From b3246e0cb10a6a32e8f652312985d36581f77c19 Mon Sep 17 00:00:00 2001
From: Joshua Nelson <jyn514@gmail.com>
Date: Tue, 29 Sep 2020 19:46:32 -0400
Subject: [PATCH] Set the proper sysroot for clippy

Clippy does its own runtime detection of the sysroot, which was
incorrect in this case (it used the beta sysroot). This overrides the
sysroot to use `stage0-sysroot` instead.

- Get `x.py clippy` to work on nightly
- Give a nice error message if nightly clippy isn't installed
---
 src/bootstrap/builder.rs | 41 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index dc4243a76d5d..c0578dea1cd5 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -850,7 +850,40 @@ impl<'a> Builder<'a> {
                 cargo.args(s.split_whitespace());
             }
             rustflags.env("RUSTFLAGS_BOOTSTRAP");
-            rustflags.arg("--cfg=bootstrap");
+            if cmd == "clippy" {
+                // clippy overwrites any sysroot we pass on the command line.
+                // Tell it to use the appropriate sysroot instead.
+                // NOTE: this can't be fixed in clippy because we explicitly don't set `RUSTC`,
+                // so it has no way of knowing the sysroot.
+                rustflags.arg("--sysroot");
+                rustflags.arg(
+                    self.sysroot(compiler)
+                        .as_os_str()
+                        .to_str()
+                        .expect("sysroot must be valid UTF-8"),
+                );
+                // Only run clippy on a very limited subset of crates (in particular, not build scripts).
+                cargo.arg("-Zunstable-options");
+                // Explicitly does *not* set `--cfg=bootstrap`, since we're using a nightly clippy.
+                let host_version = Command::new("rustc").arg("--version").output().map_err(|_| ());
+                if let Err(_) = host_version.and_then(|output| {
+                    if output.status.success()
+                        && t!(std::str::from_utf8(&output.stdout)).contains("nightly")
+                    {
+                        Ok(output)
+                    } else {
+                        Err(())
+                    }
+                }) {
+                    eprintln!(
+                        "error: `x.py clippy` requires a nightly host `rustc` toolchain with the `clippy` component"
+                    );
+                    eprintln!("help: try `rustup default nightly`");
+                    std::process::exit(1);
+                }
+            } else {
+                rustflags.arg("--cfg=bootstrap");
+            }
         }
 
         if self.config.rust_new_symbol_mangling {
@@ -975,7 +1008,6 @@ impl<'a> Builder<'a> {
         // src/bootstrap/bin/{rustc.rs,rustdoc.rs}
         cargo
             .env("RUSTBUILD_NATIVE_DIR", self.native_dir(target))
-            .env("RUSTC", self.out.join("bootstrap/debug/rustc"))
             .env("RUSTC_REAL", self.rustc(compiler))
             .env("RUSTC_STAGE", stage.to_string())
             .env("RUSTC_SYSROOT", &sysroot)
@@ -991,6 +1023,11 @@ impl<'a> Builder<'a> {
             )
             .env("RUSTC_ERROR_METADATA_DST", self.extended_error_dir())
             .env("RUSTC_BREAK_ON_ICE", "1");
+        // Clippy support is a hack and uses the default `cargo-clippy` in path.
+        // Don't override RUSTC so that the `cargo-clippy` in path will be run.
+        if cmd != "clippy" {
+            cargo.env("RUSTC", self.out.join("bootstrap/debug/rustc"));
+        }
 
         // Dealing with rpath here is a little special, so let's go into some
         // detail. First off, `-rpath` is a linker option on Unix platforms