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9359a2caad
Currently a subscripted column is expressed using the struct `column_value`:
```c++
/// A column, optionally subscripted by a value (eg, c1 or c2['abc']).
struct column_value {
const column_definition* col;
std::optional<expression> sub; ///< If present, this LHS is col[sub], otherwise just col.
}
```
It would be better to have a generic AST node for expressing arbitrary subscripted values:
```c++
/// A subscripted value, eg list_colum[2], val[sub]
struct subscript {
expression val;
expression sub;
};
```
The `subscript` struct would allow us to express more, for example:
* subscripted `column_identifier`, not only `column_definition` (needed to get rid of `relation` class)
* nested subscripts: `col[1][2]`
Adding `subscript` to `expression` variant immediately would require to implement all `expr::visit` handlers immediately in the same commit, so I took a different approach. At first the struct is just there and visit handlers are implemented one by one in advance, then at the end `subscript` is added to the `expression`. This way all the new code can be neatly divided into commits and everything is still bisectable.
There were a few cases where the existing behaviour seemed to make little sense, but I didn't change it to keep the PR focused on refactoring. I left a `FIXME` comments there and I will submit separate patches to fix them.
Closes #10139
* github.com:scylladb/scylla:
cql3: expr: Remove sub from column_value
cql3: Create a subscript in single_column_relation
cql3: expr: Add subscript to expression
cql3: Handle subscript in multi_column_range_accumulator
cql3: Handle subscript in selectable_process_selection
cql3: expr: Handle subscript in test_assignment
cql3: expr: Handle subscript in prepare_expression
cql3: Handle subscript in prepare_selectable
cql3: expr: Handle subscript in extract_clustering_prefix_restrictions
cql3: expr: Handle subscript in extract_partition_range
cql3: expr: Handle subscript in fill_prepare_context
cql3: expr: Handle subscript in evaluate
cql3: expr: Handle subscript in extract_single_column_restrictions_for_column
cql3: expr: Handle subscript in search_and_replace
cql3: expr: Handle subscript in recurse_until
cql3: expr: Implement operator<< for subscript
cql3: expr: Handle subscript in possible_lhs_values
cql3: expr: Handle subscript in is_supported_by
cql3: expr: Handle subscript in is_satisifed_by
cql3: expr: Remove unused attribute
cql3: expr: Use column_maybe_subscripted in is_one_of()
cql3: expr: Use column_maybe_subscripted in limits()
cql3: expr: Use column_maybe_subscripted in equal()
cql3: expr: add get_subscripted_column(column_maybe_subscripted)
cql3: expr: Add as_column_maybe_subscripted
cql3: expr: Make get_value_comparator work with column_maybe_subscripted
cql3: expr: Make get_value work with column_maybe_subscripted
cql3: expr: Add column_maybe_subscripted
cql3: expr: Add get_subscripted_column
cql3: expr: Add subscript struct