Truncate to one empty line in stub files (#7558)

## Summary

This PR modifies a variety of sites in which we insert up to two empty
lines to instead truncate to at most one empty line in stub files. We
already enforce this in _some_ places, but not all.

## Test Plan

`cargo test`

No changes in similarity (as expected, since this only impacts
unformatted `.pyi` files).

Before:

| project | similarity index | total files | changed files |

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99963 | 2587 | 323 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99979 | 3496 | 22 |
| warehouse | 0.99967 | 648 | 15 |
| zulip | 0.99972 | 1437 | 21 |

After:

| project | similarity index | total files | changed files |

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99963 | 2587 | 323 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99979 | 3496 | 22 |
| warehouse | 0.99967 | 648 | 15 |
| zulip | 0.99972 | 1437 | 21 |

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

@@ -0,0 +1,161 @@
+###
+# Blank lines around functions
+###
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+
+if True:
+    x = 1
+
+# comment
+
+def f():
+    pass
+
+
+x = 1
+
+
+
+# comment
+
+def f():
+    pass
+
+
+x = 1
+
+
+
+# comment
+def f():
+    pass
+
+
+x = 1
+
+# comment
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+def f():
+    pass
+
+
+x = 1
+
+
+# comment
+
+
+
+# comment
+
+
+
+def f():
+    pass
+# comment
+
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+
+# comment
+
+###
+# Blank lines around imports.
+###
+
+def f():
+    import x
+    # comment
+    import y
+
+
+def f():
+    import x
+
+    # comment
+    import y
+
+
+def f():
+    import x
+    # comment
+
+    import y
+
+
+def f():
+    import x
+    # comment
+
+
+    import y
+
+
+def f():
+    import x
+
+
+    # comment
+    import y
+
+
+def f():
+    import x
+
+    # comment
+
+    import y
+
+
+def f():
+    import x  # comment
+    # comment
+
+    import y
+
+
+def f(): pass  # comment
+# comment
+
+x = 1
+
+
+def f():
+    pass
+
+
+
+
+# comment
+
+x = 1

crates/ruff_python_formatter/src/comments/format.rs

@@ -308,7 +308,14 @@ impl Format<PyFormatContext<'_>> for FormatEmptyLines {
             NodeLevel::TopLevel => match self.lines {
                 0 | 1 => write!(f, [hard_line_break()]),
                 2 => write!(f, [empty_line()]),
-                _ => write!(f, [empty_line(), empty_line()]),
+                _ => match f.options().source_type() {
+                    PySourceType::Stub => {
+                        write!(f, [empty_line()])
+                    }
+                    PySourceType::Python | PySourceType::Ipynb => {
+                        write!(f, [empty_line(), empty_line()])
+                    }
+                },
             },
 
             NodeLevel::CompoundStatement => match self.lines {

crates/ruff_python_formatter/src/statement/suite.rs

@@ -1,7 +1,7 @@
 use ruff_formatter::{write, FormatOwnedWithRule, FormatRefWithRule, FormatRuleWithOptions};
 use ruff_python_ast::helpers::is_compound_statement;
 use ruff_python_ast::node::AnyNodeRef;
-use ruff_python_ast::{self as ast, Constant, Expr, ExprConstant, Stmt, Suite};
+use ruff_python_ast::{self as ast, Constant, Expr, ExprConstant, PySourceType, Stmt, Suite};
 use ruff_python_trivia::{lines_after, lines_after_ignoring_trivia, lines_before};
 use ruff_text_size::{Ranged, TextRange};
 
@@ -192,7 +192,14 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                     SuiteKind::TopLevel => {
                         match lines_after_ignoring_trivia(preceding.end(), source) {
                             0..=2 => empty_line().fmt(f)?,
-                            _ => write!(f, [empty_line(), empty_line()])?,
+                            _ => match source_type {
+                                PySourceType::Stub => {
+                                    empty_line().fmt(f)?;
+                                }
+                                PySourceType::Python | PySourceType::Ipynb => {
+                                    write!(f, [empty_line(), empty_line()])?;
+                                }
+                            },
                         }
                     }
                     SuiteKind::Function | SuiteKind::Class | SuiteKind::Other => {
@@ -225,8 +232,15 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                 match lines_before(start, source) {
                     0 | 1 => hard_line_break().fmt(f)?,
                     2 => empty_line().fmt(f)?,
-                    3.. => match self.kind {
+                    _ => match self.kind {
-                        SuiteKind::TopLevel => write!(f, [empty_line(), empty_line()])?,
+                        SuiteKind::TopLevel => match source_type {
+                            PySourceType::Stub => {
+                                empty_line().fmt(f)?;
+                            }
+                            PySourceType::Python | PySourceType::Ipynb => {
+                                write!(f, [empty_line(), empty_line()])?;
+                            }
+                        },
                         SuiteKind::Function | SuiteKind::Class | SuiteKind::Other => {
                             empty_line().fmt(f)?;
                         }
@@ -280,7 +294,14 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                     NodeLevel::TopLevel => match count_lines(end) {
                         0 | 1 => hard_line_break().fmt(f)?,
                         2 => empty_line().fmt(f)?,
-                        _ => write!(f, [empty_line(), empty_line()])?,
+                        _ => match source_type {
+                            PySourceType::Stub => {
+                                empty_line().fmt(f)?;
+                            }
+                            PySourceType::Python | PySourceType::Ipynb => {
+                                write!(f, [empty_line(), empty_line()])?;
+                            }
+                        },
                     },
                     NodeLevel::CompoundStatement => match count_lines(end) {
                         0 | 1 => hard_line_break().fmt(f)?,

crates/ruff_python_formatter/tests/snapshots/format@newlines.pyi.snap

@@ -0,0 +1,311 @@
+---
+source: crates/ruff_python_formatter/tests/fixtures.rs
+input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/newlines.pyi
+---
+## Input
+```py
+###
+# Blank lines around functions
+###
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+
+if True:
+    x = 1
+
+# comment
+
+def f():
+    pass
+
+
+x = 1
+
+
+
+# comment
+
+def f():
+    pass
+
+
+x = 1
+
+
+
+# comment
+def f():
+    pass
+
+
+x = 1
+
+# comment
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+def f():
+    pass
+
+
+x = 1
+
+
+# comment
+
+
+
+# comment
+
+
+
+def f():
+    pass
+# comment
+
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+
+# comment
+
+###
+# Blank lines around imports.
+###
+
+def f():
+    import x
+    # comment
+    import y
+
+
+def f():
+    import x
+
+    # comment
+    import y
+
+
+def f():
+    import x
+    # comment
+
+    import y
+
+
+def f():
+    import x
+    # comment
+
+
+    import y
+
+
+def f():
+    import x
+
+
+    # comment
+    import y
+
+
+def f():
+    import x
+
+    # comment
+
+    import y
+
+
+def f():
+    import x  # comment
+    # comment
+
+    import y
+
+
+def f(): pass  # comment
+# comment
+
+x = 1
+
+
+def f():
+    pass
+
+
+
+
+# comment
+
+x = 1
+```
+
+## Output
+```py
+###
+# Blank lines around functions
+###
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+if True:
+    x = 1
+
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+
+# comment
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+# comment
+
+###
+# Blank lines around imports.
+###
+
+def f():
+    import x
+
+    # comment
+    import y
+
+def f():
+    import x
+
+    # comment
+    import y
+
+def f():
+    import x
+    # comment
+
+    import y
+
+def f():
+    import x
+    # comment
+
+    import y
+
+def f():
+    import x
+
+    # comment
+    import y
+
+def f():
+    import x
+
+    # comment
+
+    import y
+
+def f():
+    import x  # comment
+    # comment
+
+    import y
+
+def f():
+    pass  # comment
+
+# comment
+
+x = 1
+
+def f():
+    pass
+
+# comment
+
+x = 1
+```
+
+
+