This PR finally removes the `term` class and replaces it with `expression`.
* There was some trouble with `lwt_cache_id` in `expr::function_call`.
The current code works the following way:
* for each `function_call` inside a `term` that describes a pk restriction, `prepare_context::add_pk_function_call` is called.
* `add_pk_function_call` takes a `::shared_ptr<cql3::functions::function_call>`, sets its `cache_id` and pushes this shared pointer onto a vector of all collected function calls
* Later when some condiition is met we want to clear cache ids of all those collected function calls. To do this we iterate through shared pointers collected in `prepare_context` and clear cache id for each of them.
This doesn't work with `expr::function_call` because it isn't kept inside a shared pointer.
To solve this I put the `lwt_cache_id` inside a shared pointer and then `prepare_context` collects these shared pointers to cache ids.
I also experimented with doing this without any shared pointers, maybe we could just walk through the expression and clear the cache ids ourselves. But the problem is that expressions are copied all the time, we could clear the cache in one place, but forget about a copy. Doing it using shared pointers more closely matches the original behaviour.
The experiment is on the [term2-pr3-backup-altcache](https://github.com/cvybhu/scylla/tree/term2-pr3-backup-altcache) branch
* `shared_ptr<term>` being `nullptr` could mean:
* It represents a cql value `null`
* That there is no value, like `std::nullopt` (for example in `attributes.hh`)
* That it's a mistake, it shouldn't be possible
A good way to distinguish between optional and mistake is to look for `my_term->bind_and_get()`, we then know that it's not an optional value.
* On the other hand `raw_value` cased to bool means:
* `false` - null or unset
* `true` - some value, maybe empty
I ran a simple benchmark on my laptop to see how performance is affected:
```
build/release/test/perf/perf_simple_query --smp 1 -m 1G --operations-per-shard 1000000 --task-quota-ms 10
```
* On master (a21b1fbb2f) I get:
```
176506.60 tps ( 77.0 allocs/op, 12.0 tasks/op, 45831 insns/op)
median 176506.60 tps ( 77.0 allocs/op, 12.0 tasks/op, 45831 insns/op)
median absolute deviation: 0.00
maximum: 176506.60
minimum: 176506.60
```
* On this branch I get:
```
172225.30 tps ( 75.1 allocs/op, 12.1 tasks/op, 46106 insns/op)
median 172225.30 tps ( 75.1 allocs/op, 12.1 tasks/op, 46106 insns/op)
median absolute deviation: 0.00
maximum: 172225.30
minimum: 172225.30
```
Closes#9481
* github.com:scylladb/scylla:
cql3: Remove remaining mentions of term
cql3: Remove term
cql3: Rename prepare_term to prepare_expression
cql3: Make prepare_term return an expression instead of term
cql3: expr: Add size check to evaluate_set
cql3: expr: Add expr::contains_bind_marker
cql3: expr: Rename find_atom to find_binop
cql3: expr: Add find_in_expression
cql3: Remove term in operations
cql3: Remove term in relations
cql3: Remove term in multi_column_restrictions
cql3: Remove term in term_slice, rename to bounds_slice
cql3: expr: Remove term in expression
cql3: expr: Add evaluate_IN_list(expression, options)
cql3: Remove term in column_condition
cql3: Remove term in select_statement
cql3: Remove term in update_statement
cql3: Use internal cql format in insert_prepared_json_statement cache
types: Add map_type_impl::serialize(range of <bytes, bytes>)
cql3: Remove term in cql3/attributes
cql3: expr: Add constant::view() method
cql3: expr: Implement fill_prepare_context(expression)
cql3: expr: add expr::visit that takes a mutable expression
cql3: expr: Add receiver to expr::bind_variable
595cc328b1