[refurb] implement hardcoded-string-charset (FURB156)

crates/ruff_linter/resources/test/fixtures/refurb/FURB156.py

@@ -0,0 +1,20 @@
+# Errors
+
+_ = "0123456789"
+_ = "01234567"
+_ = "0123456789abcdefABCDEF"
+_ = "abcdefghijklmnopqrstuvwxyz"
+_ = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+_ = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+_ = r"""!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~"""
+_ = " \t\n\r\v\f"
+
+_ = "" in "1234567890"
+_ = "" in "12345670"
+_ = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c'
+
+# Ok
+
+_ = "1234567890"
+_ = "1234"
+_ = "" in "1234"

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

@@ -1355,6 +1355,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
             if checker.enabled(Rule::SingleItemMembershipTest) {
                 refurb::rules::single_item_membership_test(checker, expr, left, ops, comparators);
             }
+            if checker.enabled(Rule::HardcodedStringCharset) {
+                refurb::rules::hardcoded_string_charset_comparison(checker, compare);
+            }
         }
         Expr::NumberLiteral(number_literal @ ast::ExprNumberLiteral { .. }) => {
             if checker.source_type.is_stub() && checker.enabled(Rule::NumericLiteralTooLong) {
@@ -1364,7 +1367,7 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                 refurb::rules::math_constant(checker, number_literal);
             }
         }
-        Expr::StringLiteral(ast::ExprStringLiteral { value, range: _ }) => {
+        Expr::StringLiteral(string_like @ ast::ExprStringLiteral { value, range: _ }) => {
             if checker.enabled(Rule::UnicodeKindPrefix) {
                 for string_part in value {
                     pyupgrade::rules::unicode_kind_prefix(checker, string_part);
@@ -1375,6 +1378,9 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                     ruff::rules::missing_fstring_syntax(checker, string_literal);
                 }
             }
+            if checker.enabled(Rule::HardcodedStringCharset) {
+                refurb::rules::hardcoded_string_charset_literal(checker, string_like);
+            }
         }
         Expr::If(
             if_exp @ ast::ExprIf {

crates/ruff_linter/src/codes.rs

@@ -1055,6 +1055,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Refurb, "148") => (RuleGroup::Preview, rules::refurb::rules::UnnecessaryEnumerate),
         (Refurb, "152") => (RuleGroup::Preview, rules::refurb::rules::MathConstant),
         (Refurb, "154") => (RuleGroup::Preview, rules::refurb::rules::RepeatedGlobal),
+        (Refurb, "156") => (RuleGroup::Preview, rules::refurb::rules::HardcodedStringCharset),
         (Refurb, "157") => (RuleGroup::Preview, rules::refurb::rules::VerboseDecimalConstructor),
         (Refurb, "161") => (RuleGroup::Stable, rules::refurb::rules::BitCount),
         (Refurb, "163") => (RuleGroup::Stable, rules::refurb::rules::RedundantLogBase),

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

@@ -29,6 +29,7 @@ mod tests {
     #[test_case(Rule::UnnecessaryEnumerate, Path::new("FURB148.py"))]
     #[test_case(Rule::MathConstant, Path::new("FURB152.py"))]
     #[test_case(Rule::RepeatedGlobal, Path::new("FURB154.py"))]
+    #[test_case(Rule::HardcodedStringCharset, Path::new("FURB156.py"))]
     #[test_case(Rule::VerboseDecimalConstructor, Path::new("FURB157.py"))]
     #[test_case(Rule::UnnecessaryFromFloat, Path::new("FURB164.py"))]
     #[test_case(Rule::PrintEmptyString, Path::new("FURB105.py"))]

crates/ruff_linter/src/rules/refurb/rules/hardcoded_string_charset.rs

@@ -0,0 +1,184 @@
+use crate::checkers::ast::Checker;
+use crate::importer::ImportRequest;
+use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::{CmpOp, Expr, ExprCompare, ExprStringLiteral};
+use ruff_text_size::{Ranged, TextRange};
+
+/// ## What it does
+/// Checks for uses of hardcoded charsets, which are defined in Python string module.
+///
+/// ## Why is this bad?
+/// Usage of named charsets from the standard library is more readable and less error-prone.
+///
+/// ## Example
+/// ```python
+/// x = "0123456789"
+/// y in "abcdefghijklmnopqrstuvwxyz"
+/// ```
+///
+/// Use instead
+/// ```python
+/// import string
+///
+/// x = string.digits
+/// y in string.ascii_lowercase
+/// ```
+///
+/// ## References
+/// - [Python documentation: String constants](https://docs.python.org/3/library/string.html#string-constants)
+#[violation]
+pub struct HardcodedStringCharset {
+    name: &'static str,
+}
+
+impl AlwaysFixableViolation for HardcodedStringCharset {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Use of hardcoded string charset")
+    }
+
+    fn fix_title(&self) -> String {
+        let HardcodedStringCharset { name } = self;
+        format!("Replace hardcoded charset with `string.{name}`")
+    }
+}
+
+struct NamedCharset {
+    name: &'static str,
+    bytes: &'static [u8],
+    ascii_char_set: AsciiCharSet,
+}
+
+/// Represents the set of ascii characters in form of a bitset.
+#[derive(Copy, Clone, Eq, PartialEq)]
+struct AsciiCharSet(u128);
+
+impl AsciiCharSet {
+    /// Creates the set of ascii characters from `bytes`.
+    /// Returns None if there is non-ascii byte.
+    fn from_bytes(bytes: &[u8]) -> Option<Self> {
+        bytes
+            .iter()
+            .try_fold(0, |acc, &byte| byte.is_ascii().then(|| acc | (1 << byte)))
+            .map(Self)
+    }
+
+    /// Creates the set of ascii characters from `bytes`.
+    /// Returns None if there is non-ascii byte.
+    const fn from_bytes_const(bytes: &[u8]) -> Option<Self> {
+        // TODO: remove in favor of [`Self::from_bytes`], when its implementation will be
+        //  supported in `const` fn
+        //  - https://github.com/rust-lang/rust/issues/67792
+        //  - https://github.com/rust-lang/rust/issues/87575
+        let mut bitset = 0;
+        let mut i = 0;
+        while i < bytes.len() {
+            if !bytes[i].is_ascii() {
+                return None;
+            }
+            bitset |= 1 << bytes[i];
+            i += 1;
+        }
+        Some(Self(bitset))
+    }
+
+    const fn from_bytes_const_unwrap(bytes: &[u8]) -> Self {
+        // TODO: replace with .unwrap() in the caller, when Option::unwrap will be stable in `const fn`
+        //  - https://github.com/rust-lang/rust/issues/67441)
+        match Self::from_bytes_const(bytes) {
+            Some(res) => res,
+            None => unreachable!(),
+        }
+    }
+}
+
+impl NamedCharset {
+    const fn new(name: &'static str, bytes: &'static [u8]) -> Self {
+        Self {
+            name,
+            bytes,
+            // SAFETY: The named charset is guaranteed to have only ascii bytes.
+            ascii_char_set: AsciiCharSet::from_bytes_const_unwrap(bytes),
+        }
+    }
+}
+
+const KNOWN_NAMED_CHARSETS: [NamedCharset; 9] = [
+    NamedCharset::new(
+        "ascii_letters",
+        b"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ",
+    ),
+    NamedCharset::new("ascii_lowercase", b"abcdefghijklmnopqrstuvwxyz"),
+    NamedCharset::new("ascii_uppercase", b"ABCDEFGHIJKLMNOPQRSTUVWXYZ"),
+    NamedCharset::new("digits", b"0123456789"),
+    NamedCharset::new("hexdigits", b"0123456789abcdefABCDEF"),
+    NamedCharset::new("octdigits", b"01234567"),
+    NamedCharset::new("punctuation", b"!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~"),
+    NamedCharset::new(
+        "printable",
+        b"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!\"\
+        #$%&'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c",
+    ),
+    NamedCharset::new("whitespace", b" \t\n\r\x0b\x0c"),
+];
+
+fn check_charset_as_set(bytes: &[u8]) -> Option<&NamedCharset> {
+    let ascii_char_set = AsciiCharSet::from_bytes(bytes)?;
+
+    KNOWN_NAMED_CHARSETS
+        .iter()
+        .find(|&charset| charset.ascii_char_set == ascii_char_set)
+}
+
+fn check_charset_exact(bytes: &[u8]) -> Option<&NamedCharset> {
+    KNOWN_NAMED_CHARSETS
+        .iter()
+        .find(|&charset| charset.bytes == bytes)
+}
+
+fn push_diagnostic(checker: &mut Checker, range: TextRange, charset: &NamedCharset) {
+    let name = charset.name;
+    let mut diagnostic = Diagnostic::new(HardcodedStringCharset { name }, range);
+    diagnostic.try_set_fix(|| {
+        let (edit, binding) = checker.importer().get_or_import_symbol(
+            &ImportRequest::import("string", name),
+            range.start(),
+            checker.semantic(),
+        )?;
+        Ok(Fix::safe_edits(
+            Edit::range_replacement(binding, range),
+            [edit],
+        ))
+    });
+    checker.diagnostics.push(diagnostic);
+}
+
+/// FURB156
+pub(crate) fn hardcoded_string_charset_comparison(checker: &mut Checker, compare: &ExprCompare) {
+    let ([CmpOp::In | CmpOp::NotIn], [Expr::StringLiteral(ExprStringLiteral { value, range })]) =
+        (compare.ops.as_ref(), compare.comparators.as_ref())
+    else {
+        return;
+    };
+
+    let bytes = value.to_str().as_bytes();
+
+    let Some(charset) = check_charset_as_set(bytes) else {
+        return;
+    };
+
+    // In this case the diagnostic will be emitted via string_literal check.
+    if charset.bytes == bytes {
+        return;
+    }
+
+    push_diagnostic(checker, *range, charset);
+}
+
+/// FURB156
+pub(crate) fn hardcoded_string_charset_literal(checker: &mut Checker, expr: &ExprStringLiteral) {
+    if let Some(charset) = check_charset_exact(expr.value.to_str().as_bytes()) {
+        push_diagnostic(checker, expr.range(), charset);
+    }
+}

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

@@ -3,6 +3,7 @@ pub(crate) use check_and_remove_from_set::*;
 pub(crate) use delete_full_slice::*;
 pub(crate) use for_loop_set_mutations::*;
 pub(crate) use fstring_number_format::*;
+pub(crate) use hardcoded_string_charset::*;
 pub(crate) use hashlib_digest_hex::*;
 pub(crate) use if_exp_instead_of_or_operator::*;
 pub(crate) use if_expr_min_max::*;
@@ -36,6 +37,7 @@ mod check_and_remove_from_set;
 mod delete_full_slice;
 mod for_loop_set_mutations;
 mod fstring_number_format;
+mod hardcoded_string_charset;
 mod hashlib_digest_hex;
 mod if_exp_instead_of_or_operator;
 mod if_expr_min_max;