Implement simple topological sort algorithm for sortbydeps

Based on the "depth first search" algorithm, for more infos visit:
http://en.wikipedia.org/wiki/Topological_sorting

The previous algorithm used by sortbydeps was too slow, and to work around
it the number of steps needed to get correct result was reduced greatly.
So it produced wrong results in several cases :
1) smoke001.py
2) http://bugs.archlinux.org/task/7229

More here: http://archlinux.org/pipermail/pacman-dev/2007-April/008057.html

Signed-off-by: Chantry Xavier <shiningxc@gmail.com>
Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 82 insertions, 56 deletions

diff --git a/lib/libalpm/deps.c b/lib/libalpm/deps.c
index 52fdd9ac..66b2d77c 100644
--- a/lib/libalpm/deps.c
+++ b/lib/libalpm/deps.c
@@ -29,7 +29,6 @@
 #ifdef __sun__
 #include <strings.h>
 #endif
-#include <math.h>
 
 /* libalpm */
 #include "deps.h"
@@ -46,6 +45,28 @@
 
 extern pmhandle_t *handle;
 
+static pmgraph_t *_alpm_graph_new(void)
+{
+	pmgraph_t *graph = NULL;
+
+	graph = (pmgraph_t *)malloc(sizeof(pmgraph_t));
+	if(graph) {
+		graph->state = 0;
+		graph->data = NULL;
+		graph->parent = NULL;
+		graph->children = NULL;
+		graph->childptr = NULL;
+	}
+	return(graph);
+}
+
+static void _alpm_graph_free(void *data)
+{
+	pmgraph_t *graph = data;
+	alpm_list_free(graph->children);
+	free(graph);
+}
+
 pmdepmissing_t *_alpm_depmiss_new(const char *target, pmdeptype_t type,
                                   pmdepmod_t depmod, const char *depname,
                                   const char *depversion)
@@ -108,11 +129,10 @@ int _alpm_depmiss_isin(pmdepmissing_t *needle, alpm_list_t *haystack)
 alpm_list_t *_alpm_sortbydeps(alpm_list_t *targets, pmtranstype_t mode)
 {
 	alpm_list_t *newtargs = NULL;
-	alpm_list_t *i, *j, *k, *l;
-	int change = 1;
-	int numscans = 0;
-	int numtargs = 0;
-	int maxscans;
+	alpm_list_t *i, *j, *k;
+	alpm_list_t *vertices = NULL;
+	alpm_list_t *vptr;
+	pmgraph_t *vertex;
 
 	ALPM_LOG_FUNC;
 
@@ -120,65 +140,69 @@ alpm_list_t *_alpm_sortbydeps(alpm_list_t *targets, pmtranstype_t mode)
 		return(NULL);
 	}
 
+	_alpm_log(PM_LOG_DEBUG, _("started sorting dependencies"));
+
+	/* We create the vertices */
 	for(i = targets; i; i = i->next) {
-		newtargs = alpm_list_add(newtargs, i->data);
-		numtargs++;
+		pmgraph_t *vertex = _alpm_graph_new();
+		vertex->data = (void *)i->data;
+		vertices = alpm_list_add(vertices, vertex);
 	}
 
-	maxscans = (int)sqrt(numtargs);
+	/* 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;
+			int child = 0;
+			for(k = alpm_pkg_get_depends(p_i); k && !child; k = k->next) {
+				pmdepend_t *depend = alpm_splitdep(k->data);
+				child = alpm_depcmp(p_j, depend);
+				free(depend);
+			}
+			if(child) vertex_i->children =
+				alpm_list_add(vertex_i->children, vertex_j);
+		}
+		vertex_i->childptr = vertex_i->children;
+	}
 
-	_alpm_log(PM_LOG_DEBUG, _("started sorting dependencies"));
-	while(change) {
-		alpm_list_t *tmptargs = NULL;
-		change = 0;
-		if(numscans > maxscans) {
-			_alpm_log(PM_LOG_DEBUG, _("possible dependency cycle detected"));
-			continue;
+	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) {
+				_alpm_log(PM_LOG_WARNING, _("dependency cycle detected\n"));
+			}
 		}
-		numscans++;
-		/* run thru targets, moving up packages as necessary */
-		for(i = newtargs; i; i = i->next) {
-			pmpkg_t *p = i->data;
-			_alpm_log(PM_LOG_DEBUG, "   sorting %s", alpm_pkg_get_name(p));
-			for(j = alpm_pkg_get_depends(p); j; j = j->next) {
-				pmdepend_t *depend = alpm_splitdep(j->data);
-				pmpkg_t *q = NULL;
-				if(depend == NULL) {
-					continue;
+		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;
 				}
-				/* look for depend->name -- if it's farther down in the list, then
-				 * move it up above p
-				 */
-				for(k = i->next; k; k = k->next) {
-					q = k->data;
-					const char *qname = alpm_pkg_get_name(q);
-					if(!strcmp(depend->name, qname)) {
-						if(!_alpm_pkg_find(qname, tmptargs)) {
-							change = 1;
-							tmptargs = alpm_list_add(tmptargs, q);
-						}
-						break;
-					}
-					for(l = alpm_pkg_get_provides(q); l; l = l->next) {
-						const char *provname = l->data;
-						if(!strcmp(depend->name, provname)) {
-							if(!_alpm_pkg_find(qname, tmptargs)) {
-								change = 1;
-								tmptargs = alpm_list_add(tmptargs, q);
-							}
-							break;
-						}
-					}
-				}
-				free(depend);
-			}
-			if(!_alpm_pkg_find(alpm_pkg_get_name(p), tmptargs)) {
-				tmptargs = alpm_list_add(tmptargs, p);
 			}
 		}
-		alpm_list_free(newtargs);
-		newtargs = tmptargs;
 	}
+
 	_alpm_log(PM_LOG_DEBUG, _("sorting dependencies finished"));
 
 	if(mode == PM_TRANS_TYPE_REMOVE) {
@@ -189,6 +213,8 @@ alpm_list_t *_alpm_sortbydeps(alpm_list_t *targets, pmtranstype_t mode)
 		newtargs = tmptargs;
 	}
 
+	alpm_list_free_inner(vertices, _alpm_graph_free);
+
 	return(newtargs);
 }