run-make-support: handle unavailable in-tree cargo under run-make test suite

Author: jieyouxu

src/tools/run-make-support/src/external_deps/cargo.rs

@@ -1,11 +1,17 @@
 use crate::command::Command;
-use crate::env_var;
 use crate::util::set_host_compiler_dylib_path;
 
-/// Returns a command that can be used to invoke cargo. The cargo is provided by compiletest
-/// through the `CARGO` env var.
+/// Returns a command that can be used to invoke in-tree cargo. The cargo is provided by compiletest
+/// through the `CARGO` env var, and is **only** available for the `run-make-cargo` test suite.
 pub fn cargo() -> Command {
-    let mut cmd = Command::new(env_var("CARGO"));
+    let cargo_path = std::env::var("CARGO").unwrap_or_else(|e| {
+        panic!(
+            "in-tree `cargo` should be available for `run-make-cargo` test suite, but not \
+            `run-make` test suite: {e}"
+        )
+    });
+
+    let mut cmd = Command::new(cargo_path);
     set_host_compiler_dylib_path(&mut cmd);
     cmd
 }

src/tools/run-make-support/src/lib.rs

@@ -1,7 +1,8 @@
 //! `run-make-support` is a support library for run-make tests. It provides command wrappers and
 //! convenience utility functions to help test writers reduce duplication. The support library
-//! notably is built via cargo: this means that if your test wants some non-trivial utility, such
-//! as `object` or `wasmparser`, they can be re-exported and be made available through this library.
+//! notably is built via bootstrap cargo: this means that if your test wants some non-trivial
+//! utility, such as `object` or `wasmparser`, they can be re-exported and be made available through
+//! this library.
 
 #![warn(unreachable_pub)]