rdbms-playground/src/dsl/walker/context.rs

//! `WalkContext` — per-walk mutable state that flows through the
//! walker (ADR-0024 §WalkContext, §Phase D).
//!
//! Phase D plumbed a schema reference through the context so
//! schema-aware nodes (`Ident { source: Tables }` writing
//! `current_table`, `DynamicSubgrammar` reading
//! `current_table_columns`) can resolve real entities at walk
//! time. Pre-Phase-D `default()` callers (tests, the chumsky-
//! era `parse_command(input)` signature) still work — the
//! schema slot is `None` and dynamic dispatch falls back to a
//! generic value-literal slot.

use crate::completion::{SchemaCache, TableColumn};
use crate::dsl::types::Type;
use crate::mode::Mode;

/// A single `FROM`-source binding in the active lexical scope
/// (ADR-0032 §10.1). One binding per `FROM` table or `JOIN`
/// target, populated as the walker descends through
/// `from_clause` / `join_clause`.
#[derive(Debug, Clone)]
pub struct TableBinding {
    /// The table name as the user typed it (case-preserving
    /// per ADR-0009).
    pub table: String,
    /// The optional `AS` alias or bare alias (ADR-0032 §1).
    pub alias: Option<String>,
    /// The schema-resolved columns for the table. Empty if the
    /// schema did not know the table (the unknown-table
    /// diagnostic will fire in 2d).
    pub columns: Vec<TableColumn>,
}

/// A CTE definition visible from inside its own body
/// (`WITH RECURSIVE` self-reference) and from the outer scope
/// after the body completes (ADR-0032 §10.3).
#[derive(Debug, Clone)]
pub struct CteBinding {
    pub name: String,
    pub columns: Vec<CteColumn>,
}

/// One output column derived from a CTE body's projection
/// list per ADR-0032 §10.3's derivation rules.
#[derive(Debug, Clone)]
pub struct CteColumn {
    /// `None` for computed projections without an alias —
    /// the engine assigns an implementation-defined name and
    /// the slot is silently skipped from the qualified-prefix
    /// candidate list (ADR-0032 §10.3).
    pub name: Option<String>,
    /// The resolved playground type if the body's projection
    /// yields one (a single column reference). `None` for
    /// computed columns and recursive CTE bodies (per ADR-0032
    /// Amendment 1's empirical findings).
    pub type_: Option<Type>,
}

/// One lexical scope on the walker's `from_scope_stack`.
///
/// Pushed on entry to a `Node::ScopedSubgrammar` and popped on
/// exit (ADR-0032 §10.2). The bottom of the stack is the
/// implicit top-level scope DSL paths and top-level SQL
/// statements operate in.
#[derive(Debug, Default, Clone)]
pub struct ScopeFrame {
    /// In-scope FROM-source bindings for this frame. Populated
    /// by `from_clause` / `join_clause` walks.
    pub from_scope: Vec<TableBinding>,
    /// CTE definitions visible in this frame. Populated by
    /// `with_clause` walks before each CTE's body; the body's
    /// output columns are harvested into the placeholder
    /// binding at the body's frame exit (§10.3).
    pub cte_bindings: Vec<CteBinding>,
    /// Projection-list aliases observed in this frame.
    /// `ORDER BY` slots offer these as additional candidates
    /// per ADR-0032 §10.4.
    pub projection_aliases: Vec<String>,
}

/// Per-walk state.
///
/// Carries an optional schema reference (so callers without a
/// schema continue to work) plus mutable accumulators that
/// nodes can write to during the walk:
///
/// - `current_table` / `current_table_columns` — populated when
///   an `Ident { source: Tables }` node with `writes_table:
///   true` matches a known table.
/// - `current_column` — populated by `Ident { source: Columns
///   writes_column: true }` for `set col = …` / `where col =
///   …` slots so the next value-slot picks the column's typed
///   sub-grammar.
#[derive(Debug)]
pub struct WalkContext<'a> {
    pub schema: Option<&'a SchemaCache>,
    /// The input mode this walk runs under (ADR-0030 §2). In
    /// `Mode::Simple` the walker gates out SQL-only commands —
    /// an advanced-only entry word yields the "this is SQL"
    /// hint rather than a normal parse. Defaults to
    /// `Mode::Simple`; real call sites set it from the active
    /// `App` mode.
    pub mode: Mode,
    pub current_table: Option<String>,
    pub current_table_columns: Option<Vec<TableColumn>>,
    pub current_column: Option<TableColumn>,
    /// The column type the walker is *about* to consume a value
    /// for (ADR-0024 §Phase D §typed-value-slots). Set by the
    /// walker on entry to a `Node::TypedValueSlot`, cleared on
    /// successful inner match. The hint resolver reads this to
    /// emit per-type prose ("Type an integer", "Type a date as
    /// 'YYYY-MM-DD'", …) at empty prefix at typed value slots.
    pub pending_value_type: Option<crate::dsl::types::Type>,
    /// The column name (if known) the walker is about to
    /// consume a value for.
    ///
    /// Populated by:
    /// - `Ident { source: Columns, writes_column: true }` for
    ///   `update set <col>=` and `where <col>=` positions, where
    ///   the column ident matches in the path immediately
    ///   before the value slot.
    /// - `Node::TypedValueSlot { column_name: Some(name), … }`
    ///   for the per-column typed slots in `column_value_list`
    ///   (insert-into-T-values positions, where the column name
    ///   is keyed by position in the table's column list).
    ///
    /// Cleared on successful inner match alongside
    /// `pending_value_type`.
    pub pending_value_column: Option<String>,
    /// The hint-panel `HintMode` declared by the grammar node
    /// the walker is currently inside (ADR-0024
    /// §HintMode-per-node). Set on entry to a `Node::Hinted`
    /// wrapper, cleared on successful inner match. The hint
    /// resolver reads this directly instead of inferring the
    /// slot kind from the shape of the expected set.
    pub pending_hint_mode: Option<crate::dsl::grammar::HintMode>,
    /// The columns the user explicitly listed in
    /// `insert into <T> (col1, col2, …) values (…)` (Form A),
    /// in declaration order.
    ///
    /// Populated as each ident-shape token in the leading paren
    /// matches an `Ident` node with `writes_user_listed_column:
    /// true`. `None` (default) means no explicit list was
    /// observed — the inner `values (…)` slot list then
    /// defaults to "every non-auto-generated column of the
    /// current table" (Form B `insert into T values (…)`
    /// behavior; ADR-0018 §3 — auto-generated columns are
    /// skipped from the value list because the dispatch path
    /// auto-fills them).
    pub user_listed_columns: Option<Vec<String>>,
    /// Count of active `Node::Subgrammar` frames on the walk
    /// stack (ADR-0026 §2). The walker increments on entry to a
    /// `Subgrammar`, restores the saved value on exit, and
    /// refuses past `driver::MAX_SUBGRAMMAR_DEPTH` so a
    /// pathologically nested expression fails with a friendly
    /// error instead of overflowing the process stack.
    /// `Node::ScopedSubgrammar` shares the same counter
    /// uniformly (ADR-0032 §9).
    pub subgrammar_depth: usize,
    /// The stack of lexical scope frames (ADR-0032 §10.2).
    /// The bottom frame is the implicit top-level scope DSL
    /// paths and top-level SQL statements operate in;
    /// `Node::ScopedSubgrammar` entries push and pop new frames
    /// on top. Always non-empty: the bottom frame is created at
    /// `WalkContext::new` / `with_schema` time and never popped.
    pub from_scope_stack: Vec<ScopeFrame>,
    /// Diagnostics emitted *during* the walk by node handlers
    /// that have context the post-walk path scanners can no
    /// longer reconstruct (notably the §10.3 CTE harvest, which
    /// runs at body-frame exit and has direct access to both
    /// the declared col-list and the derived columns). The
    /// walker's top-level `walk` function drains this on
    /// successful parses and folds the entries into the final
    /// diagnostic vector.
    pub pending_diagnostics: Vec<crate::dsl::walker::outcome::Diagnostic>,
    /// Set by the `writes_cte_name` ident path right after the
    /// placeholder `CteBinding` is pushed onto the outer frame.
    /// Tells the very next `walk_scoped_subgrammar` invocation
    /// that the body it's about to walk is a CTE body and that,
    /// on `Matched` exit, it should run the §10.3 harvest into
    /// the recorded placeholder. `cte_column` idents (the
    /// optional `(c1, c2)` list between the cte name and `AS`)
    /// append to `col_list` as they're seen.
    ///
    /// CTE syntax has no intervening `ScopedSubgrammar` between
    /// the cte-name ident and the body, so the timing is
    /// deterministic. Cleared by `walk_scoped_subgrammar` whether
    /// or not the inner walk matched (a speculatively-walked
    /// then-rolled-back body must not leave a stale request).
    pub pending_cte_harvest: Option<PendingCteHarvest>,
}

/// Bookkeeping for an in-progress CTE harvest (ADR-0032 §10.3
/// stage 2).
///
/// The `writes_cte_name` ident sets one of these after pushing
/// the placeholder `CteBinding`; the next
/// `walk_scoped_subgrammar` invocation takes it and runs the
/// harvest after the body matches.
#[derive(Debug, Clone)]
pub struct PendingCteHarvest {
    /// Index of the placeholder `CteBinding` in the *outer*
    /// frame's `cte_bindings`. The outer frame is
    /// `from_scope_stack[len() - 2]` at the moment the body's
    /// frame is on top.
    pub placeholder_index: usize,
    /// Explicit `(c1, c2, …)` rename list — empty when the CTE
    /// declared no column list. The harvest's derived column
    /// names are overridden positionally by this list per ADR-
    /// 0032 §10.3.
    pub col_list: Vec<String>,
    /// Span of the cte_name ident — the diagnostic anchor for
    /// `cte_arity_mismatch` if the col-list arity disagrees with
    /// the body's derived arity.
    pub cte_name: String,
    pub cte_name_span: (usize, usize),
}

impl<'a> WalkContext<'a> {
    /// Schemaless walk context — the legacy default used by
    /// pre-Phase-D callers and tests that don't care about
    /// schema-aware narrowing. Carries a single empty
    /// `ScopeFrame` on `from_scope_stack` (ADR-0032 §10.2).
    #[must_use]
    pub fn new() -> Self {
        Self {
            schema: None,
            mode: Mode::Simple,
            current_table: None,
            current_table_columns: None,
            current_column: None,
            pending_value_type: None,
            pending_value_column: None,
            pending_hint_mode: None,
            user_listed_columns: None,
            subgrammar_depth: 0,
            from_scope_stack: vec![ScopeFrame::default()],
            pending_diagnostics: Vec::new(),
            pending_cte_harvest: None,
        }
    }

    /// Schema-aware walk context. Dynamic sub-grammars read
    /// `schema` (via `current_table_columns`) to unfold typed
    /// per-column value slots.
    #[must_use]
    pub fn with_schema(schema: &'a SchemaCache) -> Self {
        Self {
            schema: Some(schema),
            mode: Mode::Simple,
            current_table: None,
            current_table_columns: None,
            current_column: None,
            pending_value_type: None,
            pending_value_column: None,
            pending_hint_mode: None,
            user_listed_columns: None,
            subgrammar_depth: 0,
            from_scope_stack: vec![ScopeFrame::default()],
            pending_diagnostics: Vec::new(),
            pending_cte_harvest: None,
        }
    }
}

impl Default for WalkContext<'_> {
    fn default() -> Self {
        Self::new()
    }
}

/// Convenience re-export so non-walker modules don't reach
/// across `completion::TableColumn` directly.
#[allow(dead_code)]
pub type ColumnInfo = TableColumn;