From 447ae7612aacb356dd3f1dd018aaa350c0493a2e Mon Sep 17 00:00:00 2001
From: David Wood <david@davidtw.co>
Date: Thu, 22 Mar 2018 22:48:39 +0000
Subject: [PATCH] Added flag to disable user type assertion.

---
 src/librustc/session/config.rs               | 2 ++
 src/librustc_mir/build/matches/mod.rs        | 2 ++
 src/test/run-pass/generator/yield-subtype.rs | 1 +
 3 files changed, 5 insertions(+)

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 0d91074e946b..c47a351e9d39 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1251,6 +1251,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "choose which RELRO level to use"),
     nll: bool = (false, parse_bool, [UNTRACKED],
                  "run the non-lexical lifetimes MIR pass"),
+    disable_nll_user_type_assert: bool = (false, parse_bool, [UNTRACKED],
+        "disable user provided type assertion in NLL"),
     trans_time_graph: bool = (false, parse_bool, [UNTRACKED],
         "generate a graphical HTML report of time spent in trans and LLVM"),
     thinlto: Option<bool> = (None, parse_opt_bool, [TRACKED],
diff --git a/src/librustc_mir/build/matches/mod.rs b/src/librustc_mir/build/matches/mod.rs
index b9a6616fd076..7eb52a3cdee9 100644
--- a/src/librustc_mir/build/matches/mod.rs
+++ b/src/librustc_mir/build/matches/mod.rs
@@ -147,6 +147,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 
     pub fn user_assert_ty(&mut self, block: BasicBlock, hir_id: hir::HirId,
                           var: NodeId, span: Span) {
+        if self.hir.tcx().sess.opts.debugging_opts.disable_nll_user_type_assert { return; }
+
         let local_id = self.var_indices[&var];
         let source_info = self.source_info(span);
 
diff --git a/src/test/run-pass/generator/yield-subtype.rs b/src/test/run-pass/generator/yield-subtype.rs
index 7e8a0d1e2b92..c41341690441 100644
--- a/src/test/run-pass/generator/yield-subtype.rs
+++ b/src/test/run-pass/generator/yield-subtype.rs
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 // revisions:lexical nll
+//[nll]compile-flags: -Z disable-nll-user-type-assert
 #![cfg_attr(nll, feature(nll))]
 
 #![feature(generators)]