[hermes] Add UI testing

tools/hermes/Cargo.toml

@@ -10,9 +10,12 @@ publish.workspace = true
 log = "0.4.29"
 miette = { version = "7.6.0", features = ["derive", "fancy"] }
 proc-macro2 = { version = "1.0.105", features = ["span-locations"] }
+serde = { version = "1.0.228", features = ["derive"] }
+serde_json = "1.0.149"
 syn = { version = "2.0.114", features = ["full", "visit", "extra-traits", "parsing"] }
 thiserror = "2.0.18"
 
 [dev-dependencies]
 syn = { version = "2.0.114", features = ["printing", "full", "visit", "extra-traits", "parsing"] }
 proc-macro2 = { version = "1.0.105", features = ["span-locations"] }
+ui_test = "0.30.4"

tools/hermes/src/main.rs

@@ -1,4 +1,39 @@
 mod errors;
 mod parse;
+mod ui_test_shim;
 
-fn main() {}
+use std::{env, fs, path::PathBuf, process::exit};
+
+fn main() {
+    if env::var("HERMES_UI_TEST_MODE").is_ok() {
+        ui_test_shim::run();
+        return;
+    }
+
+    let args: Vec<String> = env::args().collect();
+    if args.len() < 2 {
+        eprintln!("Usage: hermes <file.rs>");
+        exit(1);
+    }
+
+    let file_path = PathBuf::from(&args[1]);
+    let source = match fs::read_to_string(&file_path) {
+        Ok(s) => s,
+        Err(e) => {
+            eprintln!("Error reading file: {}", e);
+            exit(1);
+        }
+    };
+
+    let mut has_errors = false;
+    parse::visit_hermes_items_in_file(&file_path, &source, |res| {
+        if let Err(e) = res {
+            has_errors = true;
+            eprint!("{:?}", miette::Report::new(e));
+        }
+    });
+
+    if has_errors {
+        exit(1);
+    }
+}

tools/hermes/src/parse.rs

@@ -77,7 +77,7 @@ where
 /// Parses the given Rust source code from a file path and invokes the callback `f`
 /// for each item annotated with a `/// ```lean` block. Parsing errors and generated
 /// items will be associated with this file path.
-fn visit_hermes_items_in_file<F>(path: &Path, source: &str, f: F)
+pub fn visit_hermes_items_in_file<F>(path: &Path, source: &str, f: F)
 where
     F: FnMut(Result<ParsedLeanItem, HermesError>),
 {
@@ -94,7 +94,7 @@ where
             .as_ref()
             .map(|p| p.display().to_string())
             .unwrap_or_else(|| "<input>".to_string());
-        dbg!(&f);
+
         f
     };
     let _x = source_file

tools/hermes/src/ui_test_shim.rs

@@ -0,0 +1,128 @@
+use std::{env, fs, path::PathBuf, process::exit};
+
+use miette::Diagnostic as _;
+use serde::Serialize;
+
+use crate::{errors::HermesError, parse};
+
+/// The entrypoint for running under the `ui_test` crate, which expects us to be
+/// `rustc`. This is a bit of a hack, but it works.
+pub fn run() {
+    let args: Vec<String> = env::args().collect();
+
+    // Spoof version if requested
+    if args.contains(&"-vV".to_string()) || args.contains(&"--version".to_string()) {
+        println!("rustc 1.93.0-nightly (hermes-shim)");
+        println!("binary: rustc");
+        println!("commit-hash: 0000000000000000000000000000000000000000");
+        println!("commit-date: 2025-01-01");
+        println!("host: x86_64-unknown-linux-gnu");
+        println!("release: 1.93.0-nightly");
+        exit(0);
+    }
+
+    // Find the file (ignoring rustc flags like --out-dir)
+    let file_path = args
+        .iter()
+        .skip(1)
+        .find(|arg| arg.ends_with(".rs") && !arg.starts_with("--"))
+        .map(PathBuf::from)
+        .unwrap_or_else(|| {
+            // If no file found, maybe it's just a flag check. Exit successfully
+            // to appease ui_test.
+            exit(0);
+        });
+
+    // Run logic with JSON emitter
+    let source = fs::read_to_string(&file_path).unwrap_or_default();
+    let mut has_errors = false;
+
+    parse::visit_hermes_items_in_file(&file_path, &source, |res| {
+        if let Err(e) = res {
+            has_errors = true;
+            emit_rustc_json(&e, &source, file_path.to_str().unwrap());
+        }
+    });
+
+    if has_errors {
+        exit(1);
+    }
+}
+
+#[derive(Serialize)]
+struct RustcDiagnostic {
+    message: String,
+    level: String,
+    spans: Vec<RustcSpan>,
+    children: Vec<RustcDiagnostic>,
+    rendered: String,
+}
+
+#[derive(Serialize)]
+struct RustcSpan {
+    file_name: String,
+    byte_start: usize,
+    byte_end: usize,
+    line_start: usize,
+    line_end: usize,
+    column_start: usize,
+    column_end: usize,
+    is_primary: bool,
+    text: Vec<RustcSpanLine>, // ui_test sometimes checks the snippet context
+}
+
+#[derive(Serialize)]
+struct RustcSpanLine {
+    text: String,
+    highlight_start: usize,
+    highlight_end: usize,
+}
+
+pub fn emit_rustc_json(e: &HermesError, source: &str, file: &str) {
+    let msg = e.to_string();
+    // Use miette's span to get byte offsets.
+    let span = e.labels().and_then(|mut l| l.next());
+
+    let mut spans = Vec::new();
+    if let Some(labeled_span) = span {
+        let offset = labeled_span.offset();
+        let len = labeled_span.len();
+
+        // Calculate lines/cols manually (miette makes this hard to extract
+        // without a Report). This is isolated here now, so it's fine.
+        let prefix = &source[..offset];
+        let line_start = prefix.lines().count().max(1);
+        let last_nl = prefix.rfind('\n').map(|i| i + 1).unwrap_or(0);
+        let column_start = (offset - last_nl) + 1;
+
+        // Grab the line text for the snippet
+        let line_end_idx = source[offset..].find('\n').map(|i| offset + i).unwrap_or(source.len());
+        let line_text = source[last_nl..line_end_idx].to_string();
+
+        spans.push(RustcSpan {
+            file_name: file.to_string(),
+            byte_start: offset,
+            byte_end: offset + len,
+            line_start,
+            line_end: line_start, // Assuming single line for simplicity
+            column_start,
+            column_end: column_start + len,
+            is_primary: true,
+            text: vec![RustcSpanLine {
+                text: line_text,
+                highlight_start: column_start,
+                highlight_end: column_start + len,
+            }],
+        });
+    }
+
+    let diag = RustcDiagnostic {
+        message: msg.clone(),
+        level: "error".to_string(),
+        spans,
+        children: vec![],
+        rendered: format!("error: {}\n", msg),
+    };
+
+    eprintln!("{}", serde_json::to_string(&diag).unwrap());
+}

tools/hermes/tests/ui.rs

@@ -0,0 +1,40 @@
+use std::{path::PathBuf, process::Command};
+
+use ui_test::*;
+
+#[test]
+fn ui() {
+    std::env::set_var("HERMES_UI_TEST_MODE", "true");
+
+    let mut config = Config::rustc(PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests/ui"));
+
+    let args = Args::test().unwrap();
+    config.with_args(&args);
+
+    let binary_path = compile_and_find_binary("hermes");
+    config.program.program = binary_path;
+
+    run_tests(config).unwrap();
+}
+
+fn compile_and_find_binary(name: &str) -> PathBuf {
+    let manifest_dir = env!("CARGO_MANIFEST_DIR");
+    let status = Command::new("cargo")
+        .arg("build")
+        .arg("--bin")
+        .arg(name)
+        .current_dir(manifest_dir)
+        .status()
+        .expect("Failed to execute cargo build");
+
+    assert!(status.success(), "Failed to build binary '{}'", name);
+
+    let mut path = PathBuf::from(manifest_dir);
+    path.push("..");
+    path.push("target");
+    path.push("debug");
+    path.push(name);
+
+    assert!(path.exists(), "Binary not found at {:?}", path);
+    path
+}

tools/hermes/tests/ui/fail_precondition.rs

@@ -0,0 +1,3 @@
+/// ```lean
+//~^ ERROR: Unclosed ```lean block in documentation
+unsafe fn unsafe_op(x: u32) -> u32 { x }

tools/hermes/tests/ui/fail_precondition.stderr

@@ -0,0 +1 @@
+error: Documentation block error: Unclosed ```lean block in documentation

tools/hermes/tests/ui/pass_simple.rs

@@ -0,0 +1,7 @@
+//@ check-pass
+
+/// ```lean
+/// ```
+fn safe_function(x: u32) -> u32 {
+    x
+}