change coercions to include more type safety (ianstormtaylor#551)

* change coercions to include more type safety

* add trimmed

* update docs

* fix linting

.eslintrc

@@ -78,7 +78,6 @@
     "no-tabs": "error",
     "no-this-before-super": "error",
     "no-throw-literal": "error",
-    "no-undef": "error",
     "no-unneeded-ternary": "error",
     "no-unreachable": "error",
     "no-unsafe-finally": "error",

.gitignore

@@ -1,9 +1,10 @@
 .DS_Store
+.vscode
 lib/
 node_modules/
 npm-debug.log
 package-lock.json
 site/
 tmp/
 umd/
-yarn-error.log
+yarn-error.log

.prettierignore

@@ -1,3 +1,4 @@
+.vscode/
 lib/
 node_modules/
 site/

docs/guides/03-coercing-data.md

@@ -50,24 +50,22 @@ const User = defaulted(
 
 We've already covered default values, but sometimes you'll need to create coercions that aren't just defaulted `undefined` values, but instead transforming the input data from one format to another.
 
-For example, maybe you want to ensure that any string is trimmed before passing it into the validator. To do that you can define a custom coercion:
+For example, maybe you want to ensure that a number is parsed from a string before passing it into the validator. To do that you can define a custom coercion:
 
 ```ts
-import { coerce } from 'superstruct'
+import { coerce, number, string, create } from 'superstruct'
 
-const TrimmedString = coerce(string(), (value) => {
-  return typeof value === 'string' ? value.trim() : value
-})
+const MyNumber = coerce(number(), string(), (value) => parseFloat(value))
 ```
 
 Now instead of using `assert()` or `is()` you can use `create()` to apply your custom coercion logic:
 
 ```ts
 import { create } from 'superstruct'
 
-const data = '  a wEird str1ng        '
-const output = create(data, TrimmedString)
-// "a wEird str1ng"
+const data = '3.14'
+const output = create(data, MyNumber)
+// 3.14
 ```
 
 If the input data had been invalid or unable to be coerced an error would have been thrown instead.

docs/reference/coercions.md

@@ -30,18 +30,28 @@ masked(
 
 `masked` augments an object struct to strip any unknown properties from the input when coercing it.
 
+### `trimmed`
+
+```ts
+trimmed(string())
+```
+
+`trimmed` arguments a struct to ensure that any string input values are trimmed.
+
 ### Custom Coercions
 
 You can also define your own custom coercions that are specific to your application's requirements, like so:
 
 ```ts
-import { coerce, string } from 'superstruct'
+import { coerce, number, string, create } from 'superstruct'
 
-const PositiveInteger = coerce(string(), (value) => {
-  return typeof value === 'string' ? value.trim() : value
-})
+const MyNumber = coerce(number(), string(), (value) => parseFloat(value))
+
+const a = create(42, MyNumber) // 42
+const b = create('42', MyNumber) // 42
+const c = create(false, MyNumber) // error thrown!
 ```
 
-This allows you to customize how lenient you want to be in accepting data with your structs.
+The second argument to `coerce` is a struct narrowing the types of input values you want to try coercion. In the example above, the coercion functionn will only ever be called when the input is a string—booleans would ignore coercion and fail normally.
 
-> 🤖 Note that the `value` argument passed to coercion handlers is of type `unknown`! This is because it has yet to be validated, so it could still be anything. Make sure your coercion functions guard against unknown types.
+> 🤖 If you want to run coercion for any type of input, use the `unknown()` struct to run it in all cases.

package.json

@@ -26,14 +26,14 @@
     "@types/lodash": "^4.14.144",
     "@types/mocha": "^8.0.3",
     "@types/node": "^14.0.6",
-    "@typescript-eslint/eslint-plugin": "^2.3.3",
-    "@typescript-eslint/parser": "^2.3.3",
+    "@typescript-eslint/eslint-plugin": "^4.8.2",
+    "@typescript-eslint/parser": "^4.8.2",
     "babel-eslint": "^10.0.3",
     "babel-plugin-dev-expression": "^0.2.2",
-    "eslint": "^6.5.1",
-    "eslint-config-prettier": "^6.4.0",
-    "eslint-plugin-import": "^2.18.2",
-    "eslint-plugin-prettier": "^3.1.1",
+    "eslint": "^7.14.0",
+    "eslint-config-prettier": "^6.15.0",
+    "eslint-plugin-import": "^2.22.1",
+    "eslint-plugin-prettier": "^3.1.4",
     "is-email": "^1.0.0",
     "is-url": "^1.2.4",
     "is-uuid": "^1.0.2",

src/error.ts

@@ -29,7 +29,7 @@ export class StructError extends TypeError {
   path: Array<number | string>
   branch: Array<any>
   failures: () => Array<Failure>;
-  [key: string]: any
+  [x: string]: any
 
   constructor(failure: Failure, moreFailures: IterableIterator<Failure>) {
     const {

src/structs/coercions.ts

@@ -1,5 +1,6 @@
-import { Struct, mask } from '../struct'
-import { ObjectSchema, ObjectType, isPlainObject } from '../utils'
+import { Struct, is } from '../struct'
+import { isPlainObject } from '../utils'
+import { string, unknown } from './types'
 
 /**
  * Augment a `Struct` to add an additional coercion step to its input.
@@ -12,23 +13,28 @@ import { ObjectSchema, ObjectType, isPlainObject } from '../utils'
  * take effect! Using simply `assert()` or `is()` will not use coercion.
  */
 
-export function coerce<T, S>(
+export function coerce<T, S, C>(
   struct: Struct<T, S>,
-  coercer: Struct<T, S>['coercer']
+  condition: Struct<C, any>,
+  coercer: (value: C) => any
 ): Struct<T, S> {
   const fn = struct.coercer
   return new Struct({
     ...struct,
     coercer: (value) => {
-      return fn(coercer(value))
+      if (is(value, condition)) {
+        return fn(coercer(value))
+      } else {
+        return fn(value)
+      }
     },
   })
 }
 
 /**
  * Augment a struct to replace `undefined` values with a default.
  *
- * Note: You must use `coerce(value, Struct)` on the value to have the coercion
+ * Note: You must use `create(value, Struct)` on the value to have the coercion
  * take effect! Using simply `assert()` or `is()` will not use coercion.
  */
 
@@ -40,7 +46,7 @@ export function defaulted<T, S>(
   } = {}
 ): Struct<T, S> {
   const { strict } = options
-  return coerce(S, (x) => {
+  return coerce(S, unknown(), (x) => {
     const f = typeof fallback === 'function' ? fallback() : fallback
 
     if (x === undefined) {
@@ -75,7 +81,7 @@ export function defaulted<T, S>(
  */
 
 export function masked<T, S>(struct: Struct<T, S>): Struct<T, S> {
-  return coerce(struct, (x) => {
+  return coerce(struct, unknown(), (x) => {
     if (
       typeof struct.schema !== 'object' ||
       struct.schema == null ||
@@ -96,3 +102,14 @@ export function masked<T, S>(struct: Struct<T, S>): Struct<T, S> {
     }
   })
 }
+
+/**
+ * Augment a struct to trim string inputs.
+ *
+ * Note: You must use `create(value, Struct)` on the value to have the coercion
+ * take effect! Using simply `assert()` or `is()` will not use coercion.
+ */
+
+export function trimmed<T, S>(struct: Struct<T, S>): Struct<T, S> {
+  return coerce(struct, string(), (x) => x.trim())
+}

src/utils.ts

@@ -56,15 +56,15 @@ export function* toFailures<T, S>(
  * Check if a type is a tuple.
  */
 
-export type IsTuple<T> = T extends [infer A]
+export type IsTuple<T> = T extends [any]
   ? T
-  : T extends [infer A, infer B]
+  : T extends [any, any]
   ? T
-  : T extends [infer A, infer B, infer C]
+  : T extends [any, any, any]
   ? T
-  : T extends [infer A, infer B, infer C, infer D]
+  : T extends [any, any, any, any]
   ? T
-  : T extends [infer A, infer B, infer C, infer D, infer E]
+  : T extends [any, any, any, any, any]
   ? T
   : never
 
@@ -169,19 +169,19 @@ export type StructSchema<T> = [T] extends [string]
       | Error
       | RegExp
   ? null
-  : T extends Map<infer K, infer V>
+  : T extends Map<any, any>
   ? null
-  : T extends WeakMap<infer K, infer V>
+  : T extends WeakMap<any, any>
   ? null
-  : T extends Set<infer E>
+  : T extends Set<any>
   ? null
-  : T extends WeakSet<infer E>
+  : T extends WeakSet<any>
   ? null
   : T extends Array<infer E>
   ? T extends IsTuple<T>
     ? null
     : Struct<E>
-  : T extends Promise<infer V>
+  : T extends Promise<any>
   ? null
   : T extends object
   ? T extends IsRecord<T>

test/typings/coerce.ts

@@ -1,10 +1,10 @@
-import { assert, coerce, string } from '../..'
+import { assert, coerce, string, number } from '../..'
 import { test } from '..'
 
-test<string>((x) => {
+test<number>((x) => {
   assert(
     x,
-    coerce(string(), (x) => x)
+    coerce(number(), string(), (x) => parseFloat(x))
   )
   return x
 })

test/typings/trimmed.ts

@@ -0,0 +1,7 @@
+import { assert, string, trimmed } from '../..'
+import { test } from '..'
+
+test<string>((x) => {
+  assert(x, trimmed(string()))
+  return x
+})

test/validation/coerce/changed.ts

@@ -1,6 +1,8 @@
-import { string, coerce } from '../../..'
+import { string, unknown, coerce } from '../../..'
 
-export const Struct = coerce(string(), (x) => (x == null ? 'unknown' : x))
+export const Struct = coerce(string(), unknown(), (x) =>
+  x == null ? 'unknown' : x
+)
 
 export const data = null
 

test/validation/coerce/condition-not-met.ts

@@ -0,0 +1,17 @@
+import { string, number, coerce } from '../../..'
+
+export const Struct = coerce(string(), number(), (x) => 'known')
+
+export const data = false
+
+export const failures = [
+  {
+    value: false,
+    type: 'string',
+    refinement: undefined,
+    path: [],
+    branch: [data],
+  },
+]
+
+export const create = true

test/validation/coerce/unchanged.ts

@@ -1,6 +1,8 @@
-import { string, coerce } from '../../..'
+import { string, unknown, coerce } from '../../..'
 
-export const Struct = coerce(string(), (x) => (x == null ? 'unknown' : x))
+export const Struct = coerce(string(), unknown(), (x) =>
+  x == null ? 'unknown' : x
+)
 
 export const data = 'known'
 

test/validation/trimmed/invalid.ts

@@ -0,0 +1,17 @@
+import { string, trimmed } from '../../..'
+
+export const Struct = trimmed(string())
+
+export const data = false
+
+export const failures = [
+  {
+    value: false,
+    type: 'string',
+    refinement: undefined,
+    path: [],
+    branch: [data],
+  },
+]
+
+export const create = true

test/validation/trimmed/valid.ts

@@ -0,0 +1,9 @@
+import { string, trimmed } from '../../..'
+
+export const Struct = trimmed(string())
+
+export const data = '  valid  '
+
+export const output = 'valid'
+
+export const create = true