Stabilize new strategy for classifying imports as first party (#20268)

This stabilizes the behavior introduced in #16565 which (roughly) tries
to match an import like `import a.b.c` to an actual directory path
`a/b/c` in order to label it as first-party, rather than simply looking
for a directory `a`.

Mainly this affects the sorting of imports in the presence of namespace
packages, but a few other rules are affected as well.

Author: dylwil3

crates/ruff/tests/snapshots/integration_test__rule_f401.snap

@@ -55,6 +55,10 @@ either a redundant alias or, if already present in the file, an `__all__` entry.
 to remove third-party and standard library imports -- the fix is unsafe because the module's
 interface changes.
 
+See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc)
+for more details on how Ruff
+determines whether an import is first or third-party.
+
 ## Example
 
 ```python
@@ -83,11 +87,6 @@ else:
     print("numpy is not installed")
 ```
 
-## Preview
-When [preview](https://docs.astral.sh/ruff/preview/) is enabled,
-the criterion for determining whether an import is first-party
-is stricter, which could affect the suggested fix. See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc) for more details.
-
 ## Options
 - `lint.ignore-init-module-imports`
 - `lint.pyflakes.allowed-unused-imports`

crates/ruff/tests/snapshots/lint__output_format_sarif.snap

@@ -95,7 +95,7 @@ exit_code: 1
           "rules": [
             {
               "fullDescription": {
-                "text": "## What it does\nChecks for unused imports.\n\n## Why is this bad?\nUnused imports add a performance overhead at runtime, and risk creating\nimport cycles. They also increase the cognitive load of reading the code.\n\nIf an import statement is used to check for the availability or existence\nof a module, consider using `importlib.util.find_spec` instead.\n\nIf an import statement is used to re-export a symbol as part of a module's\npublic interface, consider using a \"redundant\" import alias, which\ninstructs Ruff (and other tools) to respect the re-export, and avoid\nmarking it as unused, as in:\n\n```python\nfrom module import member as member\n```\n\nAlternatively, you can use `__all__` to declare a symbol as part of the module's\ninterface, as in:\n\n```python\n# __init__.py\nimport some_module\n\n__all__ = [\"some_module\"]\n```\n\n## Fix safety\n\nFixes to remove unused imports are safe, except in `__init__.py` files.\n\nApplying fixes to `__init__.py` files is currently in preview. The fix offered depends on the\ntype of the unused import. Ruff will suggest a safe fix to export first-party imports with\neither a redundant alias or, if already present in the file, an `__all__` entry. If multiple\n`__all__` declarations are present, Ruff will not offer a fix. Ruff will suggest an unsafe fix\nto remove third-party and standard library imports -- the fix is unsafe because the module's\ninterface changes.\n\n## Example\n\n```python\nimport numpy as np  # unused import\n\n\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nUse instead:\n\n```python\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nTo check the availability of a module, use `importlib.util.find_spec`:\n\n```python\nfrom importlib.util import find_spec\n\nif find_spec(\"numpy\") is not None:\n    print(\"numpy is installed\")\nelse:\n    print(\"numpy is not installed\")\n```\n\n## Preview\nWhen [preview](https://docs.astral.sh/ruff/preview/) is enabled,\nthe criterion for determining whether an import is first-party\nis stricter, which could affect the suggested fix. See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc) for more details.\n\n## Options\n- `lint.ignore-init-module-imports`\n- `lint.pyflakes.allowed-unused-imports`\n\n## References\n- [Python documentation: `import`](https://docs.python.org/3/reference/simple_stmts.html#the-import-statement)\n- [Python documentation: `importlib.util.find_spec`](https://docs.python.org/3/library/importlib.html#importlib.util.find_spec)\n- [Typing documentation: interface conventions](https://typing.python.org/en/latest/spec/distributing.html#library-interface-public-and-private-symbols)\n"
+                "text": "## What it does\nChecks for unused imports.\n\n## Why is this bad?\nUnused imports add a performance overhead at runtime, and risk creating\nimport cycles. They also increase the cognitive load of reading the code.\n\nIf an import statement is used to check for the availability or existence\nof a module, consider using `importlib.util.find_spec` instead.\n\nIf an import statement is used to re-export a symbol as part of a module's\npublic interface, consider using a \"redundant\" import alias, which\ninstructs Ruff (and other tools) to respect the re-export, and avoid\nmarking it as unused, as in:\n\n```python\nfrom module import member as member\n```\n\nAlternatively, you can use `__all__` to declare a symbol as part of the module's\ninterface, as in:\n\n```python\n# __init__.py\nimport some_module\n\n__all__ = [\"some_module\"]\n```\n\n## Fix safety\n\nFixes to remove unused imports are safe, except in `__init__.py` files.\n\nApplying fixes to `__init__.py` files is currently in preview. The fix offered depends on the\ntype of the unused import. Ruff will suggest a safe fix to export first-party imports with\neither a redundant alias or, if already present in the file, an `__all__` entry. If multiple\n`__all__` declarations are present, Ruff will not offer a fix. Ruff will suggest an unsafe fix\nto remove third-party and standard library imports -- the fix is unsafe because the module's\ninterface changes.\n\nSee [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc)\nfor more details on how Ruff\ndetermines whether an import is first or third-party.\n\n## Example\n\n```python\nimport numpy as np  # unused import\n\n\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nUse instead:\n\n```python\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nTo check the availability of a module, use `importlib.util.find_spec`:\n\n```python\nfrom importlib.util import find_spec\n\nif find_spec(\"numpy\") is not None:\n    print(\"numpy is installed\")\nelse:\n    print(\"numpy is not installed\")\n```\n\n## Options\n- `lint.ignore-init-module-imports`\n- `lint.pyflakes.allowed-unused-imports`\n\n## References\n- [Python documentation: `import`](https://docs.python.org/3/reference/simple_stmts.html#the-import-statement)\n- [Python documentation: `importlib.util.find_spec`](https://docs.python.org/3/library/importlib.html#importlib.util.find_spec)\n- [Typing documentation: interface conventions](https://typing.python.org/en/latest/spec/distributing.html#library-interface-public-and-private-symbols)\n"
               },
               "help": {
                 "text": "`{name}` imported but unused; consider using `importlib.util.find_spec` to test for availability"

crates/ruff_linter/src/message/snapshots/ruff_linter__message__sarif__tests__results.snap

@@ -81,7 +81,7 @@ expression: value
           "rules": [
             {
               "fullDescription": {
-                "text": "## What it does\nChecks for unused imports.\n\n## Why is this bad?\nUnused imports add a performance overhead at runtime, and risk creating\nimport cycles. They also increase the cognitive load of reading the code.\n\nIf an import statement is used to check for the availability or existence\nof a module, consider using `importlib.util.find_spec` instead.\n\nIf an import statement is used to re-export a symbol as part of a module's\npublic interface, consider using a \"redundant\" import alias, which\ninstructs Ruff (and other tools) to respect the re-export, and avoid\nmarking it as unused, as in:\n\n```python\nfrom module import member as member\n```\n\nAlternatively, you can use `__all__` to declare a symbol as part of the module's\ninterface, as in:\n\n```python\n# __init__.py\nimport some_module\n\n__all__ = [\"some_module\"]\n```\n\n## Fix safety\n\nFixes to remove unused imports are safe, except in `__init__.py` files.\n\nApplying fixes to `__init__.py` files is currently in preview. The fix offered depends on the\ntype of the unused import. Ruff will suggest a safe fix to export first-party imports with\neither a redundant alias or, if already present in the file, an `__all__` entry. If multiple\n`__all__` declarations are present, Ruff will not offer a fix. Ruff will suggest an unsafe fix\nto remove third-party and standard library imports -- the fix is unsafe because the module's\ninterface changes.\n\n## Example\n\n```python\nimport numpy as np  # unused import\n\n\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nUse instead:\n\n```python\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nTo check the availability of a module, use `importlib.util.find_spec`:\n\n```python\nfrom importlib.util import find_spec\n\nif find_spec(\"numpy\") is not None:\n    print(\"numpy is installed\")\nelse:\n    print(\"numpy is not installed\")\n```\n\n## Preview\nWhen [preview](https://docs.astral.sh/ruff/preview/) is enabled,\nthe criterion for determining whether an import is first-party\nis stricter, which could affect the suggested fix. See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc) for more details.\n\n## Options\n- `lint.ignore-init-module-imports`\n- `lint.pyflakes.allowed-unused-imports`\n\n## References\n- [Python documentation: `import`](https://docs.python.org/3/reference/simple_stmts.html#the-import-statement)\n- [Python documentation: `importlib.util.find_spec`](https://docs.python.org/3/library/importlib.html#importlib.util.find_spec)\n- [Typing documentation: interface conventions](https://typing.python.org/en/latest/spec/distributing.html#library-interface-public-and-private-symbols)\n"
+                "text": "## What it does\nChecks for unused imports.\n\n## Why is this bad?\nUnused imports add a performance overhead at runtime, and risk creating\nimport cycles. They also increase the cognitive load of reading the code.\n\nIf an import statement is used to check for the availability or existence\nof a module, consider using `importlib.util.find_spec` instead.\n\nIf an import statement is used to re-export a symbol as part of a module's\npublic interface, consider using a \"redundant\" import alias, which\ninstructs Ruff (and other tools) to respect the re-export, and avoid\nmarking it as unused, as in:\n\n```python\nfrom module import member as member\n```\n\nAlternatively, you can use `__all__` to declare a symbol as part of the module's\ninterface, as in:\n\n```python\n# __init__.py\nimport some_module\n\n__all__ = [\"some_module\"]\n```\n\n## Fix safety\n\nFixes to remove unused imports are safe, except in `__init__.py` files.\n\nApplying fixes to `__init__.py` files is currently in preview. The fix offered depends on the\ntype of the unused import. Ruff will suggest a safe fix to export first-party imports with\neither a redundant alias or, if already present in the file, an `__all__` entry. If multiple\n`__all__` declarations are present, Ruff will not offer a fix. Ruff will suggest an unsafe fix\nto remove third-party and standard library imports -- the fix is unsafe because the module's\ninterface changes.\n\nSee [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc)\nfor more details on how Ruff\ndetermines whether an import is first or third-party.\n\n## Example\n\n```python\nimport numpy as np  # unused import\n\n\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nUse instead:\n\n```python\ndef area(radius):\n    return 3.14 * radius**2\n```\n\nTo check the availability of a module, use `importlib.util.find_spec`:\n\n```python\nfrom importlib.util import find_spec\n\nif find_spec(\"numpy\") is not None:\n    print(\"numpy is installed\")\nelse:\n    print(\"numpy is not installed\")\n```\n\n## Options\n- `lint.ignore-init-module-imports`\n- `lint.pyflakes.allowed-unused-imports`\n\n## References\n- [Python documentation: `import`](https://docs.python.org/3/reference/simple_stmts.html#the-import-statement)\n- [Python documentation: `importlib.util.find_spec`](https://docs.python.org/3/library/importlib.html#importlib.util.find_spec)\n- [Typing documentation: interface conventions](https://typing.python.org/en/latest/spec/distributing.html#library-interface-public-and-private-symbols)\n"
               },
               "help": {
                 "text": "`{name}` imported but unused; consider using `importlib.util.find_spec` to test for availability"

crates/ruff_linter/src/preview.rs

@@ -11,11 +11,6 @@ pub(crate) const fn is_py314_support_enabled(settings: &LinterSettings) -> bool
     settings.preview.is_enabled()
 }
 
-// https://github.com/astral-sh/ruff/pull/16565
-pub(crate) const fn is_full_path_match_source_strategy_enabled(settings: &LinterSettings) -> bool {
-    settings.preview.is_enabled()
-}
-
 // Rule-specific behavior
 
 // https://github.com/astral-sh/ruff/pull/15541

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

@@ -11,12 +11,10 @@ use crate::checkers::ast::{Checker, DiagnosticGuard};
 use crate::codes::Rule;
 use crate::fix;
 use crate::importer::ImportedMembers;
-use crate::preview::is_full_path_match_source_strategy_enabled;
 use crate::rules::flake8_type_checking::helpers::{
     TypingReference, filter_contained, quote_annotation,
 };
 use crate::rules::flake8_type_checking::imports::ImportBinding;
-use crate::rules::isort::categorize::MatchSourceStrategy;
 use crate::rules::isort::{ImportSection, ImportType, categorize};
 use crate::{Fix, FixAvailability, Violation};
 
@@ -67,10 +65,6 @@ use crate::{Fix, FixAvailability, Violation};
 ///
 ///
 /// ## Preview
-/// When [preview](https://docs.astral.sh/ruff/preview/) is enabled,
-/// the criterion for determining whether an import is first-party
-/// is stricter, which could affect whether this lint is triggered vs [`TC001`](https://docs.astral.sh/ruff/rules/typing-only-third-party-import/). See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc) for more details.
-///
 /// If [`lint.future-annotations`] is set to `true`, `from __future__ import
 /// annotations` will be added if doing so would enable an import to be moved into an `if
 /// TYPE_CHECKING:` block. This takes precedence over the
@@ -154,10 +148,6 @@ impl Violation for TypingOnlyFirstPartyImport {
 /// ```
 ///
 /// ## Preview
-/// When [preview](https://docs.astral.sh/ruff/preview/) is enabled,
-/// the criterion for determining whether an import is first-party
-/// is stricter, which could affect whether this lint is triggered vs [`TC001`](https://docs.astral.sh/ruff/rules/typing-only-first-party-import/). See [this FAQ section](https://docs.astral.sh/ruff/faq/#how-does-ruff-determine-which-of-my-imports-are-first-party-third-party-etc) for more details.
-///
 /// If [`lint.future-annotations`] is set to `true`, `from __future__ import
 /// annotations` will be added if doing so would enable an import to be moved into an `if
 /// TYPE_CHECKING:` block. This takes precedence over the
@@ -347,13 +337,6 @@ pub(crate) fn typing_only_runtime_import(
         let source_name = import.source_name().join(".");
 
         // Categorize the import, using coarse-grained categorization.
-        let match_source_strategy =
-            if is_full_path_match_source_strategy_enabled(checker.settings()) {
-                MatchSourceStrategy::FullPath
-            } else {
-                MatchSourceStrategy::Root
-            };
-
         let import_type = match categorize(
             &source_name,
             qualified_name.is_unresolved_import(),
@@ -365,7 +348,6 @@ pub(crate) fn typing_only_runtime_import(
             checker.settings().isort.no_sections,
             &checker.settings().isort.section_order,
             &checker.settings().isort.default_section,
-            match_source_strategy,
         ) {
             ImportSection::Known(ImportType::LocalFolder | ImportType::FirstParty) => {
                 ImportType::FirstParty