Merge branch 'maint'

[pacman-ng.git] / lib / libalpm / deps.c

/*
 *  deps.c
 *
 *  Copyright (c) 2006-2011 Pacman Development Team <pacman-dev@archlinux.org>
 *  Copyright (c) 2002-2006 by Judd Vinet <jvinet@zeroflux.org>
 *  Copyright (c) 2005 by Aurelien Foret <orelien@chez.com>
 *  Copyright (c) 2005, 2006 by Miklos Vajna <vmiklos@frugalware.org>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "config.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/* libalpm */
#include "deps.h"
#include "alpm_list.h"
#include "util.h"
#include "log.h"
#include "graph.h"
#include "package.h"
#include "db.h"
#include "handle.h"

void _alpm_dep_free(pmdepend_t *dep)
{
        FREE(dep->name);
        FREE(dep->version);
        FREE(dep);
}

static pmdepmissing_t *depmiss_new(const char *target, pmdepend_t *dep,
                const char *causingpkg)
{
        pmdepmissing_t *miss;

        ALPM_LOG_FUNC;

        MALLOC(miss, sizeof(pmdepmissing_t), RET_ERR(PM_ERR_MEMORY, NULL));

        STRDUP(miss->target, target, RET_ERR(PM_ERR_MEMORY, NULL));
        miss->depend = _alpm_dep_dup(dep);
        STRDUP(miss->causingpkg, causingpkg, RET_ERR(PM_ERR_MEMORY, NULL));

        return miss;
}

void _alpm_depmiss_free(pmdepmissing_t *miss)
{
        _alpm_dep_free(miss->depend);
        FREE(miss->target);
        FREE(miss->causingpkg);
        FREE(miss);
}

/* Does pkg1 depend on pkg2, ie. does pkg2 satisfy a dependency of pkg1? */
static int _alpm_dep_edge(pmpkg_t *pkg1, pmpkg_t *pkg2)
{
        alpm_list_t *i;
        for(i = alpm_pkg_get_depends(pkg1); i; i = i->next) {
                if(_alpm_depcmp(pkg2, i->data)) {
                        return 1;
                }
        }
        return 0;
}

/* Convert a list of pmpkg_t * to a graph structure,
 * with a edge for each dependency.
 * Returns a list of vertices (one vertex = one package)
 * (used by alpm_sortbydeps)
 */
static alpm_list_t *dep_graph_init(alpm_list_t *targets)
{
        alpm_list_t *i, *j;
        alpm_list_t *vertices = NULL;
        /* We create the vertices */
        for(i = targets; i; i = i->next) {
                pmgraph_t *vertex = _alpm_graph_new();
                vertex->data = (void *)i->data;
                vertices = alpm_list_add(vertices, vertex);
        }

        /* We compute the edges */
        for(i = vertices; i; i = i->next) {
                pmgraph_t *vertex_i = i->data;
                pmpkg_t *p_i = vertex_i->data;
                /* TODO this should be somehow combined with alpm_checkdeps */
                for(j = vertices; j; j = j->next) {
                        pmgraph_t *vertex_j = j->data;
                        pmpkg_t *p_j = vertex_j->data;
                        if(_alpm_dep_edge(p_i, p_j)) {
                                vertex_i->children =
                                        alpm_list_add(vertex_i->children, vertex_j);
                        }
                }
                vertex_i->childptr = vertex_i->children;
        }
        return vertices;
}

/* Re-order a list of target packages with respect to their dependencies.
 *
 * Example (reverse == 0):
 *   A depends on C
 *   B depends on A
 *   Target order is A,B,C,D
 *
 *   Should be re-ordered to C,A,B,D
 *
 * if reverse is > 0, the dependency order will be reversed.
 *
 * This function returns the new alpm_list_t* target list.
 *
 */
alpm_list_t *_alpm_sortbydeps(alpm_list_t *targets, int reverse)
{
        alpm_list_t *newtargs = NULL;
        alpm_list_t *vertices = NULL;
        alpm_list_t *vptr;
        pmgraph_t *vertex;

        ALPM_LOG_FUNC;

        if(targets == NULL) {
                return NULL;
        }

        _alpm_log(PM_LOG_DEBUG, "started sorting dependencies\n");

        vertices = dep_graph_init(targets);

        vptr = vertices;
        vertex = vertices->data;
        while(vptr) {
                /* mark that we touched the vertex */
                vertex->state = -1;
                int found = 0;
                while(vertex->childptr && !found) {
                        pmgraph_t *nextchild = vertex->childptr->data;
                        vertex->childptr = vertex->childptr->next;
                        if (nextchild->state == 0) {
                                found = 1;
                                nextchild->parent = vertex;
                                vertex = nextchild;
                        }
                        else if(nextchild->state == -1) {
                                pmpkg_t *vertexpkg = vertex->data;
                                pmpkg_t *childpkg = nextchild->data;
                                const char *message;

                                _alpm_log(PM_LOG_WARNING, _("dependency cycle detected:\n"));
                                if(reverse) {
                                        message =_("%s will be removed after its %s dependency\n");
                                } else {
                                        message =_("%s will be installed before its %s dependency\n");
                                }
                                _alpm_log(PM_LOG_WARNING, message, vertexpkg->name, childpkg->name);
                        }
                }
                if(!found) {
                        newtargs = alpm_list_add(newtargs, vertex->data);
                        /* mark that we've left this vertex */
                        vertex->state = 1;
                        vertex = vertex->parent;
                        if(!vertex) {
                                vptr = vptr->next;
                                while(vptr) {
                                        vertex = vptr->data;
                                        if (vertex->state == 0) break;
                                        vptr = vptr->next;
                                }
                        }
                }
        }

        _alpm_log(PM_LOG_DEBUG, "sorting dependencies finished\n");

        if(reverse) {
                /* reverse the order */
                alpm_list_t *tmptargs = alpm_list_reverse(newtargs);
                /* free the old one */
                alpm_list_free(newtargs);
                newtargs = tmptargs;
        }

        alpm_list_free_inner(vertices, _alpm_graph_free);
        alpm_list_free(vertices);

        return newtargs;
}

static int no_dep_version(void)
{
        int flags = alpm_trans_get_flags();
        return flags != -1 && (flags & PM_TRANS_FLAG_NODEPVERSION);
}

static pmdepend_t *filtered_depend(pmdepend_t *dep, int nodepversion)
{
        if(nodepversion) {
                pmdepend_t *newdep = _alpm_dep_dup(dep);
                ASSERT(newdep, return dep);
                newdep->mod = PM_DEP_MOD_ANY;
                dep = newdep;
        }
        return dep;
}

static void release_filtered_depend(pmdepend_t *dep, int nodepversion)
{
        if(nodepversion) {
                free(dep);
        }
}

static pmpkg_t *find_dep_satisfier(alpm_list_t *pkgs, pmdepend_t *dep)
{
        alpm_list_t *i;

        for(i = pkgs; i; i = alpm_list_next(i)) {
                pmpkg_t *pkg = i->data;
                if(_alpm_depcmp(pkg, dep)) {
                        return pkg;
                }
        }
        return NULL;
}

/** Find a package satisfying a specified dependency.
 * The dependency can include versions with depmod operators.
 * @param pkgs an alpm_list_t* of pmpkg_t where the satisfier will be searched
 * @param depstring package or provision name, versioned or not
 * @return a pmpkg_t* satisfying depstring
 */
pmpkg_t SYMEXPORT *alpm_find_satisfier(alpm_list_t *pkgs, const char *depstring)
{
        pmdepend_t *dep = _alpm_splitdep(depstring);
        pmpkg_t *pkg = find_dep_satisfier(pkgs, dep);
        _alpm_dep_free(dep);
        return pkg;
}

/** Checks dependencies and returns missing ones in a list.
 * Dependencies can include versions with depmod operators.
 * @param pkglist the list of local packages
 * @param reversedeps handles the backward dependencies
 * @param remove an alpm_list_t* of packages to be removed
 * @param upgrade an alpm_list_t* of packages to be upgraded (remove-then-upgrade)
 * @return an alpm_list_t* of pmdepmissing_t pointers.
 */
alpm_list_t SYMEXPORT *alpm_checkdeps(alpm_list_t *pkglist, int reversedeps,
                alpm_list_t *remove, alpm_list_t *upgrade)
{
        alpm_list_t *i, *j;
        alpm_list_t *targets, *dblist = NULL, *modified = NULL;
        alpm_list_t *baddeps = NULL;
        int nodepversion;

        ALPM_LOG_FUNC;

        targets = alpm_list_join(alpm_list_copy(remove), alpm_list_copy(upgrade));
        for(i = pkglist; i; i = i->next) {
                pmpkg_t *pkg = i->data;
                if(_alpm_pkg_find(targets, pkg->name)) {
                        modified = alpm_list_add(modified, pkg);
                } else {
                        dblist = alpm_list_add(dblist, pkg);
                }
        }
        alpm_list_free(targets);

        nodepversion = no_dep_version();

        /* look for unsatisfied dependencies of the upgrade list */
        for(i = upgrade; i; i = i->next) {
                pmpkg_t *tp = i->data;
                _alpm_log(PM_LOG_DEBUG, "checkdeps: package %s-%s\n",
                                alpm_pkg_get_name(tp), alpm_pkg_get_version(tp));

                for(j = alpm_pkg_get_depends(tp); j; j = j->next) {
                        pmdepend_t *depend = j->data;
                        depend = filtered_depend(depend, nodepversion);
                        /* 1. we check the upgrade list */
                        /* 2. we check database for untouched satisfying packages */
                        if(!find_dep_satisfier(upgrade, depend) &&
                           !find_dep_satisfier(dblist, depend)) {
                                /* Unsatisfied dependency in the upgrade list */
                                pmdepmissing_t *miss;
                                char *missdepstring = alpm_dep_compute_string(depend);
                                _alpm_log(PM_LOG_DEBUG, "checkdeps: missing dependency '%s' for package '%s'\n",
                                                missdepstring, alpm_pkg_get_name(tp));
                                free(missdepstring);
                                miss = depmiss_new(alpm_pkg_get_name(tp), depend, NULL);
                                baddeps = alpm_list_add(baddeps, miss);
                        }
                        release_filtered_depend(depend, nodepversion);
                }
        }

        if(reversedeps) {
                /* reversedeps handles the backwards dependencies, ie,
                 * the packages listed in the requiredby field. */
                for(i = dblist; i; i = i->next) {
                        pmpkg_t *lp = i->data;
                        for(j = alpm_pkg_get_depends(lp); j; j = j->next) {
                                pmdepend_t *depend = j->data;
                                depend = filtered_depend(depend, nodepversion);
                                pmpkg_t *causingpkg = find_dep_satisfier(modified, depend);
                                /* we won't break this depend, if it is already broken, we ignore it */
                                /* 1. check upgrade list for satisfiers */
                                /* 2. check dblist for satisfiers */
                                if(causingpkg &&
                                   !find_dep_satisfier(upgrade, depend) &&
                                   !find_dep_satisfier(dblist, depend)) {
                                        pmdepmissing_t *miss;
                                        char *missdepstring = alpm_dep_compute_string(depend);
                                        _alpm_log(PM_LOG_DEBUG, "checkdeps: transaction would break '%s' dependency of '%s'\n",
                                                        missdepstring, alpm_pkg_get_name(lp));
                                        free(missdepstring);
                                        miss = depmiss_new(lp->name, depend, alpm_pkg_get_name(causingpkg));
                                        baddeps = alpm_list_add(baddeps, miss);
                                }
                                release_filtered_depend(depend, nodepversion);
                        }
                }
        }

        alpm_list_free(modified);
        alpm_list_free(dblist);

        return baddeps;
}

static int dep_vercmp(const char *version1, pmdepmod_t mod,
                const char *version2)
{
        int equal = 0;

        if(mod == PM_DEP_MOD_ANY) {
                equal = 1;
        } else {
                int cmp = alpm_pkg_vercmp(version1, version2);
                switch(mod) {
                        case PM_DEP_MOD_EQ: equal = (cmp == 0); break;
                        case PM_DEP_MOD_GE: equal = (cmp >= 0); break;
                        case PM_DEP_MOD_LE: equal = (cmp <= 0); break;
                        case PM_DEP_MOD_LT: equal = (cmp < 0); break;
                        case PM_DEP_MOD_GT: equal = (cmp > 0); break;
                        default: equal = 1; break;
                }
        }
        return equal;
}

int _alpm_depcmp(pmpkg_t *pkg, pmdepend_t *dep)
{
        alpm_list_t *i;
        int satisfy = 0;

        /* check (pkg->name, pkg->version) */
        if(pkg->name_hash && dep->name_hash
                        && pkg->name_hash != dep->name_hash) {
                /* skip more expensive checks */
        } else {
                satisfy = (strcmp(pkg->name, dep->name) == 0
                                && dep_vercmp(pkg->version, dep->mod, dep->version));
                if(satisfy) {
                        return satisfy;
                }
        }

        /* check provisions, format : "name=version" */
        for(i = alpm_pkg_get_provides(pkg); i && !satisfy; i = i->next) {
                const char *provision = i->data;
                const char *provver = strchr(provision, '=');

                if(provver == NULL) { /* no provision version */
                        satisfy = (dep->mod == PM_DEP_MOD_ANY
                                        && strcmp(provision, dep->name) == 0);
                } else {
                        /* This is a bit tricker than the old code for performance reasons. To
                         * prevent the need to copy and duplicate strings, strncmp only the name
                         * portion if they are the same length, since there is a version and
                         * operator in play here. Cast is to silence sign conversion warning;
                         * we know provver >= provision if we are here. */
                        size_t namelen = (size_t)(provver - provision);
                        provver += 1;
                        satisfy = (strlen(dep->name) == namelen
                                        && strncmp(provision, dep->name, namelen) == 0
                                        && dep_vercmp(provver, dep->mod, dep->version));
                }
        }

        return satisfy;
}

pmdepend_t *_alpm_splitdep(const char *depstring)
{
        pmdepend_t *depend;
        const char *ptr, *version = NULL;

        if(depstring == NULL) {
                return NULL;
        }

        CALLOC(depend, 1, sizeof(pmdepend_t), RET_ERR(PM_ERR_MEMORY, NULL));

        /* Find a version comparator if one exists. If it does, set the type and
         * increment the ptr accordingly so we can copy the right strings. */
        if((ptr = strstr(depstring, ">="))) {
                depend->mod = PM_DEP_MOD_GE;
                version = ptr + 2;
        } else if((ptr = strstr(depstring, "<="))) {
                depend->mod = PM_DEP_MOD_LE;
                version = ptr + 2;
        } else if((ptr = strstr(depstring, "="))) {
                /* Note: we must do =,<,> checks after <=, >= checks */
                depend->mod = PM_DEP_MOD_EQ;
                version = ptr + 1;
        } else if((ptr = strstr(depstring, "<"))) {
                depend->mod = PM_DEP_MOD_LT;
                version = ptr + 1;
        } else if((ptr = strstr(depstring, ">"))) {
                depend->mod = PM_DEP_MOD_GT;
                version = ptr + 1;
        } else {
                /* no version specified, leave version and ptr NULL */
                depend->mod = PM_DEP_MOD_ANY;
        }

        /* copy the right parts to the right places */
        STRNDUP(depend->name, depstring, ptr - depstring,
                        RET_ERR(PM_ERR_MEMORY, NULL));
        depend->name_hash = _alpm_hash_sdbm(depend->name);
        if(version) {
                STRDUP(depend->version, version, RET_ERR(PM_ERR_MEMORY, NULL));
        }

        return depend;
}

pmdepend_t *_alpm_dep_dup(const pmdepend_t *dep)
{
        pmdepend_t *newdep;
        CALLOC(newdep, 1, sizeof(pmdepend_t), RET_ERR(PM_ERR_MEMORY, NULL));

        STRDUP(newdep->name, dep->name, RET_ERR(PM_ERR_MEMORY, NULL));
        newdep->name_hash = dep->name_hash;
        STRDUP(newdep->version, dep->version, RET_ERR(PM_ERR_MEMORY, NULL));
        newdep->mod = dep->mod;

        return newdep;
}

/* These parameters are messy. We check if this package, given a list of
 * targets and a db is safe to remove. We do NOT remove it if it is in the
 * target list, or if if the package was explictly installed and
 * include_explicit == 0 */
static int can_remove_package(pmdb_t *db, pmpkg_t *pkg, alpm_list_t *targets,
                int include_explicit)
{
        alpm_list_t *i;

        if(_alpm_pkg_find(targets, alpm_pkg_get_name(pkg))) {
                return 0;
        }

        if(!include_explicit) {
                /* see if it was explicitly installed */
                if(alpm_pkg_get_reason(pkg) == PM_PKG_REASON_EXPLICIT) {
                        _alpm_log(PM_LOG_DEBUG, "excluding %s -- explicitly installed\n",
                                        alpm_pkg_get_name(pkg));
                        return 0;
                }
        }

        /* TODO: checkdeps could be used here, it handles multiple providers
         * better, but that also makes it slower.
         * Also this would require to first add the package to the targets list,
         * then call checkdeps with it, then remove the package from the targets list
         * if checkdeps detected it would break something */

        /* see if other packages need it */
        for(i = _alpm_db_get_pkgcache(db); i; i = i->next) {
                pmpkg_t *lpkg = i->data;
                if(_alpm_dep_edge(lpkg, pkg) && !_alpm_pkg_find(targets, lpkg->name)) {
                        return 0;
                }
        }

        /* it's ok to remove */
        return 1;
}

/**
 * @brief Adds unneeded dependencies to an existing list of packages.
 * By unneeded, we mean dependencies that are only required by packages in the
 * target list, so they can be safely removed.
 * If the input list was topo sorted, the output list will be topo sorted too.
 *
 * @param db package database to do dependency tracing in
 * @param *targs pointer to a list of packages
 * @param include_explicit if 0, explicitly installed packages are not included
 */
void _alpm_recursedeps(pmdb_t *db, alpm_list_t *targs, int include_explicit)
{
        alpm_list_t *i, *j;

        ALPM_LOG_FUNC;

        if(db == NULL || targs == NULL) {
                return;
        }

        for(i = targs; i; i = i->next) {
                pmpkg_t *pkg = i->data;
                for(j = _alpm_db_get_pkgcache(db); j; j = j->next) {
                        pmpkg_t *deppkg = j->data;
                        if(_alpm_dep_edge(pkg, deppkg)
                                        && can_remove_package(db, deppkg, targs, include_explicit)) {
                                _alpm_log(PM_LOG_DEBUG, "adding '%s' to the targets\n",
                                                alpm_pkg_get_name(deppkg));
                                /* add it to the target list */
                                targs = alpm_list_add(targs, _alpm_pkg_dup(deppkg));
                        }
                }
        }
}

/**
 * helper function for resolvedeps: search for dep satisfier in dbs
 *
 * @param dep is the dependency to search for
 * @param dbs are the databases to search
 * @param excluding are the packages to exclude from the search
 * @param prompt if true, will cause an unresolvable dependency to issue an
 *        interactive prompt asking whether the package should be removed from
 *        the transaction or the transaction aborted; if false, simply returns
 *        an error code without prompting
 * @return the resolved package
 **/
static pmpkg_t *resolvedep(pmdepend_t *dep, alpm_list_t *dbs,
                alpm_list_t *excluding, int prompt)
{
        alpm_list_t *i, *j;
        int ignored = 0;

        alpm_list_t *providers = NULL;
        int count;

        /* 1. literals */
        for(i = dbs; i; i = i->next) {
                pmpkg_t *pkg = _alpm_db_get_pkgfromcache(i->data, dep->name);
                if(pkg && _alpm_depcmp(pkg, dep) && !_alpm_pkg_find(excluding, pkg->name)) {
                        if(_alpm_pkg_should_ignore(pkg)) {
                                int install = 0;
                                if (prompt) {
                                        QUESTION(handle->trans, PM_TRANS_CONV_INSTALL_IGNOREPKG, pkg,
                                                         NULL, NULL, &install);
                                } else {
                                        _alpm_log(PM_LOG_WARNING, _("ignoring package %s-%s\n"), pkg->name, pkg->version);
                                }
                                if(!install) {
                                        ignored = 1;
                                        continue;
                                }
                        }
                        return pkg;
                }
        }
        /* 2. satisfiers (skip literals here) */
        for(i = dbs; i; i = i->next) {
                for(j = _alpm_db_get_pkgcache(i->data); j; j = j->next) {
                        pmpkg_t *pkg = j->data;
                        if(_alpm_depcmp(pkg, dep) && strcmp(pkg->name, dep->name) != 0 &&
                                     !_alpm_pkg_find(excluding, pkg->name)) {
                                if(_alpm_pkg_should_ignore(pkg)) {
                                        int install = 0;
                                        if (prompt) {
                                                QUESTION(handle->trans, PM_TRANS_CONV_INSTALL_IGNOREPKG,
                                                                        pkg, NULL, NULL, &install);
                                        } else {
                                                _alpm_log(PM_LOG_WARNING, _("ignoring package %s-%s\n"), pkg->name, pkg->version);
                                        }
                                        if(!install) {
                                                ignored = 1;
                                                continue;
                                        }
                                }
                                _alpm_log(PM_LOG_DEBUG, "provider found (%s provides %s)\n",
                                                pkg->name, dep->name);
                                providers = alpm_list_add(providers, pkg);
                                /* keep looking for other providers in the all dbs */
                        }
                }
        }

        /* first check if one provider is already installed locally */
        for(i = providers; i; i = i->next) {
                pmpkg_t *pkg = i->data;
                if (_alpm_pkghash_find(_alpm_db_get_pkgcache_hash(handle->db_local), pkg->name)) {
                        alpm_list_free(providers);
                        return pkg;
                }
        }
        count = alpm_list_count(providers);
        if (count >= 1) {
                /* default to first provider if there is no QUESTION callback */
                int index = 0;
                if(count > 1) {
                        /* if there is more than one provider, we ask the user */
                        QUESTION(handle->trans, PM_TRANS_CONV_SELECT_PROVIDER,
                                        providers, dep, NULL, &index);
                }
                if(index >= 0 && index < count) {
                        pmpkg_t *pkg = alpm_list_getdata(alpm_list_nth(providers, index));
                        alpm_list_free(providers);
                        return pkg;
                }
                alpm_list_free(providers);
                providers = NULL;
        }

        if(ignored) { /* resolvedeps will override these */
                pm_errno = PM_ERR_PKG_IGNORED;
        } else {
                pm_errno = PM_ERR_PKG_NOT_FOUND;
        }
        return NULL;
}

/** Find a package satisfying a specified dependency.
 * First look for a literal, going through each db one by one. Then look for
 * providers. The first satisfier found is returned.
 * The dependency can include versions with depmod operators.
 * @param dbs an alpm_list_t* of pmdb_t where the satisfier will be searched
 * @param depstring package or provision name, versioned or not
 * @return a pmpkg_t* satisfying depstring
 */
pmpkg_t SYMEXPORT *alpm_find_dbs_satisfier(alpm_list_t *dbs, const char *depstring)
{
        pmdepend_t *dep;
        pmpkg_t *pkg;

        ASSERT(dbs, return NULL);

        dep = _alpm_splitdep(depstring);
        ASSERT(dep, return NULL);
        pkg = resolvedep(dep, dbs, NULL, 1);
        _alpm_dep_free(dep);
        return pkg;
}

/**
 * Computes resolvable dependencies for a given package and adds that package
 * and those resolvable dependencies to a list.
 *
 * @param localpkgs is the list of local packages
 * @param dbs_sync are the sync databases
 * @param pkg is the package to resolve
 * @param packages is a pointer to a list of packages which will be
 *        searched first for any dependency packages needed to complete the
 *        resolve, and to which will be added any [pkg] and all of its
 *        dependencies not already on the list
 * @param remove is the set of packages which will be removed in this
 *        transaction
 * @param data returns the dependency which could not be satisfied in the
 *        event of an error
 * @return 0 on success, with [pkg] and all of its dependencies not already on
 *         the [*packages] list added to that list, or -1 on failure due to an
 *         unresolvable dependency, in which case the [*packages] list will be
 *         unmodified by this function
 */
int _alpm_resolvedeps(alpm_list_t *localpkgs, alpm_list_t *dbs_sync, pmpkg_t *pkg,
                      alpm_list_t *preferred, alpm_list_t **packages,
                      alpm_list_t *remove, alpm_list_t **data)
{
        int ret = 0;
        alpm_list_t *i, *j;
        alpm_list_t *targ;
        alpm_list_t *deps = NULL;
        alpm_list_t *packages_copy;

        ALPM_LOG_FUNC;

        if(_alpm_pkg_find(*packages, pkg->name) != NULL) {
                return 0;
        }

        /* Create a copy of the packages list, so that it can be restored
           on error */
        packages_copy = alpm_list_copy(*packages);
        /* [pkg] has not already been resolved into the packages list, so put it
           on that list */
        *packages = alpm_list_add(*packages, pkg);

        _alpm_log(PM_LOG_DEBUG, "started resolving dependencies\n");
        for(i = alpm_list_last(*packages); i; i = i->next) {
                pmpkg_t *tpkg = i->data;
                targ = alpm_list_add(NULL, tpkg);
                deps = alpm_checkdeps(localpkgs, 0, remove, targ);
                alpm_list_free(targ);

                for(j = deps; j; j = j->next) {
                        pmdepmissing_t *miss = j->data;
                        pmdepend_t *missdep = alpm_miss_get_dep(miss);
                        /* check if one of the packages in the [*packages] list already satisfies
                         * this dependency */
                        if(find_dep_satisfier(*packages, missdep)) {
                                _alpm_depmiss_free(miss);
                                continue;
                        }
                        /* check if one of the packages in the [preferred] list already satisfies
                         * this dependency */
                        pmpkg_t *spkg = find_dep_satisfier(preferred, missdep);
                        if(!spkg) {
                                /* find a satisfier package in the given repositories */
                                spkg = resolvedep(missdep, dbs_sync, *packages, 0);
                        }
                        if(!spkg) {
                                pm_errno = PM_ERR_UNSATISFIED_DEPS;
                                char *missdepstring = alpm_dep_compute_string(missdep);
                                _alpm_log(PM_LOG_WARNING,
                                                _("cannot resolve \"%s\", a dependency of \"%s\"\n"),
                                                missdepstring, tpkg->name);
                                free(missdepstring);
                                if(data) {
                                        *data = alpm_list_add(*data, miss);
                                }
                                ret = -1;
                        } else {
                                _alpm_log(PM_LOG_DEBUG, "pulling dependency %s (needed by %s)\n",
                                                alpm_pkg_get_name(spkg), alpm_pkg_get_name(tpkg));
                                *packages = alpm_list_add(*packages, spkg);
                                _alpm_depmiss_free(miss);
                        }
                }
                alpm_list_free(deps);
        }

        if(ret != 0) {
                alpm_list_free(*packages);
                *packages = packages_copy;
        } else {
                alpm_list_free(packages_copy);
        }
        _alpm_log(PM_LOG_DEBUG, "finished resolving dependencies\n");
        return ret;
}

const char SYMEXPORT *alpm_miss_get_target(const pmdepmissing_t *miss)
{
        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(miss != NULL, return NULL);

        return miss->target;
}

const char SYMEXPORT *alpm_miss_get_causingpkg(const pmdepmissing_t *miss)
{
        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(miss != NULL, return NULL);

        return miss->causingpkg;
}

pmdepend_t SYMEXPORT *alpm_miss_get_dep(pmdepmissing_t *miss)
{
        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(miss != NULL, return NULL);

        return miss->depend;
}

pmdepmod_t SYMEXPORT alpm_dep_get_mod(const pmdepend_t *dep)
{
        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(dep != NULL, return -1);

        return dep->mod;
}

const char SYMEXPORT *alpm_dep_get_name(const pmdepend_t *dep)
{
        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(dep != NULL, return NULL);

        return dep->name;
}

const char SYMEXPORT *alpm_dep_get_version(const pmdepend_t *dep)
{
        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(dep != NULL, return NULL);

        return dep->version;
}

/** Reverse of splitdep; make a dep string from a pmdepend_t struct.
 * The string must be freed!
 * @param dep the depend to turn into a string
 * @return a string-formatted dependency with operator if necessary
 */
char SYMEXPORT *alpm_dep_compute_string(const pmdepend_t *dep)
{
        const char *name, *opr, *ver;
        char *str;
        size_t len;

        ALPM_LOG_FUNC;

        /* Sanity checks */
        ASSERT(dep != NULL, return NULL);

        if(dep->name) {
                name = dep->name;
        } else {
                name = "";
        }

        switch(dep->mod) {
                case PM_DEP_MOD_ANY:
                        opr = "";
                        break;
                case PM_DEP_MOD_GE:
                        opr = ">=";
                        break;
                case PM_DEP_MOD_LE:
                        opr = "<=";
                        break;
                case PM_DEP_MOD_EQ:
                        opr = "=";
                        break;
                case PM_DEP_MOD_LT:
                        opr = "<";
                        break;
                case PM_DEP_MOD_GT:
                        opr = ">";
                        break;
                default:
                        opr = "";
                        break;
        }

        if(dep->mod != PM_DEP_MOD_ANY && dep->version) {
                ver = dep->version;
        } else {
                ver = "";
        }

        /* we can always compute len and print the string like this because opr
         * and ver will be empty when PM_DEP_MOD_ANY is the depend type. the
         * reassignments above also ensure we do not do a strlen(NULL). */
        len = strlen(name) + strlen(opr) + strlen(ver) + 1;
        MALLOC(str, len, RET_ERR(PM_ERR_MEMORY, NULL));
        snprintf(str, len, "%s%s%s", name, opr, ver);

        return str;
}
/* vim: set ts=2 sw=2 noet: */