deps.c

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/*
 *  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 <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"
#include "trans.h"

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

static alpm_depmissing_t *depmiss_new(const char *target, alpm_depend_t *dep,
        const char *causingpkg)
{
    alpm_depmissing_t *miss;

    MALLOC(miss, sizeof(alpm_depmissing_t), return NULL);

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

    return miss;
}

void _alpm_depmiss_free(alpm_depmissing_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(alpm_pkg_t *pkg1, alpm_pkg_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 alpm_pkg_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) {
        alpm_graph_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) {
        alpm_graph_t *vertex_i = i->data;
        alpm_pkg_t *p_i = vertex_i->data;
        /* TODO this should be somehow combined with alpm_checkdeps */
        for(j = vertices; j; j = j->next) {
            alpm_graph_t *vertex_j = j->data;
            alpm_pkg_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_handle_t *handle,
        alpm_list_t *targets, int reverse)
{
    alpm_list_t *newtargs = NULL;
    alpm_list_t *vertices = NULL;
    alpm_list_t *vptr;
    alpm_graph_t *vertex;

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

    _alpm_log(handle, ALPM_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) {
            alpm_graph_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) {
                alpm_pkg_t *vertexpkg = vertex->data;
                alpm_pkg_t *childpkg = nextchild->data;
                const char *message;

                _alpm_log(handle, ALPM_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(handle, ALPM_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(handle, ALPM_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(alpm_handle_t *handle)
{
    int flags = alpm_trans_get_flags(handle);
    return flags != -1 && (flags & ALPM_TRANS_FLAG_NODEPVERSION);
}

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

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

static alpm_pkg_t *find_dep_satisfier(alpm_list_t *pkgs, alpm_depend_t *dep)
{
    alpm_list_t *i;

    for(i = pkgs; i; i = i->next) {
        alpm_pkg_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 alpm_pkg_t where the satisfier will be searched
 * @param depstring package or provision name, versioned or not
 * @return a alpm_pkg_t* satisfying depstring
 */
alpm_pkg_t SYMEXPORT *alpm_find_satisfier(alpm_list_t *pkgs, const char *depstring)
{
    alpm_depend_t *dep = _alpm_splitdep(depstring);
    if(!dep) {
        return NULL;
    }
    alpm_pkg_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 handle the context handle
 * @param pkglist the list of local packages
 * @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)
 * @param reversedeps handles the backward dependencies
 * @return an alpm_list_t* of alpm_depmissing_t pointers.
 */
alpm_list_t SYMEXPORT *alpm_checkdeps(alpm_handle_t *handle,
        alpm_list_t *pkglist, alpm_list_t *remove, alpm_list_t *upgrade,
        int reversedeps)
{
    alpm_list_t *i, *j;
    alpm_list_t *dblist = NULL, *modified = NULL;
    alpm_list_t *baddeps = NULL;
    int nodepversion;

    CHECK_HANDLE(handle, return NULL);

    for(i = pkglist; i; i = i->next) {
        alpm_pkg_t *pkg = i->data;
        if(_alpm_pkg_find(remove, pkg->name) || _alpm_pkg_find(upgrade, pkg->name)) {
            modified = alpm_list_add(modified, pkg);
        } else {
            dblist = alpm_list_add(dblist, pkg);
        }
    }

    nodepversion = no_dep_version(handle);

    /* look for unsatisfied dependencies of the upgrade list */
    for(i = upgrade; i; i = i->next) {
        alpm_pkg_t *tp = i->data;
        _alpm_log(handle, ALPM_LOG_DEBUG, "checkdeps: package %s-%s\n",
                tp->name, tp->version);

        for(j = alpm_pkg_get_depends(tp); j; j = j->next) {
            alpm_depend_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 */
                alpm_depmissing_t *miss;
                char *missdepstring = alpm_dep_compute_string(depend);
                _alpm_log(handle, ALPM_LOG_DEBUG, "checkdeps: missing dependency '%s' for package '%s'\n",
                        missdepstring, tp->name);
                free(missdepstring);
                miss = depmiss_new(tp->name, 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) {
            alpm_pkg_t *lp = i->data;
            for(j = alpm_pkg_get_depends(lp); j; j = j->next) {
                alpm_depend_t *depend = j->data;
                depend = filtered_depend(depend, nodepversion);
                alpm_pkg_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)) {
                    alpm_depmissing_t *miss;
                    char *missdepstring = alpm_dep_compute_string(depend);
                    _alpm_log(handle, ALPM_LOG_DEBUG, "checkdeps: transaction would break '%s' dependency of '%s'\n",
                            missdepstring, lp->name);
                    free(missdepstring);
                    miss = depmiss_new(lp->name, depend, causingpkg->name);
                    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, alpm_depmod_t mod,
        const char *version2)
{
    int equal = 0;

    if(mod == ALPM_DEP_MOD_ANY) {
        equal = 1;
    } else {
        int cmp = alpm_pkg_vercmp(version1, version2);
        switch(mod) {
            case ALPM_DEP_MOD_EQ: equal = (cmp == 0); break;
            case ALPM_DEP_MOD_GE: equal = (cmp >= 0); break;
            case ALPM_DEP_MOD_LE: equal = (cmp <= 0); break;
            case ALPM_DEP_MOD_LT: equal = (cmp < 0); break;
            case ALPM_DEP_MOD_GT: equal = (cmp > 0); break;
            default: equal = 1; break;
        }
    }
    return equal;
}

int _alpm_depcmp_literal(alpm_pkg_t *pkg, alpm_depend_t *dep)
{
    if(pkg->name_hash != dep->name_hash
            || strcmp(pkg->name, dep->name) != 0) {
        /* skip more expensive checks */
        return 0;
    }
    return dep_vercmp(pkg->version, dep->mod, dep->version);
}

int _alpm_depcmp(alpm_pkg_t *pkg, alpm_depend_t *dep)
{
    alpm_list_t *i;
    int satisfy = _alpm_depcmp_literal(pkg, dep);

    if(satisfy) {
        return satisfy;
    }

    /* check provisions, name and version if available */
    for(i = alpm_pkg_get_provides(pkg); i && !satisfy; i = i->next) {
        alpm_depend_t *provision = i->data;

        if(dep->mod == ALPM_DEP_MOD_ANY) {
            /* any version will satisfy the requirement */
            satisfy = (provision->name_hash == dep->name_hash
                    && strcmp(provision->name, dep->name) == 0);
        } else if(provision->mod == ALPM_DEP_MOD_EQ) {
            /* provision specifies a version, so try it out */
            satisfy = (provision->name_hash == dep->name_hash
                    && strcmp(provision->name, dep->name) == 0
                    && dep_vercmp(provision->version, dep->mod, dep->version));
        }
    }

    return satisfy;
}

alpm_depend_t *_alpm_splitdep(const char *depstring)
{
    alpm_depend_t *depend;
    const char *ptr, *version;
    size_t deplen;

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

    MALLOC(depend, sizeof(alpm_depend_t), return NULL);
    deplen = strlen(depstring);

    /* 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 = memchr(depstring, '<', deplen))) {
        if(ptr[1] == '=') {
            depend->mod = ALPM_DEP_MOD_LE;
            version = ptr + 2;
        } else {
            depend->mod = ALPM_DEP_MOD_LT;
            version = ptr + 1;
        }
    } else if((ptr = memchr(depstring, '>', deplen))) {
        if(ptr[1] == '=') {
            depend->mod = ALPM_DEP_MOD_GE;
            version = ptr + 2;
        } else {
            depend->mod = ALPM_DEP_MOD_GT;
            version = ptr + 1;
        }
    } else if((ptr = memchr(depstring, '=', deplen))) {
        /* Note: we must do =,<,> checks after <=, >= checks */
        depend->mod = ALPM_DEP_MOD_EQ;
        version = ptr + 1;
    } else {
        /* no version specified, leave ptr NULL and set version to NULL */
        depend->mod = ALPM_DEP_MOD_ANY;
        depend->version = NULL;
        version = NULL;
    }

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

    return depend;
}

alpm_depend_t *_alpm_dep_dup(const alpm_depend_t *dep)
{
    alpm_depend_t *newdep;
    CALLOC(newdep, 1, sizeof(alpm_depend_t), return NULL);

    STRDUP(newdep->name, dep->name, return NULL);
    newdep->name_hash = dep->name_hash;
    STRDUP(newdep->version, dep->version, return 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(alpm_db_t *db, alpm_pkg_t *pkg,
        alpm_list_t *targets, int include_explicit)
{
    alpm_list_t *i;

    if(_alpm_pkg_find(targets, pkg->name)) {
        return 0;
    }

    if(!include_explicit) {
        /* see if it was explicitly installed */
        if(alpm_pkg_get_reason(pkg) == ALPM_PKG_REASON_EXPLICIT) {
            _alpm_log(db->handle, ALPM_LOG_DEBUG,
                    "excluding %s -- explicitly installed\n", pkg->name);
            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) {
        alpm_pkg_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
 * @return 0 on success, -1 on errors
 */
int _alpm_recursedeps(alpm_db_t *db, alpm_list_t *targs, int include_explicit)
{
    alpm_list_t *i, *j;

    if(db == NULL || targs == NULL) {
        return -1;
    }

    for(i = targs; i; i = i->next) {
        alpm_pkg_t *pkg = i->data;
        for(j = _alpm_db_get_pkgcache(db); j; j = j->next) {
            alpm_pkg_t *deppkg = j->data;
            if(_alpm_dep_edge(pkg, deppkg)
                    && can_remove_package(db, deppkg, targs, include_explicit)) {
                alpm_pkg_t *copy;
                _alpm_log(db->handle, ALPM_LOG_DEBUG, "adding '%s' to the targets\n",
                        deppkg->name);
                /* add it to the target list */
                if(_alpm_pkg_dup(deppkg, &copy)) {
                    return -1;
                }
                targs = alpm_list_add(targs, copy);
            }
        }
    }
    return 0;
}

/**
 * helper function for resolvedeps: search for dep satisfier in dbs
 *
 * @param handle the context handle
 * @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 alpm_pkg_t *resolvedep(alpm_handle_t *handle, alpm_depend_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) {
        alpm_pkg_t *pkg = _alpm_db_get_pkgfromcache(i->data, dep->name);
        if(pkg && _alpm_depcmp_literal(pkg, dep)
                && !_alpm_pkg_find(excluding, pkg->name)) {
            if(_alpm_pkg_should_ignore(handle, pkg)) {
                int install = 0;
                if(prompt) {
                    QUESTION(handle, ALPM_QUESTION_INSTALL_IGNOREPKG, pkg,
                             NULL, NULL, &install);
                } else {
                    _alpm_log(handle, ALPM_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) {
            alpm_pkg_t *pkg = j->data;
            /* with hash != hash, we can even skip the strcmp() as we know they can't
             * possibly be the same string */
            if(pkg->name_hash != dep->name_hash && _alpm_depcmp(pkg, dep)
                    && !_alpm_pkg_find(excluding, pkg->name)) {
                if(_alpm_pkg_should_ignore(handle, pkg)) {
                    int install = 0;
                    if(prompt) {
                        QUESTION(handle, ALPM_QUESTION_INSTALL_IGNOREPKG,
                                    pkg, NULL, NULL, &install);
                    } else {
                        _alpm_log(handle, ALPM_LOG_WARNING, _("ignoring package %s-%s\n"),
                                pkg->name, pkg->version);
                    }
                    if(!install) {
                        ignored = 1;
                        continue;
                    }
                }
                _alpm_log(handle, ALPM_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) {
        alpm_pkg_t *pkg = i->data;
        if(_alpm_db_get_pkgfromcache(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, ALPM_QUESTION_SELECT_PROVIDER,
                    providers, dep, NULL, &index);
        }
        if(index >= 0 && index < count) {
            alpm_list_t *nth = alpm_list_nth(providers, index);
            alpm_pkg_t *pkg = nth->data;
            alpm_list_free(providers);
            return pkg;
        }
        alpm_list_free(providers);
        providers = NULL;
    }

    if(ignored) { /* resolvedeps will override these */
        handle->pm_errno = ALPM_ERR_PKG_IGNORED;
    } else {
        handle->pm_errno = ALPM_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 handle the context handle
 * @param dbs an alpm_list_t* of alpm_db_t where the satisfier will be searched
 * @param depstring package or provision name, versioned or not
 * @return a alpm_pkg_t* satisfying depstring
 */
alpm_pkg_t SYMEXPORT *alpm_find_dbs_satisfier(alpm_handle_t *handle,
        alpm_list_t *dbs, const char *depstring)
{
    alpm_depend_t *dep;
    alpm_pkg_t *pkg;

    CHECK_HANDLE(handle, return NULL);
    ASSERT(dbs, RET_ERR(handle, ALPM_ERR_WRONG_ARGS, NULL));

    dep = _alpm_splitdep(depstring);
    ASSERT(dep, return NULL);
    pkg = resolvedep(handle, 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 handle the context handle
 * @param localpkgs is the list of local packages
 * @param pkg is the package to resolve
 * @param preferred packages to prefer when resolving
 * @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_handle_t *handle, alpm_list_t *localpkgs,
        alpm_pkg_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;

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

    if(handle->trans->flags & ALPM_TRANS_FLAG_RECURSE) {
        /* removing local packages from the equation causes the entire dep chain to
         * get pulled for each target- e.g., pactree -u output */
        localpkgs = NULL;
    }

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

        for(j = deps; j; j = j->next) {
            alpm_depmissing_t *miss = j->data;
            alpm_depend_t *missdep = miss->depend;
            /* 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 */
            alpm_pkg_t *spkg = find_dep_satisfier(preferred, missdep);
            if(!spkg) {
                /* find a satisfier package in the given repositories */
                spkg = resolvedep(handle, missdep, handle->dbs_sync, *packages, 0);
            }
            if(!spkg) {
                handle->pm_errno = ALPM_ERR_UNSATISFIED_DEPS;
                char *missdepstring = alpm_dep_compute_string(missdep);
                _alpm_log(handle, ALPM_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(handle, ALPM_LOG_DEBUG,
                        "pulling dependency %s (needed by %s)\n",
                        spkg->name, tpkg->name);
                *packages = alpm_list_add(*packages, spkg);
                _alpm_depmiss_free(miss);
            }
        }
        alpm_list_free(deps);
    }

    if(handle->trans->flags & ALPM_TRANS_FLAG_NEEDED) {
        /* remove any deps that were pulled that match installed version */
        /* odd loop syntax so we can modify the list as we iterate */
        i = *packages;
        while(i) {
            alpm_pkg_t *tpkg = i->data;
            alpm_pkg_t *local = _alpm_db_get_pkgfromcache(
                    handle->db_local, tpkg->name);
            if(local && _alpm_pkg_compare_versions(tpkg, local) == 0) {
                /* with the NEEDED flag, packages up to date are not reinstalled */
                _alpm_log(handle, ALPM_LOG_DEBUG,
                        "not adding dep %s-%s as it is not needed, same version\n",
                        local->name, local->version);
                j = i;
                i = i->next;
                *packages = alpm_list_remove_item(*packages, j);
                free(j);
            } else {
                i = i->next;
            }
        }
    }

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

/** Reverse of splitdep; make a dep string from a alpm_depend_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 alpm_depend_t *dep)
{
    const char *name, *opr, *ver;
    char *str;
    size_t len;

    ASSERT(dep != NULL, return NULL);

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

    switch(dep->mod) {
        case ALPM_DEP_MOD_ANY:
            opr = "";
            break;
        case ALPM_DEP_MOD_GE:
            opr = ">=";
            break;
        case ALPM_DEP_MOD_LE:
            opr = "<=";
            break;
        case ALPM_DEP_MOD_EQ:
            opr = "=";
            break;
        case ALPM_DEP_MOD_LT:
            opr = "<";
            break;
        case ALPM_DEP_MOD_GT:
            opr = ">";
            break;
        default:
            opr = "";
            break;
    }

    if(dep->mod != ALPM_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 ALPM_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, return NULL);
    snprintf(str, len, "%s%s%s", name, opr, ver);

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