[ruff] Fix false positive for re.split with empty string pattern (RUF055)

crates/ruff_linter/resources/test/fixtures/ruff/RUF055_0.py

@@ -98,3 +98,8 @@ def dashrepl(matchobj):
 re.sub(r'abc', "", s)
 re.sub(r"""abc""", "", s)
 re.sub(r'''abc''', "", s)
+
+# Empty pattern: re.split("", s) should not be flagged because
+# str.split("") raises ValueError while re.split("", s) succeeds
+re.split("", s)
+re.split(r"", s)

crates/ruff_linter/resources/test/fixtures/ruff/RUF055_3.py

@@ -21,4 +21,7 @@
 re.match(rb"ab[c]", b_src)
 re.search(rb"ab[c]", b_src)
 re.fullmatch(rb"ab[c]", b_src)
-re.split(rb"ab[c]", b_src) 
+re.split(rb"ab[c]", b_src)
+
+# Empty pattern: re.split(rb"", b_src) should not be flagged
+re.split(rb"", b_src)

crates/ruff_linter/src/rules/ruff/rules/unnecessary_regular_expression.rs

@@ -118,6 +118,12 @@ pub(crate) fn unnecessary_regular_expression(checker: &Checker, call: &ExprCall)
         return;
     }
 
+    // `str.split("")` raises `ValueError: empty separator` while `re.split("", s)` succeeds,
+    // so skip the diagnostic for `re.split` with an empty pattern.
+    if matches!(re_func.kind, ReFuncKind::Split) && literal.is_empty() {
+        return;
+    }
+
     // Now we know the pattern is a string literal with no metacharacters, so
     // we can proceed with the str method replacement.
     let new_expr = re_func.replacement();
@@ -362,6 +368,15 @@ enum Literal<'a> {
     Bytes(&'a ExprBytesLiteral),
 }
 
+impl Literal<'_> {
+    fn is_empty(&self) -> bool {
+        match self {
+            Literal::Str(str_lit) => str_lit.value.is_empty(),
+            Literal::Bytes(bytes_lit) => bytes_lit.value.is_empty(),
+        }
+    }
+}
+
 /// Try to resolve `name` to either a string or bytes literal in `semantic`.
 fn resolve_literal<'a>(name: &'a Expr, semantic: &'a SemanticModel) -> Option<Literal<'a>> {
     if let Some(str_lit) = resolve_string_literal(name, semantic) {

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__preview__RUF055_RUF055_0.py.snap

@@ -243,6 +243,7 @@ help: Replace with `s.replace(r'abc', "")`
 98  + s.replace(r'abc', "")
 99  | re.sub(r"""abc""", "", s)
 100 | re.sub(r'''abc''', "", s)
+101 | 
 
 RUF055 [*] Plain string pattern passed to `re` function
    --> RUF055_0.py:99:1
@@ -260,6 +261,8 @@ help: Replace with `s.replace(r"""abc""", "")`
     - re.sub(r"""abc""", "", s)
 99  + s.replace(r"""abc""", "")
 100 | re.sub(r'''abc''', "", s)
+101 | 
+102 | # Empty pattern: re.split("", s) should not be flagged because
 
 RUF055 [*] Plain string pattern passed to `re` function
    --> RUF055_0.py:100:1
@@ -268,10 +271,15 @@ RUF055 [*] Plain string pattern passed to `re` function
  99 | re.sub(r"""abc""", "", s)
 100 | re.sub(r'''abc''', "", s)
     | ^^^^^^^^^^^^^^^^^^^^^^^^^
+101 |
+102 | # Empty pattern: re.split("", s) should not be flagged because
     |
 help: Replace with `s.replace(r'''abc''', "")`
 97  | # these double as tests for preserving raw string quoting style
 98  | re.sub(r'abc', "", s)
 99  | re.sub(r"""abc""", "", s)
     - re.sub(r'''abc''', "", s)
 100 + s.replace(r'''abc''', "")
+101 | 
+102 | # Empty pattern: re.split("", s) should not be flagged because
+103 | # str.split("") raises ValueError while re.split("", s) succeeds