[pyflakes] Improve error message for UndefinedName when a builtin was added in a newer version than specified in Ruff config (F821) (#13293)

crates/ruff_linter/src/checkers/ast/analyze/unresolved_references.rs

@@ -1,5 +1,6 @@
 use ruff_diagnostics::Diagnostic;
 use ruff_python_semantic::Exceptions;
+use ruff_python_stdlib::builtins::version_builtin_was_added;
 
 use crate::checkers::ast::Checker;
 use crate::codes::Rule;
@@ -35,9 +36,12 @@ pub(crate) fn unresolved_references(checker: &mut Checker) {
                     }
                 }
 
+                let symbol_name = reference.name(checker.locator);
+
                 checker.diagnostics.push(Diagnostic::new(
                     pyflakes::rules::UndefinedName {
-                        name: reference.name(checker.locator).to_string(),
+                        name: symbol_name.to_string(),
+                        minor_version_builtin_added: version_builtin_was_added(symbol_name),
                     },
                     reference.range(),
                 ));

crates/ruff_linter/src/rules/pyflakes/mod.rs

@@ -208,6 +208,18 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn f821_with_builtin_added_on_new_py_version_but_old_target_version_specified() {
+        let diagnostics = test_snippet(
+            "PythonFinalizationError",
+            &LinterSettings {
+                target_version: crate::settings::types::PythonVersion::Py312,
+                ..LinterSettings::for_rule(Rule::UndefinedName)
+            },
+        );
+        assert_messages!(diagnostics);
+    }
+
     #[test_case(Rule::UnusedVariable, Path::new("F841_4.py"))]
     #[test_case(Rule::UnusedImport, Path::new("__init__.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_24/__init__.py"))]

crates/ruff_linter/src/rules/pyflakes/rules/undefined_name.rs

@@ -19,17 +19,35 @@ use ruff_macros::{derive_message_formats, violation};
 ///     return n * 2
 /// ```
 ///
+/// ## Options
+/// - [`target-version`]: Can be used to configure which symbols Ruff will understand
+///   as being available in the `builtins` namespace.
+///
 /// ## References
 /// - [Python documentation: Naming and binding](https://docs.python.org/3/reference/executionmodel.html#naming-and-binding)
 #[violation]
 pub struct UndefinedName {
     pub(crate) name: String,
+    pub(crate) minor_version_builtin_added: Option<u8>,
 }
 
 impl Violation for UndefinedName {
     #[derive_message_formats]
     fn message(&self) -> String {
-        let UndefinedName { name } = self;
+        let UndefinedName {
+            name,
+            minor_version_builtin_added,
+        } = self;
+        let tip = minor_version_builtin_added.map(|version_added| {
+            format!(
+                r#"Consider specifying `requires-python = ">= 3.{version_added}"` or `tool.ruff.target-version = "py3{version_added}"` in your `pyproject.toml` file."#
+            )
+        });
+
+        if let Some(tip) = tip {
+            format!("Undefined name `{name}`. {tip}")
+        } else {
             format!("Undefined name `{name}`")
         }
+    }
 }

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__f821_with_builtin_added_on_new_py_version_but_old_target_version_specified.snap

@@ -0,0 +1,8 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+<filename>:1:1: F821 Undefined name `PythonFinalizationError`. Consider specifying `requires-python = ">= 3.13"` or `tool.ruff.target-version = "py313"` in your `pyproject.toml` file.
+  |
+1 | PythonFinalizationError
+  | ^^^^^^^^^^^^^^^^^^^^^^^ F821
+  |

crates/ruff_python_stdlib/src/builtins.rs

@@ -23,11 +23,7 @@ pub const MAGIC_GLOBALS: &[&str] = &[
     "__file__",
 ];
 
-/// Return the list of builtins for the given Python minor version.
-///
-/// Intended to be kept in sync with [`is_python_builtin`].
-pub fn python_builtins(minor_version: u8, is_notebook: bool) -> Vec<&'static str> {
-    let mut builtins = vec![
+static ALWAYS_AVAILABLE_BUILTINS: &[&str] = &[
     "ArithmeticError",
     "AssertionError",
     "AttributeError",
@@ -180,24 +176,28 @@ pub fn python_builtins(minor_version: u8, is_notebook: bool) -> Vec<&'static str
     "type",
     "vars",
     "zip",
-    ];
+];
+static PY310_PLUS_BUILTINS: &[&str] = &["EncodingWarning", "aiter", "anext"];
+static PY311_PLUS_BUILTINS: &[&str] = &["BaseExceptionGroup", "ExceptionGroup"];
+static PY313_PLUS_BUILTINS: &[&str] = &["PythonFinalizationError"];
 
+/// Return the list of builtins for the given Python minor version.
+///
+/// Intended to be kept in sync with [`is_python_builtin`].
+pub fn python_builtins(minor_version: u8, is_notebook: bool) -> Vec<&'static str> {
+    let mut builtins = ALWAYS_AVAILABLE_BUILTINS.to_vec();
     if minor_version >= 10 {
-        builtins.extend(&["EncodingWarning", "aiter", "anext"]);
+        builtins.extend(PY310_PLUS_BUILTINS);
     }
-
     if minor_version >= 11 {
-        builtins.extend(&["BaseExceptionGroup", "ExceptionGroup"]);
+        builtins.extend(PY311_PLUS_BUILTINS);
     }
-
     if minor_version >= 13 {
-        builtins.push("PythonFinalizationError");
+        builtins.extend(PY313_PLUS_BUILTINS);
     }
-
     if is_notebook {
         builtins.extend(IPYTHON_BUILTINS);
     }
-
     builtins
 }
 
@@ -370,6 +370,22 @@ pub fn is_python_builtin(name: &str, minor_version: u8, is_notebook: bool) -> bo
     )
 }
 
+/// Return `Some(version)`, where `version` corresponds to the Python minor version
+/// in which the builtin was added
+pub fn version_builtin_was_added(name: &str) -> Option<u8> {
+    if PY310_PLUS_BUILTINS.contains(&name) {
+        Some(10)
+    } else if PY311_PLUS_BUILTINS.contains(&name) {
+        Some(11)
+    } else if PY313_PLUS_BUILTINS.contains(&name) {
+        Some(13)
+    } else if ALWAYS_AVAILABLE_BUILTINS.contains(&name) {
+        Some(0)
+    } else {
+        None
+    }
+}
+
 /// Returns `true` if the given name is that of a Python builtin iterator.
 pub fn is_iterator(name: &str) -> bool {
     matches!(