fix: format Symbol paths in validation errors

src/error.ts

@@ -37,7 +37,9 @@ export class StructError extends TypeError {
     const { message, explanation, ...rest } = failure
     const { path } = failure
     const msg =
-      path.length === 0 ? message : `At path: ${path.join('.')} -- ${message}`
+      path.length === 0
+        ? message
+        : `At path: ${path.map((key) => (typeof key === 'symbol' ? key.toString() : key)).join('.')} -- ${message}`
     super(explanation ?? msg)
     if (explanation != null) this.cause = msg
     Object.assign(this, rest)

test/api/symbol-path.test.ts

@@ -0,0 +1,97 @@
+import { describe, expect, it } from 'vitest'
+import {
+  any,
+  array,
+  assert,
+  is,
+  map,
+  number,
+  object,
+  string,
+  StructError,
+  validate,
+} from '../../src'
+
+describe('symbol paths', () => {
+  it('returns an error for an invalid value at a symbol map key', () => {
+    const key = Symbol('key')
+    const data = new Map([[key, 42]])
+    const [error, value] = validate(data, map(any(), string()))
+    expect(value).toBeUndefined()
+    expect(error).toBeInstanceOf(StructError)
+    expect(error?.message).toBe(
+      'At path: Symbol(key) -- Expected a string, but received: 42'
+    )
+    expect(error?.path).toStrictEqual([key])
+    expect(error?.key).toBe(key)
+  })
+
+  it('returns an error for an invalid symbol map key', () => {
+    const key = Symbol('key')
+    const [error] = validate(new Map([[key, 42]]), map(string(), number()))
+    expect(error).toBeInstanceOf(StructError)
+    expect(error?.message).toBe(
+      'At path: Symbol(key) -- Expected a string, but received: Symbol(key)'
+    )
+    expect(error?.path).toStrictEqual([key])
+  })
+
+  it('formats symbols in nested paths without changing the path', () => {
+    const key = Symbol()
+    const data = { records: [new Map([[key, 42]])] }
+    const [error] = validate(
+      data,
+      object({ records: array(map(any(), string())) })
+    )
+    expect(error?.message).toBe(
+      'At path: records.0.Symbol() -- Expected a string, but received: 42'
+    )
+    expect(error?.path).toStrictEqual(['records', 0, key])
+  })
+
+  it('returns false from is instead of throwing for a symbol path', () => {
+    expect(is(new Map([[Symbol('key'), 42]]), map(any(), string()))).toBe(false)
+  })
+
+  it('throws a StructError from assert for a symbol path', () => {
+    expect(() =>
+      assert(new Map([[Symbol('key'), 42]]), map(any(), string()))
+    ).toThrow(StructError)
+  })
+
+  it('preserves custom error messages and the symbol path in the cause', () => {
+    const [error] = validate(
+      new Map([[Symbol('key'), 42]]),
+      map(any(), string()),
+      { message: 'Invalid map' }
+    )
+    expect(error?.message).toBe('Invalid map')
+    expect(error?.cause).toBe(
+      'At path: Symbol(key) -- Expected a string, but received: 42'
+    )
+  })
+
+  it('retains symbol identity in all failures', () => {
+    const first = Symbol('key')
+    const second = Symbol('key')
+    const [error] = validate(
+      new Map([
+        [first, 1],
+        [second, 2],
+      ]),
+      map(any(), string())
+    )
+    expect(error?.failures().map((failure) => failure.path)).toStrictEqual([
+      [first],
+      [second],
+    ])
+  })
+
+  it('continues accepting valid symbol-keyed maps', () => {
+    const data = new Map([[Symbol('key'), 'value']])
+    expect(validate(data, map(any(), string()))).toStrictEqual([
+      undefined,
+      data,
+    ])
+  })
+})