rdr: fix SpanRef resolution and optimize metadata encoding

- Fix decoder to use span_file_data source map for -Zstable-crate-hash crates
- Add preload_all_source_files for deterministic BytePos ordering
- Enable -Zstable-crate-hash for library builds and copy .spans to sysroot
- Encode fn_arg_idents with SpanRef
- Add transform_span_ref_for_export to convert local stable_ids to exported
  stable_ids when encoding predicate queries to metadata

Refactor span conversion into SpanConversionState and add lazy_array_with
and lazy_array_with_mut helpers that scope borrows per-item. This avoids
intermediate Vec allocations and HashMap cloning when encoding arrays
that need span transformation, while avoiding borrow conflicts with
encode(&mut self).

Author: davidbarsky

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -8,7 +8,6 @@ use rustc_middle::ty::{
 use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::{Span, SpanRef};
-use rustc_span::def_id::{DefId, LocalDefId};
 
 fn convert_to_span_ref<'tcx>(
     tcx: TyCtxt<'tcx>,

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -43,8 +43,9 @@ pub(super) fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredic
     let inferred_outlives = tcx.inferred_outlives_of(def_id);
     if !inferred_outlives.is_empty() {
         debug!("predicates_of: inferred_outlives_of({:?}) = {:?}", def_id, inferred_outlives,);
-        let inferred_outlives_iter =
-            inferred_outlives.iter().map(|(clause, span)| ((*clause).upcast(tcx), tcx.resolve_span_ref(*span)));
+        let inferred_outlives_iter = inferred_outlives
+            .iter()
+            .map(|(clause, span)| ((*clause).upcast(tcx), tcx.resolve_span_ref(*span)));
         if result.predicates.is_empty() {
             result.predicates = tcx.arena.alloc_from_iter(inferred_outlives_iter);
         } else {

compiler/rustc_metadata/src/creader.rs

@@ -658,6 +658,8 @@ impl CStore {
                 .map_err(|err| CrateError::MissingSpanFile(crate_name, err))?;
         }
 
+        crate_metadata.preload_all_source_files(tcx, self);
+
         self.set_crate_data(cnum, crate_metadata);
 
         Ok(cnum)

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -2126,8 +2126,11 @@ impl<'a> CrateMetadataRef<'a> {
         tcx: TyCtxt<'_>,
         target_stable_id: rustc_span::StableSourceFileId,
     ) -> Option<ImportedSourceFile> {
-        // Iterate through all source files in this crate's metadata
-        let num_files = self.root.source_map.size();
+        let num_files = if let Some(span_data) = self.cdata.span_file_data() {
+            span_data.source_map.size()
+        } else {
+            self.root.source_map.size()
+        };
         debug!(
             ?target_stable_id,
             crate_name = ?self.cdata.root.header.name,
@@ -2266,6 +2269,25 @@ impl CrateMetadata {
         Ok(())
     }
 
+    /// Pre-imports all source files to ensure deterministic `BytePos` values for
+    /// diagnostic output ordering.
+    pub(crate) fn preload_all_source_files(&self, tcx: TyCtxt<'_>, cstore: &CStore) {
+        let cref = CrateMetadataRef { cdata: self, cstore };
+        let num_files = if let Some(span_data) = self.span_file_data() {
+            span_data.source_map.size()
+        } else {
+            self.root.source_map.size()
+        };
+        debug!(
+            crate_name = ?self.root.header.name,
+            num_files,
+            "preload_all_source_files: importing all source files"
+        );
+        for file_index in 0..num_files {
+            let _ = cref.imported_source_file(tcx, file_index as u32);
+        }
+    }
+
     /// Lazily loads the span file data if a span file path is configured.
     /// Returns None if no span file exists or if loading fails.
     fn span_file_data(&self) -> Option<&SpanFileData> {