From 47d80f29a7bb4f9fdf7153b112f4b5fde6b45a14 Mon Sep 17 00:00:00 2001
From: Dhruv Manilawala <dhruvmanila@gmail.com>
Date: Tue, 28 Nov 2023 14:38:25 -0600
Subject: [PATCH] Lexer start of line is false only for `Mode::Expression`
 (#8880)

## Summary

This PR fixes the bug in the lexer where the `Mode::Ipython` wasn't
being considered when initializing the soft keyword transformer which
wraps the lexer. This means that if the source code starts with either
`match` or `type` keyword, then the keywords were being considered as
name tokens instead. For example,

```python
match foo:
    case bar:
        pass
```

This would transform the `match` keyword into an identifier if the mode
is `Ipython`.

The fix is to reverse the condition in the soft keyword initializer so
that any new modes are by default considered as the lexer being at start
of line.

## Test Plan

Add a new test case for `Mode::Ipython` and verify the snapshot.

fixes: #8870
---
 crates/ruff_python_parser/src/lexer.rs        |  8 +++
 ..._tests__match_softkeyword_in_notebook.snap | 66 +++++++++++++++++++
 .../ruff_python_parser/src/soft_keywords.rs   |  2 +-
 3 files changed, 75 insertions(+), 1 deletion(-)
 create mode 100644 crates/ruff_python_parser/src/snapshots/ruff_python_parser__lexer__tests__match_softkeyword_in_notebook.snap

diff --git a/crates/ruff_python_parser/src/lexer.rs b/crates/ruff_python_parser/src/lexer.rs
index 2ce3d17c8e..3831bc28d0 100644
--- a/crates/ruff_python_parser/src/lexer.rs
+++ b/crates/ruff_python_parser/src/lexer.rs
@@ -2160,6 +2160,14 @@ f"{(lambda x:{x})}"
         assert_debug_snapshot!(lex_source(source));
     }
 
+    #[test]
+    fn test_match_softkeyword_in_notebook() {
+        let source = r"match foo:
+    case bar:
+        pass";
+        assert_debug_snapshot!(lex_jupyter_source(source));
+    }
+
     fn lex_fstring_error(source: &str) -> FStringErrorType {
         match lex(source, Mode::Module).find_map(std::result::Result::err) {
             Some(err) => match err.error {
diff --git a/crates/ruff_python_parser/src/snapshots/ruff_python_parser__lexer__tests__match_softkeyword_in_notebook.snap b/crates/ruff_python_parser/src/snapshots/ruff_python_parser__lexer__tests__match_softkeyword_in_notebook.snap
new file mode 100644
index 0000000000..0512714bd4
--- /dev/null
+++ b/crates/ruff_python_parser/src/snapshots/ruff_python_parser__lexer__tests__match_softkeyword_in_notebook.snap
@@ -0,0 +1,66 @@
+---
+source: crates/ruff_python_parser/src/lexer.rs
+expression: lex_jupyter_source(source)
+---
+[
+    (
+        Match,
+        0..5,
+    ),
+    (
+        Name {
+            name: "foo",
+        },
+        6..9,
+    ),
+    (
+        Colon,
+        9..10,
+    ),
+    (
+        Newline,
+        10..11,
+    ),
+    (
+        Indent,
+        11..15,
+    ),
+    (
+        Case,
+        15..19,
+    ),
+    (
+        Name {
+            name: "bar",
+        },
+        20..23,
+    ),
+    (
+        Colon,
+        23..24,
+    ),
+    (
+        Newline,
+        24..25,
+    ),
+    (
+        Indent,
+        25..33,
+    ),
+    (
+        Pass,
+        33..37,
+    ),
+    (
+        Newline,
+        37..37,
+    ),
+    (
+        Dedent,
+        37..37,
+    ),
+    (
+        Dedent,
+        37..37,
+    ),
+]
diff --git a/crates/ruff_python_parser/src/soft_keywords.rs b/crates/ruff_python_parser/src/soft_keywords.rs
index f7aab9c113..6d14dc7f37 100644
--- a/crates/ruff_python_parser/src/soft_keywords.rs
+++ b/crates/ruff_python_parser/src/soft_keywords.rs
@@ -31,7 +31,7 @@ where
     pub fn new(lexer: I, mode: Mode) -> Self {
         Self {
             underlying: lexer.multipeek(), // spell-checker:ignore multipeek
-            start_of_line: matches!(mode, Mode::Module),
+            start_of_line: !matches!(mode, Mode::Expression),
         }
     }
 }