make Linter threadsafe

examples/dlint/main.rs

@@ -95,22 +95,21 @@ fn run_linter(
     get_recommended_rules()
   };
   let file_diagnostics = Arc::new(Mutex::new(BTreeMap::new()));
+  let linter_builder = LinterBuilder::default().rules(rules.clone());
+
+  let linter = linter_builder.build();
+  debug!("Configured rules: {}", rules.len());
+
+  if rules.is_empty() {
+    bail!("There's no rule to be run!");
+  }
+
   paths
     .par_iter()
     .try_for_each(|file_path| -> Result<(), AnyError> {
       let source_code = std::fs::read_to_string(file_path)?;
 
-      debug!("Configured rules: {}", rules.len());
-
-      if rules.is_empty() {
-        bail!("There's no rule to be run!");
-      }
-
-      let linter_builder = LinterBuilder::default().rules(rules.clone());
-
-      let linter = linter_builder.build();
-
-      let (parsed_source, diagnostics) = linter.lint_file(LintFileOptions {
+      let (parsed_source, diagnostics) = linter.clone().lint_file(LintFileOptions {
         filename: file_path.to_string_lossy().to_string(),
         source_code,
         media_type: MediaType::from_path(file_path),

src/linter.rs

@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 // Copyright 2020-2021 the Deno authors. All rights reserved. MIT license.
 use crate::ast_parser::parse_program;
 use crate::context::Context;
@@ -63,8 +65,10 @@ impl LinterBuilder {
   }
 }
 
+/// A linter instance. It can be cheaply cloned and shared between threads.
+#[derive(Clone)]
 pub struct Linter {
-  ctx: LinterContext,
+  ctx: Arc<LinterContext>,
 }
 
 /// TODO(bartlomieju): docstring
@@ -114,7 +118,7 @@ impl Linter {
       rules,
     );
 
-    Linter { ctx }
+    Linter { ctx: Arc::new(ctx) }
   }
 
   pub fn lint_file(