fix minContains: 0, closes #1819 (#1820)

Author: epoberezkin

lib/vocabularies/applicator/contains.ts

@@ -63,13 +63,12 @@ const def: CodeKeywordDefinition = {
     const valid = gen.name("valid")
     if (max === undefined && min === 1) {
       validateItems(valid, () => gen.if(valid, () => gen.break()))
+    } else if (min === 0) {
+      gen.let(valid, true)
+      if (max !== undefined) gen.if(_`${data}.length > 0`, validateItemsWithCount)
     } else {
       gen.let(valid, false)
-      if (min === 0) {
-        gen.if(_`${data}.length > 0`, validateItemsWithCount, () => gen.assign(valid, true))
-      } else {
-        validateItemsWithCount()
-      }
+      validateItemsWithCount()
     }
     cxt.result(valid, () => cxt.reset())
 

spec/issues/1819_mincontains.spec.ts

@@ -0,0 +1,19 @@
+import _Ajv from "../ajv2020"
+import * as assert from "assert"
+
+describe("`minContains: 0` without valid items (issue #1819)", () => {
+  const ajv = new _Ajv()
+
+  const schema = {
+    type: "array",
+    minContains: 0,
+    maxContains: 1,
+    contains: {type: "number"},
+  }
+
+  const validate = ajv.compile(schema)
+
+  it("no items valid", () => assert.strictEqual(validate(["foo"]), true))
+  it("1 item valid", () => assert.strictEqual(validate(["foo", 1]), true))
+  it("2 items invalid", () => assert.strictEqual(validate(["foo", 1, 2]), false))
+})