custom/external clippy support for bootstrapping

config.example.toml

@@ -230,6 +230,13 @@
 # use this rustfmt binary instead as the stage0 snapshot rustfmt.
 #rustfmt = "/path/to/rustfmt"
 
+# Instead of downloading the src/stage0 version of cargo-clippy specified,
+# use this cargo-clippy binary instead as the stage0 snapshot cargo-clippy.
+#
+# Note that this option should be used with the same toolchain as the `rustc` option above. 
+# Otherwise, clippy is likely to fail due to a toolchain conflict.
+#cargo-clippy = "/path/to/cargo-clippy"
+
 # Whether to build documentation by default. If false, rustdoc and
 # friends will still be compiled but they will not be used to generate any
 # documentation.

src/bootstrap/src/core/builder.rs

@@ -1298,8 +1298,12 @@ impl<'a> Builder<'a> {
 
     pub fn cargo_clippy_cmd(&self, run_compiler: Compiler) -> BootstrapCommand {
         if run_compiler.stage == 0 {
-            // `ensure(Clippy { stage: 0 })` *builds* clippy with stage0, it doesn't use the beta clippy.
-            let cargo_clippy = self.build.config.download_clippy();
+            let cargo_clippy = self
+                .config
+                .initial_cargo_clippy
+                .clone()
+                .unwrap_or_else(|| self.build.config.download_clippy());
+
             let mut cmd = command(cargo_clippy);
             cmd.env("CARGO", &self.initial_cargo);
             return cmd;

src/bootstrap/src/core/config/config.rs

@@ -344,6 +344,7 @@ pub struct Config {
     // These are either the stage0 downloaded binaries or the locally installed ones.
     pub initial_cargo: PathBuf,
     pub initial_rustc: PathBuf,
+    pub initial_cargo_clippy: Option<PathBuf>,
 
     #[cfg(not(test))]
     initial_rustfmt: RefCell<RustfmtState>,
@@ -834,6 +835,7 @@ define_config! {
         cargo: Option<PathBuf> = "cargo",
         rustc: Option<PathBuf> = "rustc",
         rustfmt: Option<PathBuf> = "rustfmt",
+        cargo_clippy: Option<PathBuf> = "cargo-clippy",
         docs: Option<bool> = "docs",
         compiler_docs: Option<bool> = "compiler-docs",
         library_docs_private_items: Option<bool> = "library-docs-private-items",
@@ -1439,6 +1441,7 @@ impl Config {
             cargo,
             rustc,
             rustfmt,
+            cargo_clippy,
             docs,
             compiler_docs,
             library_docs_private_items,
@@ -1491,6 +1494,14 @@ impl Config {
             config.out = absolute(&config.out).expect("can't make empty path absolute");
         }
 
+        if cargo_clippy.is_some() && rustc.is_none() {
+            println!(
+                "WARNING: Using `build.cargo-clippy` without `build.rustc` usually fails due to toolchain conflict."
+            );
+        }
+
+        config.initial_cargo_clippy = cargo_clippy;
+
         config.initial_rustc = if let Some(rustc) = rustc {
             if !flags.skip_stage0_validation {
                 config.check_stage0_version(&rustc, "rustc");

src/bootstrap/src/utils/change_tracker.rs

@@ -235,4 +235,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Info,
         summary: "The `build.profiler` option now tries to use source code from `download-ci-llvm` if possible, instead of checking out the `src/llvm-project` submodule.",
     },
+    ChangeInfo {
+        change_id: 129152,
+        severity: ChangeSeverity::Info,
+        summary: "New option `build.cargo-clippy` added for supporting the use of custom/external clippy.",
+    },
 ];