`getLocation()` will now exists for all entities. When there is no
valid location, the location will still not be emitted in the DB, but
on the QL side we will then assign a special `UnknownLocation` with
empty filename and 0 for line/column start/end.
This unknown location is currently emitted (with a unique `@` key) at
the start of every extraction, but we can move it elsewhere (and
possibly in a unique global trap file) at a later stage, possibly after
or when we rework the trap file strategy.
This should solve flakiness that was observed on the control flow tests,
which is probably caused by the `nodes` predicate in the `TestOutput`
class in `ControlFlowGraphImplShared.qll` not able to assign a proper
rank when the node does not have a location.
While the (removed) comment is correct and the frontend can be called in
different modes, both `swift build` and `xcodebuild` always use
`-primary-files` when compiling Swift projects.
The other mode was present only within our test runner (`qltest.sh`), so
removing it and doing what the official build systems do simplifies our
code base.
Additionally, file archival is now a separate function/operation.
This checks in the trapgen script generating trap entries in C++.
The codegen suite has been slightly reorganized, moving the templates
directory up one level and chopping everything into smaller bazel
packages. Running tests is now done via
```
bazel run //swift/codegen/test
```
With respect to the PoC, the nested `codeql::trap` namespace has been
dropped in favour of a `Trap` prefix (or suffix in case of entries)
within the `codeql` namespace. Also, generated C++ code is not checked
in in git any more, and generated during build. Finally, labels get
printed in hex in the trap file.
`TrapLabel` is for the moment only default-constructible, so only one
single label is possible. `TrapArena`, that is responsible for creating
disjoint labels will come in a later commit.
