From 4b4ae59599ee17fcf78901aa0cf0bdd31869c1ae Mon Sep 17 00:00:00 2001
From: Travis Cross <tc@traviscross.com>
Date: Wed, 14 May 2025 13:16:27 +0000
Subject: [PATCH] Fix grammar for `RangePatternBound` regarding literals

The compiler, in parsing, accepts many more kinds of literals in the
bound of a range pattern than what we had documented, and as with
`PatternWithoutRange`, the parser allows each of these literals to be
prefixed with `-`.  E.g.

```rust
#[cfg(any())]
match () {
    ..-true | ..-false => (),
    ..-'x' => (),
    ..-b'x' => (),
    ..-"x" => (),
    ..-r"x" => (),
    ..-br"x" => (),
    ..-c"x" => (),
    ..-cr"x" => (),
    ..-1 => (),
    ..-1.1 => (),
}
```

Let's fix this by adjusting the `RangePatternBound` production to use
`LiteralPattern`.  In a separate PR, we've adjusted `LiteralPattern`
to allow for a minus sign ahead of all literal expressions.

To help the reader, let's also add a note that highlights that what we
discuss later as being allowed semantically is more restrictive than
what we allow in parsing (and therefore in the grammar).
---
 src/patterns.md | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/patterns.md b/src/patterns.md
index 2d9ddb5ac..d28d58cd9 100644
--- a/src/patterns.md
+++ b/src/patterns.md
@@ -497,10 +497,7 @@ ObsoleteRangePattern ->
     RangePatternBound `...` RangePatternBound
 
 RangePatternBound ->
-      CHAR_LITERAL
-    | BYTE_LITERAL
-    | `-`? INTEGER_LITERAL
-    | `-`? FLOAT_LITERAL
+      LiteralPattern
     | PathExpression
 ```
 
@@ -553,7 +550,11 @@ A bound is written as one of:
 
 * A character, byte, integer, or float literal.
 * A `-` followed by an integer or float literal.
-* A [path]
+* A [path].
+
+> [!NOTE]
+>
+> We syntactically accept more than this for a *[RangePatternBound]*. We later reject the other things semantically.
 
 r[patterns.range.constraint-bound-path]
 If a bound is written as a path, after macro resolution, the path must resolve to a constant item of the type `char`, an integer type, or a float type.