[pylint] Detect more exotic NaN literals in PLW0177 (#18630)

Co-authored-by: Micha Reiser <micha@reiser.io>

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

@@ -92,3 +92,8 @@ if y == np.inf:
 # OK
 if x == "nan":
     pass
+
+# PLW0117
+# https://github.com/astral-sh/ruff/issues/18596
+assert x == float("-NaN ")
+assert x == float(" \n+nan   \t")

crates/ruff_linter/src/linter.rs

@@ -39,6 +39,8 @@ use crate::settings::{LinterSettings, TargetVersion, flags};
 use crate::source_kind::SourceKind;
 use crate::{Locator, directives, fs, warn_user_once};
 
+pub(crate) mod float;
+
 pub struct LinterResult {
     /// A collection of diagnostic messages generated by the linter.
     pub messages: Vec<Message>,

crates/ruff_linter/src/linter/float.rs

@@ -0,0 +1,39 @@
+use ruff_python_ast as ast;
+
+/// Checks if `expr` is a string literal that represents NaN.
+/// E.g., `"NaN"`, `"-nAn"`, `"+nan"`, or even `" -NaN \n \t"`
+/// Returns `None` if it's not. Else `Some("nan")`, `Some("-nan")`, or `Some("+nan")`.
+pub(crate) fn as_nan_float_string_literal(expr: &ast::Expr) -> Option<&'static str> {
+    find_any_ignore_ascii_case(expr, &["nan", "+nan", "-nan"])
+}
+
+/// Returns `true` if `expr` is a string literal that represents a non-finite float.
+/// E.g., `"NaN"`, "-inf", `"Infinity"`, or even `" +Inf \n \t"`.
+/// Return `None` if it's not. Else the lowercased, trimmed string literal,
+/// e.g., `Some("nan")`, `Some("-inf")`, or `Some("+infinity")`.
+pub(crate) fn as_non_finite_float_string_literal(expr: &ast::Expr) -> Option<&'static str> {
+    find_any_ignore_ascii_case(
+        expr,
+        &[
+            "nan",
+            "+nan",
+            "-nan",
+            "inf",
+            "+inf",
+            "-inf",
+            "infinity",
+            "+infinity",
+            "-infinity",
+        ],
+    )
+}
+
+fn find_any_ignore_ascii_case(expr: &ast::Expr, patterns: &[&'static str]) -> Option<&'static str> {
+    let value = &expr.as_string_literal_expr()?.value;
+
+    let value = value.to_str().trim();
+    patterns
+        .iter()
+        .find(|other| value.eq_ignore_ascii_case(other))
+        .copied()
+}

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

@@ -1,10 +1,12 @@
 use ruff_macros::{ViolationMetadata, derive_message_formats};
+
 use ruff_python_ast::{self as ast, Expr};
 use ruff_python_semantic::SemanticModel;
 use ruff_text_size::Ranged;
 
 use crate::Violation;
 use crate::checkers::ast::Checker;
+use crate::linter::float::as_nan_float_string_literal;
 
 /// ## What it does
 /// Checks for comparisons against NaN values.
@@ -113,14 +115,10 @@ fn is_nan_float(expr: &Expr, semantic: &SemanticModel) -> bool {
         return false;
     }
 
-    let [Expr::StringLiteral(ast::ExprStringLiteral { value, .. })] = &**args else {
+    let [expr] = &**args else {
         return false;
     };
-
-    if !matches!(
-        value.to_str(),
-        "nan" | "NaN" | "NAN" | "Nan" | "nAn" | "naN" | "nAN" | "NAn"
-    ) {
+    if as_nan_float_string_literal(expr).is_none() {
         return false;
     }
 

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLW0177_nan_comparison.py.snap

@@ -107,3 +107,20 @@ nan_comparison.py:60:10: PLW0177 Comparing against a NaN value; use `math.isnan`
 61 |
 62 |     # No errors
    |
+
+nan_comparison.py:98:13: PLW0177 Comparing against a NaN value; use `math.isnan` instead
+   |
+96 | # PLW0117
+97 | # https://github.com/astral-sh/ruff/issues/18596
+98 | assert x == float("-NaN ")
+   |             ^^^^^^^^^^^^^^ PLW0177
+99 | assert x == float(" \n+nan   \t")
+   |
+
+nan_comparison.py:99:13: PLW0177 Comparing against a NaN value; use `math.isnan` instead
+   |
+97 | # https://github.com/astral-sh/ruff/issues/18596
+98 | assert x == float("-NaN ")
+99 | assert x == float(" \n+nan   \t")
+   |             ^^^^^^^^^^^^^^^^^^^^^ PLW0177
+   |

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

@@ -140,6 +140,7 @@ pub(crate) fn unnecessary_from_float(checker: &Checker, call: &ExprCall) {
         let Some(float) = float.as_string_literal_expr() else {
             break 'short_circuit;
         };
+        // FIXME: use `as_non_finite_float_string_literal` instead.
         if !matches!(
             float.value.to_str().to_lowercase().as_str(),
             "inf" | "-inf" | "infinity" | "-infinity" | "nan"

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

@@ -1,10 +1,12 @@
 use ruff_macros::{ViolationMetadata, derive_message_formats};
+
 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;
+use crate::linter::float::as_non_finite_float_string_literal;
 use crate::{Edit, Fix, FixAvailability, Violation};
 
 /// ## What it does
@@ -150,35 +152,13 @@ pub(crate) fn verbose_decimal_constructor(checker: &Checker, call: &ast::ExprCal
             let [float] = arguments.args.as_ref() else {
                 return;
             };
-            let Some(float) = float.as_string_literal_expr() else {
+            let Some(float_str) = as_non_finite_float_string_literal(float) else {
                 return;
             };
 
-            let trimmed = float.value.to_str().trim();
-            let mut matches_non_finite_keyword = false;
-            for non_finite_keyword in [
-                "inf",
-                "+inf",
-                "-inf",
-                "infinity",
-                "+infinity",
-                "-infinity",
-                "nan",
-                "+nan",
-                "-nan",
-            ] {
-                if trimmed.eq_ignore_ascii_case(non_finite_keyword) {
-                    matches_non_finite_keyword = true;
-                    break;
-                }
-            }
-            if !matches_non_finite_keyword {
-                return;
-            }
-
             let mut replacement = checker.locator().slice(float).to_string();
             // `Decimal(float("-nan")) == Decimal("nan")`
-            if trimmed.eq_ignore_ascii_case("-nan") {
+            if float_str == "-nan" {
                 // Here we do not attempt to remove just the '-' character.
                 // It may have been encoded (e.g. as '\N{hyphen-minus}')
                 // in the original source slice, and the added complexity