Use single newlines in .pyi import sorting (#1142)

resources/test/fixtures/isort/insert_empty_lines.pyi

@@ -0,0 +1,41 @@
+import a
+import b
+x = 1
+import os
+import sys
+def f():
+    pass
+if True:
+    x = 1
+    import collections
+    import typing
+class X: pass
+y = 1
+import os
+import sys
+"""Docstring"""
+
+if True:
+    import os
+
+
+def f():
+    pass
+
+
+if True:
+    import os
+def f():
+    pass
+
+if True:
+    x = 1
+    import collections
+    import typing
+    class X: pass
+
+if True:
+    x = 1
+    import collections
+    import typing
+    def f(): pass

src/check_imports.rs

@@ -1,5 +1,7 @@
 //! Lint rules based on import analysis.
 
+use std::path::Path;
+
 use rustpython_parser::ast::Suite;
 
 use crate::ast::visitor::Visitor;
@@ -33,8 +35,9 @@ pub fn check_imports(
     directives: &IsortDirectives,
     settings: &Settings,
     autofix: bool,
+    path: &Path,
 ) -> Vec<Check> {
-    let mut tracker = ImportTracker::new(directives);
+    let mut tracker = ImportTracker::new(directives, path);
     for stmt in python_ast {
         tracker.visit_stmt(stmt);
     }

src/isort/mod.rs

@@ -559,6 +559,7 @@ mod tests {
     #[test_case(Path::new("force_wrap_aliases.py"))]
     #[test_case(Path::new("import_from_after_import.py"))]
     #[test_case(Path::new("insert_empty_lines.py"))]
+    #[test_case(Path::new("insert_empty_lines.pyi"))]
     #[test_case(Path::new("leading_prefix.py"))]
     #[test_case(Path::new("no_reorder_within_section.py"))]
     #[test_case(Path::new("no_wrap_star.py"))]

src/isort/snapshots/ruff__isort__tests__insert_empty_lines.pyi.snap

@@ -0,0 +1,65 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 3
+    column: 0
+  fix:
+    content: "import a\nimport b\n\n"
+    location:
+      row: 1
+      column: 0
+    end_location:
+      row: 3
+      column: 0
+- kind: UnsortedImports
+  location:
+    row: 4
+    column: 0
+  end_location:
+    row: 6
+    column: 0
+  fix:
+    content: "import os\nimport sys\n\n"
+    location:
+      row: 4
+      column: 0
+    end_location:
+      row: 6
+      column: 0
+- kind: UnsortedImports
+  location:
+    row: 14
+    column: 0
+  end_location:
+    row: 16
+    column: 0
+  fix:
+    content: "import os\nimport sys\n\n"
+    location:
+      row: 14
+      column: 0
+    end_location:
+      row: 16
+      column: 0
+- kind: UnsortedImports
+  location:
+    row: 33
+    column: 0
+  end_location:
+    row: 35
+    column: 0
+  fix:
+    content: "    import collections\n    import typing\n\n"
+    location:
+      row: 33
+      column: 0
+    end_location:
+      row: 35
+      column: 0
+

src/isort/track.rs

@@ -1,3 +1,5 @@
+use std::path::Path;
+
 use rustpython_ast::{
     Alias, Arg, Arguments, Boolop, Cmpop, Comprehension, Constant, Excepthandler,
     ExcepthandlerKind, Expr, ExprContext, Keyword, MatchCase, Operator, Pattern, Stmt, StmtKind,
@@ -20,16 +22,18 @@ pub struct Block<'a> {
 }
 
 pub struct ImportTracker<'a> {
-    blocks: Vec<Block<'a>>,
     directives: &'a IsortDirectives,
+    pyi: bool,
+    blocks: Vec<Block<'a>>,
     split_index: usize,
     nested: bool,
 }
 
 impl<'a> ImportTracker<'a> {
-    pub fn new(directives: &'a IsortDirectives) -> Self {
+    pub fn new(directives: &'a IsortDirectives, path: &'a Path) -> Self {
         Self {
             directives,
+            pyi: path.extension().map_or(false, |ext| ext == "pyi"),
             blocks: vec![Block::default()],
             split_index: 0,
             nested: false,
@@ -41,6 +45,34 @@ impl<'a> ImportTracker<'a> {
         self.blocks[index].imports.push(stmt);
     }
 
+    fn trailer_for(&self, stmt: &'a Stmt) -> Option<Trailer> {
+        if self.pyi {
+            // Black treats interface files differently, limiting to one newline
+            // (`Trailing::Sibling`), and avoiding inserting any newlines in nested function
+            // blocks.
+            if self.nested
+                && matches!(
+                    stmt.node,
+                    StmtKind::FunctionDef { .. } | StmtKind::AsyncFunctionDef { .. }
+                )
+            {
+                None
+            } else {
+                Some(Trailer::Sibling)
+            }
+        } else if self.nested {
+            Some(Trailer::Sibling)
+        } else {
+            Some(match &stmt.node {
+                StmtKind::FunctionDef { .. } | StmtKind::AsyncFunctionDef { .. } => {
+                    Trailer::FunctionDef
+                }
+                StmtKind::ClassDef { .. } => Trailer::ClassDef,
+                _ => Trailer::Sibling,
+            })
+        }
+    }
+
     fn finalize(&mut self, trailer: Option<Trailer>) {
         let index = self.blocks.len() - 1;
         if !self.blocks[index].imports.is_empty() {
@@ -62,17 +94,7 @@ where
         // Track manual splits.
         while self.split_index < self.directives.splits.len() {
             if stmt.location.row() >= self.directives.splits[self.split_index] {
-                self.finalize(Some(if self.nested {
+                self.finalize(self.trailer_for(stmt));
-                    Trailer::Sibling
-                } else {
-                    match &stmt.node {
-                        StmtKind::FunctionDef { .. } | StmtKind::AsyncFunctionDef { .. } => {
-                            Trailer::FunctionDef
-                        }
-                        StmtKind::ClassDef { .. } => Trailer::ClassDef,
-                        _ => Trailer::Sibling,
-                    }
-                }));
                 self.split_index += 1;
             } else {
                 break;
@@ -87,17 +109,7 @@ where
         {
             self.track_import(stmt);
         } else {
-            self.finalize(Some(if self.nested {
+            self.finalize(self.trailer_for(stmt));
-                Trailer::Sibling
-            } else {
-                match &stmt.node {
-                    StmtKind::FunctionDef { .. } | StmtKind::AsyncFunctionDef { .. } => {
-                        Trailer::FunctionDef
-                    }
-                    StmtKind::ClassDef { .. } => Trailer::ClassDef,
-                    _ => Trailer::Sibling,
-                }
-            }));
         }
 
         // Track scope.

src/linter.rs

@@ -92,6 +92,7 @@ pub(crate) fn check_path(
                         &directives.isort,
                         settings,
                         autofix,
+                        path,
                     ));
                 }
             }