Import SourceFiles from crate before decoding foreign Span

Fixes #92163
Fixes #92014

When writing to the incremental cache, we encode all `Span`s
we encounter, regardless of whether or not their `SourceFile`
comes from the local crate, or from a foreign crate.

When we decode a `Span`, we use the `StableSourceFileId` we encoded
to locate the matching `SourceFile` in the current session. If this
id corresponds to a `SourceFile` from another crate, then we need to
have already imported that `SourceFile` into our current session.

This usually happens automatically during resolution / macro expansion,
when we try to resolve definitions from other crates. In certain cases,
however, we may try to load a `Span` from a transitive dependency
without having ever imported the `SourceFile`s from that crate, leading
to an ICE.

This PR fixes the issue by calling `imported_source_files()`
when we encounter a `SourceFile` with a foreign `CrateNum`.
This ensures that all `SourceFile`s from that crate are imported
into the current session.

compiler/rustc_query_impl/src/on_disk_cache.rs

@@ -495,6 +495,20 @@ impl<'a, 'tcx> CacheDecoder<'a, 'tcx> {
             .entry(index)
             .or_insert_with(|| {
                 let stable_id = file_index_to_stable_id[&index].translate(tcx);
+
+                // If this `SourceFile` is from a foreign crate, then make sure
+                // that we've imported all of the source files from that crate.
+                // This has usually already been done during macro invocation.
+                // However, when encoding query results like `TypeckResults`,
+                // we might encode an `AdtDef` for a foreign type (because it
+                // was referenced in the body of the function). There is no guarantee
+                // that we will load the source files from that crate during macro
+                // expansion, so we use `import_source_files` to ensure that the foreign
+                // source files are actually imported before we call `source_file_by_stable_id`.
+                if stable_id.cnum != LOCAL_CRATE {
+                    self.tcx.cstore_untracked().import_source_files(self.tcx.sess, stable_id.cnum);
+                }
+
                 source_map
                     .source_file_by_stable_id(stable_id)
                     .expect("failed to lookup `SourceFile` in new context")