Remove B904's lowercase exemption (#5751)

## Summary

It looks like bugbear, [from the
start](PyCQA/flake8-bugbear#181 (comment)),
has had an exemption here to exempt `raise lower_case_var`. I looked at
Hypothesis and Trio, which are mentioned in that issue, and Hypothesis
has exactly one case of this, and Trio has none, so IMO it doesn't seem
worth special-casing.

Closes #5664.

crates/ruff/resources/test/fixtures/flake8_bugbear/B904.py

@@ -14,9 +14,10 @@
 except Exception as err:
     assert err
     raise Exception("No cause here...")
-except BaseException as base_err:
-    # Might use this instead of bare raise with the `.with_traceback()` method
-    raise base_err
+except BaseException as err:
+    raise err
+except BaseException as err:
+    raise some_other_err
 finally:
     raise Exception("Nothing to chain from, so no warning here")
 

crates/ruff/src/checkers/ast/mod.rs

@@ -3897,7 +3897,7 @@ where
                     }
                 }
                 if self.enabled(Rule::RaiseWithoutFromInsideExcept) {
-                    flake8_bugbear::rules::raise_without_from_inside_except(self, body);
+                    flake8_bugbear::rules::raise_without_from_inside_except(self, name, body);
                 }
                 if self.enabled(Rule::BlindExcept) {
                     flake8_blind_except::rules::blind_except(self, type_.as_deref(), name, body);

crates/ruff/src/rules/flake8_bugbear/rules/raise_without_from_inside_except.rs

@@ -1,10 +1,10 @@
-use rustpython_parser::ast::{self, Expr, Stmt};
+use rustpython_parser::ast;
+use rustpython_parser::ast::Stmt;
 
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::helpers::RaiseStatementVisitor;
 use ruff_python_ast::statement_visitor::StatementVisitor;
-use ruff_python_stdlib::str::is_cased_lowercase;
 
 use crate::checkers::ast::Checker;
 
@@ -60,7 +60,11 @@ impl Violation for RaiseWithoutFromInsideExcept {
 }
 
 /// B904
-pub(crate) fn raise_without_from_inside_except(checker: &mut Checker, body: &[Stmt]) {
+pub(crate) fn raise_without_from_inside_except(
+    checker: &mut Checker,
+    name: Option<&str>,
+    body: &[Stmt],
+) {
     let raises = {
         let mut visitor = RaiseStatementVisitor::default();
         visitor.visit_body(body);
@@ -70,14 +74,28 @@ pub(crate) fn raise_without_from_inside_except(checker: &mut Checker, body: &[St
     for (range, exc, cause) in raises {
         if cause.is_none() {
             if let Some(exc) = exc {
-                match exc {
-                    Expr::Name(ast::ExprName { id, .. }) if is_cased_lowercase(id) => {}
-                    _ => {
-                        checker
-                            .diagnostics
-                            .push(Diagnostic::new(RaiseWithoutFromInsideExcept, range));
+                // If the raised object is bound to the same name, it's a re-raise, which is
+                // allowed (but may be flagged by other diagnostics).
+                //
+                // For example:
+                // ```python
+                // try:
+                //     ...
+                // except ValueError as exc:
+                //     raise exc
+                // ```
+                if let Some(name) = name {
+                    if exc
+                        .as_name_expr()
+                        .map_or(false, |ast::ExprName { id, .. }| name == id)
+                    {
+                        continue;
                     }
                 }
+
+                checker
+                    .diagnostics
+                    .push(Diagnostic::new(RaiseWithoutFromInsideExcept, range));
             }
         }
     }

crates/ruff/src/rules/flake8_bugbear/snapshots/ruff__rules__flake8_bugbear__tests__B904_B904.py.snap

@@ -27,33 +27,43 @@ B904.py:16:5: B904 Within an `except` clause, raise exceptions with `raise ... f
 15 |     assert err
 16 |     raise Exception("No cause here...")
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ B904
-17 | except BaseException as base_err:
-18 |     # Might use this instead of bare raise with the `.with_traceback()` method
+17 | except BaseException as err:
+18 |     raise err
    |
 
-B904.py:62:9: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
+B904.py:20:5: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
    |
-60 | except Exception as e:
-61 |     if ...:
-62 |         raise RuntimeError("boom!")
+18 |     raise err
+19 | except BaseException as err:
+20 |     raise some_other_err
+   |     ^^^^^^^^^^^^^^^^^^^^ B904
+21 | finally:
+22 |     raise Exception("Nothing to chain from, so no warning here")
+   |
+
+B904.py:63:9: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
+   |
+61 | except Exception as e:
+62 |     if ...:
+63 |         raise RuntimeError("boom!")
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ B904
-63 |     else:
-64 |         raise RuntimeError("bang!")
+64 |     else:
+65 |         raise RuntimeError("bang!")
    |
 
-B904.py:64:9: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
+B904.py:65:9: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
    |
-62 |         raise RuntimeError("boom!")
-63 |     else:
-64 |         raise RuntimeError("bang!")
+63 |         raise RuntimeError("boom!")
+64 |     else:
+65 |         raise RuntimeError("bang!")
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ B904
    |
 
-B904.py:72:13: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
+B904.py:73:13: B904 Within an `except` clause, raise exceptions with `raise ... from err` or `raise ... from None` to distinguish them from errors in exception handling
    |
-70 |     match 0:
-71 |         case 0:
-72 |             raise RuntimeError("boom!")
+71 |     match 0:
+72 |         case 0:
+73 |             raise RuntimeError("boom!")
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ B904
    |