Remove As (#2602)

* Start to remove the `As` bound on `SimpleArtithmetic`

This just introduces standard numeric bounds, assuming a minimum of
`u32`. Also included is a saturating from/into trait allowing ergonomic
infallible conversion when you don't care if it saturates.

* Remove As from Balances trait

* Remove As from Aura module

* Remove As from Babe module

* Expunge `As` from contract

* Council module

* Democracy

* Finality tracker

* Grandpa

* First bit of indices

* indices

* Line lengths

* session

* system

* Staking

* Square up all other uses of As.

* RHD update

* Fix build/test

* Remove As trait

* line widths

* Remove final As ref

* Update srml/staking/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/client/src/cht.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/client/db/src/light.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* whitespace

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>
Co-Authored-By: André Silva <andre.beat@gmail.com>

* Bring back u32 check for number on CLI

substrate/core/client/db/src/utils.rs

@@ -19,6 +19,7 @@
 
 use std::sync::Arc;
 use std::io;
+use std::convert::TryInto;
 
 use kvdb::{KeyValueDB, DBTransaction};
 use kvdb_rocksdb::{Database, DatabaseConfig};
@@ -28,7 +29,10 @@ use client;
 use parity_codec::Decode;
 use trie::DBValue;
 use runtime_primitives::generic::BlockId;
-use runtime_primitives::traits::{As, Block as BlockT, Header as HeaderT, Zero};
+use runtime_primitives::traits::{
+	Block as BlockT, Header as HeaderT, Zero, UniqueSaturatedFrom,
+	UniqueSaturatedInto, SaturatedConversion, CheckedConversion
+};
 use crate::DatabaseSettings;
 
 /// Number of columns in the db. Must be the same for both full && light dbs.
@@ -78,10 +82,8 @@ pub type NumberIndexKey = [u8; 4];
 ///
 /// In the current database schema, this kind of key is only used for
 /// lookups into an index, NOT for storing header data or others.
-pub fn number_index_key<N>(n: N) -> NumberIndexKey where N: As<u64> {
-	let n: u64 = n.as_();
-	assert!(n & 0xffffffff00000000 == 0);
-
+pub fn number_index_key<N: TryInto<u32>>(n: N) -> NumberIndexKey {
+	let n = n.checked_into::<u32>().unwrap();
 	[
 		(n >> 24) as u8,
 		((n >> 16) & 0xff) as u8,
@@ -93,7 +95,7 @@ pub fn number_index_key<N>(n: N) -> NumberIndexKey where N: As<u64> {
 /// Convert number and hash into long lookup key for blocks that are
 /// not in the canonical chain.
 pub fn number_and_hash_to_lookup_key<N, H>(number: N, hash: H) -> Vec<u8> where
-	N: As<u64>,
+	N: TryInto<u32>,
 	H: AsRef<[u8]>
 {
 	let mut lookup_key = number_index_key(number).to_vec();
@@ -103,18 +105,20 @@ pub fn number_and_hash_to_lookup_key<N, H>(number: N, hash: H) -> Vec<u8> where
 
 /// Convert block lookup key into block number.
 /// all block lookup keys start with the block number.
-pub fn lookup_key_to_number<N>(key: &[u8]) -> client::error::Result<N> where N: As<u64> {
+pub fn lookup_key_to_number<N>(key: &[u8]) -> client::error::Result<N> where
+	N: From<u32>
+{
 	if key.len() < 4 {
 		return Err(client::error::Error::Backend("Invalid block key".into()));
 	}
-	Ok((key[0] as u64) << 24
-		| (key[1] as u64) << 16
-		| (key[2] as u64) << 8
-		| (key[3] as u64)).map(As::sa)
+	Ok((key[0] as u32) << 24
+		| (key[1] as u32) << 16
+		| (key[2] as u32) << 8
+		| (key[3] as u32)).map(Into::into)
 }
 
 /// Delete number to hash mapping in DB transaction.
-pub fn remove_number_to_key_mapping<N: As<u64>>(
+pub fn remove_number_to_key_mapping<N: TryInto<u32>>(
 	transaction: &mut DBTransaction,
 	key_lookup_col: Option<u32>,
 	number: N,
@@ -123,7 +127,7 @@ pub fn remove_number_to_key_mapping<N: As<u64>>(
 }
 
 /// Remove key mappings.
-pub fn remove_key_mappings<N: As<u64>, H: AsRef<[u8]>>(
+pub fn remove_key_mappings<N: TryInto<u32>, H: AsRef<[u8]>>(
 	transaction: &mut DBTransaction,
 	key_lookup_col: Option<u32>,
 	number: N,
@@ -135,7 +139,7 @@ pub fn remove_key_mappings<N: As<u64>, H: AsRef<[u8]>>(
 
 /// Place a number mapping into the database. This maps number to current perceived
 /// block hash at that position.
-pub fn insert_number_to_key_mapping<N: As<u64> + Clone, H: AsRef<[u8]>>(
+pub fn insert_number_to_key_mapping<N: TryInto<u32> + Clone, H: AsRef<[u8]>>(
 	transaction: &mut DBTransaction,
 	key_lookup_col: Option<u32>,
 	number: N,
@@ -149,7 +153,7 @@ pub fn insert_number_to_key_mapping<N: As<u64> + Clone, H: AsRef<[u8]>>(
 }
 
 /// Insert a hash to key mapping in the database.
-pub fn insert_hash_to_key_mapping<N: As<u64>, H: AsRef<[u8]> + Clone>(
+pub fn insert_hash_to_key_mapping<N: TryInto<u32>, H: AsRef<[u8]> + Clone>(
 	transaction: &mut DBTransaction,
 	key_lookup_col: Option<u32>,
 	number: N,
@@ -171,7 +175,7 @@ pub fn block_id_to_lookup_key<Block>(
 	id: BlockId<Block>
 ) -> Result<Option<Vec<u8>>, client::error::Error> where
 	Block: BlockT,
-	::runtime_primitives::traits::NumberFor<Block>: As<u64>,
+	::runtime_primitives::traits::NumberFor<Block>: UniqueSaturatedFrom<u64> + UniqueSaturatedInto<u64>,
 {
 	let res = match id {
 		BlockId::Number(n) => db.get(