deno_lint 0.84.0

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.

use super::program_ref;
use super::{Context, LintRule};
use crate::tags::{self, Tags};
use crate::Program;
use crate::ProgramRef;
use deno_ast::swc::common::comments::Comment;
use deno_ast::swc::{
  ast::*,
  ecma_visit::{noop_visit_type, Visit, VisitWith},
};
use deno_ast::SourceRangedForSpanned;
use derive_more::Display;

#[derive(Debug)]
pub struct NoFallthrough;

const CODE: &str = "no-fallthrough";

#[derive(Display)]
enum NoFallthroughMessage {
  #[display(fmt = "Fallthrough is not allowed")]
  Unexpected,
}

#[derive(Display)]
enum NoFallthroughHint {
  #[display(
    fmt = "Add `break` or comment `/* falls through */` to your case statement"
  )]
  BreakOrComment,
}

impl LintRule for NoFallthrough {
  fn tags(&self) -> Tags {
    &[tags::RECOMMENDED]
  }

  fn code(&self) -> &'static str {
    CODE
  }

  fn lint_program_with_ast_view<'view>(
    &self,
    context: &mut Context<'view>,
    program: Program<'view>,
  ) {
    let program = program_ref(program);
    let mut visitor = NoFallthroughVisitor { context };
    match program {
      ProgramRef::Module(m) => visitor.visit_module(m),
      ProgramRef::Script(s) => visitor.visit_script(s),
    }
  }
}

struct NoFallthroughVisitor<'c, 'view> {
  context: &'c mut Context<'view>,
}

impl Visit for NoFallthroughVisitor<'_, '_> {
  noop_visit_type!();

  fn visit_switch_cases(&mut self, cases: &[SwitchCase]) {
    let mut should_emit_err = false;
    let mut prev_range = None;

    'cases: for case in cases.iter() {
      case.visit_with(self);

      if should_emit_err {
        let comments = self.context.leading_comments_at(case.start());
        if !allow_fall_through(comments) {
          if let Some(prev_range) = prev_range.take() {
            self.context.add_diagnostic_with_hint(
              prev_range,
              CODE,
              NoFallthroughMessage::Unexpected,
              NoFallthroughHint::BreakOrComment,
            );
          }
        }
      }
      should_emit_err = true;
      let mut stops_exec = false;

      // Handle return / throw / break / continue
      for (idx, stmt) in case.cons.iter().enumerate() {
        let last = idx + 1 == case.cons.len();
        let metadata = self.context.control_flow().meta(stmt.start());
        stops_exec |= metadata.map(|v| v.stops_execution()).unwrap_or(false);
        if stops_exec {
          should_emit_err = false;
        }

        if last {
          let comments = self.context.trailing_comments_at(stmt.end());
          if allow_fall_through(comments) {
            should_emit_err = false;
            // User comment beats everything
            prev_range = Some(case.range());
            continue 'cases;
          }
        }
      }

      let empty = case.cons.is_empty()
        || matches!(case.cons.as_slice(), [Stmt::Block(b)] if b.stmts.is_empty());

      if empty {
        should_emit_err = false;
      }

      prev_range = Some(case.range());
    }
  }
}

fn allow_fall_through<'c>(
  mut comments: impl Iterator<Item = &'c Comment>,
) -> bool {
  comments.any(|comment| {
    let l = comment.text.to_ascii_lowercase();
    l.contains("fallthrough")
      || l.contains("falls through")
      || l.contains("fall through")
  })
}

#[cfg(test)]
mod tests {
  use super::*;

  #[test]
  fn no_fallthrough_valid() {
    assert_lint_ok! {
      NoFallthrough,
      "switch(foo) { case 0: a(); /* falls through */ case 1: b(); }",
      "switch(foo) { case 0: a()\n /* falls through */ case 1: b(); }",
      "switch(foo) { case 0: a(); /* fall through */ case 1: b(); }",
      "switch(foo) { case 0: a(); /* fallthrough */ case 1: b(); }",
      "switch(foo) { case 0: a(); /* FALLS THROUGH */ case 1: b(); }",
      "function foo() { switch(foo) { case 0: a(); return; case 1: b(); }; }",
      "switch(foo) { case 0: a(); throw 'foo'; case 1: b(); }",
      "while (a) { switch(foo) { case 0: a(); continue; case 1: b(); } }",
      "switch(foo) { case 0: a(); break; case 1: b(); }",
      "switch(foo) { case 0: case 1: a(); break; case 2: b(); }",
      "switch(foo) { case 0: case 1: break; case 2: b(); }",
      "switch(foo) { case 0: case 1: break; default: b(); }",
      "switch(foo) { case 0: case 1: a(); }",
      "switch(foo) { case 0: case 1: a(); break; }",
      "switch(foo) { case 0: case 1: break; }",
      "switch(foo) { case 0:\n case 1: break; }",
      "switch(foo) { case 0: // comment\n case 1: break; }",
      "function foo() { switch(foo) { case 0: case 1: return; } }",
      "function foo() { switch(foo) { case 0: {return;}\n case 1: {return;} } }",
      "switch(foo) { case 0: case 1: {break;} }",
      "switch(foo) { }",
      "switch(foo) { case 0: switch(bar) { case 2: break; } /* falls through */ case 1: break; }",
      "function foo() { switch(foo) { case 1: return a; a++; }}",
      "switch (foo) { case 0: a(); /* falls through */ default:  b(); /* comment */ }",
      "switch (foo) { case 0: a(); /* falls through */ default: /* comment */ b(); }",
      "switch (foo) { case 0: if (a) { break; } else { throw 0; } default: b(); }",
      "switch (foo) { case 0: try { break; } finally {} default: b(); }",
      "switch (foo) { case 0: try {} finally { break; } default: b(); }",
      "switch (foo) { case 0: try { throw 0; } catch (err) { break; } default: b(); }",
      "switch (foo) { case 0: do { throw 0; } while(a); default: b(); }",
      "switch('test') { case 'symbol':\n case 'function': default: b(); }",
      "switch('test') { case 'symbol':\n case 'function':\n default: b(); }",
      "switch('test') { case 'symbol': case 'function': default: b(); }",
      "switch(foo) { case 1:\n\n default: a(); }",
      "switch(foo) { case 1:\n// comment\n default: a(); }",

      // https://github.com/denoland/deno_lint/issues/746
      r#"
switch(someValue) {
  case 0: {
    // nothing to do for this value
  } break;
  case 1:
    break;
}
      "#,
      r#"
switch(someValue) {
  case 0: {
    // nothing to do for this value
  } break;
  default:
    console.log(42);
}
      "#,
    };
  }

  #[test]
  fn no_fallthrough_invalid() {
    assert_lint_err! {
      NoFallthrough,
      "switch(foo) { case 0: a();\ncase 1: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0: a();\ndefault: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0: a(); default: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0: if (a) { break; } default: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0: try { throw 0; } catch (err) {} default: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0: while (a) { break; } default: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0:\n\n b()\n default: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ],
      "switch(foo) { case 0: a(); /* falling through */ default: b() }": [
        {
          col: 14,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ]
    };
  }

  #[test]
  #[ignore = "It ends with break statement"]
  fn no_fallthrough_invalid_2() {
    assert_lint_err! {
      NoFallthrough,
      "switch(foo) { case 0: do { break; } while (a); default: b() }": [
        {
          col: 47,
          message: NoFallthroughMessage::Unexpected,
          hint: NoFallthroughHint::BreakOrComment,
        }
      ]
    };
  }
}