1 files changed, 93 insertions, 0 deletions
diff --git a/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs b/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs
new file mode 100644
index 000000000..231994a97
--- /dev/null
+++ b/src/doc/rustc-dev-guide/examples/rustc-driver-interacting-with-the-ast.rs
@@ -0,0 +1,93 @@
+#![feature(rustc_private)]
+
+// NOTE: For the example to compile, you will need to first run the following:
+//   rustup component add rustc-dev llvm-tools-preview
+
+// version: 1.62.0-nightly (7c4b47696 2022-04-30)
+
+extern crate rustc_ast_pretty;
+extern crate rustc_error_codes;
+extern crate rustc_errors;
+extern crate rustc_hash;
+extern crate rustc_hir;
+extern crate rustc_interface;
+extern crate rustc_session;
+extern crate rustc_span;
+
+use std::{path, process, str};
+
+use rustc_ast_pretty::pprust::item_to_string;
+use rustc_errors::registry;
+use rustc_session::config::{self, CheckCfg};
+use rustc_span::source_map;
+
+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 config = rustc_interface::Config {
+        opts: config::Options {
+            maybe_sysroot: Some(path::PathBuf::from(sysroot)),
+            ..config::Options::default()
+        },
+        input: config::Input::Str {
+            name: source_map::FileName::Custom("main.rs".to_string()),
+            input: r#"
+fn main() {
+    let message = "Hello, World!";
+    println!("{message}");
+}
+"#
+            .to_string(),
+        },
+        diagnostic_output: rustc_session::DiagnosticOutput::Default,
+        crate_cfg: rustc_hash::FxHashSet::default(),
+        crate_check_cfg: CheckCfg::default(),
+        input_path: None,
+        output_dir: None,
+        output_file: None,
+        file_loader: None,
+        lint_caps: rustc_hash::FxHashMap::default(),
+        parse_sess_created: None,
+        register_lints: None,
+        override_queries: None,
+        make_codegen_backend: None,
+        registry: registry::Registry::new(&rustc_error_codes::DIAGNOSTICS),
+    };
+    rustc_interface::run_compiler(config, |compiler| {
+        compiler.enter(|queries| {
+            // TODO: add this to -Z unpretty
+            let ast_krate = queries.parse().unwrap().take();
+            for item in ast_krate.items {
+                println!("{}", item_to_string(&item));
+            }
+
+            // Analyze the crate and inspect the types under the cursor.
+            queries.global_ctxt().unwrap().take().enter(|tcx| {
+                // Every compilation contains a single crate.
+                let hir_krate = tcx.hir();
+                // Iterate over the top-level items in the crate, looking for the main function.
+                for id in hir_krate.items() {
+                    let item = hir_krate.item(id);
+                    // Use pattern-matching to find a specific node inside the main function.
+                    if let rustc_hir::ItemKind::Fn(_, _, body_id) = item.kind {
+                        let expr = &tcx.hir().body(body_id).value;
+                        if let rustc_hir::ExprKind::Block(block, _) = expr.kind {
+                            if let rustc_hir::StmtKind::Local(local) = block.stmts[0].kind {
+                                if let Some(expr) = local.init {
+                                    let hir_id = expr.hir_id; // hir_id identifies the string "Hello, world!"
+                                    let def_id = tcx.hir().local_def_id(item.hir_id()); // def_id identifies the main function
+                                    let ty = tcx.typeck(def_id).node_type(hir_id);
+                                    println!("{expr:#?}: {ty:?}");
+                                }
+                            }
+                        }
+                    }
+                }
+            })
+        });
+    });
+}