chore: new xtask to check stale paths in autolabel defintions

.cargo/config.toml

@@ -1,2 +1,3 @@
 [alias]
 unpublished = "run --package xtask-unpublished --"
+stale-label = "run --package xtask-stale-label --"

.github/workflows/main.yml

@@ -36,6 +36,13 @@ jobs:
       # TODO: check every members
       - run: cargo clippy -p cargo --lib --no-deps -- -D warnings
 
+  stale-label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: rustup update stable && rustup default stable
+      - run: cargo stale-label
+
   # Ensure Cargo.lock is up-to-date
   lockfile:
     runs-on: ubuntu-latest

crates/xtask-stale-label/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "xtask-stale-label"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+toml_edit = "0.19"

crates/xtask-stale-label/src/main.rs

@@ -0,0 +1,91 @@
+//! ```text
+//! NAME
+//!         stale-label
+//!
+//! SYNOPSIS
+//!         stale-label
+//!
+//! DESCRIPTION
+//!         Detect stale paths in autolabel definitions in triagebot.toml.
+//!         Probably autofix them in the future.
+//! ```
+
+use std::fmt::Write as _;
+use std::path::PathBuf;
+use std::process;
+use toml_edit::Document;
+
+fn main() {
+    let pkg_root = std::env!("CARGO_MANIFEST_DIR");
+    let ws_root = PathBuf::from(format!("{pkg_root}/../.."));
+    let path = {
+        let path = ws_root.join("triagebot.toml");
+        path.canonicalize().unwrap_or(path)
+    };
+
+    eprintln!("Checking file {path:?}\n");
+
+    let mut failed = 0;
+    let mut passed = 0;
+
+    let toml = std::fs::read_to_string(path).expect("read from file");
+    let doc = toml.parse::<Document>().expect("a toml");
+    let autolabel = doc["autolabel"].as_table().expect("a toml table");
+
+    for (label, value) in autolabel.iter() {
+        let Some(trigger_files) = value.get("trigger_files") else {
+            continue
+        };
+        let trigger_files = trigger_files.as_array().expect("an array");
+        let missing_files: Vec<_> = trigger_files
+            .iter()
+            // Hey TOML content is strict UTF-8.
+            .map(|v| v.as_str().unwrap())
+            .filter(|f| {
+                // triagebot checks with `starts_with` only.
+                // See https://github.com/rust-lang/triagebot/blob/0e4b48ca86ffede9cc70fb1611e658e4d013bce2/src/handlers/autolabel.rs#L45
+                let path = ws_root.join(f);
+                if path.exists() {
+                    return false;
+                }
+                let Some(mut read_dir) = path.parent().and_then(|p| p.read_dir().ok()) else {
+                    return true;
+                };
+                !read_dir.any(|e| {
+                    e.unwrap()
+                        .path()
+                        .strip_prefix(&ws_root)
+                        .unwrap()
+                        .to_str()
+                        .unwrap()
+                        .starts_with(f)
+                })
+            })
+            .collect();
+
+        failed += missing_files.len();
+        passed += trigger_files.len() - missing_files.len();
+
+        if missing_files.is_empty() {
+            continue;
+        }
+
+        let mut msg = String::new();
+        writeln!(
+            &mut msg,
+            "missing files defined in `autolabel.{label}.trigger_files`:"
+        )
+        .unwrap();
+        for f in missing_files.iter() {
+            writeln!(&mut msg, "\t {f}").unwrap();
+        }
+        eprintln!("{msg}");
+    }
+
+    let result = if failed == 0 { "ok" } else { "FAILED" };
+    eprintln!("test result: {result}. {passed} passed; {failed} failed;");
+
+    if failed > 0 {
+        process::exit(1);
+    }
+}