fix adding default arguments

Author: RalfJung

src/bin/cargo-miri.rs

@@ -173,6 +173,7 @@ fn main() {
                 .chain(Some(sys_root))
                 .collect()
         };
+        args.splice(0..0, miri::miri_default_args().iter().map(ToString::to_string));
 
         // this check ensures that dependencies are built but not interpreted and the final crate is
         // interpreted but not built
@@ -186,7 +187,6 @@ fn main() {
             Command::new("rustc")
         };
 
-        miri::add_miri_default_args(&mut args);
         args.extend_from_slice(&["--cfg".to_owned(), r#"feature="cargo-miri""#.to_owned()]);
 
         match command.args(&args).status() {

src/bin/miri-rustc-tests.rs

@@ -156,6 +156,7 @@ fn main() {
                 true
             }
         }).collect();
+        args.splice(1..1, miri::miri_default_args().iter().map(ToString::to_string));
         // file to process
         args.push(path.display().to_string());
 
@@ -165,8 +166,6 @@ fn main() {
             args.push(Path::new(&std::env::var("HOME").unwrap()).join(".xargo").join("HOST").display().to_string());
         }
 
-        miri::add_miri_default_args(&mut args);
-
         // A threadsafe buffer for writing.
         #[derive(Default, Clone)]
         struct BufWriter(Arc<Mutex<Vec<u8>>>);

src/bin/miri.rs

@@ -232,8 +232,8 @@ fn main() {
         args.push(sysroot_flag);
         args.push(find_sysroot());
     }
-    // Finally, add the default flags all the way in the beginning.
-    miri::add_miri_default_args(&mut args);
+    // Finally, add the default flags all the way in the beginning, but after the binary name.
+    args.splice(1..1, miri::miri_default_args().iter().map(ToString::to_string));
 
     trace!("rustc arguments: {:?}", args);
     let result = rustc_driver::run(move || {

src/lib.rs

@@ -52,16 +52,11 @@ pub use crate::stacked_borrows::{Borrow, Stack, Stacks, Mut as MutBorrow, BorSta
 
 /// Insert rustc arguments at the beginning of the argument listthat miri wants to be
 /// set per default, for maximal validation power.
-pub fn add_miri_default_args(args: &mut Vec<String>) {
+pub fn miri_default_args() -> &'static [&'static str] {
     // The flags here should be kept in sync with what bootstrap adds when `test-miri` is
     // set, which happens in `bootstrap/bin/rustc.rs` in the rustc sources; and also
     // kept in sync with `xargo/build.sh` in this repo and `appveyor.yml`.
-
-    // Inserting at index 1, after the binary name
-    args.splice(1..1,
-        ["-Zalways-encode-mir", "-Zmir-emit-retag", "-Zmir-opt-level=0"]
-        .iter().map(|s| s.to_string())
-    );
+    &["-Zalways-encode-mir", "-Zmir-emit-retag", "-Zmir-opt-level=0"]
 }
 
 // Used by priroda