compiletest: register --minicore-path flag and //@ add-core-stubs directive

src/tools/compiletest/src/common.rs

@@ -392,6 +392,11 @@ pub struct Config {
 
     /// Command for visual diff display, e.g. `diff-tool --color=always`.
     pub diff_command: Option<String>,
+
+    /// 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/directive-list.rs

@@ -3,6 +3,7 @@
 /// a best-effort approximation for diagnostics. Add new headers to this list when needed.
 const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     // tidy-alphabetical-start
+    "add-core-stubs",
     "assembly-output",
     "aux-bin",
     "aux-build",

src/tools/compiletest/src/header.rs

@@ -198,6 +198,9 @@ 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 add_core_stubs: bool,
 }
 
 mod directives {
@@ -243,6 +246,7 @@ 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 ADD_CORE_STUBS: &'static str = "add-core-stubs";
     // This isn't a real directive, just one that is probably mistyped often
     pub const INCORRECT_COMPILER_FLAGS: &'static str = "compiler-flags";
 }
@@ -300,6 +304,7 @@ pub fn new() -> Self {
             filecheck_flags: vec![],
             no_auto_check_cfg: false,
             has_enzyme: false,
+            add_core_stubs: false,
         }
     }
 
@@ -564,6 +569,8 @@ fn split_flags(flags: &str) -> Vec<String> {
                     }
 
                     config.set_name_directive(ln, NO_AUTO_CHECK_CFG, &mut self.no_auto_check_cfg);
+
+                    self.update_add_core_stubs(ln, config);
                 },
             );
 
@@ -677,6 +684,27 @@ pub fn pass_mode(&self, config: &Config) -> Option<PassMode> {
     pub fn local_pass_mode(&self) -> Option<PassMode> {
         self.pass_mode
     }
+
+    pub fn update_add_core_stubs(&mut self, ln: &str, config: &Config) {
+        let add_core_stubs = config.parse_name_directive(ln, directives::ADD_CORE_STUBS);
+        if add_core_stubs {
+            if !matches!(config.mode, Mode::Ui | Mode::Codegen | Mode::Assembly) {
+                panic!(
+                    "`add-core-stubs` is currently 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!("`add-core-stubs` cannot be used to run the test binary");
+            }
+
+            self.add_core_stubs = add_core_stubs;
+        }
+    }
 }
 
 /// If the given line begins with the appropriate comment prefix for a directive,

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

@@ -152,6 +152,7 @@ fn build(&mut self) -> Config {
             "--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

@@ -181,7 +181,8 @@ pub fn parse_config(args: Vec<String>) -> Config {
             "compiletest-diff-tool",
             "What custom diff tool to use for displaying compiletest tests.",
             "COMMAND",
-        );
+        )
+        .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" {
@@ -371,7 +372,10 @@ fn make_absolute(path: PathBuf) -> PathBuf {
         git_merge_commit_email: matches.opt_str("git-merge-commit-email").unwrap(),
 
         profiler_runtime: matches.opt_present("profiler-runtime"),
+
         diff_command: matches.opt_str("compiletest-diff-tool"),
+
+        minicore_path: opt_path(matches, "minicore-path"),
     }
 }
 
@@ -409,6 +413,7 @@ 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());
 }