chore/error: remove from str conversion and add deprecation notificat… (#7472)

* chore/error: remove from str conversion and add deprecation notifications

* fixup changes

* fix test looking for gone ::Msg variant

* another test fix

* one is duplicate, the other is not, so duplicates reported are n-1

* darn spaces

Co-authored-by: Andronik Ordian <write@reusable.software>

* remove pointless doc comments of error variants without any value

* low hanging fruits (for a tall person)

* moar error type variants

* avoid the storage modules for now

They are in need of a refactor, and the pain is rather large
removing all String error and DefaultError occurences.

* chore remove pointless error generic

* fix test for mocks, add a bunch of non_exhaustive

* max line width

* test fixes due to error changes

* fin

* error outputs... again

* undo stderr adjustments

* Update client/consensus/slots/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* remove closure clutter

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* more error types

* introduce ApiError

* extract Mock error

* ApiError refactor

* even more error types

* the last for now

* chore unused deps

* another extraction

* reduce should panic, due to extended error messages

* error test happiness

* shift error lines by one

* doc tests

* white space

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Into -> From

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* remove pointless codec

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* avoid pointless self import

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Bernhard Schuster <bernhard@parity.io>
Co-authored-by: Andronik Ordian <write@reusable.software>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/primitives/api/src/lib.rs

@@ -74,6 +74,7 @@ use sp_core::OpaqueMetadata;
 #[cfg(feature = "std")]
 use std::{panic::UnwindSafe, cell::RefCell};
 
+
 /// Maximum nesting level for extrinsics.
 pub const MAX_EXTRINSIC_DEPTH: u32 = 256;
 
@@ -288,7 +289,7 @@ pub use sp_api_proc_macro::impl_runtime_apis;
 ///         /// Sets the error type that is being used by the mock implementation.
 ///         /// The error type is used by all runtime apis. It is only required to
 ///         /// be specified in one trait implementation.
-///         type Error = String;
+///         type Error = sp_api::ApiError;
 ///
 ///         fn build_block() -> Block {
 ///              unimplemented!("Not Required in tests")
@@ -315,6 +316,7 @@ pub use sp_api_proc_macro::impl_runtime_apis;
 /// # use sp_runtime::{traits::Block as BlockT, generic::BlockId};
 /// # use sp_test_primitives::Block;
 /// # use sp_core::NativeOrEncoded;
+/// # use codec;
 /// #
 /// # sp_api::decl_runtime_apis! {
 /// #     /// Declare the api trait.
@@ -331,15 +333,15 @@ pub use sp_api_proc_macro::impl_runtime_apis;
 ///
 /// sp_api::mock_impl_runtime_apis! {
 ///     impl Balance<Block> for MockApi {
-///         type Error = String;
+///         type Error = sp_api::ApiError;
 ///         #[advanced]
-///         fn get_balance(&self, at: &BlockId<Block>) -> Result<NativeOrEncoded<u64>, String> {
+///         fn get_balance(&self, at: &BlockId<Block>) -> Result<NativeOrEncoded<u64>, Self::Error> {
 ///             println!("Being called at: {}", at);
 ///
 ///             Ok(self.balance.into())
 ///         }
 ///         #[advanced]
-///         fn set_balance(at: &BlockId<Block>, val: u64) -> Result<NativeOrEncoded<()>, String> {
+///         fn set_balance(at: &BlockId<Block>, val: u64) -> Result<NativeOrEncoded<()>, Self::Error> {
 ///             if let BlockId::Number(1) = at {
 ///                 println!("Being called to set balance to: {}", val);
 ///             }
@@ -392,12 +394,42 @@ pub trait ConstructRuntimeApi<Block: BlockT, C: CallApiAt<Block>> {
 	fn construct_runtime_api<'a>(call: &'a C) -> ApiRef<'a, Self::RuntimeApi>;
 }
 
+/// An error describing which API call failed.
+#[cfg_attr(feature = "std", derive(Debug, thiserror::Error, Eq, PartialEq))]
+#[cfg_attr(feature = "std", error("Failed to execute API call {tag}"))]
+#[cfg(feature = "std")]
+pub struct ApiError {
+    tag: &'static str,
+    #[source]
+    error: codec::Error,
+}
+
+#[cfg(feature = "std")]
+impl From<(&'static str, codec::Error)> for ApiError {
+    fn from((tag, error): (&'static str, codec::Error)) -> Self {
+        Self {
+            tag,
+            error,
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl ApiError {
+	pub fn new(tag: &'static str, error: codec::Error) -> Self {
+		Self {
+			tag,
+			error,
+		}
+	}
+}
+
 /// Extends the runtime api traits with an associated error type. This trait is given as super
 /// trait to every runtime api trait.
 #[cfg(feature = "std")]
 pub trait ApiErrorExt {
 	/// Error type used by the runtime apis.
-	type Error: std::fmt::Debug + From<String>;
+	type Error: std::fmt::Debug + From<ApiError>;
 }
 
 /// Extends the runtime api implementation with some common functionality.
@@ -506,7 +538,7 @@ pub struct CallApiAtParams<'a, Block: BlockT, C, NC, Backend: StateBackend<HashF
 #[cfg(feature = "std")]
 pub trait CallApiAt<Block: BlockT> {
 	/// Error type used by the implementation.
-	type Error: std::fmt::Debug + From<String>;
+	type Error: std::fmt::Debug + From<ApiError>;
 
 	/// The state backend that is used to store the block states.
 	type StateBackend: StateBackend<HashFor<Block>>;