Treat nested classes and functions as "standard" siblings (#1095)

resources/test/fixtures/isort/insert_empty_lines.py

@@ -27,3 +27,15 @@ 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/isort/snapshots/ruff__isort__tests__insert_empty_lines.py.snap

@@ -47,4 +47,34 @@ expression: checks
     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
+- kind: UnsortedImports
+  location:
+    row: 39
+    column: 0
+  end_location:
+    row: 41
+    column: 0
+  fix:
+    content: "    import collections\n    import typing\n\n"
+    location:
+      row: 39
+      column: 0
+    end_location:
+      row: 41
+      column: 0
 

src/isort/track.rs

@@ -60,12 +60,17 @@ 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(match &stmt.node {
+                // TODO(charlie): Track nesting semantically, rather than via column index.
+                self.finalize(Some(if stmt.location.column() == 0 {
+                    match &stmt.node {
                         StmtKind::FunctionDef { .. } | StmtKind::AsyncFunctionDef { .. } => {
                             Trailer::FunctionDef
                         }
                         StmtKind::ClassDef { .. } => Trailer::ClassDef,
                         _ => Trailer::Sibling,
+                    }
+                } else {
+                    Trailer::Sibling
                 }));
                 self.split_index += 1;
             } else {
@@ -81,12 +86,17 @@ where
         {
             self.track_import(stmt);
         } else {
-            self.finalize(Some(match &stmt.node {
+            // TODO(charlie): Track nesting semantically, rather than via column index.
+            self.finalize(Some(if stmt.location.column() == 0 {
+                match &stmt.node {
                     StmtKind::FunctionDef { .. } | StmtKind::AsyncFunctionDef { .. } => {
                         Trailer::FunctionDef
                     }
                     StmtKind::ClassDef { .. } => Trailer::ClassDef,
                     _ => Trailer::Sibling,
+                }
+            } else {
+                Trailer::Sibling
             }));
         }