Add test to build crates used by r-a on stable

compiler/rustc_type_ir/src/elaborate.rs

@@ -237,7 +237,7 @@ pub fn supertrait_def_ids<I: Interner>(
     cx: I,
     trait_def_id: I::DefId,
 ) -> impl Iterator<Item = I::DefId> {
-    let mut set: HashSet<I::DefId> = HashSet::default();
+    let mut set = HashSet::default();
     let mut stack = vec![trait_def_id];
 
     set.insert(trait_def_id);

src/tools/run-make-support/src/external_deps/cargo.rs

@@ -0,0 +1,7 @@
+use crate::command::Command;
+use crate::env_var;
+
+/// Returns a command that can be used to invoke Cargo.
+pub fn cargo() -> Command {
+    Command::new(env_var("BOOTSTRAP_CARGO"))
+}

src/tools/run-make-support/src/external_deps/mod.rs

@@ -2,6 +2,7 @@
 //! such as `cc` or `python`.
 
 pub mod c_build;
+pub mod cargo;
 pub mod cc;
 pub mod clang;
 pub mod htmldocck;

src/tools/run-make-support/src/external_deps/rustc.rs

@@ -36,10 +36,13 @@ pub struct Rustc {
 
 crate::macros::impl_common_helpers!(Rustc);
 
+pub fn rustc_path() -> String {
+    env_var("RUSTC")
+}
+
 #[track_caller]
 fn setup_common() -> Command {
-    let rustc = env_var("RUSTC");
-    let mut cmd = Command::new(rustc);
+    let mut cmd = Command::new(rustc_path());
     set_host_rpath(&mut cmd);
     cmd
 }

src/tools/run-make-support/src/lib.rs

@@ -48,6 +48,7 @@ pub use external_deps::{c_build, cc, clang, htmldocck, llvm, python, rustc, rust
 // These rely on external dependencies.
 pub use cc::{cc, cxx, extra_c_flags, extra_cxx_flags, Cc};
 pub use c_build::{build_native_dynamic_lib, build_native_static_lib, build_native_static_lib_optimized, build_native_static_lib_cxx};
+pub use cargo::cargo;
 pub use clang::{clang, Clang};
 pub use htmldocck::htmldocck;
 pub use llvm::{
@@ -56,7 +57,7 @@ pub use llvm::{
     LlvmProfdata, LlvmReadobj,
 };
 pub use python::python_command;
-pub use rustc::{aux_build, bare_rustc, rustc, Rustc};
+pub use rustc::{aux_build, bare_rustc, rustc, rustc_path, Rustc};
 pub use rustdoc::{bare_rustdoc, rustdoc, Rustdoc};
 
 /// [`diff`][mod@diff] is implemented in terms of the [similar] library.
@@ -96,3 +97,4 @@ pub use assertion_helpers::{
 pub use string::{
     count_regex_matches_in_files_with_extension, invalid_utf8_contains, invalid_utf8_not_contains,
 };
+use crate::external_deps::cargo;

tests/run-make/rustc-crates-on-stable/rmake.rs

@@ -0,0 +1,42 @@
+//! Checks if selected rustc crates can be compiled on the stable channel (or a "simulation" of it).
+//! These crates are designed to be used by downstream users.
+
+use run_make_support::{cargo, run_in_tmpdir, rustc_path, source_root};
+
+fn main() {
+    run_in_tmpdir(|| {
+        // Use the stage0 beta cargo for the compilation (it shouldn't really matter which cargo we
+        // use)
+        let cargo = cargo()
+            // Ensure `proc-macro2`'s nightly detection is disabled
+            .env("RUSTC_STAGE", "0")
+            .env("RUSTC", rustc_path())
+            // We want to disallow all nightly features to simulate a stable build
+            .env("RUSTFLAGS", "-Zallow-features=")
+            .arg("build")
+            .arg("--manifest-path")
+            .arg(source_root().join("Cargo.toml"))
+            .args(&[
+                "--config",
+                r#"workspace.exclude=["library/core"]"#,
+                // Avoid depending on transitive rustc crates
+                "--no-default-features",
+                // Emit artifacts in this temporary directory, not in the source_root's `target`
+                // folder
+                "--target-dir",
+                ".",
+            ])
+            // Check that these crates can be compiled on "stable"
+            .args(&[
+                "-p",
+                "rustc_type_ir",
+                "-p",
+                "rustc_next_trait_solver",
+                "-p",
+                "rustc_pattern_analysis",
+                "-p",
+                "rustc_lexer",
+            ])
+            .run();
+    });
+}