feat(engine): extend CollationEquality with resolveCollation

src/main/kotlin/kestrel/engine/CollationEquality.kt

@@ -0,0 +1,94 @@
+package kestrel.engine
+
+import kestrel.catalog.TableSchema
+import kestrel.sql.ast.CollateExpression
+import kestrel.sql.ast.ColumnExpression
+import kestrel.sql.ast.Expression
+import kestrel.storage.Collation
+import kestrel.storage.Value
+
+/**
+ * Resolves which [Collation] governs equality/ordering for [expression]'s own value, with the same
+ * two-tier precedence [compareOrderKeyValues] already uses for `ORDER BY`: an explicit `COLLATE` on
+ * [expression] itself wins; failing that, a bare [ColumnExpression]'s own declared `COLLATE` (see
+ * [kestrel.catalog.Column.collation]), reported by [declaredCollationOf]; [Collation.Binary]
+ * otherwise. Shared by [compareOrderKeyValues] and every equality-based dedup below so both sides of
+ * the COLLATE story (ordering and equality) agree on which collation a given expression uses.
+ */
+fun resolveCollation(expression: Expression, declaredCollationOf: (ColumnExpression) -> Collation?): Collation =
+    (expression as? CollateExpression)?.collation
+        ?: (expression as? ColumnExpression)?.let(declaredCollationOf)
+        ?: Collation.Binary
+
+/**
+ * Folds [values] (one grouping/`DISTINCT` key, whose entries line up positionally with
+ * [expressions]) into a key usable as a [Map]/[Set] bucket or a `distinctBy` selector: a
+ * [Value.TextValue] under a collation resolved (via [resolveCollation]) to anything but
+ * [Collation.Binary] is rewritten through [Collation.canonicalize] first, so e.g. `'Bob'` and
+ * `'bob'` land in the same bucket under a `NOCASE`-declared column, while every other value keeps
+ * its own `equals`/`hashCode` - a call site with no declared collation anywhere behaves exactly as
+ * it did before this function existed, since [Collation.Binary]'s [Collation.canonicalize] is the
+ * identity.
+ */
+fun collationFoldedKey(
+    values: List<Value>,
+    expressions: List<Expression>,
+    declaredCollationOf: (ColumnExpression) -> Collation?
+): List<Value> = values.mapIndexed { index, value ->
+    if (value !is Value.TextValue) value
+    else Value.TextValue(resolveCollation(expressions[index], declaredCollationOf).canonicalize(value.value))
+}
+
+/**
+ * [collationFoldedKey]'s counterpart for a PRIMARY KEY / `UNIQUE` constraint / `UNIQUE` index
+ * uniqueness check, where the "expression" naming each key column is always just that column
+ * itself - a bare index into [schema], not an arbitrary [Expression] tree - so the collation to
+ * apply is always [kestrel.catalog.Column.collation] directly rather than something resolved
+ * through [resolveCollation]'s explicit-`COLLATE`-wins rule (a `PRIMARY KEY`/`UNIQUE` column list
+ * has no expressions to attach an explicit `COLLATE` to in the first place). Used by
+ * [kestrel.engine.Executor]'s in-memory `enforcePrimaryKeyUniqueness`/`enforceUniqueConstraints`/
+ * `enforceUniqueIndexes`, [kestrel.store.sql.DiskTable]'s heap-scanned
+ * `rejectDuplicateUniqueConstraints`/`backfillSecondaryIndex`, and (via
+ * [kestrel.store.sql.DiskTable]'s `encodePrimaryKey`/`compositeKey`/`equalRangeFor`) the disk
+ * engine's own B+Tree-backed PRIMARY KEY and `CREATE UNIQUE INDEX` key encoding itself - folding
+ * only ever changes what bytes a [kestrel.store.codec.KeyCodec] index key encodes to, never the
+ * row values a [kestrel.store.heap.RecordId] resolves to, so it is safe for lookup/ordering
+ * without corrupting any stored row.
+ */
+fun collationFoldedUniquenessKey(schema: TableSchema, columnIndices: List<Int>, values: List<Value>): List<Value> =
+    values.mapIndexed { position, value ->
+        if (value !is Value.TextValue) value
+        else Value.TextValue(schema.columns[columnIndices[position]].collation.canonicalize(value.value))
+    }
+
+/**
+ * Single-column counterpart of [collationFoldedKey], for an aggregate's own `DISTINCT` dedup
+ * (`COUNT`/`SUM`/`AVG`/`MIN`/`MAX(DISTINCT ...)`), which has already reduced its argument down to a
+ * flat list of values rather than whole rows.
+ */
+fun List<Value>.distinctByCollation(collation: Collation): List<Value> =
+    distinctBy { value -> if (value is Value.TextValue) collation.canonicalize(value.value) else value }
+
+/**
+ * SQLite's own two-tier rule for a binary comparison's collating sequence, in decreasing
+ * precedence: (1) an explicit `COLLATE` on either operand, left first; (2) either operand's own
+ * declared column `COLLATE` (via [declaredCollationOf], with [Collation.Binary] treated the same
+ * as "no declaration" so it never out-ranks the *other* side purely by appearing first - see
+ * [resolveCollation]'s own doc for the identical reasoning), left first; (3) [Collation.Binary].
+ * Kept as two separate passes (not one combined per-side [resolveCollation] check) so an explicit
+ * `COLLATE` on the *right* operand still outranks the *left* operand's own declared column
+ * collation. Shared by [kestrel.engine.Evaluator]'s `=`/`<>`/`BETWEEN`/`CASE` comparisons and the
+ * hash-join fast path in [kestrel.engine.SelectRunner] (`hashJoinKeys`/`executeJoin`), so a
+ * `JOIN ... ON a.x = b.x` bucket lookup agrees with what evaluating the exact same condition
+ * row-by-row through [kestrel.engine.Evaluator] would have decided.
+ */
+fun pairCollation(
+    left: Expression,
+    right: Expression,
+    declaredCollationOf: (ColumnExpression) -> Collation?
+): Collation {
+    fun explicitOf(expression: Expression) = (expression as? CollateExpression)?.collation
+    fun declaredOf(expression: Expression) =
+        (expression as? ColumnExpression)?.let(declaredCollationOf)?.takeIf { it != Collation.Binary }
+    return explicitOf(left) ?: explicitOf(right) ?: declaredOf(left) ?: declaredOf(right) ?: Collation.Binary
+}

src/main/kotlin/kestrel/engine/Evaluator.kt

@@ -1,36 +1,112 @@
 package kestrel.engine
 
+import java.math.BigDecimal
+import java.math.RoundingMode
+import java.time.LocalDate
 import kestrel.KestrelException
 import kestrel.catalog.TableSchema
+import kestrel.engine.function.ScalarFunctions
+import kestrel.sql.ast.BetweenExpression
 import kestrel.sql.ast.BinaryExpression
 import kestrel.sql.ast.BinaryOperator
+import kestrel.sql.ast.CallExpression
+import kestrel.sql.ast.CaseExpression
+import kestrel.sql.ast.CastExpression
+import kestrel.sql.ast.CollateExpression
 import kestrel.sql.ast.ColumnExpression
+import kestrel.sql.ast.ExistsExpression
 import kestrel.sql.ast.Expression
 import kestrel.sql.ast.FunctionExpression
+import kestrel.sql.ast.InExpression
+import kestrel.sql.ast.InSubqueryExpression
+import kestrel.sql.ast.IsNullExpression
+import kestrel.sql.ast.LikeExpression
+import kestrel.sql.ast.CurrentValueExpression
 import kestrel.sql.ast.LiteralExpression
+import kestrel.sql.ast.MergeActionExpression
+import kestrel.sql.ast.NextValueExpression
+import kestrel.sql.ast.ParameterExpression
+import kestrel.sql.ast.ScalarSubqueryExpression
+import kestrel.sql.ast.SelectStatement
 import kestrel.sql.ast.UnaryExpression
 import kestrel.sql.ast.UnaryOperator
+import kestrel.sql.ast.WindowExpression
+import kestrel.storage.Collation
+import kestrel.storage.ColumnType
+import kestrel.storage.DecimalColumns
 import kestrel.storage.Row
 import kestrel.storage.Value
 import kestrel.storage.typeName
 
 fun interface ColumnResolver {
     fun resolve(expression: ColumnExpression): Value
+
+    /**
+     * The [Collation] [expression] was declared with in its `CREATE TABLE ... COLLATE name` (its
+     * [kestrel.catalog.Column.collation]), or `null` when this resolver has no such column to
+     * report one for - a computed/derived row (a set operation's output, a LATERAL subquery's own
+     * result), an ambiguous reference across more than one source, or simply a resolver that never
+     * bothered to override this default. [Evaluator.collationOf] only ever calls this for a bare
+     * [ColumnExpression] with no [kestrel.sql.ast.CollateExpression] of its own - an explicit
+     * `COLLATE` in the query always wins over whatever this returns. A default method (not the SAM
+     * member) so every existing lambda-shaped `ColumnResolver { expression -> ... }` construction
+     * keeps compiling unchanged and simply reports "no declared collation" - only the resolvers
+     * built directly over a [kestrel.catalog.TableSchema] bother to override it.
+     */
+    fun declaredCollation(expression: ColumnExpression): Collation? = null
 }
 
-class Evaluator(private val resolver: ColumnResolver? = null) {
-    constructor(schema: TableSchema?, row: Row?) : this(schema?.let { active ->
-        ColumnResolver { expression ->
+fun interface SubqueryRunner {
+    fun run(select: SelectStatement, outer: ColumnResolver?): SelectResult
+}
+
+/**
+ * Bridges NEXTVAL/CURRVAL evaluation to whichever [kestrel.catalog.Catalog] and per-session state
+ * actually own sequence counters - kept as its own interface (not a `fun interface` like
+ * [ColumnResolver]/[SubqueryRunner]) because it needs two independent operations, not one.
+ * [kestrel.engine.Executor] is the only implementation; every other [Evaluator] construction site
+ * (SELECT projections, WHERE clauses read-side, CHECK constraints, trigger `WHEN` clauses) omits it,
+ * so [evaluateNextValue]/[evaluateCurrentValue] throw there exactly like a missing [SubqueryRunner]
+ * already does for a subquery - deliberately: a volatile, side-effecting call being evaluated an
+ * engine-implementation-defined number of times (once for filtering, again for projecting the same
+ * row, ...) is exactly the ambiguity real databases warn about, so this engine only ever allows it
+ * where a row's assignment is evaluated exactly once by construction (see
+ * [kestrel.engine.Executor.executeInsertInner]/`executeUpdateInner`).
+ */
+interface SequenceAccess {
+    fun nextValue(sequenceName: String): Long
+    fun currentValue(sequenceName: String): Long
+}
+
+class Evaluator(
+    private val resolver: ColumnResolver? = null,
+    private val subqueries: SubqueryRunner? = null,
+    private val sequences: SequenceAccess? = null,
+    /** Bound only by [kestrel.engine.Executor.evaluateMergeReturning]'s per-row [Evaluator] - see [MergeActionExpression]'s own doc for why every other call site leaves this null and lets MERGE_ACTION() throw. */
+    private val mergeAction: String? = null
+) {
+    constructor(schema: TableSchema?, row: Row?, subqueries: SubqueryRunner? = null, sequences: SequenceAccess? = null) : this(
+        schema?.let { active ->
+            object : ColumnResolver {
+                override fun resolve(expression: ColumnExpression): Value {
                     val index = active.columnIndex(expression.name)
                         ?: throw KestrelException("no such column: ${expression.name}")
-            row!!.values[index]
+                    return row!!.values[index]
                 }
-    })
+
+                override fun declaredCollation(expression: ColumnExpression): Collation? =
+                    active.column(expression.name)?.collation
+            }
+        },
+        subqueries,
+        sequences
+    )
 
     fun evaluate(expression: Expression): Value = when (expression) {
         is LiteralExpression -> expression.value
         is ColumnExpression -> evaluateColumn(expression)
         is UnaryExpression -> evaluateUnary(expression)
+        is CollateExpression -> evaluate(expression.operand)
         is BinaryExpression -> evaluateBinary(expression)
         is FunctionExpression -> throw KestrelException(
             "aggregate function ${expression.name} is not allowed here"