Don't mutate a schema with a transform keyword while compiling it.

spec/transform.spec.ts

@@ -129,4 +129,15 @@ describe('keyword "transform"', () => {
       data.should.deep.equal(["ab"])
     })
   })
+
+  ajvs.forEach((ajv, i) => {
+    it(`shouldn't mutate the transform array of the schema while compiling it #${i}`, () => {
+      const data = {p: "  trimObject  "}
+      const schema = {type: "object", properties: {p: {type: "string", transform: ["trimLeft"]}}}
+      ajv.validate(schema, data).should.equal(true)
+      data.should.deep.equal({p: "trimObject  "})
+
+      schema.properties.p.transform.should.deep.equal(["trimLeft"])
+    })
+  })
 })

src/definitions/transform.ts

@@ -54,13 +54,15 @@ function _getDef(): CodeKeywordDefinition {
 
       function transformExpr(ts: string[]): Code {
         if (!ts.length) return data
-        const t = ts.pop() as string
+        const t = ts[ts.length - 1]
+        const remaining = ts.slice(0, -1)
+
         if (!(t in transform)) throw new Error(`transform: unknown transformation ${t}`)
         const func = gen.scopeValue("func", {
           ref: transform[t as TransformName],
           code: _`require("ajv-keywords/dist/definitions/transform").transform${getProperty(t)}`,
         })
-        const arg = transformExpr(ts)
+        const arg = transformExpr(remaining)
         return cfg && t === "toEnumCase" ? _`${func}(${arg}, ${cfg})` : _`${func}(${arg})`
       }
     },