[refurb] Parse more exotic decimal strings in verbose-decimal-constructor (FURB157) (#14098)

FURB157 suggests replacing expressions like `Decimal("123")` with
`Decimal(123)`. This PR extends the rule to cover cases where the input
string to `Decimal` can be easily transformed into an integer literal.

For example:

```python
Decimal("1__000")   # fix: `Decimal(1000)`
```

Note: we do not implement the full decimal parsing logic from CPython on
the grounds that certain acceptable string inputs to the `Decimal`
constructor may be presumed purposeful on the part of the developer. For
example, as in the linked issue, `Decimal("١٢٣")` is valid and equal to
`Decimal(123)`, but we do not suggest a replacement in this case.

Closes #13807

crates/ruff_linter/resources/test/fixtures/refurb/FURB157.py

@@ -15,3 +15,23 @@ decimal.Decimal("0")
 Decimal(0)
 Decimal("Infinity")
 decimal.Decimal(0)
+
+# Handle Python's Decimal parsing
+# See https://github.com/astral-sh/ruff/issues/13807
+
+# Errors
+Decimal("1_000")
+Decimal("__1____000") 
+
+# Ok
+Decimal("2e-4")
+Decimal("2E-4")
+Decimal("_1.234__")
+Decimal("2e4")
+Decimal("2e+4")
+Decimal("2E4")
+Decimal("1.2") 
+# Ok: even though this is equal to `Decimal(123)`,
+# we assume that a developer would
+# only write it this way if they meant to.
+Decimal("١٢٣") 

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

@@ -3,6 +3,7 @@ use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::{self as ast, Expr};
 use ruff_python_trivia::PythonWhitespace;
 use ruff_text_size::Ranged;
+use std::borrow::Cow;
 
 use crate::checkers::ast::Checker;
 
@@ -75,13 +76,20 @@ pub(crate) fn verbose_decimal_constructor(checker: &mut Checker, call: &ast::Exp
             value: str_literal, ..
         }) => {
             // Parse the inner string as an integer.
-            let trimmed = str_literal.to_str().trim_whitespace();
-
+            //
+            // For reference, a string argument to `Decimal` is parsed in CPython
+            // using this regex:
+            // https://github.com/python/cpython/blob/ac556a2ad1213b8bb81372fe6fb762f5fcb076de/Lib/_pydecimal.py#L6060-L6077
+            // _after_ trimming whitespace from the string and removing all occurrences of "_".
+            let mut trimmed = Cow::from(str_literal.to_str().trim_whitespace());
+            if memchr::memchr(b'_', trimmed.as_bytes()).is_some() {
+                trimmed = Cow::from(trimmed.replace('_', ""));
+            }
             // Extract the unary sign, if any.
             let (unary, rest) = if let Some(trimmed) = trimmed.strip_prefix('+') {
-                ("+", trimmed)
+                ("+", Cow::from(trimmed))
             } else if let Some(trimmed) = trimmed.strip_prefix('-') {
-                ("-", trimmed)
+                ("-", Cow::from(trimmed))
             } else {
                 ("", trimmed)
             };
@@ -90,7 +98,7 @@ pub(crate) fn verbose_decimal_constructor(checker: &mut Checker, call: &ast::Exp
             let rest = rest.trim_start_matches('0');
 
             // Verify that the rest of the string is a valid integer.
-            if !rest.chars().all(|c| c.is_ascii_digit()) {
+            if !rest.bytes().all(|c| c.is_ascii_digit()) {
                 return;
             };
 
@@ -159,3 +167,26 @@ pub(crate) fn verbose_decimal_constructor(checker: &mut Checker, call: &ast::Exp
 
     checker.diagnostics.push(diagnostic);
 }
+
+// // Slightly modified from [CPython regex] to ignore  https://github.com/python/cpython/blob/ac556a2ad1213b8bb81372fe6fb762f5fcb076de/Lib/_pydecimal.py#L6060-L6077
+// static DECIMAL_PARSER_REGEX: LazyLock<Regex> = LazyLock::new(|| {
+//     Regex::new(
+//         r"(?x)                   # Verbose mode for comments
+// ^                                             # Start of string
+// (?P<sign>[-+])?                               # Optional sign
+// (?:
+//     (?P<int>\d*)                              # Integer part (can be empty)
+//     (\.(?P<frac>\d+))?                        # Optional fractional part
+//     (E(?P<exp>[-+]?\d+))?                     # Optional exponent
+// |
+//     Inf(inity)?                               # Infinity
+// |
+//     (?P<signal>s)?                            # Optional signal
+//     NaN                                       # NaN
+//     (?P<diag>\d*)                             # Optional diagnostic info
+// )
+// $                                             # End of string
+// ",
+//     )
+//     .unwrap()
+// });

crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB157_FURB157.py.snap

@@ -166,3 +166,43 @@ FURB157.py:12:17: FURB157 [*] Verbose expression in `Decimal` constructor
 13 13 | 
 14 14 | # OK
 15 15 | Decimal(0)
+
+FURB157.py:23:9: FURB157 [*] Verbose expression in `Decimal` constructor
+   |
+22 | # Errors
+23 | Decimal("1_000")
+   |         ^^^^^^^ FURB157
+24 | Decimal("__1____000") 
+   |
+   = help: Replace with `1000`
+
+ℹ Safe fix
+20 20 | # See https://github.com/astral-sh/ruff/issues/13807
+21 21 | 
+22 22 | # Errors
+23    |-Decimal("1_000")
+   23 |+Decimal(1000)
+24 24 | Decimal("__1____000") 
+25 25 | 
+26 26 | # Ok
+
+FURB157.py:24:9: FURB157 [*] Verbose expression in `Decimal` constructor
+   |
+22 | # Errors
+23 | Decimal("1_000")
+24 | Decimal("__1____000") 
+   |         ^^^^^^^^^^^^ FURB157
+25 | 
+26 | # Ok
+   |
+   = help: Replace with `1000`
+
+ℹ Safe fix
+21 21 | 
+22 22 | # Errors
+23 23 | Decimal("1_000")
+24    |-Decimal("__1____000") 
+   24 |+Decimal(1000) 
+25 25 | 
+26 26 | # Ok
+27 27 | Decimal("2e-4")