From f5be8a4cdaa4c053bce5ae70c4e94246052107a1 Mon Sep 17 00:00:00 2001
From: Christopher Durham <cad97@cad97.com>
Date: Wed, 17 Aug 2022 07:27:02 -0500
Subject: [PATCH] Add `rustc --print rustc-path`

---
 compiler/rustc_driver/src/lib.rs            |  4 +++
 compiler/rustc_session/src/config.rs        | 28 +++++++++++++--------
 src/test/run-make/print-rustc-path/Makefile |  9 +++++++
 3 files changed, 30 insertions(+), 11 deletions(-)
 create mode 100644 src/test/run-make/print-rustc-path/Makefile

diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index 94639bf8e1ee4..2e678cd54fd87 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -725,6 +725,10 @@ fn print_crate_info(
             | TargetFeatures => {
                 codegen_backend.print(*req, sess);
             }
+            RustcPath => match env::current_exe() {
+                Ok(exe) => println!("{}", exe.display()),
+                Err(_) => early_error(ErrorOutputType::default(), "failed to get rustc path"),
+            },
             // Any output here interferes with Cargo's parsing of other printed output
             NativeStaticLibs => {}
             LinkArgs => {}
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 68519c8fa828e..3ff6c368e1ef4 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -545,6 +545,7 @@ pub enum PrintRequest {
     NativeStaticLibs,
     StackProtectorStrategies,
     LinkArgs,
+    RustcPath,
 }
 
 pub enum Input {
@@ -1777,6 +1778,20 @@ fn collect_print_requests(
         cg.target_feature = String::new();
     }
 
+    let gate = |req, opt| {
+        if unstable_opts.unstable_options {
+            req
+        } else {
+            early_error(
+                error_format,
+                &format!(
+                    "the `-Z unstable-options` flag must also be passed to \
+                        enable the {opt} print option",
+                ),
+            );
+        }
+    };
+
     prints.extend(matches.opt_strs("print").into_iter().map(|s| match &*s {
         "crate-name" => PrintRequest::CrateName,
         "file-names" => PrintRequest::FileNames,
@@ -1791,18 +1806,9 @@ fn collect_print_requests(
         "tls-models" => PrintRequest::TlsModels,
         "native-static-libs" => PrintRequest::NativeStaticLibs,
         "stack-protector-strategies" => PrintRequest::StackProtectorStrategies,
-        "target-spec-json" => {
-            if unstable_opts.unstable_options {
-                PrintRequest::TargetSpec
-            } else {
-                early_error(
-                    error_format,
-                    "the `-Z unstable-options` flag must also be passed to \
-                     enable the target-spec-json print option",
-                );
-            }
-        }
+        "target-spec-json" => gate(PrintRequest::TargetSpec, "target-spec-json"),
         "link-args" => PrintRequest::LinkArgs,
+        "rustc-path" => gate(PrintRequest::RustcPath, "rustc-path"),
         req => early_error(error_format, &format!("unknown print request `{req}`")),
     }));
 
diff --git a/src/test/run-make/print-rustc-path/Makefile b/src/test/run-make/print-rustc-path/Makefile
new file mode 100644
index 0000000000000..b008578082962
--- /dev/null
+++ b/src/test/run-make/print-rustc-path/Makefile
@@ -0,0 +1,9 @@
+-include ../../run-make-fulldeps/tools.mk
+
+ifdef IS_WINDOWS
+all:
+	$(RUSTC) -Zunstable-options --print rustc-path | $(CGREP) bin\rustc
+else
+all:
+	$(RUSTC) -Zunstable-options --print rustc-path | $(CGREP) bin/rustc
+endif