Review comments

Author: bjorn3

src/bin/miri.rs

@@ -233,9 +233,20 @@ impl rustc_driver::Callbacks for MiriBeRustCompilerCalls {
     #[allow(rustc::potential_query_instability)] // rustc_codegen_ssa (where this code is copied from) also allows this lint
     fn config(&mut self, config: &mut Config) {
         if config.opts.prints.is_empty() && self.target_crate {
-            // Avoid warnings about unsupported crate types
-            #[allow(rustc::bad_opt_access)]
-            config.opts.crate_types.retain(|&c| c == CrateType::Executable || c == CrateType::Rlib);
+            #[allow(rustc::bad_opt_access)] // tcx does not exist yet
+            {
+                let any_crate_types = !config.opts.crate_types.is_empty();
+                // Avoid warnings about unsupported crate types.
+                config
+                    .opts
+                    .crate_types
+                    .retain(|&c| c == CrateType::Executable || c == CrateType::Rlib);
+                if any_crate_types {
+                    // Assert that we didn't remove all crate types if any crate type was passed on
+                    // the cli. Otherwise we might silently change what kind of crate we are building.
+                    assert!(!config.opts.crate_types.is_empty());
+                }
+            }
 
             // Queries overridden here affect the data stored in `rmeta` files of dependencies,
             // which will be used later in non-`MIRI_BE_RUSTC` mode.