From: Niko Matsakis <niko@alum.mit.edu>
Date: Sat, 15 Jul 2017 10:47:30 +0000 (-0400)
Subject: add some comments to `Obligation`
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=e7efce23618adcc9c960e1518d00883da8a8c444;hp=803bd761278e6e06baabfd5aa1aa15e75c4a16a4;p=rust.git

add some comments to `Obligation`
---

diff --git a/src/librustc/traits/mod.rs b/src/librustc/traits/mod.rs
index c1ffc10c3c0..027ad4174bd 100644
--- a/src/librustc/traits/mod.rs
+++ b/src/librustc/traits/mod.rs
@@ -77,10 +77,21 @@ pub enum IntercrateMode {
 /// scope. The eventual result is usually a `Selection` (defined below).
 #[derive(Clone, PartialEq, Eq, Hash)]
 pub struct Obligation<'tcx, T> {
+    /// Why do we have to prove this thing?
     pub cause: ObligationCause<'tcx>,
+
+    /// In which environment should we prove this thing?
     pub param_env: ty::ParamEnv<'tcx>,
-    pub recursion_depth: usize,
+
+    /// What are we trying to prove?
     pub predicate: T,
+
+    /// If we started proving this as a result of trying to prove
+    /// something else, track the total depth to ensure termination.
+    /// If this goes over a certain threshold, we abort compilation --
+    /// in such cases, we can not say whether or not the predicate
+    /// holds for certain. Stupid halting problem. Such a drag.
+    pub recursion_depth: usize,
 }
 
 pub type PredicateObligation<'tcx> = Obligation<'tcx, ty::Predicate<'tcx>>;