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| <h1 id="example-type-checking-through-rustc_driver"><a class="header" href="#example-type-checking-through-rustc_driver">Example: Type checking through <code>rustc_driver</code></a></h1> |
| <p><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver"><code>rustc_driver</code></a> allows you to interact with Rust code at various stages of compilation.</p> |
| <h2 id="getting-the-type-of-an-expression"><a class="header" href="#getting-the-type-of-an-expression">Getting the type of an expression</a></h2> |
| <p>To get the type of an expression, use the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/trait.Callbacks.html#method.after_analysis"><code>after_analysis</code></a> callback to get a <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html"><code>TyCtxt</code></a>.</p> |
| <pre><pre class="playground"><code class="language-rust">// Tested with nightly-2025-03-28 |
| |
| #![feature(rustc_private)] |
| |
| extern crate rustc_ast; |
| extern crate rustc_ast_pretty; |
| extern crate rustc_data_structures; |
| extern crate rustc_driver; |
| extern crate rustc_error_codes; |
| extern crate rustc_errors; |
| extern crate rustc_hash; |
| extern crate rustc_hir; |
| extern crate rustc_interface; |
| extern crate rustc_middle; |
| extern crate rustc_session; |
| extern crate rustc_span; |
| |
| use std::io; |
| use std::path::Path; |
| use std::sync::Arc; |
| |
| use rustc_ast_pretty::pprust::item_to_string; |
| use rustc_driver::{Compilation, run_compiler}; |
| use rustc_interface::interface::{Compiler, Config}; |
| use rustc_middle::ty::TyCtxt; |
| |
| struct MyFileLoader; |
| |
| impl rustc_span::source_map::FileLoader for MyFileLoader { |
| fn file_exists(&self, path: &Path) -> bool { |
| path == Path::new("main.rs") |
| } |
| |
| fn read_file(&self, path: &Path) -> io::Result<String> { |
| if path == Path::new("main.rs") { |
| Ok(r#" |
| fn main() { |
| let message = "Hello, World!"; |
| println!("{message}"); |
| } |
| "# |
| .to_string()) |
| } else { |
| Err(io::Error::other("oops")) |
| } |
| } |
| |
| fn read_binary_file(&self, _path: &Path) -> io::Result<Arc<[u8]>> { |
| Err(io::Error::other("oops")) |
| } |
| } |
| |
| struct MyCallbacks; |
| |
| impl rustc_driver::Callbacks for MyCallbacks { |
| fn config(&mut self, config: &mut Config) { |
| config.file_loader = Some(Box::new(MyFileLoader)); |
| } |
| |
| fn after_crate_root_parsing( |
| &mut self, |
| _compiler: &Compiler, |
| krate: &mut rustc_ast::Crate, |
| ) -> Compilation { |
| for item in &krate.items { |
| println!("{}", item_to_string(&item)); |
| } |
| |
| Compilation::Continue |
| } |
| |
| fn after_analysis(&mut self, _compiler: &Compiler, tcx: TyCtxt<'_>) -> Compilation { |
| // Iterate over the top-level items in the crate, looking for the main function. |
| for id in tcx.hir_free_items() { |
| let item = &tcx.hir_item(id); |
| // Use pattern-matching to find a specific node inside the main function. |
| if let rustc_hir::ItemKind::Fn { body, .. } = item.kind { |
| let expr = &tcx.hir_body(body).value; |
| if let rustc_hir::ExprKind::Block(block, _) = expr.kind { |
| if let rustc_hir::StmtKind::Let(let_stmt) = block.stmts[0].kind { |
| if let Some(expr) = let_stmt.init { |
| let hir_id = expr.hir_id; // hir_id identifies the string "Hello, world!" |
| let def_id = item.hir_id().owner.def_id; // def_id identifies the main function |
| let ty = tcx.typeck(def_id).node_type(hir_id); |
| println!("{expr:#?}: {ty:?}"); |
| } |
| } |
| } |
| } |
| } |
| |
| Compilation::Stop |
| } |
| } |
| |
| fn main() { |
| run_compiler( |
| &[ |
| // The first argument, which in practice contains the name of the binary being executed |
| // (i.e. "rustc") is ignored by rustc. |
| "ignored".to_string(), |
| "main.rs".to_string(), |
| ], |
| &mut MyCallbacks, |
| ); |
| }</code></pre></pre> |
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