Explain disabled span hashing.

rust-lang · Dec 25, 2022 · 7b6ead2 · 7b6ead2
1 parent 5b9360b
commit 7b6ead2
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
@@ -104,6 +104,10 @@ fn assert_default_hashing_controls<CTX: HashStableContext>(ctx: &CTX, msg: &str)
         // `-Z incremental-ignore-spans` option. Normally, this option is disabled,
         // which will cause us to require that this method always be called with `Span` hashing
         // enabled.
+        //
+        // Span hashing can also be disabled without `-Z incremental-ignore-spans`.
+        // This is the case for instance when building a hash for name mangling.
+        // Such configuration must not be used for metadata.
         HashingControls { hash_spans }
             if hash_spans == !ctx.unstable_opts_incremental_ignore_spans() => {}
         other => panic!("Attempted hashing of {msg} with non-default HashingControls: {:?}", other),