core/crypto: Add `has_rand_bytes`

This allows runtime detection as to if `rand_bytes` is supported or not,
and lets us enable the test-case on all of the supported targets.

core/crypto/crypto.odin

@@ -1,3 +1,7 @@
+/*
+package crypto implements a selection of cryptography algorithms and useful
+helper routines.
+*/
 package crypto
 
 import "core:mem"
@@ -51,3 +55,9 @@ rand_bytes :: proc (dst: []byte) {
 
 	_rand_bytes(dst)
 }
+
+// has_rand_bytes returns true iff the target has support for accessing the
+// system entropty source.
+has_rand_bytes :: proc () -> bool {
+	return _has_rand_bytes()
+}

core/crypto/rand_bsd.odin

@@ -10,3 +10,7 @@ foreign libc {
 _rand_bytes :: proc(dst: []byte) {
 	arc4random_buf(raw_data(dst), len(dst))
 }
+
+_has_rand_bytes :: proc () -> bool {
+	return true
+}

core/crypto/rand_darwin.odin

@@ -10,3 +10,7 @@ _rand_bytes :: proc(dst: []byte) {
 		panic(fmt.tprintf("crypto/rand_bytes: SecRandomCopyBytes returned non-zero result: %v %s", res, msg))
 	}
 }
+
+_has_rand_bytes :: proc () -> bool {
+	return true
+}

core/crypto/rand_generic.odin

@@ -9,3 +9,7 @@ package crypto
 _rand_bytes :: proc(dst: []byte) {
 	unimplemented("crypto: rand_bytes not supported on this OS")
 }
+
+_has_rand_bytes :: proc () -> bool {
+	return false
+}

core/crypto/rand_js.odin

@@ -18,3 +18,7 @@ _rand_bytes :: proc(dst: []byte) {
 		dst = dst[to_read:]
 	}
 }
+
+_has_rand_bytes :: proc () -> bool {
+	return true
+}

core/crypto/rand_linux.odin

@@ -34,3 +34,7 @@ _rand_bytes :: proc (dst: []byte) {
 		dst = dst[n_read:]
 	}
 }
+
+_has_rand_bytes :: proc () -> bool {
+	return true
+}

core/crypto/rand_windows.odin

@@ -21,3 +21,7 @@ _rand_bytes :: proc(dst: []byte) {
 		}
 	}
 }
+
+_has_rand_bytes :: proc () -> bool {
+	return true
+}

tests/core/crypto/test_core_crypto.odin

@@ -347,7 +347,7 @@ test_x25519 :: proc(t: ^testing.T) {
 test_rand_bytes :: proc(t: ^testing.T) {
 	tc.log(t, "Testing rand_bytes")
 
-	if ODIN_OS != .Linux {
+	if !crypto.has_rand_bytes() {
 		tc.log(t, "rand_bytes not supported - skipping")
 		return
 	}