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Add helpful comments to tt_prepend_space.

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This commit is contained in:
Nicholas Nethercote 2023-08-04 11:40:45 +10:00
parent 434bfc3162
commit 3bb85b73b5
1 changed files with 11 additions and 0 deletions
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11
compiler/rustc_ast_pretty/src/pprust/state.rs
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@ -150,6 +150,8 @@ pub fn print_crate<'a>(
/// and also addresses some specific regressions described in #63896 and #73345.
fn tt_prepend_space(tt: &TokenTree, prev: &TokenTree) -> bool {
if let TokenTree::Token(token, _) = prev {
// No space after these tokens, e.g. `x.y`, `$e`
// (The carets point to `prev`.) ^ ^
if matches!(token.kind, token::Dot | token::Dollar) {
return false;
}
@ -158,10 +160,19 @@ fn tt_prepend_space(tt: &TokenTree, prev: &TokenTree) -> bool {
}
}
match tt {
// No space before these tokens, e.g. `foo,`, `println!`, `x.y`
// (The carets point to `token`.) ^ ^ ^
//
// FIXME: having `Not` here works well for macro invocations like
// `println!()`, but is bad when `!` means "logical not" or "the never
// type", where the lack of space causes ugliness like this:
// `Fn() ->!`, `x =! y`, `if! x { f(); }`.
TokenTree::Token(token, _) => !matches!(token.kind, token::Comma | token::Not | token::Dot),
// No space before parentheses if preceded by these tokens, e.g. `foo(...)`
TokenTree::Delimited(_, Delimiter::Parenthesis, _) => {
!matches!(prev, TokenTree::Token(Token { kind: token::Ident(..), .. }, _))
}
// No space before brackets if preceded by these tokens, e.g. `#[...]`
TokenTree::Delimited(_, Delimiter::Bracket, _) => {
!matches!(prev, TokenTree::Token(Token { kind: token::Pound, .. }, _))
}