Make Module#prepend affect ancestor chain even if argument already included in receiver

Previously, if a class included a module and then prepended the
same module, the prepend had no effect.  This changes the behavior
so that the prepend has an effect unless the module is already
prepended the receiver.

While here, rename the origin_seen variable in include_modules_at,
since it is misleading. The variable tracks whether c has been seen,
not whether the origin of klass has been.

Fixes [Bug #17423]

1 files changed, 29 insertions, 22 deletions

diff --git a/class.c b/class.c
index 47f35b1f90..a62ae669f8 100644
--- a/class.c
+++ b/class.c
@@ -1010,36 +1010,43 @@ include_modules_at(const VALUE klass, VALUE c, VALUE module, int search_super)
     VALUE p, iclass, origin_stack = 0;
     int method_changed = 0, constant_changed = 0, add_subclass;
     long origin_len;
-    struct rb_id_table *const klass_m_tbl = RCLASS_M_TBL(RCLASS_ORIGIN(klass));
+    VALUE klass_origin = RCLASS_ORIGIN(klass);
+    struct rb_id_table *const klass_m_tbl = RCLASS_M_TBL(klass_origin);
     VALUE original_klass = klass;
 
     while (module) {
-        int origin_seen = FALSE;
+        int c_seen = FALSE;
 	int superclass_seen = FALSE;
 	struct rb_id_table *tbl;
 
-        if (klass == c)
-            origin_seen = TRUE;
+        if (klass == c) {
+            c_seen = TRUE;
+        }
 	if (klass_m_tbl && klass_m_tbl == RCLASS_M_TBL(module))
 	    return -1;
-	/* ignore if the module included already in superclasses */
-        for (p = RCLASS_SUPER(klass); p; p = RCLASS_SUPER(p)) {
-	    int type = BUILTIN_TYPE(p);
-            if (c == p)
-                origin_seen = TRUE;
-	    if (type == T_ICLASS) {
-		if (RCLASS_M_TBL(p) == RCLASS_M_TBL(module)) {
-                    if (!superclass_seen && origin_seen) {
-			c = p;  /* move insertion point */
-		    }
-		    goto skip;
-		}
-	    }
-	    else if (type == T_CLASS) {
-		if (!search_super) break;
-                superclass_seen = TRUE;
-	    }
-	}
+        if (klass_origin != c || search_super) {
+            /* ignore if the module included already in superclasses for include,
+             * ignore if the module included before origin class for prepend
+             */
+            for (p = RCLASS_SUPER(klass); p; p = RCLASS_SUPER(p)) {
+                int type = BUILTIN_TYPE(p);
+                if (klass_origin == p && !search_super)
+                    break;
+                if (c == p)
+                    c_seen = TRUE;
+                if (type == T_ICLASS) {
+                    if (RCLASS_M_TBL(p) == RCLASS_M_TBL(module)) {
+                        if (!superclass_seen && c_seen) {
+                            c = p;  /* move insertion point */
+                        }
+                        goto skip;
+                    }
+                }
+                else if (type == T_CLASS) {
+                    superclass_seen = TRUE;
+                }
+            }
+        }
 
         VALUE super_class = RCLASS_SUPER(c);