fix: CREATE UNIQUE INDEX actually enforces uniqueness (and persists)

src/barabadb/query/exec/context.nim

@@ -4,6 +4,7 @@
 ## Also hosts the AST-to-SQL serializer used for VIEW DDL persistence.
 import std/strutils
 import std/tables
+import std/sets
 import std/locks
 import ../ast
 import ../../storage/lsm
@@ -28,6 +29,7 @@ var restoreEnginesHook*: proc(ctx: ExecutionContext)
 proc newExecutionContext*(db: LSMTree, registry: DatabaseRegistry = nil): ExecutionContext =
   result = ExecutionContext(db: db, tables: initTable[string, TableDef](),
                    btrees: initTable[string, BTreeIndex[string, IndexEntry]](),
+                   uniqueIndexes: initHashSet[string](),
                    views: initTable[string, Node](),
                    cteTables: initTable[string, seq[Row]](),
                    ftsIndexes: initTable[string, fts.InvertedIndex](),
@@ -161,6 +163,7 @@ proc cloneForConnection*(ctx: ExecutionContext): ExecutionContext =
     svCopy[k] = v
   result = ExecutionContext(db: ctx.db, tables: ctx.tables,
                    btrees: ctx.btrees, views: ctx.views,
+                   uniqueIndexes: ctx.uniqueIndexes,
                    cteTables: initTable[string, seq[Row]](),
                    ftsIndexes: ctx.ftsIndexes,
                    vectorIndexes: ctx.vectorIndexes,

src/barabadb/query/exec/dml.nim

@@ -3,6 +3,7 @@
 ## Extracted from `executor.nim` (Task 9 of the executor split).
 import std/strutils
 import std/tables
+import std/sets
 import std/sequtils
 import ../../storage/lsm
 import ../../storage/btree
@@ -21,6 +22,28 @@ import rls
 # Table storage
 # ----------------------------------------------------------------------
 
+proc violatesUniqueIndex*(ctx: ExecutionContext, table: string, fields: seq[string],
+                          rowVals: seq[string], excludeLsmKey: string = ""): string =
+  ## Returns the colKey of the first standalone UNIQUE index this row
+  ## violates, or "" when the row is clean. idxVal is built with the exact
+  ## convention of the CREATE INDEX population loop (getValue yields "\\N"
+  ## for a missing column, values joined with "|"). excludeLsmKey lets UPDATE
+  ## ignore the row's own existing entry.
+  if ctx.uniqueIndexes.len == 0: return ""
+  for colKey in ctx.uniqueIndexes:
+    if not colKey.startsWith(table & "."): continue
+    let idxCols = colKey[table.len + 1..^1].split(".")
+    var colVals: seq[string] = @[]
+    for c in idxCols:
+      colVals.add(getValue(rowVals, fields, c))
+    let idxVal = colVals.join("|")
+    if idxVal.len == 0 or isNull(idxVal): continue
+    if colKey notin ctx.btrees: continue
+    for entry in ctx.btrees[colKey].get(idxVal):
+      if entry.lsmKey != excludeLsmKey:
+        return colKey
+  return ""
+
 proc execInsert*(ctx: ExecutionContext, table: string, fields: seq[string], values: seq[seq[string]],
                   kvPairs: var seq[(string, seq[byte])]): int =
   if not hasPrivilege(ctx, table, "INSERT"):

src/barabadb/query/exec/types.nim

@@ -1,5 +1,6 @@
 ## Executor types — shared by all exec/* modules and executor.nim
 import std/tables
+import std/sets
 import std/locks
 import ../ast
 import ../ir
@@ -92,6 +93,7 @@ type
     db*: LSMTree
     tables*: Table[string, TableDef]
     btrees*: Table[string, BTreeIndex[string, IndexEntry]]
+    uniqueIndexes*: HashSet[string]  # colKeys (table.col[.col...]) of UNIQUE standalone B-tree indexes
     views*: Table[string, Node]  # view name -> SELECT AST
     cteTables*: Table[string, seq[Row]]  # CTE name -> rows
     ftsIndexes*: Table[string, fts.InvertedIndex]  # table.col -> FTS index