Make isort's `detect-same-package` behavior configurable (#6833)

## Summary

Our first-party import detection uses a heuristic that doesn't exist in
isort: if an import appears to be from within the same package as the
containing file, we mark it as first-party. For example, if you have a
directory `./foo/__init__.py`, and you import `from foo import bar` in
`./foo/baz.py`, we'll mark that as first-party. (See:
https://github.com/astral-sh/ruff/pull/1266.)

This is often unnecessary, and arguably should be removed (though it
does have some important use-cases that are otherwise unserved -- I
believe Dagster uses it to ensure that all packages mark imports from
within the same package as first-party, but not imports _across_
different first-party packages)... but it does exist, and it does help
in cases in which the `src` field is not properly configured.

This PR adds an option to turn off this behavior:

```toml
[tool.ruff.isort]
detect-same-package = false
```

This is being introduced to help codebases migrating over from isort
that may want more consistent behavior with their current sorting.

## Test Plan

`cargo test`

crates/ruff/resources/test/fixtures/isort/detect_same_package/foo/bar.py

@@ -0,0 +1,3 @@
+import os
+import pandas
+import foo.baz

crates/ruff/resources/test/fixtures/isort/detect_same_package/pyproject.toml

@@ -0,0 +1,2 @@
+[tool.ruff]
+line-length = 88

crates/ruff/src/rules/flake8_type_checking/rules/typing_only_runtime_import.rs

@@ -283,6 +283,7 @@ pub(crate) fn typing_only_runtime_import(
                 None,
                 &checker.settings.src,
                 checker.package(),
+                checker.settings.isort.detect_same_package,
                 &checker.settings.isort.known_modules,
                 checker.settings.target_version,
             ) {

crates/ruff/src/rules/isort/categorize.rs

@@ -69,6 +69,7 @@ pub(crate) fn categorize<'a>(
     level: Option<u32>,
     src: &[PathBuf],
     package: Option<&Path>,
+    detect_same_package: bool,
     known_modules: &'a KnownModules,
     target_version: PythonVersion,
 ) -> &'a ImportSection {
@@ -88,7 +89,7 @@ pub(crate) fn categorize<'a>(
                 &ImportSection::Known(ImportType::StandardLibrary),
                 Reason::KnownStandardLibrary,
             )
-        } else if same_package(package, module_base) {
+        } else if detect_same_package && same_package(package, module_base) {
             (
                 &ImportSection::Known(ImportType::FirstParty),
                 Reason::SamePackage,
@@ -137,6 +138,7 @@ pub(crate) fn categorize_imports<'a>(
     block: ImportBlock<'a>,
     src: &[PathBuf],
     package: Option<&Path>,
+    detect_same_package: bool,
     known_modules: &'a KnownModules,
     target_version: PythonVersion,
 ) -> BTreeMap<&'a ImportSection, ImportBlock<'a>> {
@@ -148,6 +150,7 @@ pub(crate) fn categorize_imports<'a>(
             None,
             src,
             package,
+            detect_same_package,
             known_modules,
             target_version,
         );
@@ -164,6 +167,7 @@ pub(crate) fn categorize_imports<'a>(
             import_from.level,
             src,
             package,
+            detect_same_package,
             known_modules,
             target_version,
         );
@@ -180,6 +184,7 @@ pub(crate) fn categorize_imports<'a>(
             import_from.level,
             src,
             package,
+            detect_same_package,
             known_modules,
             target_version,
         );
@@ -196,6 +201,7 @@ pub(crate) fn categorize_imports<'a>(
             import_from.level,
             src,
             package,
+            detect_same_package,
             known_modules,
             target_version,
         );

crates/ruff/src/rules/isort/mod.rs

@@ -82,6 +82,7 @@ pub(crate) fn format_imports(
     force_to_top: &BTreeSet<String>,
     known_modules: &KnownModules,
     order_by_type: bool,
+    detect_same_package: bool,
     relative_imports_order: RelativeImportsOrder,
     single_line_exclusions: &BTreeSet<String>,
     split_on_trailing_comma: bool,
@@ -129,6 +130,7 @@ pub(crate) fn format_imports(
             force_to_top,
             known_modules,
             order_by_type,
+            detect_same_package,
             relative_imports_order,
             split_on_trailing_comma,
             classes,
@@ -187,6 +189,7 @@ fn format_import_block(
     force_to_top: &BTreeSet<String>,
     known_modules: &KnownModules,
     order_by_type: bool,
+    detect_same_package: bool,
     relative_imports_order: RelativeImportsOrder,
     split_on_trailing_comma: bool,
     classes: &BTreeSet<String>,
@@ -198,7 +201,14 @@ fn format_import_block(
     section_order: &[ImportSection],
 ) -> String {
     // Categorize by type (e.g., first-party vs. third-party).
-    let mut block_by_type = categorize_imports(block, src, package, known_modules, target_version);
+    let mut block_by_type = categorize_imports(
+        block,
+        src,
+        package,
+        detect_same_package,
+        known_modules,
+        target_version,
+    );
 
     let mut output = String::new();
 
@@ -1084,4 +1094,38 @@ mod tests {
         assert_messages!(snapshot, diagnostics);
         Ok(())
     }
+
+    #[test]
+    fn detect_same_package() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("isort/detect_same_package/foo/bar.py"),
+            &Settings {
+                src: vec![],
+                isort: super::settings::Settings {
+                    detect_same_package: true,
+                    ..super::settings::Settings::default()
+                },
+                ..Settings::for_rule(Rule::UnsortedImports)
+            },
+        )?;
+        assert_messages!(diagnostics);
+        Ok(())
+    }
+
+    #[test]
+    fn no_detect_same_package() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("isort/detect_same_package/foo/bar.py"),
+            &Settings {
+                src: vec![],
+                isort: super::settings::Settings {
+                    detect_same_package: false,
+                    ..super::settings::Settings::default()
+                },
+                ..Settings::for_rule(Rule::UnsortedImports)
+            },
+        )?;
+        assert_messages!(diagnostics);
+        Ok(())
+    }
 }

crates/ruff/src/rules/isort/rules/organize_imports.rs

@@ -134,6 +134,7 @@ pub(crate) fn organize_imports(
         &settings.isort.force_to_top,
         &settings.isort.known_modules,
         settings.isort.order_by_type,
+        settings.isort.detect_same_package,
         settings.isort.relative_imports_order,
         &settings.isort.single_line_exclusions,
         settings.isort.split_on_trailing_comma,

crates/ruff/src/rules/isort/settings.rs

@@ -305,6 +305,21 @@ pub struct Options {
     )]
     /// Override in which order the sections should be output. Can be used to move custom sections.
     pub section_order: Option<Vec<ImportSection>>,
+    #[option(
+        default = r#"true"#,
+        value_type = "bool",
+        example = r#"
+            detect-same-package = false
+        "#
+    )]
+    /// Whether to automatically mark imports from within the same package as first-party.
+    /// For example, when `detect-same-package = true`, then when analyzing files within the
+    /// `foo` package, any imports from within the `foo` package will be considered first-party.
+    ///
+    /// This heuristic is often unnecessary when `src` is configured to detect all first-party
+    /// sources; however, if `src` is _not_ configured, this heuristic can be useful to detect
+    /// first-party imports from _within_ (but not _across_) first-party packages.
+    pub detect_same_package: Option<bool>,
     // Tables are required to go last.
     #[option(
         default = "{}",
@@ -331,6 +346,7 @@ pub struct Settings {
     pub force_wrap_aliases: bool,
     pub force_to_top: BTreeSet<String>,
     pub known_modules: KnownModules,
+    pub detect_same_package: bool,
     pub order_by_type: bool,
     pub relative_imports_order: RelativeImportsOrder,
     pub single_line_exclusions: BTreeSet<String>,
@@ -352,6 +368,7 @@ impl Default for Settings {
             combine_as_imports: false,
             force_single_line: false,
             force_sort_within_sections: false,
+            detect_same_package: true,
             case_sensitive: false,
             force_wrap_aliases: false,
             force_to_top: BTreeSet::new(),
@@ -509,6 +526,7 @@ impl TryFrom<Options> for Settings {
             force_sort_within_sections: options.force_sort_within_sections.unwrap_or(false),
             case_sensitive: options.case_sensitive.unwrap_or(false),
             force_wrap_aliases: options.force_wrap_aliases.unwrap_or(false),
+            detect_same_package: options.detect_same_package.unwrap_or(true),
             force_to_top: BTreeSet::from_iter(options.force_to_top.unwrap_or_default()),
             known_modules: KnownModules::new(
                 known_first_party,
@@ -595,6 +613,7 @@ impl From<Settings> for Options {
             force_sort_within_sections: Some(settings.force_sort_within_sections),
             case_sensitive: Some(settings.case_sensitive),
             force_wrap_aliases: Some(settings.force_wrap_aliases),
+            detect_same_package: Some(settings.detect_same_package),
             force_to_top: Some(settings.force_to_top.into_iter().collect()),
             known_first_party: Some(
                 settings

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__detect_same_package.snap

@@ -0,0 +1,19 @@
+---
+source: crates/ruff/src/rules/isort/mod.rs
+---
+bar.py:1:1: I001 [*] Import block is un-sorted or un-formatted
+  |
+1 | / import os
+2 | | import pandas
+3 | | import foo.baz
+  |
+  = help: Organize imports
+
+ℹ Fix
+1 1 | import os
+  2 |+
+2 3 | import pandas
+  4 |+
+3 5 | import foo.baz
+
+

crates/ruff/src/rules/isort/snapshots/ruff__rules__isort__tests__no_detect_same_package.snap

@@ -0,0 +1,19 @@
+---
+source: crates/ruff/src/rules/isort/mod.rs
+---
+bar.py:1:1: I001 [*] Import block is un-sorted or un-formatted
+  |
+1 | / import os
+2 | | import pandas
+3 | | import foo.baz
+  |
+  = help: Organize imports
+
+ℹ Fix
+1 1 | import os
+2   |-import pandas
+  2 |+
+3 3 | import foo.baz
+  4 |+import pandas
+
+

ruff.schema.json

@@ -1189,6 +1189,13 @@
             "type": "string"
           }
         },
+        "detect-same-package": {
+          "description": "Whether to automatically mark imports from within the same package as first-party. For example, when `detect-same-package = true`, then when analyzing files within the `foo` package, any imports from within the `foo` package will be considered first-party.\n\nThis heuristic is often unnecessary when `src` is configured to detect all first-party sources; however, if `src` is _not_ configured, this heuristic can be useful to detect first-party imports from _within_ (but not _across_) first-party packages.",
+          "type": [
+            "boolean",
+            "null"
+          ]
+        },
         "extra-standard-library": {
           "description": "A list of modules to consider standard-library, in addition to those known to Ruff in advance.\n\nSupports glob patterns. For more information on the glob syntax, refer to the [`globset` documentation](https://docs.rs/globset/latest/globset/#syntax).",
           "type": [