Add ExtCurrentBlockNumber in SRML::Contract (#3047)

* add block number

* add ext_current_block

* add ext_current_block test

* Update srml/contracts/src/wasm/mod.rs

Co-Authored-By: Sergei Pepyakin <s.pepyakin@gmail.com>

* Update srml/contracts/src/wasm/mod.rs

Co-Authored-By: Sergei Pepyakin <s.pepyakin@gmail.com>

* change valid comment

* use BlockNumberOf<T>

* Update srml/contracts/src/exec.rs

Co-Authored-By: André Silva <andre.beat@gmail.com>

* return types copy, not reference

* version up spec_version and impl_version

* change method name current_block -> block_number

* Update srml/contracts/src/exec.rs

Co-Authored-By: Sergei Pepyakin <s.pepyakin@gmail.com>

substrate/srml/contracts/src/wasm/mod.rs

@@ -291,6 +291,8 @@ mod tests {
 		fn rent_allowance(&self) -> u64 {
 			self.rent_allowance
 		}
+
+		fn block_number(&self) -> u64 { 121 }
 	}
 
 	fn execute<E: Ext>(
@@ -1342,4 +1344,70 @@ mod tests {
 			Err("during execution"),
 		);
 	}
+
+	/// calls `ext_block_number`, loads the current block number from the scratch buffer and
+	/// compares it with the constant 121.
+	const CODE_BLOCK_NUMBER: &str = r#"
+(module
+	(import "env" "ext_block_number" (func $ext_block_number))
+	(import "env" "ext_scratch_size" (func $ext_scratch_size (result i32)))
+	(import "env" "ext_scratch_copy" (func $ext_scratch_copy (param i32 i32 i32)))
+	(import "env" "memory" (memory 1 1))
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok
+				(get_local 0)
+			)
+			(unreachable)
+		)
+	)
+
+	(func (export "call")
+		;; This stores the block height in the scratch buffer
+		(call $ext_block_number)
+
+		;; assert $ext_scratch_size == 8
+		(call $assert
+			(i32.eq
+				(call $ext_scratch_size)
+				(i32.const 8)
+			)
+		)
+
+		;; copy contents of the scratch buffer into the contract's memory.
+		(call $ext_scratch_copy
+			(i32.const 8)		;; Pointer in memory to the place where to copy.
+			(i32.const 0)		;; Offset from the start of the scratch buffer.
+			(i32.const 8)		;; Count of bytes to copy.
+		)
+
+		;; assert that contents of the buffer is equal to the i64 value of 121.
+		(call $assert
+			(i64.eq
+				(i64.load
+					(i32.const 8)
+				)
+				(i64.const 121)
+			)
+		)
+	)
+
+	(func (export "deploy"))
+)
+"#;
+
+	#[test]
+	fn block_number() {
+		let mut mock_ext = MockExt::default();
+		execute(
+			CODE_BLOCK_NUMBER,
+			&[],
+			&mut Vec::new(),
+			&mut mock_ext,
+			&mut GasMeter::with_limit(50_000, 1),
+		)
+		.unwrap();
+	}
+
 }

substrate/srml/contracts/src/wasm/runtime.rs

@@ -701,6 +701,13 @@ define_env!(Env, <E: Ext>,
 		}
 		Ok(())
 	},
+
+	// Stores the current block number of the current contract into the scratch buffer.
+	ext_block_number(ctx) => {
+		ctx.scratch_buf.clear();
+		ctx.ext.block_number().encode_to(&mut ctx.scratch_buf);
+		Ok(())
+	},
 );
 
 /// Finds duplicates in a given vector.