Rollup merge of rust-lang#47426 - varkor:default-mir-dump-dir, r=nikomatsakis

Add a default directory for -Zmir-dump-dir

The current behaviour of dumping in the current directory is rarely
desirable: a sensible default directory for dumping is much more
convenient. This makes sets the default value for `-Zmir-dump-dir`
to `mir_dump/`.

r? @eddyb

Author: kennytm

src/librustc/session/config.rs

@@ -1172,7 +1172,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "emit noalias metadata for mutable references"),
     dump_mir: Option<String> = (None, parse_opt_string, [UNTRACKED],
           "dump MIR state at various points in translation"),
-    dump_mir_dir: Option<String> = (None, parse_opt_string, [UNTRACKED],
+    dump_mir_dir: String = (String::from("mir_dump"), parse_string, [UNTRACKED],
           "the directory the MIR is dumped into"),
     dump_mir_graphviz: bool = (false, parse_bool, [UNTRACKED],
           "in addition to `.mir` files, create graphviz `.dot` files"),
@@ -2796,7 +2796,7 @@ mod tests {
         assert_eq!(reference.dep_tracking_hash(), opts.dep_tracking_hash());
         opts.debugging_opts.dump_mir = Some(String::from("abc"));
         assert_eq!(reference.dep_tracking_hash(), opts.dep_tracking_hash());
-        opts.debugging_opts.dump_mir_dir = Some(String::from("abc"));
+        opts.debugging_opts.dump_mir_dir = String::from("abc");
         assert_eq!(reference.dep_tracking_hash(), opts.dep_tracking_hash());
         opts.debugging_opts.dump_mir_graphviz = true;
         assert_eq!(reference.dep_tracking_hash(), opts.dep_tracking_hash());

src/librustc_mir/util/liveness.rs

@@ -407,10 +407,7 @@ fn dump_matched_mir_node<'a, 'tcx>(
     result: &LivenessResult,
 ) {
     let mut file_path = PathBuf::new();
-    if let Some(ref file_dir) = tcx.sess.opts.debugging_opts.dump_mir_dir {
-        let p = Path::new(file_dir);
-        file_path.push(p);
-    };
+    file_path.push(Path::new(&tcx.sess.opts.debugging_opts.dump_mir_dir));
     let item_id = tcx.hir.as_local_node_id(source.def_id).unwrap();
     let file_name = format!("rustc.node{}{}-liveness.mir", item_id, pass_name);
     file_path.push(&file_name);

src/librustc_mir/util/pretty.rs

@@ -189,11 +189,7 @@ fn dump_path(
     };
 
     let mut file_path = PathBuf::new();
-
-    if let Some(ref file_dir) = tcx.sess.opts.debugging_opts.dump_mir_dir {
-        let p = Path::new(file_dir);
-        file_path.push(p);
-    };
+    file_path.push(Path::new(&tcx.sess.opts.debugging_opts.dump_mir_dir));
 
     let item_name = tcx.hir
         .def_path(source.def_id)