Runtime logging. (#3821)

* Implement Printable for tuples.

* Add debugging function.

* Add debug 1.

* Implement  for everything.

* RuntimeDebug derive.

* Introduce RuntimeDebug.

* Add some dummy logging.

* Replace RuntimeDebug with Debug.

* Revert "Replace RuntimeDebug with Debug."

This reverts commit bc47070a8cb30241b2b590b2fa29fd195088162f.

* Working on Debug for all.

* Fix bounds.

* Add debug utils.

* Implement runtime logging.

* Add some docs and clean up.

* Clean up derives.

* Fix custom derive impl.

* Bump runtime.

* Fix long lines.

* Fix doc test.

* Use CARGO_CFG_STD.

* Revert "Use CARGO_CFG_STD."

This reverts commit ea429566de18ed0fa052571b359eb9826a64a9f4.

* Use parse_macro_input

* Update lockfile.

* Apply review suggestions.

* Remove stray re-export.

* Add no-std impl.

* Update lockfile.

substrate/core/sr-io/Cargo.toml

@@ -9,15 +9,16 @@ edition = "2018"
 rustc_version = "0.2.3"
 
 [dependencies]
-rstd = { package = "sr-std", path = "../sr-std", default-features = false }
-primitives = { package = "substrate-primitives", path = "../primitives", default-features = false }
 codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false }
 hash-db = { version = "0.15.2", default-features = false }
+primitives = { package = "substrate-primitives", path = "../primitives", default-features = false }
+rstd = { package = "sr-std", path = "../sr-std", default-features = false }
 libsecp256k1 = { version = "0.3.0", optional = true }
 tiny-keccak = { version = "1.5.0", optional = true }
 substrate-state-machine = { path = "../state-machine", optional = true }
 trie = { package = "substrate-trie", path = "../trie", optional = true }
 externalities = { package = "substrate-externalities", path = "../externalities", optional = true }
+log = { version = "0.4.8", optional = true }
 
 [features]
 default = ["std"]
@@ -31,6 +32,7 @@ std = [
 	"libsecp256k1",
 	"tiny-keccak",
 	"externalities",
+	"log",
 ]
 nightly = []
 strict = []

substrate/core/sr-io/src/lib.rs

@@ -33,6 +33,7 @@ use primitives::{
 	offchain::{
 		Timestamp, HttpRequestId, HttpRequestStatus, HttpError, StorageKind, OpaqueNetworkState,
 	},
+	LogLevel,
 };
 
 /// Error verifying ECDSA signature
@@ -158,6 +159,20 @@ export_api! {
 		fn print_utf8(utf8: &[u8]);
 		/// Print any `u8` slice as hex.
 		fn print_hex(data: &[u8]);
+
+		/// Request to print a log message (stderr) on the host.
+		///
+		/// Note that this will be only displayed if the host
+		/// is enabed to display log messages with given
+		/// level and target.
+		///
+		/// Instead of using directly, prefer setting up `RuntimeLogger`
+		/// and using `log` macros.
+		fn log(
+			level: LogLevel,
+			target: &[u8],
+			message: &[u8]
+		);
 	}
 }
 

substrate/core/sr-io/with_std.rs

@@ -192,6 +192,22 @@ impl OtherApi for () {
 	fn print_hex(data: &[u8]) {
 		println!("{}", HexDisplay::from(&data));
 	}
+
+	fn log(
+		level: LogLevel,
+		target: &[u8],
+		message: &[u8],
+	) {
+		let target = std::str::from_utf8(target).unwrap_or("invalid utf8");
+		let msg = std::str::from_utf8(message).unwrap_or("invalid utf8");
+
+		log::log!(
+			target: target,
+			log::Level::from(level),
+			"{}",
+			msg,
+		)
+	}
 }
 
 impl CryptoApi for () {

substrate/core/sr-io/without_std.rs

@@ -160,6 +160,14 @@ pub mod ext {
 		fn ext_print_hex(data: *const u8, len: u32);
 		/// Print a number
 		fn ext_print_num(value: u64);
+		/// Print a log line if logging for given level and target is enabled.
+		fn ext_log(
+			level: u32,
+			target_data: *const u8,
+			target_len: u32,
+			message_data: *const u8,
+			message_len: u32,
+		);
 
 		/// Set value for key in storage.
 		fn ext_set_storage(key_data: *const u8, key_len: u32, value_data: *const u8, value_len: u32);
@@ -780,6 +788,22 @@ impl OtherApi for () {
 			ext_print_hex.get()(data.as_ptr(), data.len() as u32);
 		}
 	}
+
+	fn log(
+		level: LogLevel,
+		target: &[u8],
+		message: &[u8]
+	) {
+		unsafe {
+			ext_log.get()(
+				level as u32,
+				target.as_ptr(),
+				target.len() as u32,
+				message.as_ptr(),
+				message.len() as u32,
+			)
+		}
+	}
 }
 
 impl HashingApi for () {