rust_analyzer_settings: force use of 'nightly' toolchain

Author: RalfJung

src/bootstrap/src/core/build_steps/setup.rs

@@ -572,6 +572,7 @@ Select which editor you would like to set up [default: None]: ";
                 "828666b021d837a33e78d870b56d34c88a5e2c85de58b693607ec574f0c27000",
                 "811fb3b063c739d261fd8590dd30242e117908f5a095d594fa04585daa18ec4d",
                 "4eecb58a2168b252077369da446c30ed0e658301efe69691979d1ef0443928f4",
+                "c394386e6133bbf29ffd32c8af0bb3d4aac354cba9ee051f29612aa9350f8f8d",
             ],
             EditorKind::Emacs => vec![
                 "51068d4747a13732440d1a8b8f432603badb1864fa431d83d0fd4f8fa57039e0",

src/etc/rust_analyzer_settings.json

@@ -34,5 +34,8 @@
     "rust-analyzer.rustc.source": "./Cargo.toml",
     "rust-analyzer.cargo.extraEnv": {
         "RUSTC_BOOTSTRAP": "1"
+    },
+    "rust-analyzer.server.extraEnv": {
+        "RUSTUP_TOOLCHAIN": "nightly"
     }
 }