Insert empty line between suite and alternative branch after def/class (

#12294)

When there is a function or class definition at the end of a suite
followed by the beginning of an alternative block, we have to insert a
single empty line between them.

In the if-else-statement example below, we insert an empty line after
the `foo` in the if-block, but none after the else-block `foo`, since in
the latter case the enclosing suite already adds empty lines.

```python
if sys.version_info >= (3, 10):
    def foo():
        return "new"
else:
    def foo():
        return "old"
class Bar:
    pass
```

To do so, we track whether the current suite is the last one in the
current statement with a new option on the suite kind.

Fixes #12199

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_formatter/resources/test/fixtures/ruff/newlines.py

@@ -249,6 +249,68 @@ def y():
     print()
 
 
+if True:
+    def a():
+        return 1
+else:
+    pass
+
+if True:
+    # fmt: off
+    def a():
+        return 1
+    # fmt: on
+else:
+    pass
+
+match True:
+    case 1:
+        def a():
+            return 1
+    case 1:
+        def a():
+            return 1
+
+try:
+    def a():
+        return 1
+except RuntimeError:
+    def a():
+        return 1
+
+try:
+    def a():
+        return 1
+finally:
+    def a():
+        return 1
+
+try:
+    def a():
+        return 1
+except RuntimeError:
+    def a():
+        return 1
+except ZeroDivisionError:
+    def a():
+        return 1
+else:
+    def a():
+        return 1
+finally:
+    def a():
+        return 1
+
+if raw:
+    def show_file(lines):
+        for line in lines:
+            pass
+            # Trailing comment not on function or class
+
+else:
+    pass
+
+
 # NOTE: Please keep this the last block in this file. This tests that we don't insert
 # empty line(s) at the end of the file due to nested function
 if True:

crates/ruff_python_formatter/resources/test/fixtures/ruff/newlines.pyi

@@ -154,8 +154,14 @@ def f():
     pass
 
 
+if True:
+    def a():
+        return 1
+else:
+    pass
 
 
 # comment
 
 x = 1
+

crates/ruff_python_formatter/src/other/elif_else_clause.rs

@@ -2,6 +2,7 @@ use ruff_python_ast::ElifElseClause;
 
 use crate::prelude::*;
 use crate::statement::stmt_if::format_elif_else_clause;
+use crate::statement::suite::SuiteKind;
 
 /// Note that this implementation misses the leading newlines before the leading comments because
 /// it does not have access to the last node of the previous branch. The `StmtIf` therefore doesn't
@@ -11,6 +12,15 @@ pub struct FormatElifElseClause;
 
 impl FormatNodeRule<ElifElseClause> for FormatElifElseClause {
     fn fmt_fields(&self, item: &ElifElseClause, f: &mut PyFormatter) -> FormatResult<()> {
-        format_elif_else_clause(item, f, None)
+        format_elif_else_clause(
+            item,
+            f,
+            None,
+            SuiteKind::Other {
+                // For stability, we can't insert an empty line if we don't know if the outer suite
+                // also does.
+                last_suite_in_statement: true,
+            },
+        )
     }
 }

crates/ruff_python_formatter/src/other/except_handler_except_handler.rs

@@ -6,26 +6,29 @@ use crate::expression::maybe_parenthesize_expression;
 use crate::expression::parentheses::Parenthesize;
 use crate::prelude::*;
 use crate::statement::clause::{clause_body, clause_header, ClauseHeader};
+use crate::statement::suite::SuiteKind;
 
 #[derive(Copy, Clone, Default)]
-pub enum ExceptHandlerKind {
+pub(crate) enum ExceptHandlerKind {
     #[default]
     Regular,
     Starred,
 }
 
 #[derive(Default)]
 pub struct FormatExceptHandlerExceptHandler {
-    except_handler_kind: ExceptHandlerKind,
+    pub(crate) except_handler_kind: ExceptHandlerKind,
+    pub(crate) last_suite_in_statement: bool,
 }
 
 impl FormatRuleWithOptions<ExceptHandlerExceptHandler, PyFormatContext<'_>>
     for FormatExceptHandlerExceptHandler
 {
-    type Options = ExceptHandlerKind;
+    type Options = FormatExceptHandlerExceptHandler;
 
     fn with_options(mut self, options: Self::Options) -> Self {
-        self.except_handler_kind = options;
+        self.except_handler_kind = options.except_handler_kind;
+        self.last_suite_in_statement = options.last_suite_in_statement;
         self
     }
 }
@@ -36,6 +39,7 @@ impl FormatNodeRule<ExceptHandlerExceptHandler> for FormatExceptHandlerExceptHan
         item: &ExceptHandlerExceptHandler,
         f: &mut PyFormatter,
     ) -> FormatResult<()> {
+        let except_handler_kind = self.except_handler_kind;
         let ExceptHandlerExceptHandler {
             range: _,
             type_,
@@ -57,7 +61,7 @@ impl FormatNodeRule<ExceptHandlerExceptHandler> for FormatExceptHandlerExceptHan
                             f,
                             [
                                 token("except"),
-                                match self.except_handler_kind {
+                                match except_handler_kind {
                                     ExceptHandlerKind::Regular => None,
                                     ExceptHandlerKind::Starred => Some(token("*")),
                                 }
@@ -84,7 +88,11 @@ impl FormatNodeRule<ExceptHandlerExceptHandler> for FormatExceptHandlerExceptHan
                         Ok(())
                     }),
                 ),
-                clause_body(body, dangling_comments),
+                clause_body(
+                    body,
+                    SuiteKind::other(self.last_suite_in_statement),
+                    dangling_comments
+                ),
             ]
         )
     }

crates/ruff_python_formatter/src/other/match_case.rs

@@ -1,14 +1,26 @@
-use ruff_formatter::write;
+use ruff_formatter::{write, FormatRuleWithOptions};
 use ruff_python_ast::AstNode;
 use ruff_python_ast::MatchCase;
 
 use crate::builders::parenthesize_if_expands;
 use crate::expression::parentheses::{NeedsParentheses, OptionalParentheses, Parentheses};
 use crate::prelude::*;
 use crate::statement::clause::{clause_body, clause_header, ClauseHeader};
+use crate::statement::suite::SuiteKind;
 
 #[derive(Default)]
-pub struct FormatMatchCase;
+pub struct FormatMatchCase {
+    last_suite_in_statement: bool,
+}
+
+impl FormatRuleWithOptions<MatchCase, PyFormatContext<'_>> for FormatMatchCase {
+    type Options = bool;
+
+    fn with_options(mut self, options: Self::Options) -> Self {
+        self.last_suite_in_statement = options;
+        self
+    }
+}
 
 impl FormatNodeRule<MatchCase> for FormatMatchCase {
     fn fmt_fields(&self, item: &MatchCase, f: &mut PyFormatter) -> FormatResult<()> {
@@ -63,7 +75,11 @@ impl FormatNodeRule<MatchCase> for FormatMatchCase {
                         Ok(())
                     }),
                 ),
-                clause_body(body, dangling_item_comments),
+                clause_body(
+                    body,
+                    SuiteKind::other(self.last_suite_in_statement),
+                    dangling_item_comments
+                ),
             ]
         )
     }

crates/ruff_python_formatter/src/statement/clause.rs

@@ -380,21 +380,14 @@ pub(crate) struct FormatClauseBody<'a> {
     trailing_comments: &'a [SourceComment],
 }
 
-impl<'a> FormatClauseBody<'a> {
-    #[must_use]
-    pub(crate) fn with_kind(mut self, kind: SuiteKind) -> Self {
-        self.kind = kind;
-        self
-    }
-}
-
 pub(crate) fn clause_body<'a>(
     body: &'a Suite,
+    kind: SuiteKind,
     trailing_comments: &'a [SourceComment],
 ) -> FormatClauseBody<'a> {
     FormatClauseBody {
         body,
-        kind: SuiteKind::default(),
+        kind,
         trailing_comments,
     }
 }

crates/ruff_python_formatter/src/statement/stmt_class_def.rs

@@ -132,7 +132,7 @@ impl FormatNodeRule<StmtClassDef> for FormatStmtClassDef {
                         Ok(())
                     }),
                 ),
-                clause_body(body, trailing_definition_comments).with_kind(SuiteKind::Class),
+                clause_body(body, SuiteKind::Class, trailing_definition_comments),
             ]
         )?;
 

crates/ruff_python_formatter/src/statement/stmt_for.rs

@@ -7,6 +7,7 @@ use crate::expression::maybe_parenthesize_expression;
 use crate::expression::parentheses::Parenthesize;
 use crate::prelude::*;
 use crate::statement::clause::{clause_body, clause_header, ClauseHeader, ElseClause};
+use crate::statement::suite::SuiteKind;
 
 #[derive(Debug)]
 struct ExprTupleWithoutParentheses<'a>(&'a Expr);
@@ -63,7 +64,11 @@ impl FormatNodeRule<StmtFor> for FormatStmtFor {
                         maybe_parenthesize_expression(iter, item, Parenthesize::IfBreaks),
                     ],
                 ),
-                clause_body(body, trailing_condition_comments),
+                clause_body(
+                    body,
+                    SuiteKind::other(orelse.is_empty()),
+                    trailing_condition_comments
+                ),
             ]
         )?;
 
@@ -85,7 +90,7 @@ impl FormatNodeRule<StmtFor> for FormatStmtFor {
                         &token("else"),
                     )
                     .with_leading_comments(leading, body.last()),
-                    clause_body(orelse, trailing),
+                    clause_body(orelse, SuiteKind::other(true), trailing),
                 ]
             )?;
         }

crates/ruff_python_formatter/src/statement/stmt_function_def.rs

@@ -66,7 +66,7 @@ impl FormatNodeRule<StmtFunctionDef> for FormatStmtFunctionDef {
                     trailing_definition_comments,
                     &format_with(|f| format_function_header(f, item)),
                 ),
-                clause_body(body, trailing_definition_comments).with_kind(SuiteKind::Function),
+                clause_body(body, SuiteKind::Function, trailing_definition_comments),
             ]
         )?;
 

crates/ruff_python_formatter/src/statement/stmt_if.rs

@@ -1,12 +1,12 @@
 use ruff_formatter::{format_args, write};
-use ruff_python_ast::AnyNodeRef;
-use ruff_python_ast::{ElifElseClause, StmtIf};
+use ruff_python_ast::{AnyNodeRef, ElifElseClause, StmtIf};
 use ruff_text_size::Ranged;
 
 use crate::expression::maybe_parenthesize_expression;
 use crate::expression::parentheses::Parenthesize;
 use crate::prelude::*;
 use crate::statement::clause::{clause_body, clause_header, ClauseHeader};
+use crate::statement::suite::SuiteKind;
 
 #[derive(Default)]
 pub struct FormatStmtIf;
@@ -35,13 +35,22 @@ impl FormatNodeRule<StmtIf> for FormatStmtIf {
                         maybe_parenthesize_expression(test, item, Parenthesize::IfBreaks),
                     ],
                 ),
-                clause_body(body, trailing_colon_comment),
+                clause_body(
+                    body,
+                    SuiteKind::other(elif_else_clauses.is_empty()),
+                    trailing_colon_comment
+                ),
             ]
         )?;
 
         let mut last_node = body.last().unwrap().into();
         for clause in elif_else_clauses {
-            format_elif_else_clause(clause, f, Some(last_node))?;
+            format_elif_else_clause(
+                clause,
+                f,
+                Some(last_node),
+                SuiteKind::other(clause == elif_else_clauses.last().unwrap()),
+            )?;
             last_node = clause.body.last().unwrap().into();
         }
 
@@ -55,6 +64,7 @@ pub(crate) fn format_elif_else_clause(
     item: &ElifElseClause,
     f: &mut PyFormatter,
     last_node: Option<AnyNodeRef>,
+    suite_kind: SuiteKind,
 ) -> FormatResult<()> {
     let ElifElseClause {
         range: _,
@@ -93,7 +103,7 @@ pub(crate) fn format_elif_else_clause(
                 }),
             )
             .with_leading_comments(leading_comments, last_node),
-            clause_body(body, trailing_colon_comment),
+            clause_body(body, suite_kind, trailing_colon_comment),
             f.options()
                 .source_map_generation()
                 .is_enabled()

crates/ruff_python_formatter/src/statement/stmt_match.rs

@@ -48,14 +48,15 @@ impl FormatNodeRule<StmtMatch> for FormatStmtMatch {
         let mut last_case = first;
 
         for case in cases_iter {
+            let last_suite_in_statement = Some(case) == cases.last();
             write!(
                 f,
                 [block_indent(&format_args!(
                     leading_alternate_branch_comments(
                         comments.leading(case),
                         last_case.body.last(),
                     ),
-                    case.format()
+                    case.format().with_options(last_suite_in_statement)
                 ))]
             )?;
             last_case = case;