1 files changed, 7 insertions, 2 deletions
diff --git a/src/bootstrap/bin/rustdoc.rs b/src/bootstrap/bin/rustdoc.rs
index 23828f4758d..d2b85f7a629 100644
--- a/src/bootstrap/bin/rustdoc.rs
+++ b/src/bootstrap/bin/rustdoc.rs
@@ -5,13 +5,18 @@
 use std::env;
 use std::ffi::OsString;
 use std::path::PathBuf;
-use std::process::Command;
+use std::process::{exit, Command};
 
 include!("../dylib_util.rs");
 
 fn main() {
     let args = env::args_os().skip(1).collect::<Vec<_>>();
-    let stage = env::var("RUSTC_STAGE").expect("RUSTC_STAGE was not set");
+    let stage = env::var("RUSTC_STAGE").unwrap_or_else(|_| {
+        // Don't panic here; it's reasonable to try and run these shims directly. Give a helpful error instead.
+        eprintln!("rustc shim: fatal: RUSTC_STAGE was not set");
+        eprintln!("rustc shim: note: use `x.py build -vvv` to see all environment variables set by bootstrap");
+        exit(101);
+    });
     let rustdoc = env::var_os("RUSTDOC_REAL").expect("RUSTDOC_REAL was not set");
     let libdir = env::var_os("RUSTDOC_LIBDIR").expect("RUSTDOC_LIBDIR was not set");
     let sysroot = env::var_os("RUSTC_SYSROOT").expect("RUSTC_SYSROOT was not set");