Stuart Cook a00818dfb4 Rollup merge of #154087 - aytey:fix-fragment-specifier-whitespace, r=Kivooeo ...

Fix whitespace after fragment specifiers in macro pretty printing

When a macro-generating-macro captures fragment specifier tokens (like `$x:ident`) as `tt` metavariables and replays them before a keyword (like `where`), the pretty printer concatenates them into an invalid fragment specifier (e.g. `$x:identwhere` instead of `$x:ident where`).

This happens because `tt` captures preserve the original token spacing. When the fragment specifier name (e.g. `ident`) was originally the last token before a closing delimiter, it retains `JointHidden` spacing. The `print_tts` function only checks `space_between` for `Spacing::Alone` tokens, so `JointHidden` tokens skip the space check entirely, causing adjacent identifier-like tokens to merge.

The fix adds a check in `print_tts` to insert a space between adjacent identifier-like tokens (identifiers and keywords) regardless of the original spacing, preventing them from being concatenated into invalid tokens.

This is similar to the existing `space_between` mechanism that prevents token merging for `Spacing::Alone` tokens, extended to also handle `Joint`/`JointHidden` cases where two identifier-like tokens would merge.

## Example

**before** (`rustc 1.96.0-nightly (3b1b0ef4d 2026-03-11)`):

```rust
#![feature(prelude_import)]
#![no_std]
extern crate std;
#[prelude_import]
use ::std::prelude::rust_2015::*;
//@ pretty-mode:expanded
//@ pp-exact:macro-fragment-specifier-whitespace.pp

// Test that fragment specifier names in macro definitions are properly
// separated from the following keyword/identifier token when pretty-printed.
// This is a regression test for a bug where `$x:ident` followed by `where`
// was pretty-printed as `$x:identwhere` (an invalid fragment specifier).

macro_rules! outer {
    ($d:tt $($params:tt)*) =>
    {
        #[macro_export] macro_rules! inner
        { ($($params)* where $d($rest:tt)*) => {}; }
    };
}
#[macro_export]
macro_rules! inner { ($x:identwhere $ ($rest : tt)*) => {}; }

fn main() {}
```

**after** (this branch):

```rust
#![feature(prelude_import)]
#![no_std]
extern crate std;
#[prelude_import]
use ::std::prelude::rust_2015::*;
//@ pretty-mode:expanded
//@ pp-exact:macro-fragment-specifier-whitespace.pp

// Test that fragment specifier names in macro definitions are properly
// separated from the following keyword/identifier token when pretty-printed.
// This is a regression test for a bug where `$x:ident` followed by `where`
// was pretty-printed as `$x:identwhere` (an invalid fragment specifier).

macro_rules! outer {
    ($d:tt $($params:tt)*) =>
    {
        #[macro_export] macro_rules! inner
        { ($($params)* where $d($rest:tt)*) => {}; }
    };
}
#[macro_export]
macro_rules! inner { ($x:ident where $ ($rest : tt)*) => {}; }

fn main() {}
```

Notice the `$x:identwhere` in the before — an invalid fragment specifier that causes a hard parse error. The after correctly separates it as `$x:ident where`.

2026-03-20 15:33:09 +11:00

..

src

Rollup merge of #154087 - aytey:fix-fragment-specifier-whitespace, r=Kivooeo

2026-03-20 15:33:09 +11:00

Cargo.toml

Use -Wunused_crate_dependencies for compiler crates.

2025-03-20 08:59:43 +11:00