[pylint] add PLR2044 empty_comment

crates/ruff_linter/resources/test/fixtures/pylint/empty_comment.py

@@ -0,0 +1,17 @@
+# this line has a non-empty comment and is OK
+    # this line is also OK, but the three following lines are not
+#
+    #
+    #    
+
+
+# this non-empty comment has trailing whitespace and is OK    
+
+
+def foo():  # this comment is OK, the one below is not
+    pass  #    
+
+
+# the lines below have no comments and are OK
+def bar():
+    pass

crates/ruff_linter/src/checkers/physical_lines.rs

@@ -32,6 +32,7 @@ pub(crate) fn check_physical_lines(
     let enforce_blank_line_contains_whitespace =
         settings.rules.enabled(Rule::BlankLineWithWhitespace);
     let enforce_copyright_notice = settings.rules.enabled(Rule::MissingCopyrightNotice);
+    let enforce_empty_comment = settings.rules.enabled(Rule::EmptyComment);
 
     let mut doc_lines_iter = doc_lines.iter().peekable();
 
@@ -68,6 +69,12 @@ pub(crate) fn check_physical_lines(
                 diagnostics.push(diagnostic);
             }
         }
+
+        if enforce_empty_comment {
+            if let Some(diagnostic) = pylint::rules::empty_comment(&line) {
+                diagnostics.push(diagnostic);
+            }
+        }
     }
 
     if enforce_no_newline_at_end_of_file {

crates/ruff_linter/src/codes.rs

@@ -264,6 +264,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "R1733") => (RuleGroup::Preview, rules::pylint::rules::UnnecessaryDictIndexLookup),
         (Pylint, "R1736") => (RuleGroup::Preview, rules::pylint::rules::UnnecessaryListIndexLookup),
         (Pylint, "R2004") => (RuleGroup::Stable, rules::pylint::rules::MagicValueComparison),
+        (Pylint, "R2044") => (RuleGroup::Stable, rules::pylint::rules::EmptyComment),
         (Pylint, "R5501") => (RuleGroup::Stable, rules::pylint::rules::CollapsibleElseIf),
         (Pylint, "R6201") => (RuleGroup::Preview, rules::pylint::rules::LiteralMembership),
         #[allow(deprecated)]

crates/ruff_linter/src/registry.rs

@@ -250,6 +250,7 @@ impl Rule {
             Rule::BidirectionalUnicode
             | Rule::BlankLineWithWhitespace
             | Rule::DocLineTooLong
+            | Rule::EmptyComment
             | Rule::LineTooLong
             | Rule::MissingCopyrightNotice
             | Rule::MissingNewlineAtEndOfFile

crates/ruff_linter/src/rules/pylint/mod.rs

@@ -40,6 +40,7 @@ mod tests {
     )]
     #[test_case(Rule::ComparisonWithItself, Path::new("comparison_with_itself.py"))]
     #[test_case(Rule::EqWithoutHash, Path::new("eq_without_hash.py"))]
+    #[test_case(Rule::EmptyComment, Path::new("empty_comment.py"))]
     #[test_case(Rule::ManualFromImport, Path::new("import_aliasing.py"))]
     #[test_case(Rule::SingleStringSlots, Path::new("single_string_slots.py"))]
     #[test_case(Rule::SysExitAlias, Path::new("sys_exit_alias_0.py"))]

crates/ruff_linter/src/rules/pylint/rules/empty_comment.rs

@@ -0,0 +1,60 @@
+use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_source_file::newlines::Line;
+use ruff_text_size::{TextRange, TextSize};
+
+/// ## What it does
+/// Checks for a # symbol appearing on a line not followed by an actual comment.
+///
+/// ## Why is this bad?
+/// Empty comments are unnecessary and can make code harder to read.
+/// Consider using a blank line instead.
+#[violation]
+pub struct EmptyComment;
+
+impl Violation for EmptyComment {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Always;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Line with empty comment")
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        Some(format!("Delete the empty comment"))
+    }
+}
+
+/// PLR2044
+pub(crate) fn empty_comment(line: &Line) -> Option<Diagnostic> {
+    if let Some((column, last_non_whitespace_char)) = line
+        .as_str()
+        .char_indices()
+        .rev()
+        .find(|&(_, c)| !c.is_whitespace())
+    {
+        if last_non_whitespace_char == '#' {
+            #[allow(clippy::cast_possible_truncation)]
+            let start = TextSize::new((line.start().to_usize() + column) as u32);
+            let last = match line
+                .as_str()
+                .char_indices()
+                .rev()
+                .find(|&(_, c)| !c.is_whitespace() && c != '#')
+            {
+                Some((i, _second_to_last_non_whitespace_char)) =>
+                {
+                    #[allow(clippy::cast_possible_truncation)]
+                    TextSize::new((line.start().to_usize() + i + 1) as u32)
+                }
+                None => line.start(),
+            };
+
+            return Some(
+                Diagnostic::new(EmptyComment, TextRange::new(start, line.end()))
+                    .with_fix(Fix::safe_edit(Edit::deletion(last, line.end()))),
+            );
+        }
+    }
+    None
+}

crates/ruff_linter/src/rules/pylint/rules/mod.rs

@@ -14,6 +14,7 @@ pub(crate) use comparison_of_constant::*;
 pub(crate) use comparison_with_itself::*;
 pub(crate) use continue_in_finally::*;
 pub(crate) use duplicate_bases::*;
+pub(crate) use empty_comment::*;
 pub(crate) use eq_without_hash::*;
 pub(crate) use global_at_module_level::*;
 pub(crate) use global_statement::*;
@@ -91,6 +92,7 @@ mod comparison_of_constant;
 mod comparison_with_itself;
 mod continue_in_finally;
 mod duplicate_bases;
+mod empty_comment;
 mod eq_without_hash;
 mod global_at_module_level;
 mod global_statement;

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLR2044_empty_comment.py.snap

@@ -0,0 +1,83 @@
+---
+source: crates/ruff_linter/src/rules/pylint/mod.rs
+---
+empty_comment.py:3:1: PLR2044 [*] Line with empty comment
+  |
+1 | # this line has a non-empty comment and is OK
+2 |     # this line is also OK, but the three following lines are not
+3 | #
+  | ^ PLR2044
+4 |     #
+5 |     #    
+  |
+  = help: Delete the empty comment
+
+ℹ Safe fix
+1 1 | # this line has a non-empty comment and is OK
+2 2 |     # this line is also OK, but the three following lines are not
+3   |-#
+  3 |+
+4 4 |     #
+5 5 |     #    
+6 6 | 
+
+empty_comment.py:4:5: PLR2044 [*] Line with empty comment
+  |
+2 |     # this line is also OK, but the three following lines are not
+3 | #
+4 |     #
+  |     ^ PLR2044
+5 |     #    
+  |
+  = help: Delete the empty comment
+
+ℹ Safe fix
+1 1 | # this line has a non-empty comment and is OK
+2 2 |     # this line is also OK, but the three following lines are not
+3 3 | #
+4   |-    #
+  4 |+
+5 5 |     #    
+6 6 | 
+7 7 | 
+
+empty_comment.py:5:5: PLR2044 [*] Line with empty comment
+  |
+3 | #
+4 |     #
+5 |     #    
+  |     ^^^^^ PLR2044
+  |
+  = help: Delete the empty comment
+
+ℹ Safe fix
+2 2 |     # this line is also OK, but the three following lines are not
+3 3 | #
+4 4 |     #
+5   |-    #    
+6 5 | 
+7 6 | 
+  7 |+
+8 8 | # this non-empty comment has trailing whitespace and is OK    
+9 9 | 
+10 10 | 
+
+empty_comment.py:12:11: PLR2044 [*] Line with empty comment
+   |
+11 | def foo():  # this comment is OK, the one below is not
+12 |     pass  #    
+   |           ^^^^^ PLR2044
+   |
+   = help: Delete the empty comment
+
+ℹ Safe fix
+9  9  | 
+10 10 | 
+11 11 | def foo():  # this comment is OK, the one below is not
+12    |-    pass  #    
+   12 |+    pass
+13 13 | 
+14 14 | 
+15 15 | # the lines below have no comments and are OK
+
+