Merge #1285

1285: feat(interface-types) Greatly improve errors r=Hywan a=Hywan

~This PR is build on top of #1284. It must be merged first. [View the exact diff](https://github.com/Hywan/wasmer/compare/feat-interface-types-instructions-string-and-memory...Hywan:feat-interface-types-better-error?expand=1).~

Errors in `wasmer-interface-types` were just `&'static str`, which isn't quite great 😉. This PR introduces the `errors` module, with structures that represent errors. A `Display` implementation maps the errors to strings.

Co-authored-by: Ivan Enderlin <ivan.enderlin@hoa-project.net>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## **[Unreleased]**
 
+- [#1285](https://github.com/wasmerio/wasmer/pull/1285) Greatly improve errors in `wasmer-interface-types`
 - [#1283](https://github.com/wasmerio/wasmer/pull/1283) Workaround for floating point arguments and return values in `DynamicFunc`s.
 
 ## 0.16.2 - 2020-03-11

lib/interface-types/src/ast.rs

@@ -5,7 +5,7 @@ use crate::interpreter::Instruction;
 use std::str;
 
 /// Represents the types supported by WIT.
-#[derive(PartialEq, Debug)]
+#[derive(PartialEq, Debug, Clone)]
 pub enum InterfaceType {
     /// A 8-bits signed integer.
     S8,

lib/interface-types/src/errors.rs

@@ -0,0 +1,232 @@
+//! The error module contains all the data structures that represent
+//! an error.
+
+use crate::{ast::InterfaceType, interpreter::Instruction};
+use std::{
+    error::Error,
+    fmt::{self, Display, Formatter},
+    result::Result,
+    string::{self, ToString},
+};
+
+/// A type alias for instruction's results.
+pub type InstructionResult<T> = Result<T, InstructionError>;
+
+/// A type alias for the interpreter result.
+pub type InterpreterResult<T> = Result<T, InstructionError>;
+
+/// Structure to represent errors when casting from an `InterfaceType`
+/// to a native value.
+#[derive(Debug)]
+pub struct WasmValueNativeCastError {
+    /// The initial type.
+    pub from: InterfaceType,
+
+    /// The targeted type.
+    ///
+    /// `InterfaceType` is used to represent the native type by
+    /// associativity.
+    pub to: InterfaceType,
+}
+
+impl Error for WasmValueNativeCastError {}
+
+impl Display for WasmValueNativeCastError {
+    fn fmt(&self, formatter: &mut Formatter) -> fmt::Result {
+        write!(formatter, "{:?}", self)
+    }
+}
+
+/// Structure to represent the errors for instructions.
+#[derive(Debug)]
+pub struct InstructionError {
+    /// The instruction that raises the error.
+    pub instruction: Instruction,
+
+    /// The error kind.
+    pub error_kind: InstructionErrorKind,
+}
+
+impl InstructionError {
+    pub(crate) fn new(instruction: Instruction, error_kind: InstructionErrorKind) -> Self {
+        Self {
+            instruction,
+            error_kind,
+        }
+    }
+}
+
+impl Error for InstructionError {}
+
+impl Display for InstructionError {
+    fn fmt(&self, formatter: &mut Formatter) -> fmt::Result {
+        write!(
+            formatter,
+            "`{}` {}",
+            (&self.instruction).to_string(),
+            self.error_kind
+        )
+    }
+}
+
+/// The kind of instruction errors.
+#[derive(Debug)]
+pub enum InstructionErrorKind {
+    /// The instruction needs to read an invocation input at index `index`, but it's missing.
+    InvocationInputIsMissing {
+        /// The invocation input index.
+        index: u32,
+    },
+
+    /// Failed to cast from a WIT value to a native value.
+    ToNative(WasmValueNativeCastError),
+
+    /// Failed to cast from `from` to `to`.
+    LoweringLifting {
+        /// The initial type.
+        from: InterfaceType,
+
+        /// The targeted type.
+        to: InterfaceType,
+    },
+
+    /// Read a value from the stack, but it doesn't have the expected
+    /// type.
+    InvalidValueOnTheStack {
+        /// The expected type.
+        expected_type: InterfaceType,
+
+        /// The received type.
+        received_type: InterfaceType,
+    },
+
+    /// Need to read some values from the stack, but it doesn't
+    /// contain enough data.
+    StackIsTooSmall {
+        /// The number of values that were needed.
+        needed: usize,
+    },
+
+    /// The local or import function doesn't exist.
+    LocalOrImportIsMissing {
+        /// The local or import function index.
+        function_index: u32,
+    },
+
+    /// Values given to a local or import function doesn't match the
+    /// function signature.
+    LocalOrImportSignatureMismatch {
+        /// The local or import function index.
+        function_index: u32,
+
+        /// The expected signature.
+        expected: (Vec<InterfaceType>, Vec<InterfaceType>),
+
+        /// The received signature.
+        received: (Vec<InterfaceType>, Vec<InterfaceType>),
+    },
+
+    /// Failed to call a local or import function.
+    LocalOrImportCall {
+        /// The local or import function index that has been called.
+        function_index: u32,
+    },
+
+    /// The memory doesn't exist.
+    MemoryIsMissing {
+        /// The memory indeX.
+        memory_index: u32,
+    },
+
+    /// Tried to read out of bounds of the memory.
+    MemoryOutOfBoundsAccess {
+        /// The access index.
+        index: usize,
+
+        /// The memory length.
+        length: usize,
+    },
+
+    /// The string contains invalid UTF-8 encoding.
+    String(string::FromUtf8Error),
+}
+
+impl Error for InstructionErrorKind {}
+
+impl Display for InstructionErrorKind {
+    fn fmt(&self, formatter: &mut Formatter) -> fmt::Result {
+        match self {
+            Self::InvocationInputIsMissing { index } => write!(
+                formatter,
+                "cannot access invocation inputs #{} because it doesn't exist",
+                index
+            ),
+
+            Self::ToNative(WasmValueNativeCastError { from, .. }) => write!(
+                formatter,
+                "failed to cast the WIT value `{:?}` to its native type",
+                from,
+            ),
+
+            Self::LoweringLifting { from, to } => {
+                write!(formatter, "failed to cast `{:?}` to `{:?}`", from, to)
+            }
+
+            Self::InvalidValueOnTheStack {
+                expected_type,
+                received_type,
+            } => write!(
+                formatter,
+                "read a value of type `{:?}` from the stack, but the type `{:?}` was expected",
+                received_type, expected_type,
+            ),
+
+            Self::StackIsTooSmall { needed } => write!(
+                formatter,
+                "needed to read `{}` value(s) from the stack, but it doesn't contain enough data",
+                needed
+            ),
+
+            Self::LocalOrImportIsMissing { function_index } => write!(
+                formatter,
+                "the local or import function `{}` doesn't exist",
+                function_index
+            ),
+
+            Self::LocalOrImportSignatureMismatch { function_index, expected, received } => write!(
+                formatter,
+                "the local or import function `{}` has the signature `{:?} -> {:?}` but it received values of kind `{:?} -> {:?}`",
+                function_index,
+                expected.0,
+                expected.1,
+                received.0,
+                received.1,
+            ),
+
+            Self::LocalOrImportCall  { function_index } => write!(
+                formatter,
+                "failed while calling the local or import function `{}`",
+                function_index
+            ),
+
+            Self::MemoryIsMissing { memory_index } => write!(
+                formatter,
+                "memory `{}` does not exist",
+                memory_index,
+            ),
+
+            Self::MemoryOutOfBoundsAccess { index, length } => write!(
+                formatter,
+                "read out of the memory bounds (index {} > memory length {})",
+                index,
+                length,
+            ),
+
+            Self::String(error) => write!(
+                formatter,
+                "{}",
+                error
+            ),
+        }
+    }
+}

lib/interface-types/src/interpreter/instruction.rs

@@ -1,7 +1,7 @@
 //use crate::ast::InterfaceType;
 
 /// Represents all the possible WIT instructions.
-#[derive(PartialEq, Debug)]
+#[derive(PartialEq, Debug, Clone, Copy)]
 pub enum Instruction {
     /// The `arg.get` instruction.
     ArgumentGet {

lib/interface-types/src/interpreter/instructions/argument_get.rs

@@ -1,12 +1,17 @@
+use crate::{
+    errors::{InstructionError, InstructionErrorKind},
+    interpreter::Instruction,
+};
+
 executable_instruction!(
-    argument_get(index: u32, instruction_name: String) -> _ {
+    argument_get(index: u32, instruction: Instruction) -> _ {
         move |runtime| -> _ {
             let invocation_inputs = runtime.invocation_inputs;
 
             if index >= (invocation_inputs.len() as u32) {
-                return Err(format!(
-                    "`{}` cannot access argument #{} because it doesn't exist.",
-                    instruction_name, index
+                return Err(InstructionError::new(
+                    instruction,
+                    InstructionErrorKind::InvocationInputIsMissing { index },
                 ));
             }
 
@@ -49,6 +54,6 @@ mod tests {
             instructions: [Instruction::ArgumentGet { index: 1 }],
             invocation_inputs: [InterfaceValue::I32(42)],
             instance: Instance::new(),
-            error: "`arg.get 1` cannot access argument #1 because it doesn't exist."
+            error: "`arg.get 1` cannot access invocation inputs #1 because it doesn't exist"
     );
 }