Add minicore test auxiliary and support //@ use-minicore directive in ui/assembly/codegen tests

src/bootstrap/src/core/build_steps/test.rs

@@ -1725,6 +1725,11 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         cmd.arg("--run-lib-path").arg(builder.sysroot_libdir(compiler, target));
         cmd.arg("--rustc-path").arg(builder.rustc(compiler));
 
+        // Minicore auxiliary lib for `no_core` tests that need `core` stubs in cross-compilation
+        // scenarios.
+        cmd.arg("--minicore-path")
+            .arg(builder.src.join("tests").join("auxiliary").join("minicore.rs"));
+
         let is_rustdoc = suite.ends_with("rustdoc-ui") || suite.ends_with("rustdoc-js");
 
         if mode == "run-make" {

src/tools/compiletest/src/command-list.rs

@@ -228,5 +228,6 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "unset-rustc-env",
     // Used by the tidy check `unknown_revision`.
     "unused-revision-names",
+    "use-minicore",
     // tidy-alphabetical-end
 ];

src/tools/compiletest/src/common.rs

@@ -387,6 +387,11 @@ pub struct Config {
     /// True if the profiler runtime is enabled for this target.
     /// Used by the "needs-profiler-runtime" directive in test files.
     pub profiler_runtime: bool,
+
+    /// Path to minicore aux library, used for `no_core` tests that need `core` stubs in
+    /// cross-compilation scenarios that do not otherwise want/need to `-Zbuild-std`. Used in e.g.
+    /// ABI tests.
+    pub minicore_path: PathBuf,
 }
 
 impl Config {

src/tools/compiletest/src/header.rs

@@ -197,6 +197,9 @@ pub struct TestProps {
     pub no_auto_check_cfg: bool,
     /// Run tests which require enzyme being build
     pub has_enzyme: bool,
+    /// Build and use `minicore` as `core` stub for `no_core` tests in cross-compilation scenarios
+    /// that don't otherwise want/need `-Z build-std`.
+    pub use_minicore: bool,
 }
 
 mod directives {
@@ -242,6 +245,7 @@ mod directives {
     pub const LLVM_COV_FLAGS: &'static str = "llvm-cov-flags";
     pub const FILECHECK_FLAGS: &'static str = "filecheck-flags";
     pub const NO_AUTO_CHECK_CFG: &'static str = "no-auto-check-cfg";
+    pub const USE_MINICORE: &'static str = "use-minicore";
     // This isn't a real directive, just one that is probably mistyped often
     pub const INCORRECT_COMPILER_FLAGS: &'static str = "compiler-flags";
 }
@@ -299,6 +303,7 @@ impl TestProps {
             filecheck_flags: vec![],
             no_auto_check_cfg: false,
             has_enzyme: false,
+            use_minicore: false,
         }
     }
 
@@ -563,6 +568,8 @@ impl TestProps {
                     }
 
                     config.set_name_directive(ln, NO_AUTO_CHECK_CFG, &mut self.no_auto_check_cfg);
+
+                    self.update_use_minicore(ln, config);
                 },
             );
 
@@ -676,6 +683,25 @@ impl TestProps {
     pub fn local_pass_mode(&self) -> Option<PassMode> {
         self.pass_mode
     }
+
+    pub fn update_use_minicore(&mut self, ln: &str, config: &Config) {
+        let use_minicore = config.parse_name_directive(ln, directives::USE_MINICORE);
+        if use_minicore {
+            if !matches!(config.mode, Mode::Ui | Mode::Codegen | Mode::Assembly) {
+                panic!("`use-minicore` is only supported for ui, codegen and assembly test modes");
+            }
+
+            // FIXME(jieyouxu): this check is currently order-dependent, but we should probably
+            // collect all directives in one go then perform a validation pass after that.
+            if self.local_pass_mode().is_some_and(|pm| pm == PassMode::Run) {
+                // `minicore` can only be used with non-run modes, because it's `core` prelude stubs
+                // and can't run.
+                panic!("`use-minicore` core stubs cannot be used to run the test binary");
+            }
+
+            self.use_minicore = use_minicore;
+        }
+    }
 }
 
 /// Extract an `(Option<line_revision>, directive)` directive from a line if comment is present.

src/tools/compiletest/src/header/tests.rs

@@ -148,6 +148,7 @@ impl ConfigBuilder {
             "--git-repository=",
             "--nightly-branch=",
             "--git-merge-commit-email=",
+            "--minicore-path=",
         ];
         let mut args: Vec<String> = args.iter().map(ToString::to_string).collect();
 

src/tools/compiletest/src/lib.rs

@@ -169,7 +169,8 @@ pub fn parse_config(args: Vec<String>) -> Config {
             "git-merge-commit-email",
             "email address used for finding merge commits",
             "EMAIL",
-        );
+        )
+        .reqopt("", "minicore-path", "path to minicore aux library", "PATH");
 
     let (argv0, args_) = args.split_first().unwrap();
     if args.len() == 1 || args[1] == "-h" || args[1] == "--help" {
@@ -356,6 +357,8 @@ pub fn parse_config(args: Vec<String>) -> Config {
         git_merge_commit_email: matches.opt_str("git-merge-commit-email").unwrap(),
 
         profiler_runtime: matches.opt_present("profiler-runtime"),
+
+        minicore_path: opt_path(matches, "minicore-path"),
     }
 }
 
@@ -393,6 +396,7 @@ pub fn log_config(config: &Config) {
     logv(c, format!("host-linker: {:?}", config.host_linker));
     logv(c, format!("verbose: {}", config.verbose));
     logv(c, format!("format: {:?}", config.format));
+    logv(c, format!("minicore_path: {:?}", config.minicore_path.display()));
     logv(c, "\n".to_string());
 }
 
@@ -874,6 +878,12 @@ fn files_related_to_test(
         related.push(path);
     }
 
+    // `minicore.rs` test auxiliary: we need to make sure tests get rerun if this changes.
+    //
+    // FIXME(jieyouxu): untangle these paths, we should provide both a path to root `tests/` or
+    // `tests/auxiliary/` and the test suite in question. `src_base` is also a terrible name.
+    related.push(config.src_base.parent().unwrap().join("auxiliary").join("minicore.rs"));
+
     related
 }
 

src/tools/compiletest/src/runtest.rs

@@ -1106,14 +1106,20 @@ impl<'test> TestCx<'test> {
         }
     }
 
-    /// `root_testpaths` refers to the path of the original test.
-    /// the auxiliary and the test with an aux-build have the same `root_testpaths`.
+    /// `root_testpaths` refers to the path of the original test. the auxiliary and the test with an
+    /// aux-build have the same `root_testpaths`.
     fn compose_and_run_compiler(
         &self,
         mut rustc: Command,
         input: Option<String>,
         root_testpaths: &TestPaths,
     ) -> ProcRes {
+        if self.props.use_minicore {
+            let minicore_path = self.build_minicore();
+            rustc.arg("--extern");
+            rustc.arg(&format!("minicore={}", minicore_path.to_str().unwrap()));
+        }
+
         let aux_dir = self.aux_output_dir();
         self.build_all_auxiliary(root_testpaths, &aux_dir, &mut rustc);
 
@@ -1127,6 +1133,37 @@ impl<'test> TestCx<'test> {
         )
     }
 
+    /// Builds `minicore`. Returns the path to the minicore rlib within the base test output
+    /// directory.
+    fn build_minicore(&self) -> PathBuf {
+        let output_file_path = self.output_base_dir().join("libminicore.rlib");
+        let mut rustc = self.make_compile_args(
+            &self.config.minicore_path,
+            TargetLocation::ThisFile(output_file_path.clone()),
+            Emit::None,
+            AllowUnused::Yes,
+            LinkToAux::No,
+            vec![],
+        );
+
+        rustc.args(&["--crate-type", "rlib"]);
+        rustc.arg("-Cpanic=abort");
+
+        let res =
+            self.compose_and_run(rustc, self.config.compile_lib_path.to_str().unwrap(), None, None);
+        if !res.status.success() {
+            self.fatal_proc_rec(
+                &format!(
+                    "auxiliary build of {:?} failed to compile: ",
+                    self.config.minicore_path.display()
+                ),
+                &res,
+            );
+        }
+
+        output_file_path
+    }
+
     /// Builds an aux dependency.
     fn build_auxiliary(
         &self,
@@ -1614,6 +1651,15 @@ impl<'test> TestCx<'test> {
 
         rustc.args(&self.props.compile_flags);
 
+        // FIXME(jieyouxu): we should report a fatal error or warning if user wrote `-Cpanic=` with
+        // something that's not `abort`, however, by moving this last we should override previous
+        // `-Cpanic=`s
+        //
+        // `minicore` requires `#![no_std]` and `#![no_core]`, which means no unwinding panics.
+        if self.props.use_minicore {
+            rustc.arg("-Cpanic=abort");
+        }
+
         rustc
     }
 
@@ -1798,34 +1844,6 @@ impl<'test> TestCx<'test> {
         (proc_res, output_path)
     }
 
-    fn compile_test_and_save_assembly(&self) -> (ProcRes, PathBuf) {
-        // This works with both `--emit asm` (as default output name for the assembly)
-        // and `ptx-linker` because the latter can write output at requested location.
-        let output_path = self.output_base_name().with_extension("s");
-        let input_file = &self.testpaths.file;
-
-        // Use the `//@ assembly-output:` directive to determine how to emit assembly.
-        let emit = match self.props.assembly_output.as_deref() {
-            Some("emit-asm") => Emit::Asm,
-            Some("bpf-linker") => Emit::LinkArgsAsm,
-            Some("ptx-linker") => Emit::None, // No extra flags needed.
-            Some(other) => self.fatal(&format!("unknown 'assembly-output' directive: {other}")),
-            None => self.fatal("missing 'assembly-output' directive"),
-        };
-
-        let rustc = self.make_compile_args(
-            input_file,
-            TargetLocation::ThisFile(output_path.clone()),
-            emit,
-            AllowUnused::No,
-            LinkToAux::Yes,
-            Vec::new(),
-        );
-
-        let proc_res = self.compose_and_run_compiler(rustc, None, self.testpaths);
-        (proc_res, output_path)
-    }
-
     fn verify_with_filecheck(&self, output: &Path) -> ProcRes {
         let mut filecheck = Command::new(self.config.llvm_filecheck.as_ref().unwrap());
         filecheck.arg("--input-file").arg(output).arg(&self.testpaths.file);

src/tools/compiletest/src/runtest/assembly.rs

@@ -1,4 +1,6 @@
-use super::TestCx;
+use std::path::PathBuf;
+
+use super::{AllowUnused, Emit, LinkToAux, ProcRes, TargetLocation, TestCx};
 
 impl TestCx<'_> {
     pub(super) fn run_assembly_test(&self) {
@@ -16,4 +18,32 @@ impl TestCx<'_> {
             self.fatal_proc_rec("verification with 'FileCheck' failed", &proc_res);
         }
     }
+
+    fn compile_test_and_save_assembly(&self) -> (ProcRes, PathBuf) {
+        // This works with both `--emit asm` (as default output name for the assembly)
+        // and `ptx-linker` because the latter can write output at requested location.
+        let output_path = self.output_base_name().with_extension("s");
+        let input_file = &self.testpaths.file;
+
+        // Use the `//@ assembly-output:` directive to determine how to emit assembly.
+        let emit = match self.props.assembly_output.as_deref() {
+            Some("emit-asm") => Emit::Asm,
+            Some("bpf-linker") => Emit::LinkArgsAsm,
+            Some("ptx-linker") => Emit::None, // No extra flags needed.
+            Some(other) => self.fatal(&format!("unknown 'assembly-output' directive: {other}")),
+            None => self.fatal("missing 'assembly-output' directive"),
+        };
+
+        let rustc = self.make_compile_args(
+            input_file,
+            TargetLocation::ThisFile(output_path.clone()),
+            emit,
+            AllowUnused::No,
+            LinkToAux::Yes,
+            Vec::new(),
+        );
+
+        let proc_res = self.compose_and_run_compiler(rustc, None, self.testpaths);
+        (proc_res, output_path)
+    }
 }

tests/assembly/compiletest-self-test/use-minicore-no-run.rs

@@ -0,0 +1,5 @@
+//! `compiletest` self-test to check that `use-minicore` is incompatible with run pass modes.
+
+//@ use-minicore
+//@ run-pass
+//@ should-fail

tests/auxiliary/minicore.rs

@@ -0,0 +1,80 @@
+//! Auxiliary `minicore` prelude which stubs out `core` items for `no_core` tests that need to work
+//! in cross-compilation scenarios where no `core` is available (that don't want nor need to
+//! `-Zbuild-std`).
+//!
+//! # Important notes
+//!
+//! - `minicore` is **only** intended for `core` items, and the stubs should match the actual `core`
+//!   items.
+//!
+//! # References
+//!
+//! This is partially adapted from `rustc_codegen_cranelift`:
+//! <https://github.com/rust-lang/rust/blob/c0b5cc9003f6464c11ae1c0662c6a7e06f6f5cab/compiler/rustc_codegen_cranelift/example/mini_core.rs>.
+// ignore-tidy-linelength
+
+#![feature(no_core, lang_items, rustc_attrs)]
+#![allow(unused, improper_ctypes_definitions, internal_features)]
+#![no_std]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
+
+#[lang = "receiver"]
+pub trait Receiver {}
+impl<T: ?Sized> Receiver for &T {}
+impl<T: ?Sized> Receiver for &mut T {}
+
+#[lang = "copy"]
+pub trait Copy {}
+
+impl Copy for bool {}
+impl Copy for u8 {}
+impl Copy for u16 {}
+impl Copy for u32 {}
+impl Copy for u64 {}
+impl Copy for u128 {}
+impl Copy for usize {}
+impl Copy for i8 {}
+impl Copy for i16 {}
+impl Copy for i32 {}
+impl Copy for isize {}
+impl Copy for f32 {}
+impl Copy for f64 {}
+impl Copy for char {}
+impl<'a, T: ?Sized> Copy for &'a T {}
+impl<T: ?Sized> Copy for *const T {}
+impl<T: ?Sized> Copy for *mut T {}
+
+#[lang = "phantom_data"]
+pub struct PhantomData<T: ?Sized>;
+impl<T: ?Sized> Copy for PhantomData<T> {}
+
+pub enum Option<T> {
+    None,
+    Some(T),
+}
+impl<T: Copy> Copy for Option<T> {}
+
+pub enum Result<T, E> {
+    Ok(T),
+    Err(E),
+}
+impl<T: Copy, E: Copy> Copy for Result<T, E> {}
+
+#[lang = "manually_drop"]
+#[repr(transparent)]
+pub struct ManuallyDrop<T: ?Sized> {
+    value: T,
+}
+impl<T: Copy + ?Sized> Copy for ManuallyDrop<T> {}
+
+#[lang = "unsafe_cell"]
+#[repr(transparent)]
+pub struct UnsafeCell<T: ?Sized> {
+    value: T,
+}
+
+// Trait stub, no `type_id` method.
+pub trait Any: 'static {}