claude@clouddev1
4f89106a63
Sub-phase 2b checkpoint 1 — adds the foundation for SQL SELECT lexical-scope discipline without changing existing walker semantics. New types in `dsl::walker::context`: - `TableBinding` — one FROM-source binding with table name, optional alias, and schema-resolved columns (§10.1). - `CteBinding` + `CteColumn` — a CTE definition visible from inside its body (WITH RECURSIVE self-reference) and from the outer scope after harvest (§10.3). - `ScopeFrame` — `from_scope`, `cte_bindings`, and `projection_aliases` for one lexical scope. Default-empty; the fields will be populated by later 2b checkpoints. `WalkContext` gains `from_scope_stack: Vec<ScopeFrame>`, initialised with one bottom frame in both `new()` and `with_schema()`. The bottom frame is the implicit top-level scope DSL paths and top-level SQL statements operate in; `Node::ScopedSubgrammar` entries push and pop additional frames on top. `current_table` / `current_table_columns` remain as direct fields for this checkpoint — converting them to derived helpers is a later 2b step. New grammar-tree variant: - `Node::ScopedSubgrammar(&'static Self)` — like `Subgrammar`, but pushes a fresh `ScopeFrame` on entry and pops it on exit (ADR-0032 §10.2). Shares `subgrammar_depth` with the plain Subgrammar variant so the MAX_SUBGRAMMAR_DEPTH = 64 cap fires uniformly across both — §9's "no new walker capability for grammar recursion" claim holds. DSL Expr (ADR-0026) and sql_expr.rs ladder (ADR-0031) recursion continue to use the plain Subgrammar variant and never push a scope. Driver gains a parallel `walk_scoped_subgrammar` arm; the push/pop is unconditional so a speculatively-walked branch a later Choice rolls back leaves the stack clean. Test coverage in `driver.rs`: - A recursive ScopedSubgrammar test grammar walks correctly through depths 0-3. - The depth cap fires the same `expression_too_deep` friendly validation error as for plain Subgrammar. - The bottom frame invariant: `WalkContext::new` seeds exactly one frame, and after a walk the stack is restored. No grammar tree references the new variant yet — the rewire of sql_select.rs CTE bodies and the sql_expr.rs additive extensions for §5/§6 are the next 2b checkpoint. Test totals: 1330 baseline + 3 = 1333 passing, 0 failed, 1 ignored. Clippy clean.