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use proc_macro2::TokenTree;
/// Reconstruct a CSS string from a proc-macro token stream.
///
/// Handles the quirks of Rust tokenization:
/// - `.class` tokenized as Punct('.') Ident(class) → joined without space
/// - `#id` tokenized as Punct('#') Ident(id) → joined without space
/// - `margin-left` tokenized as Ident(margin) Punct('-') Ident(left) → joined without space
/// - `10px` tokenized as Literal(10) Ident(px) → joined without space
/// - `0.5em` tokenized as Literal(0.5) Ident(em) → joined without space
/// - `@media` tokenized as Punct('@') Ident(media) → joined without space
/// - `:hover` / `::before` → joined without space
pub fn tokens_to_css(input: proc_macro2::TokenStream) -> String {
let tokens: Vec<TokenTree> = input.into_iter().collect();
let mut result = String::new();
build_css(&tokens, &mut result);
result
}
fn build_css(tokens: &[TokenTree], out: &mut String) {
let len = tokens.len();
let mut i = 0;
while i < len {
match &tokens[i] {
TokenTree::Group(group) => {
let delim = group.delimiter();
match delim {
proc_macro2::Delimiter::Brace => {
out.push('{');
let inner: Vec<TokenTree> = group.stream().into_iter().collect();
build_css(&inner, out);
out.push('}');
}
proc_macro2::Delimiter::Parenthesis => {
out.push('(');
let inner: Vec<TokenTree> = group.stream().into_iter().collect();
build_css(&inner, out);
out.push(')');
}
proc_macro2::Delimiter::Bracket => {
out.push('[');
let inner: Vec<TokenTree> = group.stream().into_iter().collect();
build_css(&inner, out);
out.push(']');
}
proc_macro2::Delimiter::None => {
let inner: Vec<TokenTree> = group.stream().into_iter().collect();
build_css(&inner, out);
}
}
i += 1;
}
TokenTree::Punct(p) => {
let ch = p.as_char();
match ch {
// `.class` or `.class1.class2` — no space before ident
'.' => {
// Check if previous char needs no space
if needs_space_before_punct(out) {
out.push(' ');
}
out.push('.');
// If next token is an ident or literal, join directly
if i + 1 < len && is_ident_or_literal(&tokens[i + 1]) {
i += 1;
push_token(&tokens[i], out);
}
i += 1;
}
// `#id` or `#ff0000`
'#' => {
if needs_space_before_punct(out) {
out.push(' ');
}
out.push('#');
if i + 1 < len && is_ident_or_literal(&tokens[i + 1]) {
i += 1;
push_token(&tokens[i], out);
}
i += 1;
}
// `@media`, `@keyframes`, etc.
'@' => {
if !out.is_empty() && !out.ends_with('{') && !out.ends_with('\n') {
out.push(' ');
}
out.push('@');
if i + 1 < len && is_ident(&tokens[i + 1]) {
i += 1;
push_token(&tokens[i], out);
}
i += 1;
}
// `-` could be part of a CSS property name like `margin-left`
// or a negative value like `-10px`
'-' => {
let prev_is_ident = i > 0 && is_ident(&tokens[i - 1]);
let next_is_ident_or_lit =
i + 1 < len && is_ident_or_literal(&tokens[i + 1]);
if prev_is_ident && next_is_ident_or_lit {
// `margin-left` pattern — join without spaces
out.push('-');
} else if next_is_ident_or_lit {
// Negative value like `-10px`
if needs_space_before_value(out) {
out.push(' ');
}
out.push('-');
} else {
out.push('-');
}
i += 1;
}
// `:` for property values or pseudo-selectors like `:hover`
':' => {
out.push(':');
// `::before` — double colon
if i + 1 < len && is_punct_char(&tokens[i + 1], ':') {
out.push(':');
i += 1;
}
i += 1;
}
// `;` ends a declaration
';' => {
out.push(';');
i += 1;
}
// `,` in selectors or values
',' => {
out.push(',');
i += 1;
}
// `>`, `+`, `~` combinators
'>' | '+' | '~' => {
out.push(' ');
out.push(ch);
out.push(' ');
i += 1;
}
// `*` universal selector or in calc
'*' => {
if needs_space_before_value(out) {
out.push(' ');
}
out.push('*');
i += 1;
}
// `=` in attribute selectors
'=' => {
out.push('=');
i += 1;
}
// `!` for `!important`
'!' => {
out.push(' ');
out.push('!');
if i + 1 < len && is_ident(&tokens[i + 1]) {
i += 1;
push_token(&tokens[i], out);
}
i += 1;
}
// `%` for percentages
'%' => {
out.push('%');
i += 1;
}
_ => {
out.push(ch);
i += 1;
}
}
}
TokenTree::Ident(ident) => {
let s = ident.to_string();
if needs_space_before_value(out) {
out.push(' ');
}
out.push_str(&s);
// Check if next is a literal directly after ident (shouldn't normally happen)
// or handle `10px` where literal comes before ident
i += 1;
}
TokenTree::Literal(lit) => {
let s = lit.to_string();
if needs_space_before_value(out) {
out.push(' ');
}
// String literals: strip quotes and use contents directly
if s.starts_with('"') && s.ends_with('"') {
out.push_str(&s[1..s.len() - 1]);
} else {
out.push_str(&s);
// Check if next token is an ident (unit suffix like `px`, `em`, `rem`, `%`)
if i + 1 < len && is_ident(&tokens[i + 1]) {
// Could be a unit: join directly
if is_css_unit(&tokens[i + 1]) {
i += 1;
push_token(&tokens[i], out);
}
}
}
i += 1;
}
}
}
}
fn push_token(token: &TokenTree, out: &mut String) {
match token {
TokenTree::Ident(ident) => out.push_str(&ident.to_string()),
TokenTree::Literal(lit) => {
let s = lit.to_string();
if s.starts_with('"') && s.ends_with('"') {
out.push_str(&s[1..s.len() - 1]);
} else {
out.push_str(&s);
}
}
_ => out.push_str(&token.to_string()),
}
}
fn is_ident(token: &TokenTree) -> bool {
matches!(token, TokenTree::Ident(_))
}
fn is_ident_or_literal(token: &TokenTree) -> bool {
matches!(token, TokenTree::Ident(_) | TokenTree::Literal(_))
}
fn is_punct_char(token: &TokenTree, ch: char) -> bool {
matches!(token, TokenTree::Punct(p) if p.as_char() == ch)
}
fn is_css_unit(token: &TokenTree) -> bool {
if let TokenTree::Ident(ident) = token {
let s = ident.to_string();
matches!(
s.as_str(),
"px" | "em" | "rem" | "vh" | "vw" | "vmin" | "vmax" | "ch" | "ex" | "cm" | "mm"
| "in" | "pt" | "pc" | "fr" | "s" | "ms" | "deg" | "rad" | "grad" | "turn"
| "dpi" | "dpcm" | "dppx" | "n" | "x"
)
} else {
false
}
}
fn needs_space_before_punct(out: &str) -> bool {
if out.is_empty() {
return false;
}
let last = out.chars().last().unwrap();
// No space after these
!matches!(last, '{' | '(' | '[' | ' ' | '\n' | '.' | '#' | ':' | ',' | ';')
}
fn needs_space_before_value(out: &str) -> bool {
if out.is_empty() {
return false;
}
let last = out.chars().last().unwrap();
!matches!(
last,
'{' | '(' | '[' | ' ' | '\n' | '.' | '#' | '@' | ':' | '-' | ',' | ';' | '>' | '+'
| '~' | '*' | '=' | '!'
)
}