Avoid emitting empty logical lines (#4452)

crates/ruff/resources/test/fixtures/pycodestyle/E11.py

@@ -49,3 +49,18 @@ def start():
 #:
 if False:  #
     print()
+#:
+if False:
+    print()
+
+    print()
+#:
+if False:
+    print()
+    if False:
+
+        print()
+#:
+if False:
+
+    print()

crates/ruff/src/checkers/logical_lines.rs

@@ -250,5 +250,20 @@ f()"#
             "f()",
         ];
         assert_eq!(actual, expected);
+
+        let contents = r#"
+if False:
+
+    print()
+"#
+        .trim();
+        let lxr: Vec<LexResult> = lexer::lex(contents, Mode::Module).collect();
+        let locator = Locator::new(contents);
+        let actual: Vec<String> = LogicalLines::from_tokens(&lxr, &locator)
+            .into_iter()
+            .map(|line| line.text_trimmed().to_string())
+            .collect();
+        let expected = vec!["if False:", "print()", ""];
+        assert_eq!(actual, expected);
     }
 }

crates/ruff/src/rules/pycodestyle/rules/logical_lines/mod.rs

@@ -500,11 +500,16 @@ impl LogicalLinesBuilder {
     fn finish_line(&mut self) {
         let end = self.tokens.len() as u32;
         if self.current_line.tokens_start < end {
-            self.lines.push(Line {
-                flags: self.current_line.flags,
-                tokens_start: self.current_line.tokens_start,
-                tokens_end: end,
-            });
+            let is_empty = self.tokens[self.current_line.tokens_start as usize..end as usize]
+                .iter()
+                .all(|token| token.kind.is_newline());
+            if !is_empty {
+                self.lines.push(Line {
+                    flags: self.current_line.flags,
+                    tokens_start: self.current_line.tokens_start,
+                    tokens_end: end,
+                });
+            }
 
             self.current_line = CurrentLine {
                 flags: TokenFlags::default(),

crates/ruff_python_ast/src/token_kind.rs

@@ -167,6 +167,11 @@ pub enum TokenKind {
 }
 
 impl TokenKind {
+    #[inline]
+    pub const fn is_newline(&self) -> bool {
+        matches!(self, TokenKind::Newline | TokenKind::NonLogicalNewline)
+    }
+
     #[inline]
     pub const fn is_unary(&self) -> bool {
         matches!(self, TokenKind::Plus | TokenKind::Minus | TokenKind::Star)