Auto merge of rust-lang#130693 - jieyouxu:minicore, r=<try>

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

**TODO: work in progress prototype implementation, opened early for MCP to reference**

Context: [Real cross-compiling tests instead of `#![no_core]` silliness rust-lang#130375](rust-lang#130375)

This PR introduces a prototype implementation of `minicore` auxiliary test helper. `minicore` contains stub definitions of std/core prelude items intended for consumption by tests that want the typical prelude items like `Copy` or `Result` in cross-compilation scenarios, but don't want nor need full `-Z build-std` (e.g. `tests/ui/abi/compatibility.rs`).

The `minicore` auxiliary is a single source file `tests/auxiliary/minicore.rs`. The path to this auxiliary is made avaiable from bootstrap to compiletest via the `--minicore-path` compiletest flag. The `minicore` auxiliary is then built, on demand via `//@ use-minicore` compiletest directives, for each test revision for the given target (this distinction is important for when host != target in cross-compilation scenario).

### Implementation steps

- [ ] 1. File an MCP to describe `tests/auxiliary/minicore.rs`, `--minicore-path` compiletest flag, `//@ use-minicore` compiletest directive and the behavior.
- [ ] 2. And some self-tests to sanity check the behavior.
- [ ] 3. Update rustc-dev-guide to describe the new `use-minicore` directive and provide an example, noting that `use-minicore` both requires `no_std` + `no_core` and implies `-C panic=abort` for the test file.

r? `@ghost` (not yet ready for full review, still needs some self-tests and some try-jobs)

(TODO: cc interested people once this passes initial try jobs in cross-compilation scenarios)
cc `@/workingjubilee` `@/RalfJung` `@/nikic` `@/chrisnc` (if this makes sense to you in terms of functionality and UX)

try-job: aarch64-apple
try-job: armhf-gnu
try-job: x86_64-msvc
try-job: test-various
try-job: dist-various-1

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

@@ -1731,6 +1731,9 @@ 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 tests that need std/core stubs in cross-compilation scenarios.
+        cmd.arg("--minicore-path").arg("tests/auxiliary/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

@@ -240,5 +240,6 @@ 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

@@ -392,6 +392,11 @@ pub struct Config {
     /// True if the profiler runtime is enabled for this target.
     /// Used by the "needs-profiler-support" header in test files.
     pub profiler_support: bool,
+
+    /// Path to minicore aux library, used for tests that need std and core stubs in
+    /// cross-compilation scenarios that do not otherwise need to `-Zbuild-std`. Used in e.g. ABI
+    /// tests.
+    pub minicore_path: PathBuf,
 }
 
 impl Config {

src/tools/compiletest/src/header.rs

@@ -218,6 +218,9 @@ pub struct TestProps {
     pub filecheck_flags: Vec<String>,
     /// Don't automatically insert any `--check-cfg` args
     pub no_auto_check_cfg: bool,
+    /// Build and use minicore as std/core stub for tests in cross-compilation scenarios that don't
+    /// otherwise need `-Z build-std`.
+    pub use_minicore: bool,
 }
 
 mod directives {
@@ -263,6 +266,7 @@ 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";
 }
@@ -322,6 +326,7 @@ impl TestProps {
             llvm_cov_flags: vec![],
             filecheck_flags: vec![],
             no_auto_check_cfg: false,
+            use_minicore: false,
         }
     }
 
@@ -597,6 +602,8 @@ impl TestProps {
                     }
 
                     config.set_name_directive(ln, NO_AUTO_CHECK_CFG, &mut self.no_auto_check_cfg);
+
+                    self.update_use_minicore(ln, config);
                 },
             );
 
@@ -710,6 +717,17 @@ 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");
+            }
+
+            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

@@ -149,6 +149,7 @@ 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

@@ -170,7 +170,8 @@ 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" {
@@ -357,6 +358,8 @@ pub fn parse_config(args: Vec<String>) -> Config {
         git_merge_commit_email: matches.opt_str("git-merge-commit-email").unwrap(),
 
         profiler_support: matches.opt_present("profiler-support"),
+
+        minicore_path: opt_path(matches, "minicore-path"),
     }
 }
 
@@ -394,6 +397,7 @@ 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());
 }
 

src/tools/compiletest/src/runtest.rs

@@ -827,7 +827,7 @@ impl<'test> TestCx<'test> {
             _ => AllowUnused::No,
         };
 
-        let rustc = self.make_compile_args(
+        let mut rustc = self.make_compile_args(
             &self.testpaths.file,
             output_file,
             emit,
@@ -836,6 +836,12 @@ impl<'test> TestCx<'test> {
             passes,
         );
 
+        if self.props.use_minicore {
+            let minicore_path = self.build_minicore();
+            rustc.arg("--extern");
+            rustc.arg(&format!("minicore={}", minicore_path.to_str().unwrap()));
+        }
+
         self.compose_and_run_compiler(rustc, None, self.testpaths)
     }
 
@@ -1108,8 +1114,8 @@ 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,
@@ -1129,6 +1135,37 @@ 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,
@@ -1420,6 +1457,11 @@ impl<'test> TestCx<'test> {
             rustc.arg(dir_opt);
         };
 
+        // `use-minicore` requires `#![no_std]` and `#![no_core]`, which means no unwinding panics.
+        if self.props.use_minicore {
+            rustc.arg("-Cpanic=abort");
+        }
+
         match self.config.mode {
             Incremental => {
                 // If we are extracting and matching errors in the new
@@ -1846,42 +1888,6 @@ impl<'test> TestCx<'test> {
         (proc_res, output_path)
     }
 
-    fn compile_test_and_save_assembly(&self) -> (ProcRes, PathBuf) {
-        let output_file = self.get_output_file("s");
-        let input_file = &self.testpaths.file;
-
-        let mut emit = Emit::None;
-        match self.props.assembly_output.as_ref().map(AsRef::as_ref) {
-            Some("emit-asm") => {
-                emit = Emit::Asm;
-            }
-
-            Some("bpf-linker") => {
-                emit = Emit::LinkArgsAsm;
-            }
-
-            Some("ptx-linker") => {
-                // No extra flags needed.
-            }
-
-            Some(header) => self.fatal(&format!("unknown 'assembly-output' header: {header}")),
-            None => self.fatal("missing 'assembly-output' header"),
-        }
-
-        let rustc = self.make_compile_args(
-            input_file,
-            output_file,
-            emit,
-            AllowUnused::No,
-            LinkToAux::Yes,
-            Vec::new(),
-        );
-
-        let proc_res = self.compose_and_run_compiler(rustc, None, self.testpaths);
-        let output_path = self.get_filecheck_file("s");
-        (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, TestCx};
 
 impl TestCx<'_> {
     pub(super) fn run_assembly_test(&self) {
@@ -16,4 +18,40 @@ impl TestCx<'_> {
             self.fatal_proc_rec("verification with 'FileCheck' failed", &proc_res);
         }
     }
+
+    fn compile_test_and_save_assembly(&self) -> (ProcRes, PathBuf) {
+        let output_file = self.get_output_file("s");
+        let input_file = &self.testpaths.file;
+
+        let mut emit = Emit::None;
+        match self.props.assembly_output.as_ref().map(AsRef::as_ref) {
+            Some("emit-asm") => {
+                emit = Emit::Asm;
+            }
+
+            Some("bpf-linker") => {
+                emit = Emit::LinkArgsAsm;
+            }
+
+            Some("ptx-linker") => {
+                // No extra flags needed.
+            }
+
+            Some(header) => self.fatal(&format!("unknown 'assembly-output' header: {header}")),
+            None => self.fatal("missing 'assembly-output' header"),
+        }
+
+        let rustc = self.make_compile_args(
+            input_file,
+            output_file,
+            emit,
+            AllowUnused::No,
+            LinkToAux::Yes,
+            Vec::new(),
+        );
+
+        let proc_res = self.compose_and_run_compiler(rustc, None, self.testpaths);
+        let output_path = self.get_filecheck_file("s");
+        (proc_res, output_path)
+    }
 }