[isort] Add no-lines-before Option (#1955)

Closes https://github.com/charliermarsh/ruff/issues/1916.

README.md

@@ -3135,6 +3135,24 @@ known-third-party = ["src"]
 
 ---
 
+#### [`no-lines-before`](#no-lines-before)
+
+A list of sections that should _not_ be delineated from the previous
+section via empty lines.
+
+**Default value**: `[]`
+
+**Type**: `Option<Vec<ImportType>>`
+
+**Example usage**:
+
+```toml
+[tool.ruff.isort]
+no-lines-before = ["future", "standard-library"]
+```
+
+---
+
 #### [`order-by-type`](#order-by-type)
 
 Order imports by type, which is determined by case, in addition to

resources/test/fixtures/isort/no_lines_before.py

@@ -0,0 +1,9 @@
+from __future__ import annotations
+
+from typing import Any
+
+from requests import Session
+
+from my_first_party import my_first_party_object
+
+from . import my_local_folder_object

ruff.schema.json

@@ -762,6 +762,16 @@
       },
       "additionalProperties": false
     },
+    "ImportType": {
+      "type": "string",
+      "enum": [
+        "future",
+        "standard-library",
+        "third-party",
+        "first-party",
+        "local-folder"
+      ]
+    },
     "IsortOptions": {
       "type": "object",
       "properties": {
@@ -843,6 +853,16 @@
             "type": "string"
           }
         },
+        "no-lines-before": {
+          "description": "A list of sections that should _not_ be delineated from the previous section via empty lines.",
+          "type": [
+            "array",
+            "null"
+          ],
+          "items": {
+            "$ref": "#/definitions/ImportType"
+          }
+        },
         "order-by-type": {
           "description": "Order imports by type, which is determined by case, in addition to alphabetically.",
           "type": [

src/rules/isort/categorize.rs

@@ -3,10 +3,15 @@ use std::fs;
 use std::path::{Path, PathBuf};
 
 use log::debug;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
 
 use crate::python::sys::KNOWN_STANDARD_LIBRARY;
 
-#[derive(Debug, PartialOrd, Ord, PartialEq, Eq, Clone)]
+#[derive(
+    Debug, PartialOrd, Ord, PartialEq, Eq, Clone, Serialize, Deserialize, JsonSchema, Hash,
+)]
+#[serde(deny_unknown_fields, rename_all = "kebab-case")]
 pub enum ImportType {
     Future,
     StandardLibrary,

src/rules/isort/mod.rs

@@ -575,6 +575,7 @@ pub fn format_imports(
     classes: &BTreeSet<String>,
     constants: &BTreeSet<String>,
     variables: &BTreeSet<String>,
+    no_lines_before: &BTreeSet<ImportType>,
 ) -> String {
     let trailer = &block.trailer;
     let block = annotate_imports(&block.imports, comments, locator, split_on_trailing_comma);
@@ -596,7 +597,7 @@ pub fn format_imports(
 
     // Generate replacement source code.
     let mut is_first_block = true;
-    for import_block in block_by_type.into_values() {
+    for (import_type, import_block) in block_by_type {
         let mut imports = order_imports(
             import_block,
             order_by_type,
@@ -628,7 +629,7 @@ pub fn format_imports(
         // Add a blank line between every section.
         if is_first_block {
             is_first_block = false;
-        } else {
+        } else if !no_lines_before.contains(&import_type) {
             output.append(stylist.line_ending());
         }
 
@@ -680,6 +681,7 @@ mod tests {
     use anyhow::Result;
     use test_case::test_case;
 
+    use super::categorize::ImportType;
     use super::settings::RelatveImportsOrder;
     use crate::linter::test_path;
     use crate::registry::RuleCode;
@@ -726,6 +728,7 @@ mod tests {
     #[test_case(Path::new("order_by_type_with_custom_classes.py"))]
     #[test_case(Path::new("order_by_type_with_custom_constants.py"))]
     #[test_case(Path::new("order_by_type_with_custom_variables.py"))]
+    #[test_case(Path::new("no_lines_before.py"))]
     fn default(path: &Path) -> Result<()> {
         let snapshot = format!("{}", path.to_string_lossy());
         let diagnostics = test_path(
@@ -1073,4 +1076,31 @@ mod tests {
         insta::assert_yaml_snapshot!(snapshot, diagnostics);
         Ok(())
     }
+
+    #[test_case(Path::new("no_lines_before.py"))]
+    fn no_lines_before(path: &Path) -> Result<()> {
+        let snapshot = format!("no_lines_before.py_{}", path.to_string_lossy());
+        let mut diagnostics = test_path(
+            Path::new("./resources/test/fixtures/isort")
+                .join(path)
+                .as_path(),
+            &Settings {
+                isort: super::settings::Settings {
+                    no_lines_before: BTreeSet::from([
+                        ImportType::Future,
+                        ImportType::StandardLibrary,
+                        ImportType::ThirdParty,
+                        ImportType::FirstParty,
+                        ImportType::LocalFolder,
+                    ]),
+                    ..super::settings::Settings::default()
+                },
+                src: vec![Path::new("resources/test/fixtures/isort").to_path_buf()],
+                ..Settings::for_rule(RuleCode::I001)
+            },
+        )?;
+        diagnostics.sort_by_key(|diagnostic| diagnostic.location);
+        insta::assert_yaml_snapshot!(snapshot, diagnostics);
+        Ok(())
+    }
 }

src/rules/isort/rules/organize_imports.rs

@@ -88,6 +88,7 @@ pub fn organize_imports(
         &settings.isort.classes,
         &settings.isort.constants,
         &settings.isort.variables,
+        &settings.isort.no_lines_before,
     );
 
     // Expand the span the entire range, including leading and trailing space.

src/rules/isort/settings.rs

@@ -6,6 +6,8 @@ use ruff_macros::ConfigurationOptions;
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
+use super::categorize::ImportType;
+
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize, Hash, JsonSchema)]
 #[serde(deny_unknown_fields, rename_all = "kebab-case")]
 pub enum RelatveImportsOrder {
@@ -201,6 +203,16 @@ pub struct Options {
     /// An override list of tokens to always recognize as a var
     /// for `order-by-type` regardless of casing.
     pub variables: Option<Vec<String>>,
+    #[option(
+        default = r#"[]"#,
+        value_type = "Option<Vec<ImportType>>",
+        example = r#"
+            no-lines-before = ["future", "standard-library"]
+        "#
+    )]
+    /// A list of sections that should _not_ be delineated from the previous
+    /// section via empty lines.
+    pub no_lines_before: Option<Vec<ImportType>>,
 }
 
 #[derive(Debug, Hash)]
@@ -221,6 +233,7 @@ pub struct Settings {
     pub classes: BTreeSet<String>,
     pub constants: BTreeSet<String>,
     pub variables: BTreeSet<String>,
+    pub no_lines_before: BTreeSet<ImportType>,
 }
 
 impl Default for Settings {
@@ -241,6 +254,7 @@ impl Default for Settings {
             classes: BTreeSet::new(),
             constants: BTreeSet::new(),
             variables: BTreeSet::new(),
+            no_lines_before: BTreeSet::new(),
         }
     }
 }
@@ -267,6 +281,7 @@ impl From<Options> for Settings {
             classes: BTreeSet::from_iter(options.classes.unwrap_or_default()),
             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()),
         }
     }
 }
@@ -289,6 +304,7 @@ impl From<Settings> for Options {
             classes: Some(settings.classes.into_iter().collect()),
             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()),
         }
     }
 }

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

@@ -0,0 +1,22 @@
+---
+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\n\nfrom typing import Any\n\nfrom my_first_party import my_first_party_object\nfrom requests import Session\n\nfrom . import my_local_folder_object\n"
+    location:
+      row: 1
+      column: 0
+    end_location:
+      row: 10
+      column: 0
+  parent: ~
+

src/rules/isort/snapshots/ruff__rules__isort__tests__no_lines_before.py_no_lines_before.py.snap

@@ -0,0 +1,22 @@
+---
+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\nfrom typing import Any\nfrom my_first_party import my_first_party_object\nfrom requests import Session\nfrom . import my_local_folder_object\n"
+    location:
+      row: 1
+      column: 0
+    end_location:
+      row: 10
+      column: 0
+  parent: ~
+