Rollup merge of #145463 - jieyouxu:error-suffix, r=fmease

Reject invalid literal suffixes in tuple indexing, tuple struct indexing, and struct field name position

Tracking issue: rust-lang/rust#60210
Closes rust-lang/rust#60210

## Summary

Bump the ["suffixes on a tuple index are invalid" non-lint pseudo future-incompatibility warning (#60210)][issue-60210][^non-lint] to a **hard error** across all editions, rejecting the remaining carve outs from accidentally accepted invalid suffixes since Rust **1.27**.

- We accidentally accepted invalid suffixes in tuple indexing positions in Rust **1.27**. Originally reported at https://github.com/rust-lang/rust/issues/59418.
- We tried to hard reject all invalid suffixes in https://github.com/rust-lang/rust/pull/59421, but unfortunately it turns out there were proc macros accidentally relying on it: https://github.com/rust-lang/rust/issues/60138.
- We temporarily accepted `{i,u}{32,size}` in https://github.com/rust-lang/rust/pull/60186 (the "*carve outs*") to mitigate *immediate* ecosystem impact, but it came with an FCW warning indicating that we wanted to reject it after a few Rust releases.
- Now (1.89.0) is a few Rust releases later (1.35.0), thus I'm proposing to **also reject the carve outs**.
    - `std::mem::offset_of!` stabilized in Rust **1.77.0** happens to use the same "don't expect suffix" code path which has the carve outs, so it also accepted the carve out suffixes. I'm proposing to **reject this case as well**.

## What specifically breaks?

Code that still relied on invalid `{i,u}{32,size}` suffixes being temporarily accepted by rust-lang/rust#60186 as an ecosystem impact mitigation measure (cf. rust-lang/rust#60138). Specifically, the following cases (particularly the construction of these forms in proc macros like reported in rust-lang/rust#60138):

### Position 1: Invalid `{i,u}{32,size}` suffixes in tuple indexing

```rs
fn main() {
    let _x = (42,).0invalid; // Already error, already rejected by #59421
    let _x = (42,).0i8;      // Already error, not one of the #60186 carve outs.
    let _x = (42,).0usize;   // warning: suffixes on a tuple index are invalid
}
```

### Position 2: Invalid `{i,u}{32,size}` suffixes in tuple struct indexing

```rs
fn main() {
    struct X(i32);
    let _x = X(42);
	let _x = _x.0invalid; // Already error, already rejected by #59421
    let _x = _x.0i8;      // Already error, not one of the #60186 carve outs.
    let _x = _x.0usize;   // warning: suffixes on a tuple index are invalid
}
```

### Position 3: Invalid `{i,u}{32,size}` suffixes in numeric struct field names

```rs
fn main() {
    struct X(i32, i32, i32);
    let _x = X(1, 2, 3);
    let _y = X { 0usize: 42, 1: 42, 2: 42 };    // warning: suffixes on a tuple index are invalid
	match _x {
        X { 0usize: 1, 1: 2, 2: 3 } => todo!(), // warning: suffixes on a tuple index are invalid
        _ => {}
    }
}
```

### Position 4: Invalid `{i,u}{32,size}` suffixes in `std::mem::offset_of!`

While investigating the warning, unfortunately I noticed `std::mem::offset_of!` also happens to use the "expect no suffix" code path which had the carve outs. So this was accepted since Rust **1.77.0** with the same FCW:

```rs
fn main() {
    #[repr(C)]
    pub struct Struct<T>(u8, T);

    assert_eq!(std::mem::offset_of!(Struct<u32>, 0usize), 0);
    //~^ WARN suffixes on a tuple index are invalid
}
```

### The above forms in proc macros

For instance, constructions like (see tracking issue rust-lang/rust#60210):

```rs
let i = 0;
quote! { foo.$i }
```

where the user needs to actually write

```rs
let i = syn::Index::from(0);
quote! { foo.$i }
```

### Crater results

Conducted a crater run (https://github.com/rust-lang/rust/pull/145463#issuecomment-3194920383).

- https://github.com/AmlingPalantir/r4/tree/256af3c72f094b298cd442097ef7c571d8001f29: genuine regression; "invalid suffix `usize`" in derive macro. Has a ton of other build warnings, last updated 6 years ago.
    - Exactly the kind of intended breakage. Minimized down to https://github.com/AmlingPalantir/r4/blob/256af3c72f094b298cd442097ef7c571d8001f29/validates_derive/src/lib.rs#L71-L75, where when interpolation uses `quote`'s `ToTokens` on a `usize` index (i.e. on tuple struct `Tup(())`), the generated suffix becomes `.0usize` (cf. Position 2).
    - Notified crate author of breakage in https://github.com/AmlingPalantir/r4/issues/1.
- Other failures are unrelated or spurious.

## Review remarks

- Commits 1-3 expands the test coverage to better reflect the current situation before doing any functional changes.
- Commit 4 is an intentional **breaking change**. We bump the non-lint "suffixes on a tuple index are invalid" warning into a hard error. Thus, this will need a crater run and a T-lang FCP.

## Tasks

- [x] Run crater to check if anyone is still relying on this being not a hard error. Determine degree of ecosystem breakage.
- [x] If degree of breakage seems acceptable, draft nomination report for T-lang for FCP.
- [x] Determine hard error on Edition 2024+, or on all editions.

## Accompanying Reference update

- https://github.com/rust-lang/reference/pull/1966

[^non-lint]: The FCW was implemented as a *non-lint* warning (meaning it has no associated lint name, and you can't `#![deny(..)]` it) because spans coming from proc macros could not be distinguished from regular field access. This warning was also intentionally impossible to silence. See https://github.com/rust-lang/rust/pull/60186#issuecomment-485581694.

[issue-60210]: https://github.com/rust-lang/rust/issues/60210

4 files changed, 10 insertions, 28 deletions

diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index 77dd313d9b8..72cd75f6d89 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -479,9 +479,6 @@ parse_invalid_identifier_with_leading_number = identifiers cannot start with a n
 
 parse_invalid_literal_suffix_on_tuple_index = suffixes on a tuple index are invalid
     .label = invalid suffix `{$suffix}`
-    .tuple_exception_line_1 = `{$suffix}` is *temporarily* accepted on tuple index fields as it was incorrectly accepted on stable for a few releases
-    .tuple_exception_line_2 = on proc macros, you'll want to use `syn::Index::from` or `proc_macro::Literal::*_unsuffixed` for code that will desugar to tuple field access
-    .tuple_exception_line_3 = see issue #60210 <https://github.com/rust-lang/rust/issues/60210> for more information
 
 parse_invalid_logical_operator = `{$incorrect}` is not a logical operator
     .note = unlike in e.g., Python and PHP, `&&` and `||` are used for logical operators
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 797d4830c2f..00ca5acd84d 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -1017,10 +1017,6 @@ pub(crate) struct InvalidLiteralSuffixOnTupleIndex {
     #[label]
     pub span: Span,
     pub suffix: Symbol,
-    #[help(parse_tuple_exception_line_1)]
-    #[help(parse_tuple_exception_line_2)]
-    #[help(parse_tuple_exception_line_3)]
-    pub exception: bool,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 4c02547357e..81a5d48d94e 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1163,7 +1163,10 @@ impl<'a> Parser<'a> {
                         suffix,
                     }) => {
                         if let Some(suffix) = suffix {
-                            self.expect_no_tuple_index_suffix(current.span, suffix);
+                            self.dcx().emit_err(errors::InvalidLiteralSuffixOnTupleIndex {
+                                span: current.span,
+                                suffix,
+                            });
                         }
                         match self.break_up_float(symbol, current.span) {
                             // 1e2
@@ -1239,7 +1242,8 @@ impl<'a> Parser<'a> {
         suffix: Option<Symbol>,
     ) -> Box<Expr> {
         if let Some(suffix) = suffix {
-            self.expect_no_tuple_index_suffix(ident_span, suffix);
+            self.dcx()
+                .emit_err(errors::InvalidLiteralSuffixOnTupleIndex { span: ident_span, suffix });
         }
         self.mk_expr(lo.to(ident_span), ExprKind::Field(base, Ident::new(field, ident_span)))
     }
@@ -2225,24 +2229,6 @@ impl<'a> Parser<'a> {
         })
     }
 
-    pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
-        if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
-            // #59553: warn instead of reject out of hand to allow the fix to percolate
-            // through the ecosystem when people fix their macros
-            self.dcx().emit_warn(errors::InvalidLiteralSuffixOnTupleIndex {
-                span,
-                suffix,
-                exception: true,
-            });
-        } else {
-            self.dcx().emit_err(errors::InvalidLiteralSuffixOnTupleIndex {
-                span,
-                suffix,
-                exception: false,
-            });
-        }
-    }
-
     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, Box<Expr>> {
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 3bbca622975..ed4069dae93 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -1335,7 +1335,10 @@ impl<'a> Parser<'a> {
         if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) = self.token.kind
         {
             if let Some(suffix) = suffix {
-                self.expect_no_tuple_index_suffix(self.token.span, suffix);
+                self.dcx().emit_err(errors::InvalidLiteralSuffixOnTupleIndex {
+                    span: self.token.span,
+                    suffix,
+                });
             }
             self.bump();
             Ok(Ident::new(symbol, self.prev_token.span))