feat(no-empty-file): add no-empty-file rule

src/lib.rs

@@ -122,8 +122,10 @@ mod lint_tests {
 
   #[test]
   fn empty_file() {
+    // An empty file is reported by the recommended `no-empty-file` rule.
     let diagnostics = lint_recommended_rules("");
-    assert!(diagnostics.is_empty());
+    assert_eq!(diagnostics.len(), 1);
+    assert_eq!(diagnostics[0].details.code, "no-empty-file");
   }
 
   #[test]
@@ -293,8 +295,10 @@ const _foo = 42;
 
   #[test]
   fn empty_file_with_ast() {
+    // An empty file is reported by the recommended `no-empty-file` rule.
     let parsed_source = parse("");
     let diagnostics = lint_recommended_rules_with_ast(&parsed_source);
-    assert!(diagnostics.is_empty());
+    assert_eq!(diagnostics.len(), 1);
+    assert_eq!(diagnostics[0].details.code, "no-empty-file");
   }
 }

src/rules.rs

@@ -61,6 +61,7 @@ pub mod no_duplicate_case;
 pub mod no_empty;
 pub mod no_empty_character_class;
 pub mod no_empty_enum;
+pub mod no_empty_file;
 pub mod no_empty_interface;
 pub mod no_empty_pattern;
 pub mod no_eval;
@@ -305,6 +306,7 @@ fn get_all_rules_raw() -> Vec<Box<dyn LintRule>> {
     Box::new(no_empty::NoEmpty),
     Box::new(no_empty_character_class::NoEmptyCharacterClass),
     Box::new(no_empty_enum::NoEmptyEnum),
+    Box::new(no_empty_file::NoEmptyFile),
     Box::new(no_empty_interface::NoEmptyInterface),
     Box::new(no_empty_pattern::NoEmptyPattern),
     Box::new(no_eval::NoEval),

src/rules/no_empty_file.rs

@@ -0,0 +1,181 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+use super::{Context, LintRule};
+use crate::Program;
+use deno_ast::swc::common::comments::Comment;
+use deno_ast::swc::common::comments::CommentKind;
+use deno_ast::view::{Expr, Lit, ModuleItem, Stmt};
+use deno_ast::{SourceRange, SourceRanged};
+use derive_more::Display;
+use once_cell::sync::Lazy;
+use regex::Regex;
+
+#[derive(Debug)]
+pub struct NoEmptyFile;
+
+const CODE: &str = "no-empty-file";
+
+#[derive(Display)]
+enum NoEmptyFileMessage {
+  #[display(fmt = "Empty files are not allowed")]
+  Empty,
+}
+
+#[derive(Display)]
+enum NoEmptyFileHint {
+  #[display(fmt = "Delete this file or add some code to it")]
+  DeleteOrAddCode,
+}
+
+impl LintRule for NoEmptyFile {
+  fn tags(&self) -> crate::tags::Tags {
+    &[crate::tags::RECOMMENDED]
+  }
+
+  fn code(&self) -> &'static str {
+    CODE
+  }
+
+  fn lint_program_with_ast_view<'view>(
+    &self,
+    context: &mut Context<'view>,
+    program: Program<'view>,
+  ) {
+    // A triple-slash reference directive counts as meaningful content even
+    // though it is technically a comment, so such files are exempt.
+    if context.all_comments().any(is_triple_slash_reference) {
+      return;
+    }
+
+    let is_empty = match program {
+      Program::Module(module) => module.body.iter().all(is_empty_module_item),
+      Program::Script(script) => {
+        script.body.iter().all(is_empty_top_level_stmt)
+      }
+    };
+
+    if !is_empty {
+      return;
+    }
+
+    // Cap the reported span at 100 characters to avoid emitting an enormous
+    // diagnostic for comment-heavy (but otherwise empty) files.
+    let start = program.start();
+    let text = program.text_fast(context.text_info());
+    let range = match text.char_indices().nth(100) {
+      Some((byte_offset, _)) => SourceRange::new(start, start + byte_offset),
+      None => program.range(),
+    };
+
+    context.add_diagnostic_with_hint(
+      range,
+      CODE,
+      NoEmptyFileMessage::Empty,
+      NoEmptyFileHint::DeleteOrAddCode,
+    );
+  }
+}
+
+fn is_empty_module_item(item: &ModuleItem) -> bool {
+  match item {
+    // Imports and exports are meaningful code.
+    ModuleItem::ModuleDecl(_) => false,
+    ModuleItem::Stmt(stmt) => is_empty_top_level_stmt(stmt),
+  }
+}
+
+fn is_empty_top_level_stmt(stmt: &Stmt) -> bool {
+  match stmt {
+    Stmt::Empty(_) => true,
+    // A bare string literal statement at the top level is a directive
+    // (e.g. `"use strict";`) and carries no real code.
+    Stmt::Expr(expr_stmt) => matches!(expr_stmt.expr, Expr::Lit(Lit::Str(_))),
+    Stmt::Block(block) => block.stmts.iter().all(is_empty_nested_stmt),
+    _ => false,
+  }
+}
+
+fn is_empty_nested_stmt(stmt: &Stmt) -> bool {
+  match stmt {
+    Stmt::Empty(_) => true,
+    Stmt::Block(block) => block.stmts.iter().all(is_empty_nested_stmt),
+    // Unlike at the top level, a string literal nested in a block is a real
+    // expression statement rather than a directive.
+    _ => false,
+  }
+}
+
+fn is_triple_slash_reference(comment: &Comment) -> bool {
+  if comment.kind != CommentKind::Line {
+    return false;
+  }
+
+  static TSR_REGEX: Lazy<Regex> = Lazy::new(|| {
+    Regex::new(r#"^/\s*<reference\s*(types|path|lib)\s*=\s*["|'](.*)["|']"#)
+      .unwrap()
+  });
+
+  TSR_REGEX.is_match(&comment.text)
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  // Some tests are derived from
+  // https://github.com/oxc-project/oxc/blob/main/crates/oxc_linter/src/rules/unicorn/no_empty_file.rs
+  // MIT Licensed.
+
+  #[test]
+  fn no_empty_file_valid() {
+    assert_lint_ok! {
+      NoEmptyFile,
+      "const x = 0;",
+      ";; const x = 0;",
+      "{{{;;const x = 0;}}}",
+      "'use strict';\nconst x = 0;",
+      ";;'use strict';\nconst x = 0;",
+      "{'use strict';}",
+      r#"("use strict")"#,
+      "`use strict`",
+      "({})",
+      "#!/usr/bin/env node\nconsole.log('done');",
+      "false",
+      r#"("")"#,
+      "NaN",
+      "undefined",
+      "null",
+      "[]",
+      "(() => {})()",
+      "(() => {})();",
+      r#"/// <reference types="vite/client" />"#,
+    };
+  }
+
+  #[test]
+  fn no_empty_file_invalid() {
+    assert_lint_err! {
+      NoEmptyFile,
+      "": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      " ": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "\t": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "\n": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "\r": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "\r\n": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "// comment": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "/* comment */": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "#!/usr/bin/env node": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "'use asm';": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "'use strict';": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      r#""use strict""#: [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      r#""""#: [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      ";": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      ";;": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "{}": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "{;;}": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      "{{}}": [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      r#""";"#: [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+      r#""use strict";"#: [{ col: 0, message: NoEmptyFileMessage::Empty, hint: NoEmptyFileHint::DeleteOrAddCode }],
+    };
+  }
+}