feat: error messages (cairo-book#727)

Author: TAdev0

listings/ch04-understanding-ownership/no_listing_04_no_drop_derive_fails/src/lib.cairo

@@ -2,5 +2,5 @@
 struct A {}
 
 fn main() {
-    A {}; // error: Value not dropped.
+    A {}; // error: Variable not dropped.
 }

src/SUMMARY.md

@@ -99,8 +99,9 @@
   - [B - Operators and Symbols](appendix-02-operators-and-symbols.md)
   - [C - Derivable Traits](appendix-03-derivable-traits.md)
   - [D - Common Types & Traits and the Cairo Prelude](appendix-04-common-types-and-traits-and-cairo-prelude.md)
-  - [E - Useful Development Tools](appendix-05-useful-development-tools.md)
-  - [F - Installing Cairo binaries](appendix-06-cairo-binaries.md)
+  - [E - Common Error Messages](appendix-05-common-error-messages.md)
+  - [F - Useful Development Tools](appendix-06-useful-development-tools.md)
+  - [G - Installing Cairo binaries](appendix-07-cairo-binaries.md)
 
 ---
 
@@ -157,4 +158,4 @@
 ## Appendix
 
 - [Appendix](appendix-00.md)
-  - [A - System Calls](appendix-07-system-calls.md)
+  - [A - System Calls](appendix-08-system-calls.md)

src/appendix-05-common-error-messages.md

@@ -0,0 +1,35 @@
+# Appendix E - Common Error Messages
+
+You might encounter error messages when writing Cairo code. Some of them occur very frequently, which is why we will be listing the most common error messages in this appendix to help you resolve common issues.
+
+- `Variable not dropped.`: this error message means that you are trying to make a variable with a type that do not implement the `Drop` trait go out of scope, withtout destroying it. Make sure that variables that need to be dropped at the end of the execution of a function implement the `Drop` trait or the `Destruct` trait. See [Ownership](ch04-01-what-is-ownership.md#destroying-values---example-with-feltdict) section.
+
+- `Variable was previously moved.`: this error message means that you are trying to use a variable whose ownership has already been transferred to another function. When a variable doesn't implement the `Copy` trait, it is passed by value to functions, and ownership of the variable is transferred to the function. Such a variable cannot be used anymore in the current context after its ownership has been transferred. It is often useful to use the `clone` method in this situation.
+
+- `error: Trait has no implementation in context: core::fmt::Display::<package_name::struct_name>`: this error message is encountered if you try to print an instance of a custom data type with `{}` placeholders in a `print!` or `println!` macro. To mitigate this issue, you need to either manually implement the `Display` trait for your type, or use the `Debug` trait by applying `derive(Debug)` to your type, allowing to print your instance by adding `:?` in `{}` placeholders.
+
+- `Got an exception while executing a hint: Hint Error: Failed to deserialize param #x.`: this error means that the execution failed because an entrypoint was called without the expected arguments. Make sure that the arguments you provide when calling an entrypoint are correct. There is a classic issue with `u256` variables, which are actually structs of 2 `u128`. Therefore, when calling a function that takes a `u256` as argument, you need to pass 2 values.
+
+- `Item path::item is not visible in this context.`: this error message lets us know that the path to bring an item into scope is correct, but there is a vibility issue. In cairo, all items are private to parent modules by default. To resolve this issue, make sure that all the modules on the path to items and items themselves are declared with `pub(crate)` or `pub` to have access to them.
+
+- `Identifier not found.`: this error message is a bit aspecific but might indicate that:
+  -  A variable is being used before it has been declared. Make sure to declare variables with the `let` keyword.
+  -  The path to bring an item into scope is wrongly defined. Make sure to use valid paths.
+
+## Starknet Components Related Error Messages
+
+You might encounter some errors when trying to implement components.
+Unfortunately, some of them lack meaningful error messages to help debug. This
+section aims to provide you with some pointers to help you debug your code.
+
+- `Trait not found. Not a trait.`: this error can occur when you're not importing the component's impl block
+  correctly in your contract. Make sure to respect the following syntax:
+
+  ```rust,noplayground
+  #[abi(embed_v0)]
+  impl IMPL_NAME = PATH_TO_COMPONENT::EMBEDDED_NAME<ContractState>
+  ```
+
+- `Plugin diagnostic: name is not a substorage member in the contract's Storage. Consider adding to Storage: (...)`: the compiler helps you a lot debugging this by giving you recommendation on the action to take. Basically, you forgot to add the component's storage to your contract's storage. Make sure to add the path to the component's storage annotated with the `#[substorage(v0)]` attribute to your contract's storage.
+
+- `Plugin diagnostic: name is not a nested event in the contract's Event enum. Consider adding to the Event enum:` similar to the previous error, the compiler tells you that you forgot to add the component's events to your contract's events. Make sure to add the path to the component's events to your contract's events.

…/appendix-05-useful-development-tools.md …/appendix-06-useful-development-tools.mdsrc/appendix-05-useful-development-tools.md renamed to src/appendix-06-useful-development-tools.md src/appendix-05-useful-development-tools.md renamed to src/appendix-06-useful-development-tools.md

@@ -1,4 +1,4 @@
-# Appendix E - Useful Development Tools
+# Appendix F - Useful Development Tools
 
 In this appendix, we talk about some useful development tools that the Cairo
 project provides. We’ll look at automatic formatting, quick ways to apply

src/appendix-06-cairo-binaries.md src/appendix-07-cairo-binaries.mdsrc/appendix-06-cairo-binaries.md renamed to src/appendix-07-cairo-binaries.md

@@ -1,4 +1,4 @@
-# Appendix F - Installing the Cairo Binaries
+# Appendix G - Installing the Cairo Binaries
 
 If you want to have access to the Cairo binaries, for anything that you could not achieve by purely using Scarb you can install them by following the instructions below.
 

src/appendix-07-system-calls.md src/appendix-08-system-calls.mdsrc/appendix-07-system-calls.md renamed to src/appendix-08-system-calls.md

@@ -174,8 +174,6 @@ ownable_component::Event`).
    Indeed, we don't want to expose externally the functions defined in this
    impl. However, we might still want to access them internally.
 
-<!-- TODO: Add content on impl aliases -->
-
 For example, to embed the `Ownable` component defined above, we would do the
 following:
 
@@ -195,7 +193,7 @@ with the components functions externally by calling them using the
 
 The composability of components really shines when combining multiple of them
 together. Each adds its features onto the contract. You can rely on
-[Openzeppelin's](https://github.com/OpenZeppelin/cairo-contracts) implementation
+[Openzeppelin's][OpenZeppelin Cairo Contracts] implementation
 of components to quickly plug-in all the common functionalities you need a contract
 to have.
 
@@ -206,46 +204,5 @@ Components can even [depend](./ch16-02-02-component-dependencies.md) on other co
 `TContractstate` they're generic on to implement the trait of another component.
 Before we dive into this mechanism, let's first look at [how components work under the hood](./ch16-02-01-under-the-hood.md).
 
-## Troubleshooting
-
-You might encounter some errors when trying to implement components.
-Unfortunately, some of them lack meaningful error messages to help debug. This
-section aims to provide you with some pointers to help you debug your code.
-
-- `Trait not found. Not a trait.`
-
-  This error can occur when you're not importing the component's impl block
-  correctly in your contract. Make sure to respect the following syntax:
-
-  ```rust
-  #[abi(embed_v0)]
-  impl IMPL_NAME = upgradeable::EMBEDDED_NAME<ContractState>
-  ```
-
-  Referring to our previous example, this would be:
-
-  ```rust
-  #[abi(embed_v0)]
-  impl OwnableImpl = upgradeable::Ownable<ContractState>
-  ```
-
-- `Plugin diagnostic: name is not a substorage member in the contract's Storage.
-Consider adding to Storage: (...)`
-
-  The compiler helps you a lot debugging this by giving you recommendation on
-  the action to take. Basically, you forgot to add the component's storage to
-  your contract's storage. Make sure to add the path to the component's storage
-  annotated with the `#[substorage(v0)]` attribute to your contract's storage.
-
-- `Plugin diagnostic: name is not a nested event in the contract's Event enum.
-Consider adding to the Event enum:`
-
-  Similar to the previous error, the compiler, you forgot to add the component's
-  events to your contract's events. Make sure to add the path to the component's
-  events to your contract's events.
-
-- Components functions are not accessible externally
 
-  This can happen if you forgot to annotate the component's impl block with
-  `#[abi(embed_v0)]`. Make sure to add this annotation when embedding the
-  component's impl in your contract.
+[OpenZeppelin Cairo Contracts]: https://github.com/OpenZeppelin/cairo-contracts