Indicate that trans is always dependent on typeck

src/librustc_trans/trans/base.rs

@@ -3323,6 +3323,14 @@ impl<'a, 'tcx, 'v> Visitor<'v> for TransItemsWithinModVisitor<'a, 'tcx> {
                 // giving `trans_item` access to this item, so also record a read.
                 tcx.dep_graph.with_task(DepNode::TransCrateItem(def_id), || {
                     tcx.dep_graph.read(DepNode::Hir(def_id));
+
+                    // We are going to be accessing various tables
+                    // generated by TypeckItemBody; we also assume
+                    // that the body passes type check. These tables
+                    // are not individually tracked, so just register
+                    // a read here.
+                    tcx.dep_graph.read(DepNode::TypeckItemBody(def_id));
+
                     trans_item(self.ccx, i);
                 });
 

src/test/compile-fail/dep-graph-assoc-type-trans.rs

@@ -0,0 +1,48 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test that when a trait impl changes, fns whose body uses that trait
+// must also be recompiled.
+
+// compile-flags: -Z incr-comp
+
+#![feature(rustc_attrs)]
+#![allow(warnings)]
+
+fn main() { }
+
+pub trait Foo: Sized {
+    type T;
+    fn method(self) { }
+}
+
+mod x {
+    use Foo;
+
+    #[rustc_if_this_changed]
+    impl Foo for char { type T = char; }
+
+    impl Foo for u32 { type T = u32; }
+}
+
+mod y {
+    use Foo;
+
+    #[rustc_then_this_would_need(TypeckItemBody)] //~ ERROR OK
+    #[rustc_then_this_would_need(TransCrateItem)] //~ ERROR OK
+    pub fn use_char_assoc() {
+        // Careful here: in the representation, <char as Foo>::T gets
+        // normalized away, so at a certain point we had no edge to
+        // trans.  (But now trans just depends on typeck.)
+        let x: <char as Foo>::T = 'a';
+    }
+
+    pub fn take_foo<T:Foo>(t: T) { }
+}

src/test/compile-fail/dep-graph-trait-impl.rs

@@ -40,9 +40,8 @@ mod y {
         char::method('a');
     }
 
-    // FIXME(#30741) tcx fulfillment cache not tracked
     #[rustc_then_this_would_need(TypeckItemBody)] //~ ERROR OK
-    #[rustc_then_this_would_need(TransCrateItem)] //~ ERROR no path
+    #[rustc_then_this_would_need(TransCrateItem)] //~ ERROR OK
     pub fn take_foo_with_char() {
         take_foo::<char>('a');
     }
@@ -53,9 +52,8 @@ mod y {
         u32::method(22);
     }
 
-    // FIXME(#30741) tcx fulfillment cache not tracked
     #[rustc_then_this_would_need(TypeckItemBody)] //~ ERROR OK
-    #[rustc_then_this_would_need(TransCrateItem)] //~ ERROR no path
+    #[rustc_then_this_would_need(TransCrateItem)] //~ ERROR OK
     pub fn take_foo_with_u32() {
         take_foo::<u32>(22);
     }