;
+
+		/* c1 deleted, c2 installed -> c2 first*/
+		return -1;
+	}
+	if (c2->newpkg == NULL)
+		/* c1 installed, c2 deleted -> c1 first*/
+		return 1;
+
+	return c2->newpkg->topology_sort - c1->newpkg->topology_sort;
+}
+
+int apk_solver_generate_changeset(struct apk_database *db,
+				  struct apk_package_array *solution,
+				  struct apk_changeset *changeset)
+{
+	struct apk_name *name;
+	struct apk_package *pkg, *pkg0;
+	struct apk_installed_package *ipkg;
+	int num_installs = 0, num_removed = 0, ci = 0;
+	int i, j;
+
+	/* calculate change set size */
+	for (i = 0; i < solution->num; i++) {
+		pkg = solution->item[i];
+		name = pkg->name;
+		if (pkg->ipkg == NULL || (name->flags & APK_NAME_REINSTALL))
+			num_installs++;
+		name->flags |= APK_NAME_VISITED;
+	}
+
+	list_for_each_entry(ipkg, &db->installed.packages, installed_pkgs_list) {
+		if (!(ipkg->pkg->name->flags & APK_NAME_VISITED))
+			num_removed++;
+	}
+
+	/* construct changeset */
+	apk_change_array_resize(&changeset->changes, num_installs + num_removed);
+	list_for_each_entry(ipkg, &db->installed.packages, installed_pkgs_list) {
+		if (ipkg->pkg->name->flags & APK_NAME_VISITED)
+			continue;
+		changeset->changes->item[ci].oldpkg = ipkg->pkg;
+		ci++;
+	}
+	for (i = 0; i < solution->num; i++) {
+		pkg = solution->item[i];
+		name = pkg->name;
+
+		if (pkg->ipkg == NULL || (name->flags & APK_NAME_REINSTALL)) {
+			for (j = 0; j < name->pkgs->num; j++) {
+				pkg0 = name->pkgs->item[j];
+				if (pkg0->ipkg == NULL)
+					continue;
+				changeset->changes->item[ci].oldpkg = pkg0;
+				break;
+			}
+			changeset->changes->item[ci].newpkg = pkg;
+			ci++;
+		}
+		name->flags &= ~APK_NAME_VISITED;
+	}
+
+	/* sort changeset to topology order */
+	qsort(changeset->changes->item, changeset->changes->num,
+	      sizeof(struct apk_change), compare_change);
+
+	return 0;
+}