Avoid collapsing elif and else branches during import sorting (#5964

)

## Summary

I ran into this in the wild. It looks like Ruff will collapse the `else`
and `elif` branches here (i.e., it doesn't recognize that they're too
independent import blocks):

```python
if "sdist" in cmds:
    _sdist = cmds["sdist"]
elif "setuptools" in sys.modules:
    from setuptools.command.sdist import sdist as _sdist
else:
    from setuptools.command.sdist import sdist as _sdist
    from distutils.command.sdist import sdist as _sdist
```

Likely fallout from the `elif_else_branches` refactor.

crates/ruff/resources/test/fixtures/isort/if_elif_else.py

@@ -0,0 +1,7 @@
+if "sdist" in cmds:
+    _sdist = cmds["sdist"]
+elif "setuptools" in sys.modules:
+    from setuptools.command.sdist import sdist as _sdist
+else:
+    from setuptools.command.sdist import sdist as _sdist
+    from distutils.command.sdist import sdist as _sdist

crates/ruff/resources/test/fixtures/isort/match_case.py

@@ -0,0 +1,7 @@
+match 1:
+    case 1:
+        import sys
+        import os
+    case 2:
+        import collections
+        import abc

crates/ruff/src/rules/isort/block.rs

@@ -1,5 +1,5 @@
 use ruff_text_size::{TextRange, TextSize};
-use rustpython_parser::ast::{self, ExceptHandler, MatchCase, Ranged, Stmt};
+use rustpython_parser::ast::{self, ElifElseClause, ExceptHandler, MatchCase, Ranged, Stmt};
 use std::iter::Peekable;
 use std::slice;
 
@@ -254,7 +254,6 @@ where
                 for clause in elif_else_clauses {
                     self.visit_elif_else_clause(clause);
                 }
-                self.finalize(None);
             }
             Stmt::With(ast::StmtWith { body, .. }) => {
                 for stmt in body {
@@ -331,4 +330,11 @@ where
         }
         self.finalize(None);
     }
+
+    fn visit_elif_else_clause(&mut self, elif_else_clause: &'b ElifElseClause) {
+        for stmt in &elif_else_clause.body {
+            self.visit_stmt(stmt);
+        }
+        self.finalize(None);
+    }
 }

crates/ruff/src/rules/isort/mod.rs

@@ -322,13 +322,15 @@ mod tests {
     #[test_case(Path::new("force_sort_within_sections.py"))]
     #[test_case(Path::new("force_to_top.py"))]
     #[test_case(Path::new("force_wrap_aliases.py"))]
+    #[test_case(Path::new("if_elif_else.py"))]
     #[test_case(Path::new("import_from_after_import.py"))]
     #[test_case(Path::new("inline_comments.py"))]
     #[test_case(Path::new("insert_empty_lines.py"))]
     #[test_case(Path::new("insert_empty_lines.pyi"))]
     #[test_case(Path::new("isort_skip_file.py"))]
     #[test_case(Path::new("leading_prefix.py"))]
     #[test_case(Path::new("magic_trailing_comma.py"))]
+    #[test_case(Path::new("match_case.py"))]
     #[test_case(Path::new("natural_order.py"))]
     #[test_case(Path::new("no_lines_before.py"))]
     #[test_case(Path::new("no_reorder_within_section.py"))]

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__if_elif_else.py.snap

@@ -0,0 +1,22 @@
+---
+source: crates/ruff/src/rules/isort/mod.rs
+---
+if_elif_else.py:6:1: I001 [*] Import block is un-sorted or un-formatted
+  |
+4 |       from setuptools.command.sdist import sdist as _sdist
+5 |   else:
+6 | /     from setuptools.command.sdist import sdist as _sdist
+7 | |     from distutils.command.sdist import sdist as _sdist
+  |
+  = help: Organize imports
+
+ℹ Fix
+3 3 | elif "setuptools" in sys.modules:
+4 4 |     from setuptools.command.sdist import sdist as _sdist
+5 5 | else:
+6   |-    from setuptools.command.sdist import sdist as _sdist
+7 6 |     from distutils.command.sdist import sdist as _sdist
+  7 |+
+  8 |+    from setuptools.command.sdist import sdist as _sdist
+
+

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__match_case.py.snap

@@ -0,0 +1,44 @@
+---
+source: crates/ruff/src/rules/isort/mod.rs
+---
+match_case.py:3:1: I001 [*] Import block is un-sorted or un-formatted
+  |
+1 |   match 1:
+2 |       case 1:
+3 | /         import sys
+4 | |         import os
+5 | |     case 2:
+  | |_^ I001
+6 |           import collections
+7 |           import abc
+  |
+  = help: Organize imports
+
+ℹ Fix
+1 1 | match 1:
+2 2 |     case 1:
+  3 |+        import os
+3 4 |         import sys
+4   |-        import os
+5 5 |     case 2:
+6 6 |         import collections
+7 7 |         import abc
+
+match_case.py:6:1: I001 [*] Import block is un-sorted or un-formatted
+  |
+4 |           import os
+5 |       case 2:
+6 | /         import collections
+7 | |         import abc
+  |
+  = help: Organize imports
+
+ℹ Fix
+3 3 |         import sys
+4 4 |         import os
+5 5 |     case 2:
+  6 |+        import abc
+6 7 |         import collections
+7   |-        import abc
+
+