displaystr

https://docs.rs/displaystr/
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displaystr is a Rust attribute macro that provides an ergonomic way to implement the Display trait...
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### Multiple Arguments for Format Strings

Source: https://docs.rs/displaystr/latest/displaystr

When using multiple arguments in `format_args!`, supply them as a tuple to the string literal. This example demonstrates formatting a `Vec<String>`.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Redaction(String, Vec<String>) = (
        "the data for key `{_0}` is not available, but we recovered: {}",
        _1.join("+"),
    ),
}
```

```rust
use displaystr::display;

pub enum DataStoreError {
    Redaction(String, Vec<String>),
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Redaction(_0, _1) => f.write_fmt(format_args!(
                "the data for key `{_0}` is not available, but we recovered: {}",
                _1.join("+")
            )),
        }
    }
}
```

--------------------------------

### displaystr with thiserror

Source: https://docs.rs/displaystr/latest/displaystr

This example shows how to combine `displaystr` with the `thiserror` crate to define errors, leveraging `#[from]` for automatic conversion and `#[display]` for custom formatting.

```rust
use thiserror::Error;
use displaystr::display;

#[derive(Error, Debug)]
#[display]
pub enum DataStoreError {
    Disconnect(#[from] io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

--------------------------------

### Implement Display for Enums with displaystr

Source: https://docs.rs/displaystr/latest/index.html

Use the `#[display]` attribute macro on enums to automatically implement the `Display` trait. This example shows how to map enum variants to custom string formats, including those with arguments.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Disconnect(std::io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

```rust
use displaystr::display;

pub enum DataStoreError {
    Disconnect(_0: std::io::Error),
    Redaction(_0: String),
    InvalidHeader {
        expected: String,
        found: String,
    },
    Unknown,
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Disconnect(_0) => {
                f.write_fmt(format_args!("data store disconnected"))
            }
            Self::Redaction(_0) => {
                f.write_fmt(format_args!("the data for key `{_0}` is not available"))
            }
            Self::InvalidHeader { expected, found } => {
                f.write_fmt(format_args!("invalid header (expected {expected}, found {found})"))
            }
            Self::Unknown => {
                f.write_fmt(format_args!("unknown data store error"))
            }
        }
    }
}
```

--------------------------------

### Enum Display Implementation with displaystr

Source: https://docs.rs/displaystr/latest/displaystr

Use the `#[display]` attribute macro to automatically implement the `Display` trait for enums. This example shows custom string literals for each variant, including named fields.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Disconnect(std::io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

```rust
use displaystr::display;

pub enum DataStoreError {
    Disconnect(std::io::Error),
    Redaction(String),
    InvalidHeader {
        expected: String,
        found: String,
    },
    Unknown,
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Disconnect(_0) => {
                f.write_fmt(format_args!("data store disconnected"))
            }
            Self::Redaction(_0) => {
                f.write_fmt(format_args!("the data for key `{_0}` is not available"))
            }
            Self::InvalidHeader { expected, found } => {
                f.write_fmt(format_args!("invalid header (expected {expected}, found {found})"))
            }
            Self::Unknown => {
                f.write_fmt(format_args!("unknown data store error"))
            }
        }
    }
}
```

--------------------------------

### Comparison of Display implementations with displaystr, thiserror, and displaydoc

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Illustrates the equivalent enum definitions for `DataStoreError` using `displaystr`, `thiserror`, and `displaydoc` crates. This highlights the conciseness of `displaystr`.

```rust
# use std::io;
use thiserror::Error;
use displaystr::display;

#[derive(Error, Debug)]
#[display]
pub enum DataStoreError {
    Disconnect(#[from] io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

```rust
# use std::io;
use thiserror::Error;

#[derive(Error, Debug)]
pub enum DataStoreError {
    #[error("data store disconnected")]
    Disconnect(#[from] io::Error),
    #[error("the data for key `{0}` is not available")]
    Redaction(String),
    #[error("invalid header (expected {expected:?}, found {found:?})")]
    InvalidHeader {
        expected: String,
        found: String,
    },
    #[error("unknown data store error")]
    Unknown,
}
```

```rust
# use std::io;
use thiserror::Error;
use displaydoc::Display;

#[derive(Display, Error, Debug)]
pub enum DataStoreError {
    /// data store disconnected
    Disconnect(#[source] io::Error),
    /// the data for key `{0}` is not available
    Redaction(String),
    /// invalid header (expected {expected:?}, found {found:?})
    InvalidHeader {
        expected: String,
        found: String,
    },
    /// unknown data store error
    Unknown,
}
```

--------------------------------

### Generate Doc Comment TokenTree

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Creates a `TokenTree` array representing a Rust doc comment (`///`). Useful for adding documentation to generated code.

```rust
fn doc_comment(content: &str) -> [TokenTree; 2] {
    [
        TokenTree::Punct(Punct::new('#', Spacing::Joint)),
        TokenTree::Group(Group::new(
            Delimiter::Bracket,
            TokenStream::from_iter([
                TokenTree::Ident(Ident::new("doc", Span::call_site())),
                TokenTree::Punct(Punct::new('=', Spacing::Joint)),
                TokenTree::Literal(Literal::string(content)),
            ]),
        )),
    ]
}
```

--------------------------------

### Constructing the Display Implementation in Rust

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This snippet shows the programmatic construction of the `impl Display` block for an enum using Rust's token stream API. It generates the `fmt` function with a `match` statement that iterates over enum variants.

```rust
let display_impl = TokenStream::from_iter([
        TokenTree::Ident(Ident::new("impl", Span::call_site())),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Ident(Ident::new("core", Span::call_site())),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Ident(Ident::new("fmt", Span::call_site())),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Ident(Ident::new("Display", Span::call_site())),
        TokenTree::Ident(Ident::new("for", Span::call_site())),
        TokenTree::Ident(enum_ident),
        TokenTree::Group(Group::new(
            Delimiter::Brace,
            TokenStream::from_iter([
                TokenTree::Ident(Ident::new("fn", Span::call_site())),
                TokenTree::Ident(Ident::new("fmt", Span::call_site())),
                TokenTree::Group(Group::new(
                    Delimiter::Parenthesis,
                    TokenStream::from_iter([
                        TokenTree::Punct(Punct::new('&', Spacing::Joint)),
                        TokenTree::Ident(Ident::new("self", Span::call_site())),
                        TokenTree::Punct(Punct::new(',', Spacing::Joint)),
                        TokenTree::Ident(Ident::new("f", Span::call_site())),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Punct(Punct::new('&', Spacing::Joint)),
                        TokenTree::Ident(Ident::new("mut", Span::call_site())),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Ident(Ident::new("core", Span::call_site())),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Ident(Ident::new("fmt", Span::call_site())),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                        TokenTree::Ident(Ident::new("Formatter", Span::call_site())),
                    ]),
                )),
                TokenTree::Punct(Punct::new('-', Spacing::Joint)),
                TokenTree::Punct(Punct::new('>', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Ident(Ident::new("core", Span::call_site())),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Ident(Ident::new("fmt", Span::call_site())),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Ident(Ident::new("Result", Span::call_site())),
                TokenTree::Group(Group::new(
                    Delimiter::Brace,
                    TokenStream::from_iter([
                        TokenTree::Ident(Ident::new("match", Span::call_site())),
                        TokenTree::Ident(Ident::new("self", Span::call_site())),
                        TokenTree::Group(Group::new(Delimiter::Brace, arms)),
                    ]),
                )),
            ]),
        )),
    ]);
```

--------------------------------

### Multiple Arguments for Format String

Source: https://docs.rs/displaystr

When a format string requires multiple arguments, use a tuple to provide them. The second element of the tuple can be an expression that operates on the variant's fields.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Redaction(String, Vec<String>) = (
        "the data for key `{_0}` is not available, but we recovered: {}",
        _1.join("+"),
    ),
}
```

--------------------------------

### Expanded Display Implementation for Enum

Source: https://docs.rs/displaystr

This shows the code generated by the `#[display]` macro for the `DataStoreError` enum, including the `impl Display` block.

```rust
use displaystr::display;

pub enum DataStoreError {
    Disconnect(std::io::Error),
    Redaction(String),
    InvalidHeader {
        expected: String,
        found: String,
    },
    Unknown,
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Disconnect(_0) => {
                f.write_fmt(format_args!("data store disconnected"))
            }
            Self::Redaction(_0) => {
                f.write_fmt(format_args!("the data for key `{_0}` is not available"))
            }
            Self::InvalidHeader { expected, found } => {
                f.write_fmt(format_args!("invalid header (expected {expected}, found {found})"))
            }
            Self::Unknown => {
                f.write_fmt(format_args!("unknown data store error"))
            }
        }
    }
}
```

--------------------------------

### Expanded Enum with Auto-generated Doc Comments

Source: https://docs.rs/displaystr

This illustrates the expansion of `#[display(doc)]`, showing how `///` comments are added to enum variants.

```rust
use displaystr::display;

pub enum DataStoreError {
    /// data store disconnected
    Disconnect(std::io::Error),
    /// the data for key `{_0}` is not available
    Redaction(String),
    /// invalid header (expected {expected:?}, found {found:?})
    InvalidHeader {
        expected: String,
        found: String,
    },
    /// unknown data store error
    Unknown,
}

// impl Display omitted since it's identical to the previous section
```

--------------------------------

### Generate Doc Comments with displaystr

Source: https://docs.rs/displaystr

Use `#[display(doc)]` to automatically generate `///` doc comments for enum variants based on their associated format strings.

```rust
use displaystr::display;

#[display(doc)]
pub enum DataStoreError {
    Disconnect(std::io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

--------------------------------

### Enum Display with Multiple Arguments via Tuple

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

When a format string requires multiple arguments, provide them as a tuple in the variant definition. The second element of the tuple can be an expression that evaluates to the required arguments.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Redaction(String, Vec<String>) = (
        "the data for key `{_0}` is not available, but we recovered: {}",
        _1.join("+"),
    ),
}

impl ::core::fmt::Display for DataStoreError {
```

--------------------------------

### Auto-generate Doc Comments with displaystr

Source: https://docs.rs/displaystr/latest/displaystr

Use `#[display(doc)]` to automatically generate `///` doc comments for enum variants based on their associated string literals.

```rust
use displaystr::display;

#[display(doc)]
pub enum DataStoreError {
    Disconnect(std::io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

```rust
use displaystr::display;

pub enum DataStoreError {
    /// data store disconnected
    Disconnect(std::io::Error),
    /// the data for key `{_0}` is not available
    Redaction(String),
    /// invalid header (expected {expected:?}, found {found:?})
    InvalidHeader {
        expected: String,
        found: String,
    },
    /// unknown data store error
    Unknown,
}

// impl Display omitted since it's identical to the previous section
```

--------------------------------

### Generate Enum Variant Arm for Display

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Constructs a `DisplayArm` `TokenTree` array for an enum variant, suitable for implementing `fmt::Display`. It includes the variant, destructuring pattern, and format arguments.

```rust
fn generate_arm(
    variant: &str,
    destructure: TokenTree,
    string: Literal,
    stream: TokenStream,
) -> DisplayArm {
    [
        TokenTree::Ident(Ident::new("Self", Span::call_site())),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Punct(Punct::new(':', Spacing::Joint)),
        TokenTree::Ident(Ident::new(variant, Span::call_site())),
        destructure,
        TokenTree::Punct(Punct::new('=', Spacing::Joint)),
        TokenTree::Punct(Punct::new('>', Spacing::Joint)),
        TokenTree::Ident(Ident::new("f", Span::call_site())),
        TokenTree::Punct(Punct::new('.', Spacing::Joint)),
        TokenTree::Ident(Ident::new("write_fmt", Span::call_site())),
        TokenTree::Group(Group::new(
            Delimiter::Parenthesis,
            TokenStream::from_iter([
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Ident(Ident::new("core", Span::call_site())),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
                TokenTree::Ident(Ident::new("format_args", Span::call_site())),
                TokenTree::Punct(Punct::new('!', Spacing::Joint)),
                TokenTree::Group(Group::new(
                    Delimiter::Parenthesis,
                    [TokenTree::Literal(string)]
                        .into_iter()
                        .chain(stream)
                        .collect(),
                )),
            ]),
        )),
    ]
}
```

--------------------------------

### Implement Display for Enum with displaystr

Source: https://docs.rs/displaystr

Use the `#[display]` attribute macro on enums to automatically implement the `core::fmt::Display` trait. Each enum variant can be assigned a format string, optionally referencing its fields.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Disconnect(std::io::Error) = "data store disconnected",
    Redaction(String) = "the data for key `{_0}` is not available",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
    Unknown = "unknown data store error",
}
```

--------------------------------

### Display implementation for enum variants

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This code shows the expanded implementation of the `Display` trait for an enum, generated by the `#[display]` macro. It matches enum variants and formats strings accordingly.

```rust
impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Disconnect(_0) => {
                f.write_fmt(format_args!("data store disconnected"))
            }
            Self::InvalidHeader { expected, found } => {
                f.write_fmt(format_args!("invalid header (expected {expected}, found {found})"))
            }
        }
    }
}
```

--------------------------------

### Expanded Display implementation for enum variants

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This code shows the expanded implementation of the `Display` trait for an enum, generated by the `#[display]` macro. It matches enum variants and formats strings accordingly.

```rust
pub enum DataStoreError {
    Disconnect(std::io::Error),
    InvalidHeader {
        expected: String,
        found: String,
    },
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Disconnect(_0) => {
                f.write_fmt(format_args!("data store disconnected"))
            }
            Self::InvalidHeader { expected, found } => {
                f.write_fmt(format_args!("invalid header (expected {expected}, found {found})"))
            }
        }
    }
}
```

--------------------------------

### Expanded Enum with Multiple Arguments

Source: https://docs.rs/displaystr

This shows the generated `impl Display` for an enum variant that uses multiple arguments in its format string, including an expression to format a field.

```rust
use displaystr::display;

pub enum DataStoreError {
    Redaction(String, Vec<String>),
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Redaction(_0, _1) => f.write_fmt(format_args!(
                "the data for key `{_0}` is not available, but we recovered: {}",
                _1.join("+")
            )),
        }
    }
}
```

--------------------------------

### Create CompileError Instance

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Creates a new `CompileError` with a specified span and message. Use this to define compile-time errors.

```rust
pub fn new(span: Span, message: impl AsRef<str>) -> Self {
        Self {
            span,
            message: message.as_ref().to_string(),
        }
    }
```

--------------------------------

### Implement Display for Enum with displaystr

Source: https://docs.rs/displaystr/latest/displaystr/attr.display.html

Use the `#[display]` attribute macro to automatically derive the `Display` trait for an enum. This macro allows custom string formatting for enum variants, including those with data.

```rust
use displaystr::display;

#[display]
pub enum DataStoreError {
    Disconnect(std::io::Error) = "data store disconnected",
    InvalidHeader {
        expected: String,
        found: String,
    } = "invalid header (expected {expected:?}, found {found:?})",
}
```

```rust
use displaystr::display;

pub enum DataStoreError {
    Disconnect(std::io::Error),
    InvalidHeader {
        expected: String,
        found: String,
    },
}

impl ::core::fmt::Display for DataStoreError {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        match self {
            Self::Disconnect(_0) => {
                f.write_fmt(format_args!("data store disconnected"))
            }
            Self::InvalidHeader { expected, found } => {
                f.write_fmt(format_args!("invalid header (expected {expected}, found {found})"))
            }
        }
    }
}
```

--------------------------------

### Parsing Enum Attributes and Keywords

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This code parses and collects attributes, the 'enum' keyword, and the enum identifier. It handles skipping attributes like '#[foo = bar]' and ensures the 'enum' keyword is correctly identified.

```rust
loop {
        let Some(tt) = ts.next() else {
            return CompileError::new(Span::call_site(), "expected an `enum` item")
                .into_iter()
                .collect();
        };

        match tt {
            // Skip all `OuterAttribute`
            //
            // #[foo = bar]
            // ^
            TokenTree::Punct(punct) if punct == '#' => {
                output.extend([TokenTree::Punct(punct)]);

                // #[foo = bar]
                //  ^^^^^^^^^^^
                output.extend(ts.next());
            }
            // Reached enum keyword. End parsing.
            //
            // enum Foo { ... }
            // ^^^^
            TokenTree::Ident(ident) if ident.to_string() == "enum" => {
                output.extend([TokenTree::Ident(ident)]);
                break;
            }
            // ignore any other token e.g. `pub` or `(crate)`
            tt => {
                output.extend([tt]);
            }
        }
    }
```

--------------------------------

### Handle Enum Variant Parsing Errors

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Provides a dummy arm for compilation continuation when an error occurs during enum variant string extraction. Collects compile errors.

```rust
arms.extend(generate_arm(
                            &variant_ident.to_string(),
                            destructure,
                            Literal::string(""),
                            TokenStream::new(),
                        ));
                        compile_errors.extend(compile_error);
```

--------------------------------

### Enum Error Definition with displaydoc and thiserror

Source: https://docs.rs/displaystr/latest/displaystr

Defines an enum for data store errors using both `thiserror` and `displaydoc`. `displaydoc` automatically generates `Display` implementations from doc comments.

```rust
use thiserror::Error;
use displaydoc::Display;

#[derive(Display, Error, Debug)]
pub enum DataStoreError {
    /// data store disconnected
    Disconnect(#[source] io::Error),
    /// the data for key `{0}` is not available
    Redaction(String),
    /// invalid header (expected {expected:?}, found {found:?})
    InvalidHeader {
        expected: String,
        found: String,
    },
    /// unknown data store error
    Unknown,
}
```

--------------------------------

### Handle Unit Variant with Trailing Comma

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Handles a unit variant followed by a comma, which is considered invalid as it expects a string discriminant. It generates a compile error and a dummy arm for compilation.

```rust
Some(TokenTree::Punct(punct)) if punct == ',' => {
                variant.extend([TokenTree::Punct(punct.clone())]);

                compile_errors.extend(CompileError::new(
                    variant_ident.span(),
                    "expected this variant to have a string discriminant: `= \"...\"`",
                ));

                // DUMMY arm so we compile. so rust-analyzer works better
                arms.extend(generate_arm(
                    &variant_ident.to_string(),
                    // Foo {}
                    //     ^^
                    TokenTree::Group(Group::new(Delimiter::Brace, TokenStream::new())),
                    Literal::string(""),
                    TokenStream::new(),
                ));
            }
```

--------------------------------

### Destructuring Tuple Variant Fields

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Generates destructuring bindings (e.g., '_0', '_1') for tuple variant fields. This is used when generating code to access individual fields within a variant.

```rust
let destructure = (0..variant_count)
                    .flat_map(|i| {
                        [
                            TokenTree::Ident(Ident::new(&format!("_{i}"), Span::call_site())),
                            TokenTree::Punct(Punct::new(',', Spacing::Joint)),
                        ]
                    })
                    .collect();
```

--------------------------------

### Handle Unit Variant with No Trailing Comma

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Handles the case where a unit variant is the last one and has no trailing comma. This is also considered invalid as it expects a string discriminant. It generates a compile error and a dummy arm.

```rust
None => {
                compile_errors.extend(CompileError::new(
                    variant_ident.span(),
                    "expected this variant to have a string discriminant: `= \"...\"`",
                ));

                // DUMMY arm so we compile. so rust-analyzer works better
                arms.extend(generate_arm(
                    &variant_ident.to_string(),
                    // Foo {}
                    //     ^^
                    TokenTree::Group(Group::new(Delimiter::Brace, TokenStream::new())),
                    Literal::string(""),
                    TokenStream::new(),
                ));

                break;
            }
```

--------------------------------

### Parsing Enum Variant Visibility

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Handles parsing of visibility modifiers like 'pub' and 'pub(crate)' for enum variants. It extracts these modifiers to be included in the generated code.

```rust
Some(TokenTree::Ident(ident)) if ident.to_string() == "pub" => {
                variant.extend(enum_body.next());

                match enum_body.peek() {
                    // pub(in crate)
                    //    ^^^^^^^^^^^
                    Some(TokenTree::Group(group))
                        if group.delimiter() == Delimiter::Parenthesis =>
                    {
                        variant.extend(enum_body.next());
                    }
                    _ => ()
                }
            }
```

--------------------------------

### Implement IntoIterator for CompileError

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Converts a `CompileError` into an iterator of `TokenTree`s, representing the `compile_error!($message)` macro invocation. This is useful for generating code at compile time.

```rust
impl IntoIterator for CompileError {
    type Item = TokenTree;
    type IntoIter = std::array::IntoIter<Self::Item, 3>;

    fn into_iter(self) -> Self::IntoIter {
        [
            TokenTree::Ident(Ident::new("compile_error", self.span)),
            TokenTree::Punct({
                let mut punct = Punct::new('!', Spacing::Alone);
                punct.set_span(self.span);
                punct
            }),
            TokenTree::Group({
                let mut group = Group::new(Delimiter::Brace, {
                    TokenStream::from_iter(vec![TokenTree::Literal({
                        let mut string = Literal::string(&self.message);
                        string.set_span(self.span);
                        string
                    })])
                });
                group.set_span(self.span);
                group
            }),
        ]
        .into_iter()
    }
}
```

--------------------------------

### Parsing Tuple Variant Fields

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Parses the fields of a tuple variant, like '(a, b)' in 'Foo(a, b)'. It counts the number of fields to correctly destructure them later.

```rust
Some(TokenTree::Group(fields)) if fields.delimiter() == Delimiter::Parenthesis => {
                variant.extend([TokenTree::Group(fields.clone())]);

                // Foo() has 0 variant. Otherwise, start the count at 1
                let mut fields = fields.stream().into_iter().peekable();
                let is_zero_variants = fields.peek().is_none();

                // Let's count how many commas there are between each field
                //
                // Foo(bar, baz, quux,)
                //        ^ this one
                //             ^ and this one
                //                   ^ but not this one (it is trailing)
                let mut commas = 0;

                while let Some(tt) = fields.next() {
                    match tt {
                        TokenTree::Punct(punct) if punct == ',' => {
                            // Only count non-trailing commas
                            if fields.peek().is_some() {
                                commas += 1;
                            }
                        }
                        // ignore any other tokens
                        _ => ()
                    }
                }

                // Foo() has 0 fields
                // Foo(bar) has 1 field
                // Foo(bar,) has 1 field
                // Foo(bar,baz) has 2 fields
                let variant_count = if is_zero_variants { 0 } else { 1 + commas };
```

--------------------------------

### Generate Enum Variant Arm

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Generates a match arm for an enum variant, extracting a string literal and associated stream of tokens. Used when doc comments are enabled.

```rust
arms.extend(generate_arm(
                            &variant_ident.to_string(),
                            destructure,
                            string,
                            stream,
                        ));
```

--------------------------------

### Extracting Where Clause from Enum Definition

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This code extracts the 'where' clause from an enum definition. It continues to consume tokens until it encounters the opening brace of the enum body.

```rust
let where_clause = match ts.peek() {
        Some(TokenTree::Ident(ident)) if ident.to_string() == "where" => {
            let mut where_clause = TokenStream::new();
            where_clause.extend(ts.next());

            loop {
                match ts.peek() {
                    Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::Brace => break,
                    _ => {
                        where_clause.extend(ts.next());
                    }
                }
            }

            where_clause
        }
        _ => TokenStream::new(),
    };
```

--------------------------------

### Handle Compile Error in Enum Variant Parsing

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This code arm handles compile errors during enum variant parsing, extending the list of compile errors and generating a dummy arm to ensure compilation proceeds.

```rust
Err(compile_error) => {
                        // dummy arm so we just continue compiling
                        arms.extend(generate_arm(
                            &variant_ident.to_string(),
                            destructure,
                            Literal::string(""),
                            TokenStream::new(),
                        ));
                        compile_errors.extend(compile_error);
                    }
```

--------------------------------

### Parsing Enum Body

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This snippet parses the main body of the enum definition, which is expected to be enclosed in curly braces. It prepares the stream of tokens within the braces for further processing.

```rust
let mut enum_body = match ts.next() {
        Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::Brace => {
            group.stream().into_iter().peekable()
        }
        _ => unreachable!("enum has braces"),
    };
```

--------------------------------

### Enum Error Definition with thiserror

Source: https://docs.rs/displaystr/latest/displaystr

Defines an enum for data store errors using `thiserror`. Each variant has a custom error message.

```rust
use thiserror::Error;

#[derive(Error, Debug)]
pub enum DataStoreError {
    #[error("data store disconnected")]
    Disconnect(#[from] io::Error),
    #[error("the data for key `{0}` is not available")]
    Redaction(String),
    #[error("invalid header (expected {expected:?}, found {found:?})")]
    InvalidHeader {
        expected: String,
        found: String,
    },
    #[error("unknown data store error")]
    Unknown,
}
```

--------------------------------

### Parse Enum Variant with String Discriminant

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Parses an enum variant that has a string discriminant. It extracts the string, generates documentation comments if enabled, and creates a corresponding arm for the display string generation.

```rust
Some(TokenTree::Punct(punct)) if punct == '=' => {
                // Foo = "foo",
                //       ^^^^^ 
                match extract_string(&mut enum_body) {
                    Ok((string, stream)) => {
                        if generate_doc_comments {
                            variants.extend(doc_comment(&string.to_string()));
                        }
                        // Success.
                        arms.extend(generate_arm(
                            &variant_ident.to_string(),
                            // Foo {}
                            //     ^^
                            TokenTree::Group(Group::new(Delimiter::Brace, TokenStream::new())),
                            string,
                            stream,
                        ));
                    }
                    Err(compile_error) => {
                        compile_errors.extend(compile_error);

                        // DUMMY arm so we compile. so rust-analyzer works better
                        arms.extend(generate_arm(
                            &variant_ident.to_string(),
                            // Foo {}
                            //     ^^
                            TokenTree::Group(Group::new(Delimiter::Brace, TokenStream::new())),
                            Literal::string(""),
                            TokenStream::new(),
                        ));
                    }
                }

                // Foo = "foo",
                //            ^
                match enum_body.peek() {
                    Some(TokenTree::Punct(punct)) if *punct == ',' => {
                        // trailing comma
                        variant.extend(enum_body.next());
                    }
                    _ => ()
                }
            }
```

--------------------------------

### Extracting Generics from Enum Definition

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

This snippet extracts the generic parameters of an enum, including the angle brackets and their contents. It handles cases with and without generics.

```rust
let generics = match ts.peek() {
        // opening '<'
        //
        // enum Foo <all: of_the_generics> { ... }
        //          ^
        Some(TokenTree::Punct(punct)) if *punct == '<' => {
            let mut generics = TokenStream::new();
            generics.extend(ts.next());

            loop {
                match ts.next() {
                    // closing '>'
                    //
                    // enum Foo <all: of_the_generics> { ... }
                    //                               ^
                    Some(TokenTree::Punct(punct)) if punct == '>' => {
                        generics.extend([TokenTree::Punct(punct)]);
                        break;
                    }
                    tt => {
                        generics.extend(tt);
                    }
                }
            }

            generics
        }
        _ => TokenStream::new(),
    };
```

--------------------------------

### Parse Struct Variant Fields

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Iterates through the fields of a struct variant, identifying and collecting fields that are followed by a colon, indicating a type annotation. Handles nested types and trailing commas.

```rust
loop {
                    let current = fields.next();
                    match fields.peek() {
                        Some(TokenTree::Punct(punct)) if *punct == ':' && !is_inside_type => {
                            // Self::InvalidHeader { expected, found, } => f.write_fmt(format_args!(
```

```rust
destructure.extend(current);
                            // Self::InvalidHeader { expected, found, } => f.write_fmt(format_args!(
```

```rust
destructure.extend([TokenTree::Punct(Punct::new(',', Spacing::Joint))]);
                            is_inside_type = true;
                        }
                        // foo: Bar,
                        //         ^
                        Some(TokenTree::Punct(punct)) if *punct == ',' && is_inside_type => {
                            is_inside_type = false;
                        }
                        // ignore any other tokens like `#[doc = "..."]` or `pub(crate)`
                        Some(_) => (),
                        // Reached end of the struct variant's fields
                        None => break,
                    }
                }
```

--------------------------------

### Parsing Enum Variant Attributes

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Parses attributes like #[foo = bar] preceding an enum variant. These attributes are collected before the variant's main definition.

```rust
Some(TokenTree::Punct(punct)) if *punct == '#' => {
                    // #[foo = bar]
                    // ^
                    variants.extend(enum_body.next());
                    // #[foo = bar]
                    //  ^^^^^^^^^^^
                    variants.extend(enum_body.next());
                }
```

--------------------------------

### Extract String Literal from Token Stream

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Extracts a string literal from a token stream, handling both direct literals and parenthesized expressions. Used when parsing string discriminants for enum variants.

```rust
fn extract_string(
    ts: &mut std::iter::Peekable<proc_macro::token_stream::IntoIter>,
) -> Result<(Literal, TokenStream), CompileError> {
    let next = ts.next();

    match next {
        Some(TokenTree::Literal(string)) => {
            // Success.
            Ok((string, TokenStream::new()))
        }
        Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::Parenthesis => {
            let mut stream = group.stream().into_iter();

            match stream.next() {
                Some(TokenTree::Literal(string)) => Ok((string, stream.collect())),
                Some(tt) => Err(CompileError::new(tt.span(), "expected string literal")),
                None => Err(CompileError::new(group.span(), "expected string literal")),
            }
        }
        Some(tt) => Err(CompileError::new(tt.span(), "expected string literal")),
        None => unreachable!("`=` is always followed by an expression"),
    }
}
```

--------------------------------

### Parsing Enum Variant Identifier

Source: https://docs.rs/displaystr/latest/src/displaystr/lib.rs.html

Extracts the identifier for an enum variant, such as 'Foo' in 'Foo {}' or 'Foo(a, b)'. This identifier is crucial for constructing the variant's representation.

```rust
let variant_ident = match enum_body.next() {
            Some(TokenTree::Ident(ident)) => {
                variant.extend([TokenTree::Ident(ident.clone())]);
                ident
            }
            _ => unreachable!("identifier must appear in this position"),
        };
```
Tokens:
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