First part of extend chaining

test/css/extend-chaining.css

@@ -0,0 +1,38 @@
+.a,
+.b,
+.c {
+  color: black;
+}
+.f,
+.e,
+.d {
+  color: black;
+}
+.g.h,
+.i.j.h,
+.k.j.h {
+  color: black;
+}
+.i.j,
+.k.j {
+  color: white;
+}
+.l,
+.m,
+.n,
+.o,
+.p,
+.q,
+.r,
+.s,
+.t {
+  color: black;
+}
+.u,
+.v.u.v {
+  color: black;
+}
+.w,
+.v.w.v {
+  color: black;
+}

test/css/extend-nest.css

@@ -1,12 +1,14 @@
 .sidebar,
 .sidebar2,
-.type1 .sidebar3 {
+.type1 .sidebar3,
+.type2.sidebar4 {
   width: 300px;
   background: red;
 }
 .sidebar .box,
 .sidebar2 .box,
-.type1 .sidebar3 .box {
+.type1 .sidebar3 .box,
+.type2.sidebar4 .box {
   background: #FFF;
   border: 1px solid #000;
   margin: 10px 0;
@@ -17,3 +19,6 @@
 .type1 .sidebar3 {
   background: green;
 }
+.type2.sidebar4 {
+  background: red;
+}

test/css/extend.css

@@ -34,13 +34,13 @@ div.ext7,
   width: 100px;
 }
 .ext8.ext9,
-.foo {
+.fuu {
   result: add-foo;
 }
 .ext8 .ext9,
 .ext8 + .ext9,
 .ext8 > .ext9,
-.bar,
+.buu,
 .zap,
 .zoo {
   result: bar-matched;
@@ -49,15 +49,14 @@ div.ext7,
   result: none;
 }
 .ext8 .ext9,
-.bar {
+.buu {
   result: match-nested-bar;
 }
 .ext8.ext9,
-.foo {
+.fuu {
   result: match-nested-foo;
 }
 .aa,
-.bb,
 .cc {
   color: black;
 }

test/less/errors/extend-circular.less

@@ -0,0 +1,26 @@
+// classic circular reference
+
+.x:extend(.z) {}
+.y:extend(.x) {}
+.z:extend(.y) {}
+
+//.x:extend(.z) {}
+//.y:extend(.x) {}
+//.z:extend(.y) {}
+//
+//.x:extend(.z),    <-- target 1
+///y:extend(.z) {}  <-- new 1
+//.y:extend(.x),
+//.z:extend(.x) {}  <-- new
+//.z:extend(.y),
+//.x:extend(.y) {}  <-- new
+//
+//.x:extend(.z),
+//.z:extend(.z),  <--- last iteration 1 - .parent = target 1 - .parent =
+///y:extend(.z) {}
+//.y:extend(.x),
+//.x:extend(.x),  <-- last  iteration
+//.z:extend(.x) {}
+//.z:extend(.y),  <-- potential match with 1 -> result in .z:extend(.y)
+//.y:extend(.y),    <-- last  iteration
+//.x:extend(.y) {}

test/less/errors/extend-circular.txt

@@ -0,0 +1,2 @@
+SyntaxError: extend circular reference detected. One of the circular extends is currently: .x:extend( .z) in {path}extend-circular.less on line null, column 0:
+1 

test/less/extend-chaining.less

@@ -0,0 +1,48 @@
+//very simple chaining
+.a {
+  color: black;
+}
+.b:extend(.a) {}
+.c:extend(.b) {}
+
+//very simple chaining, ordering not important
+
+.d:extend(.e) {}
+.e:extend(.f) {}
+.f {
+  color: black;
+}
+
+//extend with all
+
+.g.h {
+  color: black;
+}
+.i.j:extend(.g all) {
+  color: white;
+}
+.k:extend(.i all) {}
+
+//extend multi-chaining
+
+.l {
+  color: black;
+}
+.m:extend(.l){}
+.n:extend(.m){}
+.o:extend(.n){}
+.p:extend(.o){}
+.q:extend(.p){}
+.r:extend(.q){}
+.s:extend(.r){}
+.t:extend(.s){}
+
+// self referencing is ignored
+
+.u {color: black;}
+.v.u.v:extend(.u all){}
+
+// circular reference because the new extend product will match the existing extend
+
+.w:extend(.w) {color: black;}
+.v.w.v:extend(.w all){}

test/less/extend-nest.less

@@ -20,3 +20,10 @@
       background: green;
     }
 }
+
+.type2 {
+  &.sidebar4 {
+    &:extend(.sidebar all);
+    background: red;
+  }
+}

test/less/extend.less

@@ -59,8 +59,8 @@ div.ext5,
   }
 }
 
-.foo:extend(.ext8.ext9 all) {}
-.bar:extend(.ext8 .ext9 all) {}
+.fuu:extend(.ext8.ext9 all) {}
+.buu:extend(.ext8 .ext9 all) {}
 .zap:extend(.ext8 + .ext9 all) {}
 .zoo:extend(.ext8 > .ext9 all) {}
 
@@ -70,7 +70,7 @@ div.ext5,
     background: red;
   }
 }
-.bb:extend(.aa) {
+.bb {
   background: red;
   .bb {
     color: black;