fix: distances(algorithm='johnson') now throws an error if mode != 'o…

…ut' for directed graphs

R/structural.properties.R

@@ -396,6 +396,14 @@ distances <- function(graph, v=V(graph), to=V(graph),
   if (!is_igraph(graph)) {
     stop("Not a graph object")
   }
+
+  # make sure that the lower-level function in C gets mode == "out"
+  # unconditionally when the graph is undirected; this is used for 
+  # the selection of Johnson's algorithm in automatic mode
+  if (!is_directed(graph)) {
+    mode <- "out"
+  }
+
   v <- as.igraph.vs(graph, v)
   to <- as.igraph.vs(graph, to)
   mode <- igraph.match.arg(mode)
@@ -420,7 +428,7 @@ distances <- function(graph, v=V(graph), to=V(graph),
     weights <- NULL
     warning("Unweighted algorithm chosen, weights ignored")
   }
-  
+
   on.exit( .Call(C_R_igraph_finalizer) )
   res <- .Call(C_R_igraph_shortest_paths, graph, v-1, to-1,
                as.numeric(mode), weights, as.numeric(algorithm))

tools/stimulus/rinterface.c.in

@@ -4191,7 +4191,7 @@ SEXP R_igraph_shortest_paths(SEXP graph, SEXP pvids, SEXP pto,
   igraph_matrix_init(&res, 0, 0);
   switch (algo) {
   case 0:                       /* automatic */
-    if (negw && mode==IGRAPH_OUT && GET_LENGTH(pvids)>100) {
+    if (negw && mode == IGRAPH_OUT && GET_LENGTH(pvids)>100) {
       igraph_shortest_paths_johnson(&g, &res, vs, to, pw);
     } else if (negw) {
       igraph_shortest_paths_bellman_ford(&g, &res, vs, to, pw,
@@ -4214,6 +4214,13 @@ SEXP R_igraph_shortest_paths(SEXP graph, SEXP pvids, SEXP pto,
                                        (igraph_neimode_t) mode);
     break;
   case 4:                       /* johnson */
+    if (mode != IGRAPH_OUT) {
+      if (igraph_is_directed(&g)) {
+        Rf_error("Johnson's algorithm works with mode=\"out\" only for directed graphs");
+      } else {
+        Rf_error("Johnson's algorithm works with mode=\"all\" or mode=\"out\" only for undirected graphs");
+      }
+    }
     igraph_shortest_paths_johnson(&g, &res, vs, to, pw);
     break;
   }