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use std::fmt;
use proc_macro::TokenStream;
use quote::{quote, ToTokens};
use syn::ext::IdentExt as _;
use syn::parse::{Parse, ParseStream};
use syn::punctuated::Punctuated;
mod kw {
syn::custom_keyword!(DOCTYPE);
syn::custom_keyword!(html);
}
/// Represents an identifier separated by dashes, e.g., `foo-bar-baz`.
struct DashIdent(Punctuated<syn::Ident, syn::Token![-]>);
impl fmt::Display for DashIdent {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// Iterate through the punctuated identifiers and format them with
// dashes in between.
for pair in self.0.pairs() {
std::write!(f, "{}", pair.value())?;
// If there's a punctuation, it's a dash, so we append it.
if pair.punct().is_some() {
std::write!(f, "-")?;
}
}
Ok(())
}
}
impl Parse for DashIdent {
fn parse(input: ParseStream) -> syn::Result<Self> {
// Parse a non-empty sequence of identifiers separated by dashes.
Ok(Self(Punctuated::<syn::Ident, syn::Token![-]>::parse_separated_nonempty_with(input, syn::Ident::parse_any)?))
}
}
/// Represents the DOCTYPE declaration in HTML, e.g., `<!DOCTYPE html>`.
struct Doctype;
impl Parse for Doctype {
fn parse(input: ParseStream) -> syn::Result<Self> {
// Parse each component of the DOCTYPE declaration.
input.parse::<syn::Token![<]>()?;
input.parse::<syn::Token![!]>()?;
input.parse::<kw::DOCTYPE>()?;
input.parse::<kw::html>()?;
input.parse::<syn::Token![>]>()?;
Ok(Self)
}
}
impl fmt::Display for Doctype {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
std::write!(f, "<!DOCTYPE html>")
}
}
#[derive(Clone)]
enum Value {
/// A text literal, such as "Hello, World!"
Text(syn::LitStr),
/// A 'braced' value, such as `{1 + 1}`.
Braced(syn::Expr),
}
impl fmt::Display for Value {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
std::write!(f, "{{}}")
}
}
impl Parse for Value {
fn parse(input: ParseStream) -> syn::Result<Self> {
if input.peek(syn::LitStr) {
Ok(Self::Text(input.parse()?))
} else {
// Parse braced expressions.
let expr;
syn::braced!(expr in input);
Ok(Self::Braced(expr.parse()?))
}
}
}
impl ToTokens for Value {
fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
match self {
Value::Text(lit) => lit.to_tokens(tokens),
Value::Braced(expr) => expr.to_tokens(tokens),
}
}
}
/// Represents an HTML attribute, consisting of a name-value pair.
struct Attribute {
name: DashIdent,
value: Value,
}
impl Parse for Attribute {
fn parse(input: ParseStream) -> syn::Result<Self> {
let name = input.parse()?;
input.parse::<syn::Token![=]>()?;
let value = input.parse()?;
Ok(Self { name, value })
}
}
/// Represents an HTML tag, which can be either a start tag with attributes and
/// optional self-closing flag, or an end tag.
enum Tag {
Start {
name: DashIdent,
attributes: Vec<Attribute>,
self_closing: bool,
},
End {
name: DashIdent,
},
}
impl fmt::Display for Tag {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Tag::Start {
name,
attributes,
self_closing,
} => {
std::write!(f, "<{}", name)?;
for attr in attributes {
std::write!(f, " {}=\"{}\"", attr.name, attr.value)?;
}
if *self_closing {
std::write!(f, "/")?;
}
std::write!(f, ">")
}
Tag::End { name } => std::write!(f, "</{}>", name),
}
}
}
impl Parse for Tag {
/// Parses an HTML tag, which could be a start tag with attributes and an
/// optional self-closing indicator, or an end tag.
fn parse(input: ParseStream) -> syn::Result<Self> {
// Parse the opening angle bracket
input.parse::<syn::Token![<]>()?;
// Check if it's an end tag
let forward_slash = input.peek(syn::Token![/]);
if forward_slash {
input.parse::<syn::Token![/]>()?;
// Parse the tag name
let name: DashIdent = input.parse()?;
// Parse the closing '>'
input.parse::<syn::Token![>]>()?;
// Return the end tag variant
return Ok(Tag::End { name });
}
// Parse the tag name for start tag
let name: DashIdent = input.parse()?;
// Parse attributes if any
let mut attributes = Vec::new();
while !(input.peek(syn::Token![>])
|| (input.peek(syn::Token![/]) && input.peek2(syn::Token![>])))
{
attributes.push(input.parse()?);
}
// Check for self-closing tag
let self_closing = input.peek(syn::Token![/]);
if self_closing {
// Consume '/>'
input.parse::<syn::Token![/]>()?;
input.parse::<syn::Token![>]>()?;
} else {
// Consume '>'
input.parse::<syn::Token![>]>()?;
}
// Return the start tag variant
Ok(Tag::Start {
name,
attributes,
self_closing,
})
}
}
enum Segment {
/// Represents an HTML `<!DOCTYPE html>` declaration.
Doctype(Doctype),
/// Represents an HTML tag, which may be a start tag, an end tag or a
/// self-closing tag.
Tag(Tag),
/// Represents text or interpolated values within an HTML document.
Value(Value),
}
impl fmt::Display for Segment {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Segment::Doctype(doctype) => doctype.fmt(f),
Segment::Tag(tag) => tag.fmt(f),
Segment::Value(value) => value.fmt(f),
}
}
}
impl Parse for Segment {
fn parse(input: ParseStream) -> syn::Result<Self> {
if input.peek(syn::Token![<])
&& input.peek2(syn::Token![!])
&& input.peek3(kw::DOCTYPE)
{
Ok(Segment::Doctype(input.parse()?))
} else if input.peek(syn::Token![<]) {
Ok(Segment::Tag(input.parse()?))
} else if input.peek(syn::LitStr) || input.peek(syn::token::Brace) {
Ok(Segment::Value(input.parse()?))
} else {
Err(input.error("unexpected token"))
}
}
}
struct Template {
// Contains the segments of the HTML template.
segments: Vec<Segment>,
/// Stores values that are interpolated into the template.
values: Vec<Value>,
}
impl fmt::Display for Template {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
for segment in &self.segments {
segment.fmt(f)?;
}
Ok(())
}
}
impl Parse for Template {
fn parse(input: ParseStream) -> syn::Result<Self> {
let mut segments = vec![];
let mut values = vec![];
while !input.is_empty() {
let segment = input.parse::<Segment>()?;
if let Segment::Tag(Tag::Start { attributes, .. }) = &segment {
for attr in attributes {
values.push(attr.value.clone());
}
}
if let Segment::Value(value) = &segment {
values.push(value.clone());
}
segments.push(segment);
}
Ok(Self { segments, values })
}
}
struct WriteInput {
formatter: syn::Expr,
template: Template,
}
impl Parse for WriteInput {
fn parse(input: ParseStream) -> syn::Result<Self> {
let formatter = input.parse()?;
input.parse::<syn::Token![,]>()?;
let template = input.parse()?;
Ok(Self {
formatter,
template,
})
}
}
/// Writes HTML content with embedded Rust expressions into a buffer.
///
/// This macro simplifies writing HTML content by allowing Rust expressions to
/// be embedded directly within HTML tags. It uses `std::write!` internally,
/// thereby supporting all formatting capabilities and constraints of
/// `std::write!`.
///
/// ## Syntax
///
/// The `fhtml::write!` macro syntax closely resembles regular HTML, but allows
/// Rust expressions to be inserted within curly braces `{}`. These expressions
/// are evaluated and their results are inserted into the HTML output at the
/// corresponding location.
///
/// ## Examples
///
/// Basic usage:
///
/// ```rust
/// use std::fmt::Write;
///
/// let mut buffer = String::new();
/// fhtml_macros::write!(buffer, <div>{1 + 1}</div>);
/// // This expands to:
/// // std::write!(buffer, "<div>{}</div>", 1 + 1);
///
/// assert_eq!(buffer, "<div>2</div>");
/// ```
///
/// This example demonstrates how to use `fhtml::write!` within an
/// implementation of `std::fmt::Display`:
///
/// ```rust
/// use std::fmt;
/// use std::fmt::Write;
///
/// struct Heading {
/// title: String,
/// }
///
/// impl fmt::Display for Heading {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fhtml_macros::write!(f, <h1>{self.title}</h1>)
/// }
/// }
///
/// let heading = Heading { title: "Hello, World!".into() }.to_string();
/// assert_eq!(heading, "<h1>Hello, World!</h1>");
/// ```
///
/// ## Notes
///
/// - The macro outputs HTML directly into the provided buffer.
/// - Similar to `std::write!`, errors during writing are handled by returning a
/// `Result` indicating either success (`Ok`) or an error (`Err`).
/// - Ensure proper escaping or sanitization of user-generated content to
/// prevent injection attacks when outputting HTML.
#[proc_macro]
pub fn write(input: TokenStream) -> TokenStream {
let WriteInput {
formatter,
template,
} = syn::parse_macro_input!(input as WriteInput);
let values = &template.values;
let template = template.to_string();
let output = quote! {
::std::write!(#formatter, #template, #(#values),*)
};
output.into()
}
#[proc_macro]
pub fn formatcp(input: TokenStream) -> TokenStream {
let template = syn::parse_macro_input!(input as Template);
let values = &template.values;
let template = template.to_string();
let output = quote! {
::fhtml::const_format::formatcp!(#template, #(#values),*)
};
output.into()
}