Example of rustc interface (#621)

* Example of rustc interface (https://internals.rust-lang.org/t/using-the-rustc-interface-crate/11982)

examples/rustc-driver-example.rs

@@ -0,0 +1,103 @@
+#![feature(rustc_private)]
+
+extern crate rustc;
+extern crate rustc_error_codes;
+extern crate rustc_errors;
+extern crate rustc_hash;
+extern crate rustc_hir;
+extern crate rustc_interface;
+extern crate rustc_span;
+
+use rustc::session;
+use rustc::session::config;
+use rustc_errors::registry;
+use rustc_hash::{FxHashMap, FxHashSet};
+use rustc_interface::interface;
+use rustc_span::source_map;
+use std::path;
+use std::process;
+use std::str;
+
+fn main() {
+    let out = process::Command::new("rustc")
+        .arg("--print=sysroot")
+        .current_dir(".")
+        .output()
+        .unwrap();
+    let sysroot = str::from_utf8(&out.stdout).unwrap().trim();
+    let filename = "main.rs";
+    let contents = "static HELLO: &str = \"Hello, world!\"; fn main() { println!(\"{}\", HELLO); }";
+    let errors = registry::Registry::new(&rustc_error_codes::DIAGNOSTICS);
+    let config = interface::Config {
+        // Command line options
+        opts: config::Options {
+            maybe_sysroot: Some(path::PathBuf::from(sysroot)),
+            ..config::Options::default()
+        },
+
+        // cfg! configuration in addition to the default ones
+        // FxHashSet<(String, Option<String>)>
+        crate_cfg: FxHashSet::default(),
+
+        input: config::Input::Str {
+            name: source_map::FileName::Custom(String::from(filename)),
+            input: String::from(contents),
+        },
+        // Option<PathBuf>
+        input_path: None,
+        // Option<PathBuf>
+        output_dir: None,
+        // Option<PathBuf>
+        output_file: None,
+        // Option<Box<dyn FileLoader + Send + Sync>>
+        file_loader: None,
+        diagnostic_output: session::DiagnosticOutput::Default,
+
+        // Set to capture stderr output during compiler execution
+        // Option<Arc<Mutex<Vec<u8>>>>
+        stderr: None,
+
+        // Option<String>
+        crate_name: None,
+        // FxHashMap<lint::LintId, lint::Level>
+        lint_caps: FxHashMap::default(),
+
+        // This is a callback from the driver that is called when we're registering lints;
+        // it is called during plugin registration when we have the LintStore in a non-shared state.
+        //
+        // Note that if you find a Some here you probably want to call that function in the new
+        // function being registered.
+        // Option<Box<dyn Fn(&Session, &mut LintStore) + Send + Sync>>
+        register_lints: None,
+
+        // This is a callback from the driver that is called just after we have populated
+        // the list of queries.
+        //
+        // The second parameter is local providers and the third parameter is external providers.
+        // Option<fn(&Session, &mut ty::query::Providers<'_>, &mut ty::query::Providers<'_>)>
+        override_queries: None,
+
+        // Registry of diagnostics codes.
+        registry: errors,
+    };
+    interface::run_compiler(config, |compiler| {
+        compiler.enter(|queries| {
+            // Parse the program and print the syntax tree.
+            let parse = queries.parse().unwrap().take();
+            println!("{:#?}", parse);
+            // Analyze the program and inspect the types of definitions.
+            queries.global_ctxt().unwrap().take().enter(|tcx| {
+                for (_, item) in &tcx.hir().krate().items {
+                    match item.kind {
+                        rustc_hir::ItemKind::Static(_, _, _) | rustc_hir::ItemKind::Fn(_, _, _) => {
+                            let name = item.ident;
+                            let ty = tcx.type_of(tcx.hir().local_def_id(item.hir_id));
+                            println!("{:?}:\t{:?}", name, ty)
+                        }
+                        _ => (),
+                    }
+                }
+            })
+        });
+    });
+}