attempt to test RUSTC and RUSTC_WRAPPER shenanigans on CI

cargo-miri/bin.rs

@@ -483,6 +483,7 @@ fn setup(subcommand: &MiriCommand) {
     // The `MIRI_CALLED_FROM_XARGO` 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());
         command.env("RUSTC_REAL", &cargo_miri_path);
     } else {
         command.env("RUSTC", &cargo_miri_path);

ci.sh

@@ -38,8 +38,21 @@ function run_tests {
   else
     PYTHON=python
   fi
+  # Some environment setup that attempts to confuse the heck out of cargo-miri.
+  if [ "$HOST_TARGET" = x86_64-unknown-linux-gnu ]; then
+    # These act up on Windows (`which miri` produces a filename that does not exist?!?),
+    # so let's do this only on Linux. Also makes sure things work without these set.
+    export RUSTC=$(which rustc)
+    export MIRI=$(which miri)
+  fi
+  mkdir -p .cargo
+  echo 'build.rustc-wrapper = "thisdoesnotexist"' > .cargo/config.toml
+  # Run the actual test
   ${PYTHON} test-cargo-miri/run-test.py
   echo
+  # Clean up
+  unset RUSTC MIRI
+  rm -rf .cargo
 
   # Ensure that our benchmarks all work, on the host at least.
   if [ -z "${MIRI_TEST_TARGET+exists}" ]; then