Refactor error management

Change-type: patch

src/error.rs

@@ -2,44 +2,26 @@ use thiserror::Error;
 
 #[derive(Error, Debug)]
 pub enum Error {
-    #[error(transparent)]
-    SerializationError(#[from] serde_json::error::Error),
+    #[error("cannot read system state: ${0}")]
+    StateReadFailed(#[from] super::system::SystemReadError),
 
-    #[error(transparent)]
-    FailedToDeserializePathParams(#[from] super::extract::PathDeserializationError),
+    #[error("cannot write system state: ${0}")]
+    StateWriteFailed(#[from] super::system::SystemWriteError),
 
-    #[error(transparent)]
-    PatchFailed(#[from] json_patch::PatchError),
+    #[error("cannot extract path: ${0}")]
+    PathExtractFailed(#[from] super::extract::PathDeserializationError),
 
-    #[error("the string `{0}` is not a valid path")]
-    InvalidPath(String),
+    #[error("cannot extract target: ${0}")]
+    TargetExtractFailed(#[from] super::extract::TargetExtractError),
 
-    #[error("no target available on the context")]
-    TargetIsNone,
+    #[error("cannot extract view: ${0}")]
+    ViewExtractFailed(#[from] super::extract::ViewExtractError),
 
-    #[error("cannot expand an atom task")]
-    CannotExpandTask,
+    #[error("cannot calculate view result: ${0}")]
+    ViewResultFailed(#[from] super::extract::ViewResultError),
 
     #[error("condition failed: ${0}")]
-    ConditionFailed(String),
-
-    #[error("cannot resolve state path `{path}`: ${reason}")]
-    TargetResolveFailed {
-        path: String,
-        reason: jsonptr::resolve::ResolveError,
-    },
-
-    #[error("cannot resolve path `{path}` on system state: ${reason}")]
-    PointerResolveFailed {
-        path: String,
-        reason: jsonptr::resolve::ResolveError,
-    },
-
-    #[error("cannot assign path `{path}` on system state: ${reason}")]
-    PointerAssignFailed {
-        path: String,
-        reason: jsonptr::assign::AssignError,
-    },
+    TaskConditionFailed(#[from] super::task::ConditionFailed),
 
     #[error(transparent)]
     Other(#[from] Box<dyn std::error::Error>),

src/extract/path/mod.rs

@@ -12,7 +12,7 @@ pub use error::PathDeserializationError;
 
 impl IntoError for PathDeserializationError {
     fn into_error(self) -> Error {
-        Error::FailedToDeserializePathParams(self)
+        Error::PathExtractFailed(self)
     }
 }
 

src/extract/target.rs

@@ -1,37 +1,76 @@
-use crate::error::Error;
-use crate::system::{FromSystem, System};
-use crate::task::Context;
 use serde::de::DeserializeOwned;
 use serde::Serialize;
+use std::fmt::{self, Display};
 use std::marker::PhantomData;
 use std::ops::Deref;
 
+use crate::error::{self, IntoError};
+use crate::system::{FromSystem, System};
+use crate::task::Context;
+
+#[derive(Debug)]
+pub enum TargetExtractError {
+    Undefined,
+    SerializationFailed(serde_json::error::Error),
+    DeserializationFailed(serde_json::error::Error),
+    CannotResolvePath {
+        path: String,
+        reason: jsonptr::resolve::ResolveError,
+    },
+}
+
+impl std::error::Error for TargetExtractError {}
+
+impl Display for TargetExtractError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            TargetExtractError::SerializationFailed(err) => err.fmt(f)?,
+            TargetExtractError::DeserializationFailed(err) => err.fmt(f)?,
+            TargetExtractError::Undefined => {
+                write!(f, "no target has been defined for the context")?;
+            }
+            TargetExtractError::CannotResolvePath { path, reason } => {
+                write!(f, "cannot resolve state path `{}`: {}", path, reason)?;
+            }
+        };
+        Ok(())
+    }
+}
+
+impl IntoError for TargetExtractError {
+    fn into_error(self) -> error::Error {
+        error::Error::TargetExtractFailed(self)
+    }
+}
+
 pub struct Target<S: Clone, T = S> {
     target: T,
     _system: PhantomData<S>,
 }
 
 impl<S: Serialize + Clone, T: DeserializeOwned> FromSystem<S> for Target<S, T> {
-    type Error = Error;
+    type Error = TargetExtractError;
 
     fn from_system(_: &System, context: &Context<S>) -> Result<Self, Self::Error> {
         if context.target.is_none() {
-            return Err(Error::TargetIsNone);
+            return Err(TargetExtractError::Undefined);
         }
 
-        let tgt = serde_json::to_value(context.target.clone())?;
+        let tgt = serde_json::to_value(context.target.clone())
+            .map_err(TargetExtractError::SerializationFailed)?;
 
         // Return an error if the context path does not exist in the target object
         let pointer = context.path.as_ref();
         let value = pointer
             .resolve(&tgt)
-            .map_err(|e| Error::TargetResolveFailed {
+            .map_err(|e| TargetExtractError::CannotResolvePath {
                 path: context.path.to_string(),
                 reason: e,
             })?;
 
         // This will fail if the value cannot be deserialized into the target type
-        let target = serde_json::from_value::<T>(value.clone())?;
+        let target = serde_json::from_value::<T>(value.clone())
+            .map_err(TargetExtractError::DeserializationFailed)?;
 
         Ok(Target {
             target,

src/extract/view.rs

@@ -2,10 +2,11 @@ use json_patch::{diff, Patch};
 use jsonptr::resolve::ResolveError;
 use serde::de::DeserializeOwned;
 use serde::Serialize;
+use std::fmt::{self, Display};
 use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
 
-use crate::error::Error;
+use crate::error::{Error, IntoError};
 use crate::path::Path;
 use crate::system::{FromSystem, System};
 use crate::task::{Context, Effect, IntoEffect, IntoResult, Result};
@@ -22,6 +23,72 @@ pub struct View<S, T = S> {
     _system: PhantomData<S>,
 }
 
+#[derive(Debug)]
+pub enum ViewExtractError {
+    PathResolveFailed {
+        path: String,
+        reason: jsonptr::resolve::ResolveError,
+    },
+    DeserializationFailed(serde_json::error::Error),
+}
+
+impl std::error::Error for ViewExtractError {}
+
+impl Display for ViewExtractError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ViewExtractError::PathResolveFailed { path, reason } => {
+                write!(
+                    f,
+                    "cannot resolve path `{}` on system state: {}",
+                    path, reason
+                )?;
+            }
+            ViewExtractError::DeserializationFailed(err) => err.fmt(f)?,
+        }
+
+        Ok(())
+    }
+}
+
+impl IntoError for ViewExtractError {
+    fn into_error(self) -> Error {
+        Error::ViewExtractFailed(self)
+    }
+}
+
+#[derive(Debug)]
+pub enum ViewResultError {
+    PathAssignFailed {
+        path: String,
+        reason: jsonptr::assign::AssignError,
+    },
+    DeserializationFailed(serde_json::error::Error),
+}
+
+impl std::error::Error for ViewResultError {}
+
+impl Display for ViewResultError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ViewResultError::PathAssignFailed { path, reason } => {
+                write!(
+                    f,
+                    "cannot assign path `{}` on system state: {}",
+                    path, reason
+                )
+            }
+            ViewResultError::DeserializationFailed(err) => err.fmt(f),
+        }
+    }
+}
+
+impl IntoError for ViewResultError {
+    fn into_error(self) -> Error {
+        Error::ViewResultFailed(self)
+    }
+}
+
 impl<S, T> View<S, T> {
     pub(super) fn new(state: Option<T>, path: Path) -> Self {
         View {
@@ -48,7 +115,7 @@ impl<S, T: Default> View<S, T> {
 }
 
 impl<S, T: DeserializeOwned> FromSystem<S> for View<S, T> {
-    type Error = Error;
+    type Error = ViewExtractError;
 
     fn from_system(
         system: &System,
@@ -63,7 +130,7 @@ impl<S, T: DeserializeOwned> FromSystem<S> for View<S, T> {
         // Try to resolve the parent or fail
         parent
             .resolve(root)
-            .map_err(|e| Error::PointerResolveFailed {
+            .map_err(|e| ViewExtractError::PathResolveFailed {
                 path: context.path.to_string(),
                 reason: e,
             })?;
@@ -72,12 +139,15 @@ impl<S, T: DeserializeOwned> FromSystem<S> for View<S, T> {
         // resolved is because the value does not exist yet unless
         // the parent is a scalar
         let state: Option<T> = match pointer.resolve(root) {
-            Ok(value) => Some(serde_json::from_value::<T>(value.clone())?),
+            Ok(value) => Some(
+                serde_json::from_value::<T>(value.clone())
+                    .map_err(ViewExtractError::DeserializationFailed)?,
+            ),
             Err(e) => match e {
                 ResolveError::NotFound { .. } => None,
                 ResolveError::OutOfBounds { .. } => None,
                 _ => {
-                    return Err(Error::PointerResolveFailed {
+                    return Err(ViewExtractError::PathResolveFailed {
                         path: context.path.to_string(),
                         reason: e,
                     })
@@ -112,12 +182,13 @@ impl<S, T: Serialize> IntoResult<Patch> for View<S, T> {
         let pointer = self.path.as_ref();
 
         if let Some(state) = self.state {
-            let value = serde_json::to_value(state)?;
+            let value =
+                serde_json::to_value(state).map_err(ViewResultError::DeserializationFailed)?;
 
             // Assign the state to the copy
             pointer
                 .assign(root, value)
-                .map_err(|e| Error::PointerAssignFailed {
+                .map_err(|e| ViewResultError::PathAssignFailed {
                     path: self.path.to_string(),
                     reason: e,
                 })?;
@@ -148,7 +219,7 @@ pub struct Create<S, T = S> {
 }
 
 impl<S, T: DeserializeOwned + Default> FromSystem<S> for Create<S, T> {
-    type Error = Error;
+    type Error = ViewExtractError;
 
     fn from_system(
         system: &System,
@@ -165,7 +236,7 @@ impl<S, T: DeserializeOwned + Default> FromSystem<S> for Create<S, T> {
         // Try to resolve the parent or fail
         parent
             .resolve(root)
-            .map_err(|e| Error::PointerResolveFailed {
+            .map_err(|e| ViewExtractError::PathResolveFailed {
                 path: context.path.to_string(),
                 reason: e,
             })?;
@@ -178,7 +249,7 @@ impl<S, T: DeserializeOwned + Default> FromSystem<S> for Create<S, T> {
                 ResolveError::NotFound { .. } => (),
                 ResolveError::OutOfBounds { .. } => (),
                 _ => {
-                    return Err(Error::PointerResolveFailed {
+                    return Err(ViewExtractError::PathResolveFailed {
                         path: context.path.to_string(),
                         reason: e,
                     })
@@ -233,7 +304,7 @@ pub struct Update<S, T = S> {
 }
 
 impl<S, T: DeserializeOwned> FromSystem<S> for Update<S, T> {
-    type Error = Error;
+    type Error = ViewExtractError;
 
     fn from_system(
         system: &System,
@@ -246,11 +317,12 @@ impl<S, T: DeserializeOwned> FromSystem<S> for Update<S, T> {
         // reason, return an error
         let value = pointer
             .resolve(root)
-            .map_err(|e| Error::PointerResolveFailed {
+            .map_err(|e| ViewExtractError::PathResolveFailed {
                 path: context.path.to_string(),
                 reason: e,
             })?;
-        let state = serde_json::from_value::<T>(value.clone())?;
+        let state = serde_json::from_value::<T>(value.clone())
+            .map_err(ViewExtractError::DeserializationFailed)?;
 
         Ok(Update {
             state,