rustc: Unify impl self types in the opposite order so variance is correct

src/libcore/str.rs

@@ -1162,7 +1162,7 @@ fn is_utf8(v: [const u8]) -> bool {
 
 #[doc = "Determines if a vector of `u16` contains valid UTF-16"]
 fn is_utf16(v: [const u16]) -> bool {
-    let len = v.len();
+    let len = vec::len(v);
     let mut i = 0u;
     while (i < len) {
         let u = v[i];
@@ -1205,7 +1205,7 @@ fn to_utf16(s: str) -> [u16] {
 }
 
 fn utf16_chars(v: [const u16], f: fn(char)) {
-    let len = v.len();
+    let len = vec::len(v);
     let mut i = 0u;
     while (i < len && v[i] != 0u16) {
         let mut u = v[i];
@@ -1231,7 +1231,7 @@ fn utf16_chars(v: [const u16], f: fn(char)) {
 
 fn from_utf16(v: [const u16]) -> str {
     let mut buf = "";
-    reserve(buf, v.len());
+    reserve(buf, vec::len(v));
     utf16_chars(v) {|ch| push_char(buf, ch); }
     ret buf;
 }

src/rustc/middle/typeck.rs

@@ -1909,7 +1909,7 @@ fn lookup_method_inner(fcx: @fn_ctxt, expr: @ast::expr,
 
                 let ty = universally_quantify_regions(tcx, ty);
 
-                alt unify::unify(fcx, ty, self_ty) {
+                alt unify::unify(fcx, self_ty, ty) {
                   result::ok(_) {
                     if option::is_some(result) {
                         // FIXME[impl] score specificity to resolve ambiguity?

src/test/run-pass/impl-variance.rs

@@ -0,0 +1,12 @@
+impl extensions<T> for [const T] {
+    fn foo() -> uint { vec::len(self) }
+}
+
+fn main() {
+    let v = [const 0];
+    assert v.foo() == 1u;
+    let v = [0];
+    assert v.foo() == 1u;
+    let v = [mut 0];
+    assert v.foo() == 1u;
+}