This QL
```codeql
import python
import semmle.python.dataflow.TaintTracking
import semmle.python.security.strings.Untrusted
from CollectionKind ck
where
ck.(DictKind).getMember() instanceof StringKind
or
ck.getMember().(DictKind).getMember() instanceof StringKind
select ck, ck.getAQlClass(), ck.getMember().getAQlClass()
```
generates these 6 results.
```
1 {externally controlled string} ExternalStringDictKind UntrustedStringKind
2 {externally controlled string} StringDictKind UntrustedStringKind
3 [{externally controlled string}] SequenceKind ExternalStringDictKind
4 [{externally controlled string}] SequenceKind StringDictKind
5 {{externally controlled string}} DictKind ExternalStringDictKind
6 {{externally controlled string}} DictKind StringDictKind
```
StringDictKind was only used in *one* place in our library code. As illustrated
above, it pollutes our set of TaintKinds. Effectively, every time we make a
flow-step for dictionaries with tainted strings as values, we do it TWICE --
once for ExternalStringDictKind, and once for StringDictKind... that is just a
waste.
If I wanted to use my own TaintKind and not have any interaction with
`UntrustedStringKind` that wouldn't be possible today since these standard http
libraries import it directly. (also, I wouldn't get any sources of my custom
TaintKind from turbogears or bottle). I changed them to use the same pattern of
`ExternalStringKind` as everything else does.
Since HttpResponse is not *only* used for XSS, it is still valuable to know the
content is send as part of the response.
The *proper* solution to this problem of not all HttpResponses being vulnerable
to XSS is probably to define a new abstract class in Http.qll called
HttpResponseXSSVulnerableSink (or similar). I would like to model a few more
libraries/frameworks before fully comitting to an approach though.
In a near-future release overriding a deprecated predicate without making as
deprecated would give a compiler warning.
Not fixing the XML one. [I can see that this shouldn't be reported
anymore](https://github.com/github/codeql/pull/3520#issuecomment-631552943), and
it's not safe to remove since it was only marked as deprecated in
e6425bb4cf.
