Respect 'is not' operators split across newlines (#4977)

crates/ruff/resources/test/fixtures/pyflakes/F632.py

@@ -19,3 +19,6 @@ if ("123" != x) is 3:
 
 if "123" != (x is 3):
     pass
+
+{2 is
+not ''}

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F632_F632.py.snap

@@ -136,5 +136,26 @@ F632.py:20:14: F632 [*] Use `==` to compare constant literals
 20    |-if "123" != (x is 3):
    20 |+if "123" != (x == 3):
 21 21 |     pass
+22 22 | 
+23 23 | {2 is
+
+F632.py:23:2: F632 [*] Use `!=` to compare constant literals
+   |
+23 |       pass
+24 |   
+25 |   {2 is
+   |  __^
+26 | | not ''}
+   | |______^ F632
+   |
+   = help: Replace `is not` with `!=`
+
+ℹ Suggested fix
+20 20 | if "123" != (x is 3):
+21 21 |     pass
+22 22 | 
+23    |-{2 is
+24    |-not ''}
+   23 |+{2 != ''}
 
 

crates/ruff_python_ast/src/helpers.rs

@@ -1440,14 +1440,21 @@ impl LocatedCmpop {
     }
 }
 
-/// Extract all [`Cmpop`] operators from a source code snippet, with appropriate
+/// Extract all [`Cmpop`] operators from an expression snippet, with appropriate
 /// ranges.
 ///
 /// `RustPython` doesn't include line and column information on [`Cmpop`] nodes.
 /// `CPython` doesn't either. This method iterates over the token stream and
 /// re-identifies [`Cmpop`] nodes, annotating them with valid ranges.
 pub fn locate_cmpops(contents: &str) -> Vec<LocatedCmpop> {
-    let mut tok_iter = lexer::lex(contents, Mode::Module).flatten().peekable();
+    let mut tok_iter = lexer::lex(contents, Mode::Expression)
+        .flatten()
+        .filter(|(tok, _)|
+            // Skip whitespace, including Tok::Newline. It should be sufficient to skip
+            // Tok::NonLogicalNewline, but the lexer doesn't know that we're within an
+            // expression, and so it may confusion logical and non-logical newlines.
+            !matches!(tok, Tok::Newline | Tok::NonLogicalNewline | Tok::Comment(_)))
+        .peekable();
     let mut ops: Vec<LocatedCmpop> = vec![];
     let mut count = 0u32;
     loop {