Add nll_dump_cause helper to Session

Author: spastorino

src/librustc/session/mod.rs

@@ -437,6 +437,9 @@ impl Session {
     pub fn print_llvm_passes(&self) -> bool {
         self.opts.debugging_opts.print_llvm_passes
     }
+    pub fn nll_dump_cause(&self) -> bool {
+        self.opts.debugging_opts.nll_dump_cause
+    }
     pub fn emit_end_regions(&self) -> bool {
         self.opts.debugging_opts.emit_end_regions ||
             (self.opts.debugging_opts.mir_emit_validate > 0) ||

src/librustc_mir/borrow_check/nll/region_infer/mod.rs

@@ -248,7 +248,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             .map(|origin| RegionDefinition::new(origin))
             .collect();
 
-        let nll_dump_cause = ty::tls::with(|tcx| tcx.sess.opts.debugging_opts.nll_dump_cause);
+        let nll_dump_cause = ty::tls::with(|tcx| tcx.sess.nll_dump_cause());
 
         let mut result = Self {
             definitions,
@@ -1259,7 +1259,7 @@ impl Cause {
     pub(crate) fn label_diagnostic(&self, mir: &Mir<'_>, diag: &mut DiagnosticBuilder<'_>) {
         // The cause information is pretty messy. Only dump it as an
         // internal debugging aid if -Znll-dump-cause is given.
-        let nll_dump_cause = ty::tls::with(|tcx| tcx.sess.opts.debugging_opts.nll_dump_cause);
+        let nll_dump_cause = ty::tls::with(|tcx| tcx.sess.nll_dump_cause());
         if !nll_dump_cause {
             return;
         }