column_value_tuple overlaps both column_value and tuple_constructor
(in different respects) and can be replaced by a combination: a
tuple_constructor of column_value. The replacement is more expressive
(we can have a tuple of column_value and other expression types), though
the code (especially grammar) do not allow it yet.
So remove column_value_tuple and replace it everywhere with
tuple_constructor. Visitors get the merged behavior of the existing
tuple_constructor and column_value_tuple, which is usually trivial
since tuple_constructor and column_value_tuple came from different
hierarchies (term::raw and relation), so usually one of the types
just calls on_internal_error().
The change results in awkwards casts in two areas: WHERE clause
filtering (equal() and related), and clustering key range evaluations
(limits() and related). When equal() is replaced by recursive
evaluate(), the casts will go way (to be replaced by the evaluate())
visitor. Clustering key range extraction will remain limited
to tuples of column_value, so the prepare phase will have to vet
the expressions to ensure the casts don't fail (and use the
filtering path if they will).
Tests: unit (dev)
Closes#9274
Introduce a general-purpose search and replace function to manipulate
expressions, and use it to simplify replace_column_def() and
replace_token().
Closes#9259
* github.com:scylladb/scylla:
cql3: expr: rewrite replace_token in terms of search_and_replace()
cql3: expr: rewrite replace_column_def in terms of search_and_replace()
cql3: expr: add general-purpose search-and-replace
Use search_and_replace() to simplify replace_token(). Note the conversion
does not have 100% fidelity - the previous implementation throws on
some impossible subexpression types, and the new one passes them
through. It should be the caller's responsibility anyway, not a
side effect of replacing tokens, and since these subexpressions are
impossible there is no real effect on execution.
Note that this affects only TOKEN() calls on the partition key
columns in the right order. Other uses of the token function
(say with constants) won't be translated to the token subexpression
type. So something like
WHERE token(pk) = token(?)
would only see the left-hand side replaced, not the right-hand
side, even if it were an expression rather than a term.
We're won't introduce new expression types that are equivalent
to column_value, and search_and_replace() takes care of all
expressions that need to recurse, so we don't need std::visit()
for the search/replace lambda.
Add a recursive search-and-replace function on expressions. The
caller provides a search/replace function to operate on subexpressions,
returning nullopt if they want the default behavior of recursively
copying, or a new expression to terminate the search (in the current
subtree) and replace the current node with the returned expression.
To avoid endlessly specifying the subexpression types that get the
the common behavior (copying) since they don't contain any subexpressions,
we add a new concept LeafExpression to signify them.
Existing functions such as replace_token() can be reimplemented in
terms of search_and_replace, but that is left for later.
column_specification_or_tuple is now used internally, wrapping and
a column_specification or a vector and immediately unwrapping in
the callee. The only exceptions are bind_variable and tuple_constructor,
which handles both cases.
Use the underlying types directly instead, and add dispatching
to prepare_term_multi_column() for the two cases it handles.
column_specification_or_tuple was introduced since some terms
were prepared using a single receiver e.g. (receiver = <term>) and
some using multiple receivers (e.g. (r1, r2) = <term>. Some
term types supported both.
To hide this complexity, the term->expr conversion used a single
interface for both variations (column_expression_or_tuple), but now
that we got rid of the term class and there are no virtual functions
any more, we can just use two separate functions for the two variants.
Internally we still use column_expression_or_tuple, it can be
removed later.
Now that we have the prepare machinery exposed as expression API:s
(not just term::raw) we can avoid conversions from expressions to
term::raw when preparing subexpressions.
The test_assignment class has a test_all() helper to test
a vector of assignment_testable. But expressions are not
derived from assignment_testable, so introduce a new helper
that does the same for expressions.
So far prepare (in the term domain) was called via term::raw. To be
able to prepare in the expression domain, expose functions prepare_term()
and test_assignment() that accept expressions as arguments.
prepare_term() was chosen rather that prepare() to differentiate wrt.
the other domain that can be prepared (selectables).
While we have a bridge between expressions and term::raw, which is
derived from assignment_testable, we will soon get rid of term::raw
and so won't be able to interface with API:s that require an
assignment_testable. So add a bridge for that. The user is
function::get(), which uses assignment_testable to infer the
function overload from the argument types.
Convert the user_types::literal raw to a new expression type
usertype_constructor. I used "usertype" to convey that is is a
((user type) constructor), not a (user (type constructor)).
Add set and map styles to collection_constructor. Maps are implemented as
collection_constructor{tuple_constructor{key, value}...}. This saves
having a new expression type, and reduces the effort to implement
recursive descent evaluation for this omitted expression type.
Move them closer to prepare related functions for modification. Since
sets and maps share some implementation details in the grammar, they
are moved and converted as a unit.
Introduce a collection_constructor (similar to C++'s std::initializer_list)
to hold subexpressions being gathered into a list. Since sets, maps, and
lists construction share some attributes (all elements must be of the
same type) collection_constructor will be used for all of them, so it
also holds an enum. I used "style" for the enum since it's a weak
attribute - an empty set is also an empty map. I chose collection_constructor
rather than plain 'collection' to highlight that it's not the only way
to get a collection (selecting a collection column is another, as an
example) and to hint at what it does - construct a collection from
more primitive elements.
Introduce tuple_constructor (not a literal, since (?, ?) and (column_value,
column_value) are not literals) to represent a tuple constructed from
subexpressions. In the future we can replace column_value_tuple
with tuple_constructor(column_value, column_value, ...), but this is
not done now.
I chose the name 'tuple_constructor' since other expressions can represent
tuples (e.g. my_tuple_column, :bind_variable_of_tuple_type,
func_returning_tuple()). It also explains what the expression does.
Introduce a new expression untyped_constant that corresponds to
constants::literal, which is removed. untyped_constant is rather
ugly in that it won't exist post-prepare. We should probably instead
replace it with typed constants that use the widest possible type
(decimal and varint), and select a narrower type during the prepare
phase when we perform type inference. The conversion itseld is
straightforward.
Convert the four forms of abstract_marker to expr::bind_variable (the
name was chosen since variable is the role of the thing, while "marker"
refers more to the grammar). Having four variants is unnecessary, but
this patch doesn't do anything about that.
We reuse the expr::cast type that was previously used for selectables.
When preparing, subexpressions are converted to term::raw; this will
be removed later.
These methods will be converted to the expression variant, and
it's impossible to do this while inlined due to #include cycles. In
any case, deinlining is better.
Since there is no type_cast.cc, and since they'll become part of
expr_term call chain soon, they're moved there, even though it seems
odd for this patch. It's a waste to create type_cast.cc just for those
three functions.
The cast expression has two operands: the subexpression to cast and the
type to cast to. Since prepared and unprepared expressions are the
same type, we don't have to do anything, but prepared and unprepared
types are different. So add a variant to be able to support both.
The reason the selectable->expression transformation did not need to
do this is that casts in a selector cannot accept a user defined type.
Note those casts also have different syntax and different execution,
so we'll have to choose whether to unify the two semantics, or whether
to keep them separate. This patch does not force anything (but does hint
at unification by not including any discriminant beyond the type's
rawness). The string representation matches the part of the grammar
it was derived from (or conversion back to CQL will yield wrong
results).
Remove cql3::functions::function_call::raw and replace it with
cql3::expr::function_call, which already existed from the selector
migration to expressions. The virtual functions implementing term::raw
are made free functions and remain in place, to ease migration and
review.
Note that preparing becomes a more complicated as it needs to
account for anonymous functions, which were not representable
in the previous structure (and still cannot be created by the
parser for the term::raw path).
The parser now wraps all its arguments with the term::raw->expr
bridge, since that's what expr::function_call expects, and in
turn wraps the function call with an expr->term::raw bridge, since
that's what the rest of the parser expects. These will disappear
when the migration completes.
Since expressions can nest, and since we won't covert everything at once,
add a way to store a term::raw as an expression. We can now have a
term::raw that is internally an expression, and an expression that is
implemented as term::raw.
A term_raw_expression is a term::raw that holds an expression. It will
be used to incrementally convert the source base to expressions, while
still exposing the result to the common interface of shared_ptr<term::raw>.
Add a function, which given an expression and a column,
extracts all restrictions involving this column.
Signed-off-by: Jan Ciolek <jan.ciolek@scylladb.com>
The combination of the new types and these functions cannot happen yet,
but as they are generic functions it is better to implement them in
case it becomes possible later.
Now that all selectable::raw subclasses have been converted to
cql3::selectable::with_expression::raw, the class structure is
just a wrapper around expressions. Peel it, converting the
virtual member functions to free functions, and replacing
object instances with expression or nested_expression as the
case allows.
Add a field_selection variant element to expression. Like function_call
and cast, the structure from which a field is selectewd cannot yet be
an expression, since not all seletable::raw:s are converted. This will
be done in a later pass. This is also why printing a field selection now
does not print the selected expression; this will also be corrected later.
Add a cast variant element to expression. Like function_call, the
argument being converted cannot yet be an expression, since not
all seletable::raw:s are converted. This will be done in a later
pass. This is also why printing a cast now does not print the
casted expression; this will also be corrected later.
Rather than creating a new variant element in expression, we extend
function_call to handle both named and anonymous functions, since
most of the processing is the same.
Add a function_call variant element to hold function calls. Note
that because not all selectables are yet converted, function call
arguments are still of type selectable::raw. They will be converted
to expressions later. This is also why printing a function now
does not print its arguments; this will also be corrected later.
Create a new element in the expression variant, column_mutation_attribute,
signifying we're picking up an attribute of a column mutation (not a
column value!). We use an enum rather than a bool to choose between
writetime and ttl (the two mutation attributes) for increased
explicitness.
Although there can only be one type for the column we're operating
on (it must be an unresolved_identifer), we use a nested_expression.
This is because we'll later need to also support a column_value
as the column type after we prepare it. This is somewhat similar
to the address of operator in C, which syntactically takes any
expression but semantically operates only on lvalues.
It is convenient to initialize a nested_expression variable from
one of the types that compose the expression variant, but C++ doesn't
allow it. Add a constructor that does this. Use the new variant_element
concept to constrain the input to be one of the variant's elements.
The exression type cannot be a member of a struct that is an
element of the expression variant. This is because it would then
be required to contain itself. So introduce a nested_expression
type to indirectly hold an expression, but keep the value semantics
we expect from expressions: it is copyable and a copy has separate
identity and storage.
In fact binary_operator had to resort to this trick, so it's converted
to nested_expression in the next patch.
Introduce unresolved_identifer as an unprepared counterpart to column_value.
column_identifier_raw no longer inherits from selectable::raw, but
methods for now to reduce churn.
Adds replace_token function which takes an expression
and replaces all left hand side occurences of token()
with the given column definition.
Signed-off-by: Jan Ciolek <jan.ciolek@scylladb.com>
