do not consider indexing unsafe - reference will live safely in a container in most cases

Cython/Compiler/ExprNodes.py

@@ -2806,7 +2806,8 @@ class IndexNode(ExprNode):
     def is_ephemeral(self):
         # in most cases, indexing will return a safe reference to an object in a container,
         # so we consider the result safe if the base object is
-        return self.base.is_ephemeral()
+        return self.base.is_ephemeral() or self.base.type in (
+            basestring_type, str_type, bytes_type, unicode_type)
 
     def is_simple(self):
         if self.is_buffer_access or self.memslice_index:
@@ -10891,7 +10892,7 @@ class CoerceFromPyTypeNode(CoercionNode):
         return self
 
     def is_ephemeral(self):
-        return self.type.is_ptr and self.arg.is_temp and not self.arg.is_name
+        return self.type.is_ptr and self.arg.is_ephemeral()
 
     def generate_result_code(self, code):
         function = self.type.from_py_function

tests/errors/charptr_from_temp.pyx

@@ -18,7 +18,7 @@ cptr = s
 # temp => error
 cptr = s + b"cba"
 
-# indexing => error
+# indexing => error (but not clear enough to make it a compiler error)
 cptr = s[0]
 cdef char* x = <char*>s[0]
 
@@ -47,8 +47,9 @@ cuptr = u + u"cba"
 _ERRORS = """
 16:8: Obtaining 'char *' from externally modifiable global Python value
 19:9: Storing unsafe C derivative of temporary Python reference
-22:8: Storing unsafe C derivative of temporary Python reference
-23:5: Storing unsafe C derivative of temporary Python reference
+#22:8: Storing unsafe C derivative of temporary Python reference
+#23:5: Storing unsafe C derivative of temporary Python reference
+#23:15: Casting temporary Python object to non-numeric non-Python type
 26:8: Storing unsafe C derivative of temporary Python reference
 41:9: Obtaining 'Py_UNICODE *' from externally modifiable global Python value
 44:10: Storing unsafe C derivative of temporary Python reference