Create new rustc_smir struct to map future crates

+ Add some information to the README.md

tests/ui-fulldeps/stable-mir/crate-info.rs

@@ -0,0 +1,106 @@
+// run-pass
+// Test that users are able to use stable mir APIs to retrieve information of the current crate
+
+// ignore-stage-1
+// ignore-cross-compile
+// ignore-remote
+
+#![feature(rustc_private)]
+
+extern crate rustc_driver;
+extern crate rustc_hir;
+extern crate rustc_interface;
+extern crate rustc_middle;
+extern crate rustc_smir;
+
+use rustc_driver::{Callbacks, Compilation, RunCompiler};
+use rustc_hir::def::DefKind;
+use rustc_interface::{interface, Queries};
+use rustc_middle::ty::TyCtxt;
+use rustc_smir::{rustc_internal, stable_mir};
+use std::io::Write;
+
+const CRATE_NAME: &str = "input";
+
+/// This function uses the Stable MIR APIs to get information about the test crate.
+fn test_stable_mir(tcx: TyCtxt<'_>) {
+    // Get the local crate using stable_mir API.
+    let local = stable_mir::local_crate();
+    assert_eq!(&local.name, CRATE_NAME);
+
+    // Find items in the local crate.
+    assert!(has_root_item(tcx, &local, (DefKind::Fn, "foo_bar")));
+    assert!(has_root_item(tcx, &local, (DefKind::Mod, "foo")));
+    assert!(!has_root_item(tcx, &local, (DefKind::Fn, "foo::bar")));
+
+    // Check that we can find items in the `std` crate.
+    let std_crate = stable_mir::find_crate("std").unwrap();
+    assert!(has_root_item(tcx, &std_crate, (DefKind::Mod, "std::any")));
+    assert!(!has_root_item(tcx, &std_crate, (DefKind::Fn, "std::any::type_name")));
+}
+
+// Use internal API to find a function in a crate.
+fn has_root_item(tcx: TyCtxt, krate: &stable_mir::Crate, item: (DefKind, &str)) -> bool {
+    krate.root_items.iter().any(|crate_item| {
+        let def_id = rustc_internal::item_def_id(crate_item);
+        tcx.def_kind(def_id) == item.0 && tcx.def_path_str(def_id) == item.1
+    })
+}
+
+/// This test will generate and analyze a dummy crate using the stable mir.
+/// For that, it will first write the dummy crate into a file.
+/// It will invoke the compiler using a custom Callback implementation, which will
+/// invoke Stable MIR APIs after the compiler has finished its analysis.
+fn main() {
+    let path = "input.rs";
+    generate_input(&path).unwrap();
+    let args = vec![
+        "rustc".to_string(),
+        "--crate-type=lib".to_string(),
+        "--crate-name".to_string(),
+        CRATE_NAME.to_string(),
+        path.to_string(),
+    ];
+    rustc_driver::catch_fatal_errors(|| {
+        RunCompiler::new(&args, &mut SMirCalls {}).run().unwrap();
+    })
+    .unwrap();
+}
+
+struct SMirCalls {}
+
+impl Callbacks for SMirCalls {
+    /// Called after analysis. Return value instructs the compiler whether to
+    /// continue the compilation afterwards (defaults to `Compilation::Continue`)
+    fn after_analysis<'tcx>(
+        &mut self,
+        _compiler: &interface::Compiler,
+        queries: &'tcx Queries<'tcx>,
+    ) -> Compilation {
+        queries.global_ctxt().unwrap().enter(|tcx| {
+            test_stable_mir(tcx);
+        });
+        // No need to keep going.
+        Compilation::Stop
+    }
+}
+
+fn generate_input(path: &str) -> std::io::Result<()> {
+    let mut file = std::fs::File::create(path)?;
+    write!(
+        file,
+        r#"
+    mod foo {{
+        pub fn bar(i: i32) -> i64 {{
+            i as i64
+        }}
+    }}
+
+    pub fn foo_bar(x: i32, y: i32) -> i64 {{
+        let x_64 = foo::bar(x);
+        let y_64 = foo::bar(y);
+        x_64.wrapping_add(y_64)
+    }}"#
+    )?;
+    Ok(())
+}