cargo-miri: better debug output; reorder a comment to make it less confusing

Author: RalfJung

src/tools/miri/cargo-miri/src/phases.rs

@@ -89,8 +89,12 @@ pub fn phase_cargo_miri(mut args: impl Iterator<Item = String>) {
     let verbose = num_arg_flag("-v");
 
     // Determine the involved architectures.
-    let rustc_version = VersionMeta::for_command(miri_for_host())
-        .expect("failed to determine underlying rustc version of Miri");
+    let rustc_version = VersionMeta::for_command(miri_for_host()).unwrap_or_else(|err| {
+        panic!(
+            "failed to determine underlying rustc version of Miri ({:?}):\n{err:?}",
+            miri_for_host()
+        )
+    });
     let host = &rustc_version.host;
     let target = get_arg_flag_value("--target");
     let target = target.as_ref().unwrap_or(host);
@@ -213,7 +217,7 @@ pub fn phase_cargo_miri(mut args: impl Iterator<Item = String>) {
     }
 
     // Run cargo.
-    debug_cmd("[cargo-miri miri]", verbose, &cmd);
+    debug_cmd("[cargo-miri cargo]", verbose, &cmd);
     exec(cmd)
 }
 

src/tools/miri/cargo-miri/src/setup.rs

@@ -90,13 +90,13 @@ pub fn setup(
     let cargo_cmd = {
         let mut command = cargo();
         // Use Miri as rustc to build a libstd compatible with us (and use the right flags).
+        // We set ourselves (`cargo-miri`) instead of Miri directly to be able to patch the flags
+        // for `libpanic_abort` (usually this is done by bootstrap but we have to do it ourselves).
+        // The `MIRI_CALLED_FROM_SETUP` will mean we dispatch to `phase_setup_rustc`.
         // However, when we are running in bootstrap, we cannot just overwrite `RUSTC`,
         // because we still need bootstrap to distinguish between host and target crates.
         // In that case we overwrite `RUSTC_REAL` instead which determines the rustc used
         // for target crates.
-        // We set ourselves (`cargo-miri`) instead of Miri directly to be able to patch the flags
-        // for `libpanic_abort` (usually this is done by bootstrap but we have to do it ourselves).
-        // The `MIRI_CALLED_FROM_SETUP` will mean we dispatch to `phase_setup_rustc`.
         let cargo_miri_path = std::env::current_exe().expect("current executable path invalid");
         if env::var_os("RUSTC_STAGE").is_some() {
             assert!(env::var_os("RUSTC").is_some());