Test that all interned symbols are referenced in Clippy sources

clippy_utils/src/sym.rs

@@ -132,7 +132,6 @@ generate! {
     enum_glob_use,
     enumerate,
     err,
-    error,
     exp,
     expect_err,
     expn_data,

tests/symbols-used.rs

@@ -0,0 +1,81 @@
+// This test checks that all symbols defined in Clippy's `sym.rs` file
+// are used in Clippy. Otherwise, it will fail with a list of symbols
+// which are unused.
+//
+// This test is a no-op if run as part of the compiler test suite
+// and will always succeed.
+
+use std::collections::HashSet;
+use std::ffi::OsStr;
+use std::fs;
+
+use regex::Regex;
+use walkdir::{DirEntry, WalkDir};
+
+const SYM_FILE: &str = "clippy_utils/src/sym.rs";
+
+type Result<T, E = AnyError> = std::result::Result<T, E>;
+type AnyError = Box<dyn std::error::Error>;
+
+#[test]
+#[allow(clippy::case_sensitive_file_extension_comparisons)]
+fn all_symbols_are_used() -> Result<()> {
+    if option_env!("RUSTC_TEST_SUITE").is_some() {
+        return Ok(());
+    }
+
+    // Load all symbols defined in `SYM_FILE`.
+    let content = fs::read_to_string(SYM_FILE)?;
+    let content = content
+        .split_once("generate! {")
+        .ok_or("cannot find symbols start")?
+        .1
+        .split_once("\n}\n")
+        .ok_or("cannot find symbols end")?
+        .0;
+    let mut interned: HashSet<String> = Regex::new(r"(?m)^    (\w+)")
+        .unwrap()
+        .captures_iter(content)
+        .map(|m| m[1].to_owned())
+        .collect();
+
+    // Remove symbols used as `sym::*`.
+    let used_re = Regex::new(r"\bsym::(\w+)\b").unwrap();
+    let rs_ext = OsStr::new("rs");
+    for dir in ["clippy_lints", "clippy_lints_internal", "clippy_utils", "src"] {
+        for file in WalkDir::new(dir)
+            .into_iter()
+            .flatten()
+            .map(DirEntry::into_path)
+            .filter(|p| p.extension() == Some(rs_ext))
+        {
+            for cap in used_re.captures_iter(&fs::read_to_string(file)?) {
+                interned.remove(&cap[1]);
+            }
+        }
+    }
+
+    // Remove symbols used as part of paths.
+    let paths_re = Regex::new(r"path!\(([\w:]+)\)").unwrap();
+    for path in [
+        "clippy_utils/src/paths.rs",
+        "clippy_lints_internal/src/internal_paths.rs",
+    ] {
+        for cap in paths_re.captures_iter(&fs::read_to_string(path)?) {
+            for sym in cap[1].split("::") {
+                interned.remove(sym);
+            }
+        }
+    }
+
+    let mut extra = interned.iter().collect::<Vec<_>>();
+    if !extra.is_empty() {
+        extra.sort_unstable();
+        eprintln!("Unused symbols defined in {SYM_FILE}:");
+        for sym in extra {
+            eprintln!("  - {sym}");
+        }
+        Err(format!("extra symbols found — remove them {SYM_FILE}"))?;
+    }
+    Ok(())
+}