Add static analyzer to discourage use of panic() (#15075)

* Implement static analysis to prevent panics

* Add nopanic to nogo

* Fix violations and add exclusions

Fix violations and add exclusions for all

* Changelog fragment

* Use pass.Report instead of pass.Reportf

* Remove strings.ToLower for checking init method name

* Add exclusion for herumi init

* Move api/client/beacon template function to init and its own file

* Fix nopanic testcase

crypto/bls/herumi/init.go

@@ -3,6 +3,7 @@ package herumi
 import "github.com/herumi/bls-eth-go-binary/bls"
 
 // Init allows the required curve orders and appropriate sub-groups to be initialized.
+// lint:nopanic -- This method is called at init time only.
 func Init() {
 	if err := bls.Init(bls.BLS12_381); err != nil {
 		panic(err)

crypto/hash/htr/hashtree.go

@@ -13,7 +13,7 @@ func hashParallel(inputList [][32]byte, outputList [][32]byte, wg *sync.WaitGrou
 	defer wg.Done()
 	err := gohashtree.Hash(outputList, inputList)
 	if err != nil {
-		panic(err)
+		panic(err) // lint:nopanic -- This should never panic.
 	}
 }
 
@@ -27,7 +27,7 @@ func VectorizedSha256(inputList [][32]byte) [][32]byte {
 	if len(inputList) < minSliceSizeToParallelize {
 		err := gohashtree.Hash(outputList, inputList)
 		if err != nil {
-			panic(err)
+			panic(err) // lint:nopanic -- This should never panic.
 		}
 		return outputList
 	}
@@ -40,7 +40,7 @@ func VectorizedSha256(inputList [][32]byte) [][32]byte {
 	}
 	err := gohashtree.Hash(outputList[n*groupSize:], inputList[n*2*groupSize:])
 	if err != nil {
-		panic(err)
+		panic(err) // lint:nopanic -- This should never panic.
 	}
 	wg.Wait()
 	return outputList

crypto/keystore/keystore.go

@@ -130,7 +130,7 @@ func EncryptKey(key *Key, password string, scryptN, scryptP int) ([]byte, error)
 	authArray := []byte(password)
 	salt := make([]byte, 32)
 	if _, err := io.ReadFull(rand.Reader, salt); err != nil {
-		panic("reading from crypto/rand failed: " + err.Error())
+		panic("reading from crypto/rand failed: " + err.Error()) // lint:nopanic -- This should never happen.
 	}
 
 	derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptR, scryptP, scryptDKLen)

crypto/rand/rand.go

@@ -57,7 +57,7 @@ func (_ *source) Uint64() (val uint64) {
 	lock.RLock()
 	defer lock.RUnlock()
 	if err := binary.Read(rand.Reader, binary.BigEndian, &val); err != nil {
-		panic(err)
+		panic(err) // lint:nopanic -- Panic risk is communicated in the godoc commentary.
 	}
 	return
 }