[pylint] Implement if-stmt-min-max (PLR1730, PLR1731)

crates/ruff_linter/resources/test/fixtures/pylint/if_stmt_min_max.py

@@ -0,0 +1,136 @@
+# pylint: disable=missing-docstring, invalid-name, too-few-public-methods, redefined-outer-name
+
+value = 10
+value2 = 0
+value3 = 3
+
+# Positive
+if value < 10:  # [max-instead-of-if]
+    value = 10
+
+if value <= 10:  # [max-instead-of-if]
+    value = 10
+
+if value < value2:  # [max-instead-of-if]
+    value = value2
+
+if value > 10:  # [min-instead-of-if]
+    value = 10
+
+if value >= 10:  # [min-instead-of-if]
+    value = 10
+
+if value > value2:  # [min-instead-of-if]
+    value = value2
+
+
+class A:
+    def __init__(self):
+        self.value = 13
+
+
+A1 = A()
+if A1.value < 10:  # [max-instead-of-if]
+    A1.value = 10
+
+if A1.value > 10:  # [min-instead-of-if]
+    A1.value = 10
+
+
+class AA:
+    def __init__(self, value):
+        self.value = value
+
+    def __gt__(self, b):
+        return self.value > b
+
+    def __ge__(self, b):
+        return self.value >= b
+
+    def __lt__(self, b):
+        return self.value < b
+
+    def __le__(self, b):
+        return self.value <= b
+
+
+A1 = AA(0)
+A2 = AA(3)
+
+if A2 < A1:  # [max-instead-of-if]
+    A2 = A1
+
+if A2 <= A1:  # [max-instead-of-if]
+    A2 = A1
+
+if A2 > A1:  # [min-instead-of-if]
+    A2 = A1
+
+if A2 >= A1:  # [min-instead-of-if]
+    A2 = A1
+
+# Negative
+if value < 10:
+    value = 2
+
+if value <= 3:
+    value = 5
+
+if value < 10:
+    value = 2
+    value2 = 3
+
+if value < value2:
+    value = value3
+
+if value < 5:
+    value = value3
+
+if 2 < value <= 3:
+    value = 1
+
+if value < 10:
+    value = 10
+else:
+    value = 3
+
+if value <= 3:
+    value = 5
+elif value == 3:
+    value = 2
+
+if value > 10:
+    value = 2
+
+if value >= 3:
+    value = 5
+
+if value > 10:
+    value = 2
+    value2 = 3
+
+if value > value2:
+    value = value3
+
+if value > 5:
+    value = value3
+
+if 2 > value >= 3:
+    value = 1
+
+if value > 10:
+    value = 10
+else:
+    value = 3
+
+if value >= 3:
+    value = 5
+elif value == 3:
+    value = 2
+
+# Parenthesized expressions
+if value.attr > 3:
+    (
+        value.
+        attr
+    ) = 3

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

@@ -1117,6 +1117,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::TooManyBooleanExpressions) {
                 pylint::rules::too_many_boolean_expressions(checker, if_);
             }
+            if checker.enabled(Rule::IfStmtMinMax) {
+                pylint::rules::if_stmt_min_max(checker, if_);
+            }
             if checker.source_type.is_stub() {
                 if checker.any_enabled(&[
                     Rule::UnrecognizedVersionInfoCheck,

crates/ruff_linter/src/codes.rs

@@ -287,6 +287,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "R1711") => (RuleGroup::Stable, rules::pylint::rules::UselessReturn),
         (Pylint, "R1714") => (RuleGroup::Stable, rules::pylint::rules::RepeatedEqualityComparison),
         (Pylint, "R1722") => (RuleGroup::Stable, rules::pylint::rules::SysExitAlias),
+        (Pylint, "R1730") => (RuleGroup::Preview, rules::pylint::rules::IfStmtMinMax),
         (Pylint, "R1733") => (RuleGroup::Preview, rules::pylint::rules::UnnecessaryDictIndexLookup),
         (Pylint, "R1736") => (RuleGroup::Preview, rules::pylint::rules::UnnecessaryListIndexLookup),
         (Pylint, "R2004") => (RuleGroup::Stable, rules::pylint::rules::MagicValueComparison),

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

@@ -47,6 +47,7 @@ mod tests {
     #[test_case(Rule::EqWithoutHash, Path::new("eq_without_hash.py"))]
     #[test_case(Rule::EmptyComment, Path::new("empty_comment.py"))]
     #[test_case(Rule::ManualFromImport, Path::new("import_aliasing.py"))]
+    #[test_case(Rule::IfStmtMinMax, Path::new("if_stmt_min_max.py"))]
     #[test_case(Rule::SingleStringSlots, Path::new("single_string_slots.py"))]
     #[test_case(Rule::SysExitAlias, Path::new("sys_exit_alias_0.py"))]
     #[test_case(Rule::SysExitAlias, Path::new("sys_exit_alias_1.py"))]

crates/ruff_linter/src/rules/pylint/rules/if_stmt_min_max.rs

@@ -0,0 +1,196 @@
+use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::comparable::ComparableExpr;
+use ruff_python_ast::parenthesize::parenthesized_range;
+use ruff_python_ast::{self as ast, CmpOp, Stmt};
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+use crate::fix::snippet::SourceCodeSnippet;
+
+/// ## What it does
+/// Checks for `if` statements that can be replaced with `min()` or `max()`
+/// calls.
+///
+/// ## Why is this bad?
+/// An `if` statement that selects the lesser or greater of two sub-expressions
+/// can be replaced with a `min()` or `max()` call respectively. When possible,
+/// prefer `min()` and `max()`, as they're more concise and readable than the
+/// equivalent `if` statements.
+///
+/// ## Example
+/// ```python
+/// if score > highest_score:
+///     highest_score = score
+/// ```
+///
+/// Use instead:
+/// ```python
+/// highest_score = max(highest_score, score)
+/// ```
+///
+/// ## References
+/// - [Python documentation: max function](https://docs.python.org/3/library/functions.html#max)
+/// - [Python documentation: min function](https://docs.python.org/3/library/functions.html#min)
+#[violation]
+pub struct IfStmtMinMax {
+    min_max: MinMax,
+    replacement: SourceCodeSnippet,
+}
+
+impl Violation for IfStmtMinMax {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let Self {
+            min_max,
+            replacement,
+        } = self;
+        if let Some(replacement) = replacement.full_display() {
+            format!("Replace `if` statement with `{replacement}`")
+        } else {
+            format!("Replace `if` statement with `{min_max}` call")
+        }
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        let Self {
+            min_max,
+            replacement,
+        } = self;
+        if let Some(replacement) = replacement.full_display() {
+            Some(format!("Replace with `{replacement}`"))
+        } else {
+            Some(format!("Replace with `{min_max}` call"))
+        }
+    }
+}
+
+/// R1730, R1731
+pub(crate) fn if_stmt_min_max(checker: &mut Checker, stmt_if: &ast::StmtIf) {
+    let ast::StmtIf {
+        test,
+        body,
+        elif_else_clauses,
+        range: _,
+    } = stmt_if;
+
+    if !elif_else_clauses.is_empty() {
+        return;
+    }
+
+    let [body @ Stmt::Assign(ast::StmtAssign {
+        targets: body_targets,
+        value: body_value,
+        ..
+    })] = body.as_slice()
+    else {
+        return;
+    };
+    let [body_target] = body_targets.as_slice() else {
+        return;
+    };
+
+    let Some(ast::ExprCompare {
+        ops,
+        left,
+        comparators,
+        ..
+    }) = test.as_compare_expr()
+    else {
+        return;
+    };
+
+    // Ignore, e.g., `foo < bar < baz`.
+    let [op] = &**ops else {
+        return;
+    };
+
+    // Determine whether to use `min()` or `max()`, and whether to flip the
+    // order of the arguments, which is relevant for breaking ties.
+    let (min_max, flip_args) = match op {
+        CmpOp::Gt => (MinMax::Max, true),
+        CmpOp::GtE => (MinMax::Max, false),
+        CmpOp::Lt => (MinMax::Min, true),
+        CmpOp::LtE => (MinMax::Min, false),
+        _ => return,
+    };
+
+    let [right] = &**comparators else {
+        return;
+    };
+
+    let _min_or_max = match op {
+        CmpOp::Gt | CmpOp::GtE => MinMax::Min,
+        CmpOp::Lt | CmpOp::LtE => MinMax::Max,
+        _ => return,
+    };
+
+    let left_cmp = ComparableExpr::from(left);
+    let body_target_cmp = ComparableExpr::from(body_target);
+    let right_statement_cmp = ComparableExpr::from(right);
+    let body_value_cmp = ComparableExpr::from(body_value);
+    if left_cmp != body_target_cmp || right_statement_cmp != body_value_cmp {
+        return;
+    }
+
+    let (arg1, arg2) = if flip_args {
+        (left.as_ref(), right)
+    } else {
+        (right, left.as_ref())
+    };
+
+    let replacement = format!(
+        "{} = {min_max}({}, {})",
+        checker.locator().slice(
+            parenthesized_range(
+                body_target.into(),
+                body.into(),
+                checker.indexer().comment_ranges(),
+                checker.locator().contents()
+            )
+            .unwrap_or(body_target.range())
+        ),
+        checker.locator().slice(arg1),
+        checker.locator().slice(arg2),
+    );
+
+    let mut diagnostic = Diagnostic::new(
+        IfStmtMinMax {
+            min_max,
+            replacement: SourceCodeSnippet::from_str(replacement.as_str()),
+        },
+        stmt_if.range(),
+    );
+
+    if checker.semantic().is_builtin(min_max.as_str()) {
+        diagnostic.set_fix(Fix::safe_edit(Edit::range_replacement(
+            replacement,
+            stmt_if.range(),
+        )));
+    }
+
+    checker.diagnostics.push(diagnostic);
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum MinMax {
+    Min,
+    Max,
+}
+
+impl MinMax {
+    fn as_str(self) -> &'static str {
+        match self {
+            Self::Min => "min",
+            Self::Max => "max",
+        }
+    }
+}
+
+impl std::fmt::Display for MinMax {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(fmt, "{}", self.as_str())
+    }
+}

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

@@ -21,6 +21,7 @@ pub(crate) use eq_without_hash::*;
 pub(crate) use global_at_module_level::*;
 pub(crate) use global_statement::*;
 pub(crate) use global_variable_not_assigned::*;
+pub(crate) use if_stmt_min_max::*;
 pub(crate) use import_outside_top_level::*;
 pub(crate) use import_private_name::*;
 pub(crate) use import_self::*;
@@ -116,6 +117,7 @@ mod eq_without_hash;
 mod global_at_module_level;
 mod global_statement;
 mod global_variable_not_assigned;
+mod if_stmt_min_max;
 mod import_outside_top_level;
 mod import_private_name;
 mod import_self;