Previously the Operation enum consisted of:
- Operation::Scan
- Operation::Search
- Operation::Subquery
Which was always a dumb hack because what we really are doing is
an Operation::Scan on a "virtual"/"pseudo" table (overloaded names...)
derived from a subquery appearing in the FROM clause.
Hence, refactor the relevant data structures so that the Table enum
now contains a new variant:
Table::FromClauseSubquery
And the Operation enum only consists of Scan and Search.
No functional changes (intended, at least!)
We've run into trouble in multiple places due to the fact that
we delete terms from the where clause (e.g. when a constant condition
is removed, or the term becomes part of an index seek key).
A simpler solution is to add a flag indicating that the term is
consumed (used), so that it is not translated in the main loop
anymore when WHERE clause terms are evaluated.
TLDR: no need to call either of:
program.emit_insn_with_label_dependency() -> just call program.emit_insn()
program.defer_label_resolution() -> just call program.resolve_label()
Changes:
- make BranchOffset an explicit enum (Label, Offset, Placeholder)
- remove program.emit_insn_with_label_dependency() - label dependency is automatically detected
- for label to offset mapping, use a hashmap from label(negative i32) to offset (positive u32)
- resolve all labels in program.build()
- remove program.defer_label_resolution() - all labels are resolved in build()
