Add empty line after import block (#6200)

## Summary

Ensures that, given:

```python
import os
x = 1
```

We format like:

```python
import os

x = 1
```

crates/ruff_python_formatter/src/statement/suite.rs

@@ -58,17 +58,13 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
             return Ok(());
         };
 
-        // First entry has never any separator, doesn't matter which one we take;
+        // First entry has never any separator, doesn't matter which one we take.
         joiner.entry(first, &first.format());
 
         let mut last = first;
-        let mut is_last_function_or_class_definition = is_class_or_function_definition(first);
 
         for statement in iter {
-            let is_current_function_or_class_definition =
-                is_class_or_function_definition(statement);
-
-            if is_last_function_or_class_definition || is_current_function_or_class_definition {
+            if is_class_or_function_definition(last) || is_class_or_function_definition(statement) {
                 match self.level {
                     SuiteLevel::TopLevel => {
                         joiner.entry_with_separator(
@@ -81,6 +77,8 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                         joiner.entry_with_separator(&empty_line(), &statement.format(), statement);
                     }
                 }
+            } else if is_import_definition(last) && !is_import_definition(statement) {
+                joiner.entry_with_separator(&empty_line(), &statement.format(), statement);
             } else if is_compound_statement(last) {
                 // Handles the case where a body has trailing comments. The issue is that RustPython does not include
                 // the comments in the range of the suite. This means, the body ends right after the last statement in the body.
@@ -124,7 +122,6 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                 joiner.entry(statement, &statement.format());
             }
 
-            is_last_function_or_class_definition = is_current_function_or_class_definition;
             last = statement;
         }
 
@@ -143,6 +140,10 @@ const fn is_class_or_function_definition(stmt: &Stmt) -> bool {
     )
 }
 
+const fn is_import_definition(stmt: &Stmt) -> bool {
+    matches!(stmt, Stmt::Import(_) | Stmt::ImportFrom(_))
+}
+
 impl FormatRuleWithOptions<Suite, PyFormatContext<'_>> for FormatSuite {
     type Options = SuiteLevel;
 

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__fmtonoff.py.snap

@@ -198,20 +198,21 @@ d={'a':1,
 ```diff
 --- Black
 +++ Ruff
-@@ -6,10 +6,9 @@
+@@ -6,10 +6,10 @@
  
  from library import some_connection, some_decorator
  # fmt: off
 -from third_party import (X,
 -                         Y, Z)
 +from third_party import X, Y, Z
++
  # fmt: on
 -f"trigger 3.6 mode"
 +f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
  # Comment 1
  
  # Comment 2
-@@ -17,26 +16,40 @@
+@@ -17,26 +17,40 @@
  
  # fmt: off
  def func_no_args():
@@ -270,7 +271,7 @@ d={'a':1,
  # fmt: on
  def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r""):
      offset = attr.ib(default=attr.Factory(lambda: _r.uniform(1, 2)))
-@@ -63,15 +76,15 @@
+@@ -63,15 +77,15 @@
  
  something = {
      # fmt: off
@@ -289,13 +290,14 @@ d={'a':1,
          # fmt: on
          goes + here,
          andhere,
-@@ -80,38 +93,35 @@
+@@ -80,38 +94,36 @@
  
  def import_as_names():
      # fmt: off
 -    from hello import a,        b
 -    'unformatted'
 +    from hello import a, b
++
 +    "unformatted"
      # fmt: on
  
@@ -338,7 +340,7 @@ d={'a':1,
      # fmt: on
  
  
-@@ -132,10 +142,10 @@
+@@ -132,10 +144,10 @@
      """Another known limitation."""
      # fmt: on
      # fmt: off
@@ -353,7 +355,7 @@ d={'a':1,
      # fmt: on
      # fmt: off
      # ...but comments still get reformatted even though they should not be
-@@ -153,9 +163,7 @@
+@@ -153,9 +165,7 @@
              )
          )
          # fmt: off
@@ -364,7 +366,7 @@ d={'a':1,
          # fmt: on
      _type_comment_re = re.compile(
          r"""
-@@ -178,7 +186,7 @@
+@@ -178,7 +188,7 @@
          $
          """,
          # fmt: off
@@ -373,7 +375,7 @@ d={'a':1,
          # fmt: on
      )
  
-@@ -216,8 +224,7 @@
+@@ -216,8 +226,7 @@
      xxxxxxxxxx_xxxxxxxxxxx_xxxxxxx_xxxxxxxxx=5,
  )
  # fmt: off
@@ -399,6 +401,7 @@ from third_party import X, Y, Z
 from library import some_connection, some_decorator
 # fmt: off
 from third_party import X, Y, Z
+
 # fmt: on
 f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 # Comment 1
@@ -486,6 +489,7 @@ def subscriptlist():
 def import_as_names():
     # fmt: off
     from hello import a, b
+
     "unformatted"
     # fmt: on
 

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__function.py.snap

@@ -107,17 +107,16 @@ def __await__(): return (yield)
 ```diff
 --- Black
 +++ Ruff
-@@ -5,8 +5,7 @@
- from third_party import X, Y, Z
+@@ -6,7 +6,7 @@
 
  from library import some_connection, some_decorator
--
+ 
 -f"trigger 3.6 mode"
 +f"NOT_YET_IMPLEMENTED_ExprJoinedStr"
 
 
  def func_no_args():
-@@ -65,18 +64,14 @@
+@@ -65,18 +65,14 @@
 
  def spaces2(result=_core.Value(None)):
      assert fut is self._read_fut, (fut, self._read_fut)
@@ -153,6 +152,7 @@ import sys
 from third_party import X, Y, Z
 
 from library import some_connection, some_decorator
+
 f"NOT_YET_IMPLEMENTED_ExprJoinedStr"