From 6111d0e6733802d63d2c0a1b80889987f78bc91e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sami=20Koskim=C3=A4ki?= <koskomi@gmail.com>
Date: Sat, 22 Jul 2023 09:28:49 +0300
Subject: [PATCH] further type speedup and simplification

---
 src/parser/select-parser.ts | 24 ++++++++++++++----------
 src/util/column-type.ts     | 28 +++++++++++++++++-----------
 src/util/type-utils.ts      | 22 +++++++++++++---------
 3 files changed, 44 insertions(+), 30 deletions(-)

diff --git a/src/parser/select-parser.ts b/src/parser/select-parser.ts
index f48a02d09..ce46a7801 100644
--- a/src/parser/select-parser.ts
+++ b/src/parser/select-parser.ts
@@ -42,11 +42,13 @@ export type SelectArg<
   | ReadonlyArray<SE>
   | ((eb: ExpressionBuilder<DB, TB>) => ReadonlyArray<SE>)
 
-export type Selection<DB, TB extends keyof DB, SE> = {
-  [A in ExtractAliasFromSelectExpression<SE>]: SelectType<
-    ExtractTypeFromSelectExpression<DB, TB, SE, A>
-  >
-}
+export type Selection<DB, TB extends keyof DB, SE> = [SE] extends [unknown]
+  ? {
+      [A in ExtractAliasFromSelectExpression<SE>]: SelectType<
+        ExtractTypeFromSelectExpression<DB, TB, SE, A>
+      >
+    }
+  : never
 
 type ExtractAliasFromSelectExpression<SE> = SE extends string
   ? ExtractAliasFromStringSelectExpression<SE>
@@ -151,11 +153,13 @@ type ExtractTypeFromStringSelectExpression<
     : never
   : never
 
-export type AllSelection<DB, TB extends keyof DB> = Selectable<{
-  [C in AnyColumn<DB, TB>]: {
-    [T in TB]: C extends keyof DB[T] ? DB[T][C] : never
-  }[TB]
-}>
+export type AllSelection<DB, TB extends keyof DB> = [DB] extends [unknown]
+  ? Selectable<{
+      [C in AnyColumn<DB, TB>]: {
+        [T in TB]: C extends keyof DB[T] ? DB[T][C] : never
+      }[TB]
+    }>
+  : never
 
 export function parseSelectArg(
   selection: SelectArg<any, any, SelectExpression<any, any>>
diff --git a/src/util/column-type.ts b/src/util/column-type.ts
index cdbf0d5d5..c52cb3dd7 100644
--- a/src/util/column-type.ts
+++ b/src/util/column-type.ts
@@ -149,9 +149,11 @@ export type UpdateKeys<R> = {
  * // }
  * ```
  */
-export type Selectable<R> = {
-  [K in NonNeverSelectKeys<R>]: SelectType<R[K]>
-}
+export type Selectable<R> = [R] extends [unknown]
+  ? {
+      [K in NonNeverSelectKeys<R>]: SelectType<R[K]>
+    }
+  : never
 
 /**
  * Given a table interface, extracts the insert type from all
@@ -174,11 +176,13 @@ export type Selectable<R> = {
  * // }
  * ```
  */
-export type Insertable<R> = {
-  [K in NonNullableInsertKeys<R>]: InsertType<R[K]>
-} & {
-  [K in NullableInsertKeys<R>]?: InsertType<R[K]>
-}
+export type Insertable<R> = [R] extends [unknown]
+  ? {
+      [K in NonNullableInsertKeys<R>]: InsertType<R[K]>
+    } & {
+      [K in NullableInsertKeys<R>]?: InsertType<R[K]>
+    }
+  : never
 
 /**
  * Given a table interface, extracts the update type from all
@@ -200,6 +204,8 @@ export type Insertable<R> = {
  * // }
  * ```
  */
-export type Updateable<R> = {
-  [K in UpdateKeys<R>]?: UpdateType<R[K]>
-}
+export type Updateable<R> = [R] extends [unknown]
+  ? {
+      [K in UpdateKeys<R>]?: UpdateType<R[K]>
+    }
+  : never
diff --git a/src/util/type-utils.ts b/src/util/type-utils.ts
index c1d35408c..46028f50a 100644
--- a/src/util/type-utils.ts
+++ b/src/util/type-utils.ts
@@ -35,19 +35,23 @@ import { KyselyTypeError } from './type-error.js'
  * // Columns == 'id' | 'name' | 'species'
  * ```
  */
-export type AnyColumn<DB, TB extends keyof DB> = DrainOuterGeneric<
-  {
-    [T in TB]: keyof DB[T]
-  }[TB] &
-    string
->
+export type AnyColumn<DB, TB extends keyof DB> = [DB] extends [unknown]
+  ? {
+      [T in TB]: keyof DB[T]
+    }[TB] &
+      string
+  : never
 
 /**
  * Extracts a column type.
  */
-export type ExtractColumnType<DB, TB extends keyof DB, C> = {
-  [T in TB]: C extends keyof DB[T] ? DB[T][C] : never
-}[TB]
+export type ExtractColumnType<DB, TB extends keyof DB, C> = [C] extends [
+  unknown
+]
+  ? {
+      [T in TB]: C extends keyof DB[T] ? DB[T][C] : never
+    }[TB]
+  : never
 
 /**
  * Given a database type and a union of table names in that db, returns