Add option to customize the nll-facts' folder location

compiler/rustc_mir/src/borrow_check/nll.rs

@@ -275,8 +275,8 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     let polonius_output = all_facts.and_then(|all_facts| {
         if infcx.tcx.sess.opts.debugging_opts.nll_facts {
             let def_path = infcx.tcx.def_path(def_id);
-            let dir_path =
-                PathBuf::from("nll-facts").join(def_path.to_filename_friendly_no_crate());
+            let dir_path = PathBuf::from(&infcx.tcx.sess.opts.debugging_opts.nll_facts_dir)
+                .join(def_path.to_filename_friendly_no_crate());
             all_facts.write_to_dir(dir_path, location_table).unwrap();
         }
 

compiler/rustc_session/src/options.rs

@@ -969,6 +969,8 @@ fn parse_target_feature(slot: &mut String, v: Option<&str>) -> bool {
         "use new LLVM pass manager (default: no)"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],
         "dump facts from NLL analysis into side files (default: no)"),
+    nll_facts_dir: String = ("nll-facts".to_string(), parse_string, [UNTRACKED],
+        "the directory the NLL facts are dumped into (default: `nll-facts`)"),
     no_analysis: bool = (false, parse_no_flag, [UNTRACKED],
         "parse and expand the source, but run no analysis"),
     no_codegen: bool = (false, parse_no_flag, [TRACKED],