[flake8-pyi] Implement PYI064

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI064.py

@@ -0,0 +1,21 @@
+from typing import Final, Literal
+
+x: Final[Literal[True]] = True  # PYI064
+y: Final[Literal[None]] = None  # PYI064
+z: Final[Literal[  # PYI064
+    "this is a really long literal, that won't be rendered in the issue text"
+]] = "this is a really long literal, that won't be rendered in the issue text"
+
+# This should be fixable, and marked as safe
+w1: Final[Literal[123]]  # PYI064
+
+# This should not be fixable
+w2: Final[Literal[123]] = "random value"  # PYI064
+
+n1: Final[Literal[True, False]] = True # No issue here
+n2: Literal[True] = True  # No issue here
+
+PlatformName = Literal["linux", "macos", "windows"]
+PLATFORMS: Final[set[PlatformName]] = {"linux", "macos", "windows"}  # No issue here
+
+foo: Final[{1, 2, 3}] = {1, 2, 3}  # No issue here

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI064.pyi

@@ -0,0 +1,19 @@
+from typing import Final, Literal
+
+x: Final[Literal[True]]  # PYI064
+y: Final[Literal[None]] = None  # PYI064
+z: Final[Literal["this is a really long literal, that won't be rendered in the issue text"]]  # PYI064
+
+# This should be fixable, and marked as safe
+w1: Final[Literal[123]]  # PYI064
+
+# This should not be fixable
+w2: Final[Literal[123]] = "random value"  # PYI064
+
+n1: Final[Literal[True, False]] # No issue here
+n2: Literal[True]  # No issue here
+
+PlatformName = Literal["linux", "macos", "windows"]
+PLATFORMS: Final[set[PlatformName]] = {"linux", "macos", "windows"}  # No issue here
+
+foo: Final[{1, 2, 3}] = {1, 2, 3}  # No issue here

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

@@ -1633,6 +1633,13 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 if checker.enabled(Rule::TSuffixedTypeAlias) {
                     flake8_pyi::rules::t_suffixed_type_alias(checker, target);
                 }
+            } else if checker
+                .semantic
+                .match_typing_expr(helpers::map_subscript(annotation), "Final")
+            {
+                if checker.enabled(Rule::RedundantFinalLiteral) {
+                    flake8_pyi::rules::redundant_final_literal(checker, assign_stmt);
+                }
             }
         }
         Stmt::TypeAlias(ast::StmtTypeAlias { name, .. }) => {

crates/ruff_linter/src/codes.rs

@@ -811,6 +811,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Pyi, "058") => (RuleGroup::Stable, rules::flake8_pyi::rules::GeneratorReturnFromIterMethod),
         (Flake8Pyi, "059") => (RuleGroup::Preview, rules::flake8_pyi::rules::GenericNotLastBaseClass),
         (Flake8Pyi, "062") => (RuleGroup::Preview, rules::flake8_pyi::rules::DuplicateLiteralMember),
+        (Flake8Pyi, "064") => (RuleGroup::Preview, rules::flake8_pyi::rules::RedundantFinalLiteral),
 
         // flake8-pytest-style
         (Flake8PytestStyle, "001") => (RuleGroup::Stable, rules::flake8_pytest_style::rules::PytestFixtureIncorrectParenthesesStyle),

crates/ruff_linter/src/rules/flake8_pyi/mod.rs

@@ -63,6 +63,8 @@ mod tests {
     #[test_case(Rule::PatchVersionComparison, Path::new("PYI004.pyi"))]
     #[test_case(Rule::QuotedAnnotationInStub, Path::new("PYI020.py"))]
     #[test_case(Rule::QuotedAnnotationInStub, Path::new("PYI020.pyi"))]
+    #[test_case(Rule::RedundantFinalLiteral, Path::new("PYI064.py"))]
+    #[test_case(Rule::RedundantFinalLiteral, Path::new("PYI064.pyi"))]
     #[test_case(Rule::RedundantLiteralUnion, Path::new("PYI051.py"))]
     #[test_case(Rule::RedundantLiteralUnion, Path::new("PYI051.pyi"))]
     #[test_case(Rule::RedundantNumericUnion, Path::new("PYI041.py"))]

crates/ruff_linter/src/rules/flake8_pyi/rules/mod.rs

@@ -21,6 +21,7 @@ pub(crate) use pass_in_class_body::*;
 pub(crate) use pass_statement_stub_body::*;
 pub(crate) use prefix_type_params::*;
 pub(crate) use quoted_annotation_in_stub::*;
+pub(crate) use redundant_final_literal::*;
 pub(crate) use redundant_literal_union::*;
 pub(crate) use redundant_numeric_union::*;
 pub(crate) use simple_defaults::*;
@@ -61,6 +62,7 @@ mod pass_in_class_body;
 mod pass_statement_stub_body;
 mod prefix_type_params;
 mod quoted_annotation_in_stub;
+mod redundant_final_literal;
 mod redundant_literal_union;
 mod redundant_numeric_union;
 mod simple_defaults;

crates/ruff_linter/src/rules/flake8_pyi/rules/redundant_final_literal.rs

@@ -0,0 +1,143 @@
+use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::{self as ast, comparable::ComparableExpr};
+use ruff_source_file::Locator;
+use ruff_text_size::{Ranged, TextSize};
+
+use crate::checkers::ast::Checker;
+use crate::fix::snippet::SourceCodeSnippet;
+
+/// ## What it does
+/// Checks for redundant `Final[Literal[...]]` annotations.
+///
+/// ## Why is this bad?
+/// A `Final[Literal[...]]` annotation can be replaced with `Final`; the literal
+/// use is unnecessary.
+///
+/// ## Example
+///
+/// ```python
+/// x: Final[Literal[42]]
+/// y: Final[Literal[42]] = 42
+/// ```
+///
+/// Use instead:
+/// ```python
+/// x: Final = 42
+/// y: Final = 42
+/// ```
+#[violation]
+pub struct RedundantFinalLiteral {
+    literal: SourceCodeSnippet,
+}
+
+impl Violation for RedundantFinalLiteral {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let RedundantFinalLiteral { literal } = self;
+        format!(
+            "`Final[Literal[{literal}]]` can be replaced with a bare `Final`",
+            literal = literal.truncated_display()
+        )
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        Some("Replace with `Final`".to_string())
+    }
+}
+
+/// PYI064
+pub(crate) fn redundant_final_literal(checker: &mut Checker, ann_assign: &ast::StmtAnnAssign) {
+    if !checker.semantic().seen_typing() {
+        return;
+    }
+
+    let ast::StmtAnnAssign {
+        value: assign_value,
+        annotation,
+        ..
+    } = ann_assign;
+
+    let ast::Expr::Subscript(annotation) = &**annotation else {
+        return;
+    };
+
+    // Ensure it is `Final[Literal[...]]`.
+    let ast::Expr::Subscript(ast::ExprSubscript {
+        value,
+        slice: literal,
+        ..
+    }) = &*annotation.slice
+    else {
+        return;
+    };
+    if !checker.semantic().match_typing_expr(value, "Literal") {
+        return;
+    }
+
+    // Discards tuples like `Literal[1, 2, 3]` and complex literals like `Literal[{1, 2}]`.
+    if !matches!(
+        &**literal,
+        ast::Expr::StringLiteral(_)
+            | ast::Expr::BytesLiteral(_)
+            | ast::Expr::NumberLiteral(_)
+            | ast::Expr::BooleanLiteral(_)
+            | ast::Expr::NoneLiteral(_)
+            | ast::Expr::EllipsisLiteral(_)
+    ) {
+        return;
+    }
+
+    let mut diagnostic = Diagnostic::new(
+        RedundantFinalLiteral {
+            literal: SourceCodeSnippet::from_str(checker.locator().slice(literal.range())),
+        },
+        ann_assign.range(),
+    );
+
+    // The literal value and the assignment value being different doesn't make sense, so we skip
+    // fixing in that case.
+    if let Some(assign_value) = assign_value.as_ref() {
+        if ComparableExpr::from(assign_value) == ComparableExpr::from(literal) {
+            diagnostic.set_fix(generate_fix(annotation, None, checker.locator()));
+        }
+    } else {
+        diagnostic.set_fix(generate_fix(annotation, Some(literal), checker.locator()));
+    }
+
+    checker.diagnostics.push(diagnostic);
+}
+
+/// Generate a fix to convert a `Final[Literal[...]]` annotation to a `Final` annotation.
+fn generate_fix(
+    annotation: &ast::ExprSubscript,
+    literal: Option<&ast::Expr>,
+    locator: &Locator,
+) -> Fix {
+    // Remove the `Literal[...]` part from `Final[Literal[...]]`.
+    let deletion = Edit::range_deletion(
+        annotation
+            .slice
+            .range()
+            .sub_start(TextSize::new(1))
+            .add_end(TextSize::new(1)),
+    );
+
+    // If a literal was provided, insert an assignment.
+    //
+    // For example, change `x: Final[Literal[42]]` to `x: Final = 42`.
+    if let Some(literal) = literal {
+        let assignment = Edit::insertion(
+            format!(
+                " = {literal_source}",
+                literal_source = locator.slice(literal)
+            ),
+            annotation.end(),
+        );
+        Fix::safe_edits(deletion, std::iter::once(assignment))
+    } else {
+        Fix::safe_edit(deletion)
+    }
+}

crates/ruff_linter/src/rules/flake8_pyi/snapshots/ruff_linter__rules__flake8_pyi__tests__PYI064_PYI064.py.snap

@@ -0,0 +1,97 @@
+---
+source: crates/ruff_linter/src/rules/flake8_pyi/mod.rs
+---
+PYI064.py:3:1: PYI064 [*] `Final[Literal[True]]` can be replaced with a bare `Final`
+  |
+1 | from typing import Final, Literal
+2 | 
+3 | x: Final[Literal[True]] = True  # PYI064
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI064
+4 | y: Final[Literal[None]] = None  # PYI064
+5 | z: Final[Literal[  # PYI064
+  |
+  = help: Replace with `Final`
+
+ℹ Safe fix
+1 1 | from typing import Final, Literal
+2 2 | 
+3   |-x: Final[Literal[True]] = True  # PYI064
+  3 |+x: Final = True  # PYI064
+4 4 | y: Final[Literal[None]] = None  # PYI064
+5 5 | z: Final[Literal[  # PYI064
+6 6 |     "this is a really long literal, that won't be rendered in the issue text"
+
+PYI064.py:4:1: PYI064 [*] `Final[Literal[None]]` can be replaced with a bare `Final`
+  |
+3 | x: Final[Literal[True]] = True  # PYI064
+4 | y: Final[Literal[None]] = None  # PYI064
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI064
+5 | z: Final[Literal[  # PYI064
+6 |     "this is a really long literal, that won't be rendered in the issue text"
+  |
+  = help: Replace with `Final`
+
+ℹ Safe fix
+1 1 | from typing import Final, Literal
+2 2 | 
+3 3 | x: Final[Literal[True]] = True  # PYI064
+4   |-y: Final[Literal[None]] = None  # PYI064
+  4 |+y: Final = None  # PYI064
+5 5 | z: Final[Literal[  # PYI064
+6 6 |     "this is a really long literal, that won't be rendered in the issue text"
+7 7 | ]] = "this is a really long literal, that won't be rendered in the issue text"
+
+PYI064.py:5:1: PYI064 [*] `Final[Literal[...]]` can be replaced with a bare `Final`
+  |
+3 |   x: Final[Literal[True]] = True  # PYI064
+4 |   y: Final[Literal[None]] = None  # PYI064
+5 | / z: Final[Literal[  # PYI064
+6 | |     "this is a really long literal, that won't be rendered in the issue text"
+7 | | ]] = "this is a really long literal, that won't be rendered in the issue text"
+  | |______________________________________________________________________________^ PYI064
+8 |   
+9 |   # This should be fixable, and marked as safe
+  |
+  = help: Replace with `Final`
+
+ℹ Safe fix
+2 2 | 
+3 3 | x: Final[Literal[True]] = True  # PYI064
+4 4 | y: Final[Literal[None]] = None  # PYI064
+5   |-z: Final[Literal[  # PYI064
+6   |-    "this is a really long literal, that won't be rendered in the issue text"
+7   |-]] = "this is a really long literal, that won't be rendered in the issue text"
+  5 |+z: Final = "this is a really long literal, that won't be rendered in the issue text"
+8 6 | 
+9 7 | # This should be fixable, and marked as safe
+10 8 | w1: Final[Literal[123]]  # PYI064
+
+PYI064.py:10:1: PYI064 [*] `Final[Literal[123]]` can be replaced with a bare `Final`
+   |
+ 9 | # This should be fixable, and marked as safe
+10 | w1: Final[Literal[123]]  # PYI064
+   | ^^^^^^^^^^^^^^^^^^^^^^^ PYI064
+11 | 
+12 | # This should not be fixable
+   |
+   = help: Replace with `Final`
+
+ℹ Safe fix
+7  7  | ]] = "this is a really long literal, that won't be rendered in the issue text"
+8  8  | 
+9  9  | # This should be fixable, and marked as safe
+10    |-w1: Final[Literal[123]]  # PYI064
+   10 |+w1: Final = 123  # PYI064
+11 11 | 
+12 12 | # This should not be fixable
+13 13 | w2: Final[Literal[123]] = "random value"  # PYI064
+
+PYI064.py:13:1: PYI064 `Final[Literal[123]]` can be replaced with a bare `Final`
+   |
+12 | # This should not be fixable
+13 | w2: Final[Literal[123]] = "random value"  # PYI064
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI064
+14 | 
+15 | n1: Final[Literal[True, False]] = True # No issue here
+   |
+   = help: Replace with `Final`