warn when py314 selected and not in preview

Author: dylwil3

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