How do I get core.typed to pass the following SHA256 code?

Question

I thought I would try out core.typed in the hope of removing the :pre conditions in the following code.

(ns quizry.sha256
  (:require
   [clojure.core.typed :as ct])
  (:import
   [java.security MessageDigest]))

(defn utf8-array
  "input as an array of UTF-8 bytes"
  [input]
  {:pre [(string? input)]}
  (.getBytes input "UTF-8"))

(defn sha256-digest
  "sha-256 array digest of input"
  [input]
  {:pre [(string? input)]}
  (let [hasher (MessageDigest/getInstance "SHA-256")]
    (->> input utf8-array (.update hasher))
    (.digest hasher)))

(ct/ann sha256 [String -> String])

(defn sha256
  "generates the sha256 string hash of input"
  [input]
  {:pre [(string? input)]}
  (let [digest (-> input sha256-digest seq)]
    (apply str (map #(format "%02x" (bit-and % 0xff)) digest))))

If I run (clojure.core.typed/check-ns), I get the following:

Start collecting quizry.sha256
Finished collecting quizry.sha256
Collected 1 namespaces in 621.542571 msecs
Not checking clojure.core.typed (tagged :collect-only in ns metadata)
Start checking quizry.sha256
Checked quizry.sha256 in 1337.109049 msecs
Checked 2 namespaces (approx. 2326 lines) in 1990.843467 msecs
Type Error (quizry/sha256.clj:11:3) Unresolved instance method invocation 

Add type hints to resolve the host call.

Suggested methods:

 java.lang.String
 \
  public byte[] getBytes()
  public void getBytes(int, int, byte[], int)
  public byte[] getBytes(java.nio.charset.Charset)
  public byte[] getBytes(java.lang.String).

Hint: use *warn-on-reflection* to identify reflective calls
in: (.getBytes input UTF-8)


Type Error (quizry/sha256.clj:18:5) Unresolved instance method invocation .

Hint: use *warn-on-reflection* to identify reflective calls
in: (.update hasher (utf8-array input))


Type Error (quizry/sha256.clj:19:5) Cannot call instance method java.security.MessageDigest/digest on type (clojure.core.typed/U java.security.MessageDigest nil)
in: (.digest hasher)


Type Error (quizry/sha256.clj:28:22) Static method clojure.lang.Numbers/and could not be applied to arguments:


Domains:
    ct/AnyInteger ct/AnyInteger

Arguments:
    ct/Any (ct/Value 255)

Ranges:
    java.lang.Long

in: (clojure.lang.Numbers/and p1__36892# 255)
in: (format %02x (clojure.lang.Numbers/and p1__36892# 255))
uizry/sha256.clj:28:2

ExceptionInfo Type Checker: Found 4 errors  clojure.core/ex-info (core.clj:4403)

I am new to core.typed, and don't really understand the errors. I'm looking to get core.type to pass the following namespace. I would appreciate it even more if you also explained what these errors mean, and what I should be thinking when I see them. Thank you.

Answer 1

Unresolved reflection are type errors in core.typed.

This is how core.typed tells you it's found reflection, and its best guesses as to which methods you mean to invoke.

Suggested methods:

 java.lang.String
 \
  public byte[] getBytes()
  public void getBytes(int, int, byte[], int)
  public byte[] getBytes(java.nio.charset.Charset)
  public byte[] getBytes(java.lang.String).

Hint: use *warn-on-reflection* to identify reflective calls
in: (.getBytes input UTF-8)

So there are 4 possible methods on java.lang.String that core.typed has identified for the (.getBytes input UTF-8) call. You obviously want the one with String parameter, so add type hints as usual to resolve the method.

(defn utf8-array
  "input as an array of UTF-8 bytes"
  [^String input]
  {:pre [(string? input)]}
  (.getBytes input "UTF-8"))