due to ruff type checking constraints, do a best effort for E0307 for…

… checking return results of __str__ of constants

crates/ruff/resources/test/fixtures/pylint/invalid_return_type_str.py

@@ -1,5 +1,28 @@
 class Str:
-    """__str__ returns int"""
+    def __str__(self):
+        return 1
+
+class Float:
+    def __str__(self):
+        return 3.05
+
+class Int:
+    def __str__(self):
+        return 0
+
+class Bool:
+    def __str__(self):
+        return False
+
+class Str2:
+    def __str__(self):
+        x = "ruff"
+        return x
+
+# TODO fixme once Ruff has better type checking
+def return_int():
+    return 3
 
+class ComplexReturn:
     def __str__(self):
-        return 1
+        return return_int()

crates/ruff/src/rules/pylint/rules/invalid_str_return.rs

@@ -29,9 +29,9 @@ fn is_str_returning(body: &[Stmt]) -> Option<Diagnostic> {
     let mut visitor = ReturnStatementVisitor::default();
     visitor.visit_body(body);
     for expr in visitor.returns.into_iter().flatten() {
-        if !matches!(
+        if matches!(
             expr,
-            Expr::Constant(ref constant) if constant.value.is_str()
+            Expr::Constant(ref constant) if constant.value.is_bool() || constant.value.is_int() || constant.value.is_tuple() || constant.value.is_float()
         ) {
             return Some(Diagnostic::new(InvalidStrReturnType, expr.range()));
         }

crates/ruff/src/rules/pylint/snapshots/ruff__rules__pylint__tests__PLE0307_invalid_return_type_str.py.snap

@@ -1,11 +1,44 @@
 ---
 source: crates/ruff/src/rules/pylint/mod.rs
 ---
-invalid_return_type_str.py:5:16: PLE0307 __str__ does not return str
+invalid_return_type_str.py:3:16: PLE0307 __str__ does not return str
   |
-5 |     def __str__(self):
-6 |         return 1
+3 | class Str:
+4 |     def __str__(self):
+5 |         return 1
   |                ^ PLE0307
+6 | 
+7 | class Float:
   |
 
+invalid_return_type_str.py:7:16: PLE0307 __str__ does not return str
+   |
+ 7 | class Float:
+ 8 |     def __str__(self):
+ 9 |         return 3.05
+   |                ^^^^ PLE0307
+10 |     
+11 | class Int:
+   |
+
+invalid_return_type_str.py:11:16: PLE0307 __str__ does not return str
+   |
+11 | class Int:
+12 |     def __str__(self):
+13 |         return 0
+   |                ^ PLE0307
+14 |     
+15 | class Bool:
+   |
+
+invalid_return_type_str.py:15:16: PLE0307 __str__ does not return str
+   |
+15 | class Bool:
+16 |     def __str__(self):
+17 |         return False
+   |                ^^^^^ PLE0307
+18 |     
+19 | class Str2:
+   |
+