feat: Add isort option lines-after-imports (#2440)

Fixes https://github.com/charliermarsh/ruff/issues/2243

Adds support for the isort option [lines_after_imports](https://pycqa.github.io/isort/docs/configuration/options.html#lines-after-imports) to insert blank lines between imports and the follow up code.

src/rules/isort/mod.rs

@@ -3,11 +3,12 @@
 use std::collections::BTreeSet;
 use std::path::{Path, PathBuf};
 
+use itertools::Either::{Left, Right};
+
 use annotate::annotate_imports;
 use categorize::categorize_imports;
 pub use categorize::{categorize, ImportType};
 use comments::Comment;
-use itertools::Either::{Left, Right};
 use normalize::normalize_imports;
 use order::order_imports;
 use settings::RelativeImportsOrder;
@@ -127,6 +128,7 @@ pub fn format_imports(
     constants: &BTreeSet<String>,
     variables: &BTreeSet<String>,
     no_lines_before: &BTreeSet<ImportType>,
+    lines_after_imports: isize,
 ) -> String {
     let trailer = &block.trailer;
     let block = annotate_imports(&block.imports, comments, locator, split_on_trailing_comma);
@@ -214,11 +216,23 @@ pub fn format_imports(
     match trailer {
         None => {}
         Some(Trailer::Sibling) => {
-            output.push_str(stylist.line_ending());
+            if lines_after_imports >= 0 {
+                for _ in 0..lines_after_imports {
+                    output.push_str(stylist.line_ending());
+                }
+            } else {
+                output.push_str(stylist.line_ending());
+            }
         }
         Some(Trailer::FunctionDef | Trailer::ClassDef) => {
-            output.push_str(stylist.line_ending());
-            output.push_str(stylist.line_ending());
+            if lines_after_imports >= 0 {
+                for _ in 0..lines_after_imports {
+                    output.push_str(stylist.line_ending());
+                }
+            } else {
+                output.push_str(stylist.line_ending());
+                output.push_str(stylist.line_ending());
+            }
         }
     }
     output
@@ -232,13 +246,14 @@ mod tests {
     use anyhow::Result;
     use test_case::test_case;
 
-    use super::categorize::ImportType;
-    use super::settings::RelativeImportsOrder;
     use crate::assert_yaml_snapshot;
     use crate::registry::Rule;
     use crate::settings::Settings;
     use crate::test::{test_path, test_resource_path};
 
+    use super::categorize::ImportType;
+    use super::settings::RelativeImportsOrder;
+
     #[test_case(Path::new("add_newline_before_comments.py"))]
     #[test_case(Path::new("combine_as_imports.py"))]
     #[test_case(Path::new("combine_import_from.py"))]
@@ -641,4 +656,25 @@ mod tests {
         assert_yaml_snapshot!(snapshot, diagnostics);
         Ok(())
     }
+
+    #[test_case(Path::new("lines_after_imports_nothing_after.py"))]
+    #[test_case(Path::new("lines_after_imports_func_after.py"))]
+    #[test_case(Path::new("lines_after_imports_class_after.py"))]
+    fn lines_after_imports(path: &Path) -> Result<()> {
+        let snapshot = format!("lines_after_imports_{}", path.to_string_lossy());
+        let mut diagnostics = test_path(
+            Path::new("isort").join(path).as_path(),
+            &Settings {
+                isort: super::settings::Settings {
+                    lines_after_imports: 3,
+                    ..super::settings::Settings::default()
+                },
+                src: vec![test_resource_path("fixtures/isort")],
+                ..Settings::for_rule(Rule::UnsortedImports)
+            },
+        )?;
+        diagnostics.sort_by_key(|diagnostic| diagnostic.location);
+        assert_yaml_snapshot!(snapshot, diagnostics);
+        Ok(())
+    }
 }

src/rules/isort/rules/organize_imports.rs

@@ -55,6 +55,7 @@ fn matches_ignoring_indentation(val1: &str, val2: &str) -> bool {
         })
 }
 
+#[allow(clippy::cast_sign_loss)]
 /// I001
 pub fn organize_imports(
     block: &Block,
@@ -117,6 +118,7 @@ pub fn organize_imports(
         &settings.isort.constants,
         &settings.isort.variables,
         &settings.isort.no_lines_before,
+        settings.isort.lines_after_imports,
     );
 
     // Expand the span the entire range, including leading and trailing space.

src/rules/isort/settings.rs

@@ -213,6 +213,17 @@ pub struct Options {
     /// A list of sections that should _not_ be delineated from the previous
     /// section via empty lines.
     pub no_lines_before: Option<Vec<ImportType>>,
+    #[option(
+        default = r#"-1"#,
+        value_type = "int",
+        example = r#"
+            # Use a single line after each import block.
+            lines-after-imports = 1
+        "#
+    )]
+    /// The number of blank lines to place after imports.
+    /// -1 for automatic determination.
+    pub lines_after_imports: Option<isize>,
 }
 
 #[derive(Debug, Hash)]
@@ -234,6 +245,7 @@ pub struct Settings {
     pub constants: BTreeSet<String>,
     pub variables: BTreeSet<String>,
     pub no_lines_before: BTreeSet<ImportType>,
+    pub lines_after_imports: isize,
 }
 
 impl Default for Settings {
@@ -255,6 +267,7 @@ impl Default for Settings {
             constants: BTreeSet::new(),
             variables: BTreeSet::new(),
             no_lines_before: BTreeSet::new(),
+            lines_after_imports: -1,
         }
     }
 }
@@ -282,6 +295,7 @@ impl From<Options> for Settings {
             constants: BTreeSet::from_iter(options.constants.unwrap_or_default()),
             variables: BTreeSet::from_iter(options.variables.unwrap_or_default()),
             no_lines_before: BTreeSet::from_iter(options.no_lines_before.unwrap_or_default()),
+            lines_after_imports: options.lines_after_imports.unwrap_or(-1),
         }
     }
 }
@@ -305,6 +319,7 @@ impl From<Settings> for Options {
             constants: Some(settings.constants.into_iter().collect()),
             variables: Some(settings.variables.into_iter().collect()),
             no_lines_before: Some(settings.no_lines_before.into_iter().collect()),
+            lines_after_imports: Some(settings.lines_after_imports),
         }
     }
 }

src/rules/isort/snapshots/ruff__rules__isort__tests__lines_after_imports_lines_after_imports_class_after.py.snap

@@ -0,0 +1,34 @@
+---
+source: src/rules/isort/mod.rs
+expression: diagnostics
+---
+- kind:
+    UnsortedImports: ~
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 10
+    column: 0
+  fix:
+    content:
+      - from __future__ import annotations
+      - ""
+      - from typing import Any
+      - ""
+      - from my_first_party import my_first_party_object
+      - from requests import Session
+      - ""
+      - from . import my_local_folder_object
+      - ""
+      - ""
+      - ""
+      - ""
+    location:
+      row: 1
+      column: 0
+    end_location:
+      row: 10
+      column: 0
+  parent: ~
+

src/rules/isort/snapshots/ruff__rules__isort__tests__lines_after_imports_lines_after_imports_func_after.py.snap

@@ -0,0 +1,34 @@
+---
+source: src/rules/isort/mod.rs
+expression: diagnostics
+---
+- kind:
+    UnsortedImports: ~
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 21
+    column: 0
+  fix:
+    content:
+      - from __future__ import annotations
+      - ""
+      - from typing import Any
+      - ""
+      - from my_first_party import my_first_party_object
+      - from requests import Session
+      - ""
+      - from . import my_local_folder_object
+      - ""
+      - ""
+      - ""
+      - ""
+    location:
+      row: 1
+      column: 0
+    end_location:
+      row: 21
+      column: 0
+  parent: ~
+

src/rules/isort/snapshots/ruff__rules__isort__tests__lines_after_imports_lines_after_imports_nothing_after.py.snap

@@ -0,0 +1,31 @@
+---
+source: src/rules/isort/mod.rs
+expression: diagnostics
+---
+- kind:
+    UnsortedImports: ~
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 10
+    column: 0
+  fix:
+    content:
+      - from __future__ import annotations
+      - ""
+      - from typing import Any
+      - ""
+      - from my_first_party import my_first_party_object
+      - from requests import Session
+      - ""
+      - from . import my_local_folder_object
+      - ""
+    location:
+      row: 1
+      column: 0
+    end_location:
+      row: 10
+      column: 0
+  parent: ~
+