Add Python 3.14 to configuration options (#17647)

A small PR that just updates the various settings/configurations to
allow Python 3.14. At the moment selecting that target version will
have no impact compared to Python 3.13 - except that a warning
is emitted if the user does so with `preview` disabled.

crates/ruff_linter/src/linter.rs

@@ -30,14 +30,14 @@ use crate::fix::{fix_file, FixResult};
 use crate::message::Message;
 use crate::noqa::add_noqa;
 use crate::package::PackageRoot;
-use crate::preview::is_unsupported_syntax_enabled;
+use crate::preview::{is_py314_support_enabled, is_unsupported_syntax_enabled};
 use crate::registry::{AsRule, Rule, RuleSet};
 #[cfg(any(feature = "test-rules", test))]
 use crate::rules::ruff::rules::test_rules::{self, TestRule, TEST_RULES};
 use crate::settings::types::UnsafeFixes;
 use crate::settings::{flags, LinterSettings};
 use crate::source_kind::SourceKind;
-use crate::{directives, fs, Locator};
+use crate::{directives, fs, warn_user_once, Locator};
 
 pub struct LinterResult {
     /// A collection of diagnostic messages generated by the linter.
@@ -450,6 +450,11 @@ pub fn lint_only(
     source: ParseSource,
 ) -> LinterResult {
     let target_version = settings.resolve_target_version(path);
+
+    if matches!(target_version, PythonVersion::PY314) && !is_py314_support_enabled(settings) {
+        warn_user_once!("Support for Python 3.14 is under development and may be unstable. Enable `preview` to remove this warning.");
+    }
+
     let parsed = source.into_parsed(source_kind, source_type, target_version);
 
     // Map row and column locations to byte slices (lazily).
@@ -559,6 +564,10 @@ pub fn lint_fix<'a>(
 
     let target_version = settings.resolve_target_version(path);
 
+    if matches!(target_version, PythonVersion::PY314) && !is_py314_support_enabled(settings) {
+        warn_user_once!("Support for Python 3.14 is under development and may be unstable. Enable `preview` to remove this warning.");
+    }
+
     // Continuously fix until the source code stabilizes.
     loop {
         // Parse once.

crates/ruff_linter/src/preview.rs

@@ -18,6 +18,10 @@ pub(crate) const fn is_unsupported_syntax_enabled(settings: &LinterSettings) ->
     settings.preview.is_enabled()
 }
 
+pub(crate) const fn is_py314_support_enabled(settings: &LinterSettings) -> bool {
+    settings.preview.is_enabled()
+}
+
 // Rule-specific behavior
 
 // https://github.com/astral-sh/ruff/pull/17136

crates/ruff_linter/src/settings/types.rs

@@ -34,6 +34,7 @@ pub enum PythonVersion {
     Py311,
     Py312,
     Py313,
+    Py314,
 }
 
 impl Default for PythonVersion {
@@ -55,6 +56,7 @@ impl TryFrom<ast::PythonVersion> for PythonVersion {
             ast::PythonVersion::PY311 => Ok(Self::Py311),
             ast::PythonVersion::PY312 => Ok(Self::Py312),
             ast::PythonVersion::PY313 => Ok(Self::Py313),
+            ast::PythonVersion::PY314 => Ok(Self::Py314),
             _ => Err(format!("unrecognized python version {value}")),
         }
     }
@@ -84,6 +86,7 @@ impl PythonVersion {
             Self::Py311 => (3, 11),
             Self::Py312 => (3, 12),
             Self::Py313 => (3, 13),
+            Self::Py314 => (3, 14),
         }
     }
 }

crates/ruff_python_ast/src/python_version.rs

@@ -30,6 +30,10 @@ impl PythonVersion {
         major: 3,
         minor: 13,
     };
+    pub const PY314: PythonVersion = PythonVersion {
+        major: 3,
+        minor: 14,
+    };
 
     pub fn iter() -> impl Iterator<Item = PythonVersion> {
         [
@@ -40,6 +44,7 @@ impl PythonVersion {
             PythonVersion::PY311,
             PythonVersion::PY312,
             PythonVersion::PY313,
+            PythonVersion::PY314,
         ]
         .into_iter()
     }
@@ -49,6 +54,7 @@ impl PythonVersion {
         Self::PY37
     }
 
+    // TODO: change this to 314 when it is released
     pub const fn latest() -> Self {
         Self::PY313
     }