refactor: remove failure and f64 for no_std

src/error.rs

@@ -1,12 +1,26 @@
-pub use failure::Fail;
 pub type Result<T> = core::result::Result<T, Error>;
 
-#[derive(Fail, Debug, PartialEq, Eq, Clone)]
+#[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Error {
-    #[fail(display = "Get root on an empty MMR")]
     GetRootOnEmpty,
-    #[fail(display = "Inconsistent store")]
     InconsistentStore,
-    #[fail(display = "Store error {}", _0)]
     StoreError(crate::string::String),
 }
+
+impl core::fmt::Display for Error {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        use Error::*;
+        match self {
+            GetRootOnEmpty => write!(f, "Get root on an empty MMR")?,
+            InconsistentStore => write!(f, "Inconsistent store")?,
+            StoreError(msg) => write!(f, "Store error {}", msg)?,
+        }
+        Ok(())
+    }
+}
+
+cfg_if::cfg_if! {
+    if #[cfg(feature = "std")] {
+        impl ::std::error::Error for Error {}
+    }
+}