Stop sorting Spans' SyntaxContext, as that is incompatible with incremental

Author: oli-obk

compiler/rustc_span/src/hygiene.rs

@@ -42,9 +42,15 @@ use std::fmt;
 use std::hash::Hash;
 
 /// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct SyntaxContext(u32);
 
+// To ensure correctness of incremental compilation,
+// `SyntaxContext` must not implement `Ord` or `PartialOrd`.
+// See https://github.com/rust-lang/rust/issues/90317.
+impl !Ord for SyntaxContext {}
+impl !PartialOrd for SyntaxContext {}
+
 #[derive(Debug, Encodable, Decodable, Clone)]
 pub struct SyntaxContextData {
     outer_expn: ExpnId,

compiler/rustc_span/src/lib.rs

@@ -460,21 +460,21 @@ impl Ord for SpanData {
         let SpanData {
             lo: s_lo,
             hi: s_hi,
-            ctxt: s_ctxt,
+            ctxt: _,
             // `LocalDefId` does not implement `Ord`.
             // The other fields are enough to determine in-file order.
             parent: _,
         } = self;
         let SpanData {
             lo: o_lo,
             hi: o_hi,
-            ctxt: o_ctxt,
+            ctxt: _,
             // `LocalDefId` does not implement `Ord`.
             // The other fields are enough to determine in-file order.
             parent: _,
         } = other;
 
-        (s_lo, s_hi, s_ctxt).cmp(&(o_lo, o_hi, o_ctxt))
+        (s_lo, s_hi).cmp(&(o_lo, o_hi))
     }
 }