2 files changed, 15 insertions, 32 deletions
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index ba0ad9230c8..483e32c6453 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -43,9 +43,15 @@ use std::hash::Hash;
 use tracing::{debug, trace};
 
 /// 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,
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index b3f3899542d..266956d63d7 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -467,46 +467,23 @@ impl FileName {
 /// `SpanData` is public because `Span` uses a thread-local interner and can't be
 /// sent to other threads, but some pieces of performance infra run in a separate thread.
 /// Using `Span` is generally preferred.
-#[derive(Clone, Copy, Hash, PartialEq, Eq)]
+#[derive(Clone, Copy, Hash, PartialEq, Eq, derivative::Derivative)]
+#[derivative(PartialOrd, Ord)]
 pub struct SpanData {
     pub lo: BytePos,
     pub hi: BytePos,
     /// Information about where the macro came from, if this piece of
     /// code was created by a macro expansion.
+    #[derivative(PartialOrd = "ignore", Ord = "ignore")]
+    // `SyntaxContext` does not implement `Ord`.
+    // The other fields are enough to determine in-file order.
     pub ctxt: SyntaxContext,
+    #[derivative(PartialOrd = "ignore", Ord = "ignore")]
+    // `LocalDefId` does not implement `Ord`.
+    // The other fields are enough to determine in-file order.
     pub parent: Option<LocalDefId>,
 }
 
-// Order spans by position in the file.
-impl Ord for SpanData {
-    fn cmp(&self, other: &Self) -> Ordering {
-        let SpanData {
-            lo: s_lo,
-            hi: s_hi,
-            ctxt: s_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,
-            // `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))
-    }
-}
-
-impl PartialOrd for SpanData {
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
 impl SpanData {
     #[inline]
     pub fn span(&self) -> Span {