resolve warning messages (#495)

Cargo.lock

@@ -62,6 +62,12 @@ dependencies = [
  "constant_time_eq",
 ]
 
+[[package]]
+name = "bumpalo"
+version = "3.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "12ae9db68ad7fac5fe51304d20f016c911539251075a214f8e663babefa35187"
+
 [[package]]
 name = "cc"
 version = "1.0.52"
@@ -257,6 +263,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "js-sys"
+version = "0.3.39"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa5a448de267e7358beaf4a5d849518fe9a0c13fce7afd44b06e68550e5562a7"
+dependencies = [
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "kernel32-sys"
 version = "0.2.2"
@@ -477,6 +492,12 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "once_cell"
+version = "1.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1c601810575c99596d4afc46f78a678c80105117c379eb3650cf99b8a21ce5b"
+
 [[package]]
 name = "ordered-float"
 version = "0.5.2"
@@ -571,6 +592,21 @@ version = "0.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d813022b2e00774a48eaf43caaa3c20b45f040ba8cbf398e2e8911a06668dbe6"
 
+[[package]]
+name = "ring"
+version = "0.16.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "703516ae74571f24b465b4a1431e81e2ad51336cb0ded733a55a1aa3eccac196"
+dependencies = [
+ "cc",
+ "libc",
+ "once_cell",
+ "spin",
+ "untrusted",
+ "web-sys",
+ "winapi 0.3.8",
+]
+
 [[package]]
 name = "rug"
 version = "1.8.0"
@@ -653,6 +689,7 @@ dependencies = [
  "ordered-float",
  "prolog_parser",
  "ref_thread_local",
+ "ring",
  "rug",
  "rustyline",
  "unicode_reader",
@@ -715,6 +752,12 @@ version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c7cb5678e1615754284ec264d9bb5b4c27d2018577fd90ac0ceb578591ed5ee4"
 
+[[package]]
+name = "spin"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
+
 [[package]]
 name = "static_assertions"
 version = "0.3.4"
@@ -769,6 +812,12 @@ dependencies = [
  "void",
 ]
 
+[[package]]
+name = "untrusted"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a156c684c91ea7d62626509bce3cb4e1d9ed5c4d978f7b4352658f96a4c26b4a"
+
 [[package]]
 name = "utf8parse"
 version = "0.2.0"
@@ -787,6 +836,70 @@ version = "0.9.0+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
 
+[[package]]
+name = "wasm-bindgen"
+version = "0.2.62"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3c7d40d09cdbf0f4895ae58cf57d92e1e57a9dd8ed2e8390514b54a47cc5551"
+dependencies = [
+ "cfg-if",
+ "wasm-bindgen-macro",
+]
+
+[[package]]
+name = "wasm-bindgen-backend"
+version = "0.2.62"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3972e137ebf830900db522d6c8fd74d1900dcfc733462e9a12e942b00b4ac94"
+dependencies = [
+ "bumpalo",
+ "lazy_static",
+ "log",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.2.62"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2cd85aa2c579e8892442954685f0d801f9129de24fa2136b2c6a539c76b65776"
+dependencies = [
+ "quote",
+ "wasm-bindgen-macro-support",
+]
+
+[[package]]
+name = "wasm-bindgen-macro-support"
+version = "0.2.62"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8eb197bd3a47553334907ffd2f16507b4f4f01bbec3ac921a7719e0decdfe72a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-backend",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
+version = "0.2.62"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a91c2916119c17a8e316507afaaa2dd94b47646048014bbdf6bef098c1bb58ad"
+
+[[package]]
+name = "web-sys"
+version = "0.3.39"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8bc359e5dd3b46cb9687a051d50a2fdd228e4ba7cf6fcf861a5365c3d671a642"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "winapi"
 version = "0.2.8"

src/prolog/machine/system_calls.rs

@@ -5183,10 +5183,24 @@ impl MachineState {
             }
             &SystemClauseType::CryptoRandomByte => {
                 let arg = self[temp_v!(1)];
-                let mut bytes: Vec<u8> = vec![0];
-                rng().fill(&mut bytes);
+                let mut bytes: [u8; 1] = [0];
+
+                match rng().fill(&mut bytes) {
+                    Ok(()) => {
+                    }
+                    Err(_) => {
+                        // the error payload here is of type 'Unspecified',
+                        // which contains no information whatsoever. So, for now,
+                        // just fail.
+                        self.fail = true;
+                        return Ok(());
+                    }
+                }
+
+                let byte = self.heap.to_unifiable(
+                    HeapCellValue::Integer(Rc::new(Integer::from(bytes[0])))
+                );
 
-                let byte = self.heap.put_constant(Constant::Integer(Rc::new(Integer::from(bytes[0]))));
                 self.unify(arg, byte);
             }
         };
@@ -5196,7 +5210,7 @@ impl MachineState {
 }
 
 
-fn rng() -> &'static SecureRandom {
+fn rng() -> &'static dyn SecureRandom {
     use std::ops::Deref;
 
     lazy_static! {