Auto merge of rust-lang#109002 - michaelvanstraten:master, r=petrochenkov

Added byte position range for `proc_macro::Span`

Currently, the [`Debug`](https://doc.rust-lang.org/beta/proc_macro/struct.Span.html#impl-Debug-for-Span) implementation for [`proc_macro::Span`](https://doc.rust-lang.org/beta/proc_macro/struct.Span.html#) calls the debug function implemented in the trait implementation of `server::Span` for the type `Rustc` in the `rustc-expand` crate.

The current implementation, of the referenced function, looks something like this:
```rust
fn debug(&mut self, span: Self::Span) -> String {
    if self.ecx.ecfg.span_debug {
        format!("{:?}", span)
    } else {
        format!("{:?} bytes({}..{})", span.ctxt(), span.lo().0, span.hi().0)
    }
}
```

It returns the byte position of the [`Span`](https://doc.rust-lang.org/beta/proc_macro/struct.Span.html#) as an interpolated string.

Because this is currently the only way to get a spans position in the file, I might lead someone, who is interested in this information, to parsing this interpolated string back into a range of bytes, which I think is a very non-rusty way.

The proposed `position()`, method implemented in this PR, gives the ability to directly get this info.
It returns a [`std::ops::Range`](https://doc.rust-lang.org/std/ops/struct.Range.html#) wrapping the lowest and highest byte of the [`Span`](https://doc.rust-lang.org/beta/proc_macro/struct.Span.html#).

I put it behind the `proc_macro_span` feature flag because many of the other functions that have a similar footprint also are annotated with it, I don't actually know if this is right.

It would be great if somebody could take a look at this, thank you very much in advanced.

Author: bors

proc_macro/src/bridge/mod.rs

@@ -14,6 +14,7 @@ use std::hash::Hash;
 use std::marker;
 use std::mem;
 use std::ops::Bound;
+use std::ops::Range;
 use std::panic;
 use std::sync::atomic::AtomicUsize;
 use std::sync::Once;
@@ -93,6 +94,7 @@ macro_rules! with_api {
                 fn source_file($self: $S::Span) -> $S::SourceFile;
                 fn parent($self: $S::Span) -> Option<$S::Span>;
                 fn source($self: $S::Span) -> $S::Span;
+                fn byte_range($self: $S::Span) -> Range<usize>;
                 fn start($self: $S::Span) -> LineColumn;
                 fn end($self: $S::Span) -> LineColumn;
                 fn before($self: $S::Span) -> $S::Span;
@@ -519,3 +521,7 @@ pub struct ExpnGlobals<Span> {
 compound_traits!(
     struct ExpnGlobals<Span> { def_site, call_site, mixed_site }
 );
+
+compound_traits!(
+    struct Range<T> { start, end }
+);

proc_macro/src/lib.rs

@@ -44,7 +44,7 @@ mod diagnostic;
 pub use diagnostic::{Diagnostic, Level, MultiSpan};
 
 use std::cmp::Ordering;
-use std::ops::RangeBounds;
+use std::ops::{Range, RangeBounds};
 use std::path::PathBuf;
 use std::str::FromStr;
 use std::{error, fmt};
@@ -488,6 +488,12 @@ impl Span {
         Span(self.0.source())
     }
 
+    /// Returns the span's byte position range in the source file.
+    #[unstable(feature = "proc_macro_span", issue = "54725")]
+    pub fn byte_range(&self) -> Range<usize> {
+        self.0.byte_range()
+    }
+
     /// Gets the starting line/column in the source file for this span.
     #[unstable(feature = "proc_macro_span", issue = "54725")]
     pub fn start(&self) -> LineColumn {