# UserFacingError
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Pretty printed errors for your CLI application.
This repository contains:
1. A new trait, **UFE**, that you can implement on your Error types to pretty print them
2. A new type, UserFacingError, that you can use to construct pretty CLI error messages
3. Ability to convert your error types into UserFacingErrors
UserFacingError is an error type, or trait, that helps you format and print good looking error messages for users of your CLI application. These errors are intended for consumption by humans, not your program. They are divided into 3 parts: summary, reasons and help text.
**Summary:** A String representing a one-line description of your error. A summary is mandatory and is printed boldly in red.
**Reasons:** A vector of Strings explaining in more detail _why_ this error occured. Reasons are optional and if the terminal supports color, the bullet point ('-') will be colored yellow. Each reason will be printed on its own line.
**Help Text:** A String explaining additional information, including what the user can do about the error, or where to file a bug. Help text is optional and if the terminal supports color it will be printed _dimly_.
If the user has colors enabled on their terminal, it may look something like this:
## Table of Contents
- [Background](#background)
- [Install](#install)
- [Usage](#usage)
- [UFE Trait](#ufe-trait)
- [Default Implementations](#default-implementations)
- [Summary](#summary)
- [Reasons](#reasons)
- [Helptext](#helptext)
- [Trait Methods](#trait-methods)
- [Print](#print)
- [Print and Exit](#print-and-exit)
- [Into UFE](#into-ufe)
- [UserFacingError Type](#userfacingerror-type)
- [Construction](#construction)
- [Builder Pattern](#builder-pattern)
- [From Other Errors](#from-other-error-types)
- [Methods](#methods)
- [Update](#update)
- [Push](#push)
- [Clear Reasons](#clear-reasons)
- [Clear Help Text](#clear-help-text)
- [Maintainers](#maintainers)
- [Contributing](#contributing)
- [License](#license)
## Background
UserFacingError makes it easy to print errors to users of your command line applications in a sensible, pretty format.
I love Rust's Result types, and using enums for matching and &str for error messages. It's great for development but less great for end users of CLI applications. For this I made a `UserFacingError` which can be used to quickly construct a pretty error message suitable to inform users what went wrong and what they can do about it.
## Install
Add the following to your Cargo.toml:
```yaml
[dependencies]
user-error = "1.2.6"
```
## Usage
### UFE Trait
You can trivially implement the UFE trait on your custom error types, allowing you to pretty print them to stderr. The UFE trait requires your type also implements the Error trait.
```rust
#[derive(Debug)]
struct MyError {}
impl Display for MyError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "MyError")
}
}
impl Error for MyError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
None
}
}
// Trivial implementation
impl UFE for MyError {}
```
#### Default Implementations
There are three functions you may optionally implement:
1. `.summary() -> String` - returns a string to be used as the error summary
2. `.reasons() -> Option<Vec<String>>` - optionally return a Vec of Strings representing the causes of the error
3. `.helptext() -> Option<String>` - optionally return a String representing follow up advice on how to resolve the error
##### Summary
By default, the error summary is the String provided by calling `.to_string()` on the error and then prefixing it with "Error: ".
##### Reasons
By default the list of reasons is created by recursively calling `.source()` and prefixing each error in the chaing with a bullet point.
##### Helptext
By default no helptext is added to custom types that implement UFE. You'll either have to provide your own implementation, or call `.into_ufe()` to convert your error type to a UserFacingError and use the provided `.help(&str)` function to add one.
```rust
use user_error::{UserFacingError, UFE};
// Custom Error Type
#[derive(Debug)]
struct MyError { mssg: String, src: Option<Box<dyn Error>> }
impl Display for MyError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}", self.mssg.to_string())
}
}
impl Error for MyError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
self.src.as_deref()
}
}
impl UFE for MyError {}
fn main() {
let me = MyError {
mssg: "Program Failed".into(),
src: Some(Box::new(MyError {
mssg: "Reason 1".into(),
src: Some(Box::new(MyError {
mssg: "Reason 2".into(),
src: None,
})),
})),
};
me.print();
println!("-----")
me.into_ufe().help("Helptext Added").print();
}
```
This prints:
```text
Error: Program Failed
- Reason 1
- Reason 2
-----
Error: Program Failed
- Reason 1
- Reason 2
Helptext Added
```
#### Trait Methods
UFE provides three useful methods:
1. `.print()` - Pretty print the error
2. `.print_and_exit()` - Pretty print the error and terminate the process
3. `.into_ufe()` - consume a custom Error type and return a UserFacingError
You could override these methods but then there is not much point in using this crate :p
This prints:
```text
Error: Program Failed!
- Bad luck
```
#### Print
Pretty prints the UserFacingError to stderr.
```rust
use user_error::UserFacingError;
fn main() {
UserFacingError::new("Failed to build project")
.reason("Database config could not be parsed")
.reason("`db.config` not found")
.help("Try: touch db.config")
.print_and_exit();
}
```
This prints:
```text
Error: Failed to build project
- Database config could not be parsed
- `db.config` not found
Try: touch db.config
```
#### Print and Exit
Since constructing this error is likely the last thing your program will do, you can also call `.print_and_exit()` to print the error and then terminate the process with status code 1 as a convenience.
```rust
use user_error::UserFacingError;
fn main() {
UserFacingError::new("Failed to build project")
.reason("Database config could not be parsed")
.print_and_exit();
}
```
This prints:
```text
Error: Failed to build project
- Database config could not be parsed
```
### UserFacingError Type
#### Construction
There are two ways to create a new UserFacingError:
1. Using a builder pattern
2. From other std Errors
##### Builder Pattern
```rust
use user_error::UserFacingError;
fn main() {
UserFacingError::new("Failed to build project")
.reason("Database could not be parsed")
.reason("File \"main.db\" not found")
.help("Try: touch main.db")
.print()
}
```
This prints:
```text
Error: Failed to build project
- Database could not be parsed
- File "main.db" not found
Try: touch main.db
```
If the user has colors enabled on their terminal, it may look something like this:
##### From Other Error Types
You can also create a UserFacingError from other types that implement std::error::Error.
The summary will be the result of error.to_string() and the list of reasons will be any errors in the error chain constructed by recursively calling .source()
```rust
use user_error::UserFacingError;
use std::io::(Error, ErrorKind);
fn main() {
/* Lose the type */
fn dyn_error() -> Box<dyn Error> {
let ioe = Error::new(ErrorKind::Other, "MyError");
Box::new(ioe)
}
/* Convert to UFE */
let ufe: UserFacingError = dyn_error().into();
}
```
#### Methods
UserFacingErrors have 6 non-builder methods:
1. `.update(&str)` - Change the error summary
2. `.push(&str)` - Change the error summary, add the previous summary to the list of reasons
3. `.clear_reasons()` - Remove all reasons
4. `.clear_help()` - Remove the helptext
5. `.print()` - Pretty print the error (uses the default UFE implementation)
6. `.print_and_exit()` - Pretty print the error and terminate the process (uses the default UFE implementation)
##### Update
You can call `.update(&str)` on a UserFacingError to change the error summary.
```rust
use user_error::UserFacingError;
fn do_thing() -> Result<(), UserFacingError> {
Err(UserFacingError::new("Didn't do the thing!")
.reason("Just didn't happen"))
}
fn main() {
match do_thing() {
Ok(_) => println!("Success!"),
Err(E) => {
e.update("Program Failed!").print()
}
}
}
```
This prints:
```text
Error: Program Failed!
- Just didn't happen
```
##### Push
You can call `.push(&str)` on a UserFacingError to change the error summary and add the old error summary to the list of reasons. It adds the summary to the front of the list of reasons.
```rust
use user_error::UserFacingError;
fn do_thing() -> Result<(), UserFacingError> {
Err(UserFacingError::new("Didn't do the thing!")
.reason("Just didn't happen"))
}
fn main() {
match do_thing() {
Ok(_) => println!("Success!"),
Err(E) => {
e.update("Program Failed!").print()
}
}
}
```
This prints:
```text
Error: Program Failed!
- Didn't do the thing!
- Just didn't happen
```
##### Clear Reasons
Calling this removes all reasons from a UserFacingError.
```rust
use user_error::UserFacingError;
fn main() {
let ufe = UserFacingError::new("Program Failed!")
.reason("Program internal error message");
/* --- */
ufe.clear_reasons();
ufe.print_and_exit();
}
```
This prints:
```text
Error: Program Failed!
```
##### Clear Help Text
Calling this removes the help text from a UserFacingError.
```rust
use user_error::UserFacingError;
fn main() {
let ufe = UserFacingError::new("Program Failed!")
.reason("Bad luck")
.help("Try running it again?");
/* --- */
ufe.clear_help();
ufe.print_and_exit();
}
```
This prints:
```text
Error: Program Failed!
- Bad luck
```
## Maintainers
- Amy Jie [@xvrqt](https://twitter.com/xvrqt)
## Contributing
Feel free to dive in! [Open an issue](https://github.com/xvrqt/user-error/issues/new) or submit PRs.
### Contributors
- Amy Jie [@xvrqt](https://twitter.com/xvrqt)
## License
[MIT](LICENSE) © Amy Jie