Use miri inside the target directory used by rustc as Miri's target directory

.github/workflows/ci.yml

@@ -77,18 +77,13 @@ jobs:
           rustup-toolchain-install-master \
             -f \
             -n master "$RUSTC_HASH" \
+            -c cargo \
             -c rust-src \
             -c rustc-dev \
             -c llvm-tools \
             --host ${{ matrix.host_target }}
           rustup default master
 
-      # We need a nightly Cargo to run tests that depend on unstable Cargo features.
-      - name: Install latest nightly
-        uses: actions-rs/toolchain@v1
-        with:
-          toolchain: nightly
-
       - name: Show Rust version
         run: |
           rustup show

cargo-miri/bin.rs

@@ -113,7 +113,7 @@ fn has_arg_flag(name: &str) -> bool {
 }
 
 /// Yields all values of command line flag `name` as `Ok(arg)`, and all other arguments except
-/// the flag as `Err(arg)`.
+/// the flag as `Err(arg)`. (The flag `name` itself is not yielded at all, only its values are.)
 struct ArgSplitFlagValue<'a, I> {
     args: TakeWhile<I, fn(&String) -> bool>,
     name: &'a str,
@@ -500,7 +500,7 @@ fn detect_target_dir() -> PathBuf {
     // Check this `Result` after `status.success()` is checked, so we don't print the error
     // to stderr if `cargo metadata` is also printing to stderr.
     let metadata: Result<Metadata, _> = serde_json::from_reader(child.stdout.take().unwrap());
-    let status = child.wait().expect("failed to wait `cargo metadata` to exit");
+    let status = child.wait().expect("failed to wait for `cargo metadata` to exit");
     if !status.success() {
         std::process::exit(status.code().unwrap_or(-1));
     }
@@ -578,7 +578,9 @@ fn phase_cargo_miri(mut args: env::Args) {
                 }
                 target_dir = Some(value.into());
             }
-            Err(arg) => drop(cmd.arg(arg)),
+            Err(arg) => {
+                cmd.arg(arg);
+            }
         }
     }
 

rustup-toolchain

@@ -39,7 +39,7 @@ fi
 
 # Install and setup new toolchain.
 rustup toolchain uninstall miri
-rustup-toolchain-install-master -n miri -c rust-src -c rustc-dev -c llvm-tools -- "$NEW_COMMIT"
+rustup-toolchain-install-master -n miri -c cargo -c rust-src -c rustc-dev -c llvm-tools -- "$NEW_COMMIT"
 rustup override set miri
 
 # Cleanup.