Add unknown-rule (astral-sh#15085)

Co-authored-by: Carl Meyer <[email protected]>

crates/red_knot_python_semantic/resources/mdtest/suppressions/knot-ignore.md

@@ -84,11 +84,10 @@ def test(  # knot: ignore
 
 ## Can't suppress `revealed-type` diagnostics
 
-TODO: Emit an error that the rule code is unknown: `unknown-rule`
-
 ```py
 a = 10
 # revealed: Literal[10]
+# error: [unknown-rule] "Unknown rule `revealed-type`"
 reveal_type(a)  # knot: ignore[revealed-type]
 ```
 
@@ -164,3 +163,10 @@ severity: `knot: possibly-undefined-reference=error`
 
 a = 4 / 0  # error: [division-by-zero]
 ```
+
+## Unknown rule
+
+```py
+# error: [unknown-rule] "Unknown rule `is-equal-14`"
+a = 10 + 4  # knot: ignore[is-equal-14]
+```

crates/red_knot_python_semantic/src/lib.rs

@@ -3,7 +3,7 @@ use std::hash::BuildHasherDefault;
 use rustc_hash::FxHasher;
 
 use crate::lint::{LintRegistry, LintRegistryBuilder};
-use crate::suppression::UNUSED_IGNORE_COMMENT;
+use crate::suppression::{UNKNOWN_RULE, UNUSED_IGNORE_COMMENT};
 pub use db::Db;
 pub use module_name::ModuleName;
 pub use module_resolver::{resolve_module, system_module_search_paths, KnownModule, Module};
@@ -49,4 +49,5 @@ pub fn default_lint_registry() -> &'static LintRegistry {
 pub fn register_lints(registry: &mut LintRegistryBuilder) {
     types::register_lints(registry);
     registry.register_lint(&UNUSED_IGNORE_COMMENT);
+    registry.register_lint(&UNKNOWN_RULE);
 }

crates/red_knot_python_semantic/src/lint.rs

@@ -374,7 +374,7 @@ impl LintRegistry {
     }
 }
 
-#[derive(Error, Debug, Clone)]
+#[derive(Error, Debug, Clone, PartialEq, Eq)]
 pub enum GetLintError {
     /// The name maps to this removed lint.
     #[error("lint {0} has been removed")]
@@ -444,6 +444,11 @@ impl RuleSelection {
         self.lints.get(&lint).copied()
     }
 
+    /// Returns `true` if the `lint` is enabled.
+    pub fn is_enabled(&self, lint: LintId) -> bool {
+        self.severity(lint).is_some()
+    }
+
     /// Enables `lint` and configures with the given `severity`.
     ///
     /// Overrides any previous configuration for the lint.