Reuse metadata file from work products.

Author: cjgillot

Cargo.lock

@@ -3932,6 +3932,7 @@ dependencies = [
  "rustc_fs_util",
  "rustc_hir",
  "rustc_hir_pretty",
+ "rustc_incremental",
  "rustc_index",
  "rustc_macros",
  "rustc_middle",

compiler/rustc_metadata/Cargo.toml

@@ -21,6 +21,7 @@ rustc_fluent_macro = { path = "../rustc_fluent_macro" }
 rustc_fs_util = { path = "../rustc_fs_util" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
+rustc_incremental = { path = "../rustc_incremental" }
 rustc_target = { path = "../rustc_target" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -2163,15 +2163,36 @@ impl<D: Decoder> Decodable<D> for EncodedMetadata {
     }
 }
 
+#[instrument(level = "trace", skip(tcx))]
 pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path) {
+    let dep_node = tcx.metadata_dep_node();
+
+    if tcx.dep_graph.is_fully_enabled()
+        && let work_product_id = &rustc_middle::dep_graph::WorkProductId::from_cgu_name("metadata")
+        && let Some(work_product) = tcx.dep_graph.previous_work_product(work_product_id)
+        && tcx.try_mark_green(&dep_node)
+    {
+        let saved_path = &work_product.saved_files["rmeta"];
+        let incr_comp_session_dir = tcx.sess.incr_comp_session_dir_opt().unwrap();
+        let source_file = rustc_incremental::in_incr_comp_dir(&incr_comp_session_dir, saved_path);
+        debug!("copying preexisting metadata from {source_file:?} to {path:?}");
+        match rustc_fs_util::link_or_copy(&source_file, path) {
+            Ok(_) => {}
+            Err(err) => {
+                tcx.sess.emit_fatal(FailCreateFileEncoder { err });
+            }
+        };
+        return;
+    };
+
     let _prof_timer = tcx.prof.verbose_generic_activity("generate_crate_metadata");
 
     // Since encoding metadata is not in a query, and nothing is cached,
     // there's no need to do dep-graph tracking for any of it.
     tcx.dep_graph.assert_ignored();
 
     join(
-        || encode_metadata_impl(tcx, path),
+        || tcx.dep_graph.with_task(dep_node, tcx, path, encode_metadata_impl, None),
         || {
             if tcx.sess.threads() == 1 {
                 return;

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -112,6 +112,7 @@ rustc_query_append!(define_dep_nodes![
     [] fn TraitSelect() -> (),
     [] fn CompileCodegenUnit() -> (),
     [] fn CompileMonoItem() -> (),
+    [] fn Metadata() -> (),
 ]);
 
 // WARNING: `construct` is generic and does not know that `CompileCodegenUnit` takes `Symbol`s as keys.
@@ -129,6 +130,12 @@ pub(crate) fn make_compile_mono_item<'tcx>(
     DepNode::construct(tcx, DepKind::CompileMonoItem, mono_item)
 }
 
+// WARNING: `construct` is generic and does not know that `Metadata` takes `()`s as keys.
+// Be very careful changing this type signature!
+pub(crate) fn make_metadata(tcx: TyCtxt<'_>) -> DepNode {
+    DepNode::construct(tcx, DepKind::Metadata, &())
+}
+
 pub type DepNode = rustc_query_system::dep_graph::DepNode<DepKind>;
 
 // We keep a lot of `DepNode`s in memory during compilation. It's not

compiler/rustc_middle/src/dep_graph/mod.rs

@@ -12,7 +12,7 @@ pub use rustc_query_system::dep_graph::{
 };
 
 pub use dep_node::{label_strs, DepKind, DepNode, DepNodeExt};
-pub(crate) use dep_node::{make_compile_codegen_unit, make_compile_mono_item};
+pub(crate) use dep_node::{make_compile_codegen_unit, make_compile_mono_item, make_metadata};
 
 pub type DepGraph = rustc_query_system::dep_graph::DepGraph<DepKind>;
 

compiler/rustc_middle/src/ty/context.rs

@@ -2126,6 +2126,10 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn module_children_local(self, def_id: LocalDefId) -> &'tcx [ModChild] {
         self.resolutions(()).module_children.get(&def_id).map_or(&[], |v| &v[..])
     }
+
+    pub fn metadata_dep_node(self) -> crate::dep_graph::DepNode {
+        crate::dep_graph::make_metadata(self)
+    }
 }
 
 /// Parameter attributes that can only be determined by examining the body of a function instead

compiler/rustc_query_impl/src/plumbing.rs

@@ -782,6 +782,16 @@ macro_rules! define_queries {
                 }
             }
 
+            pub fn Metadata<'tcx>() -> DepKindStruct<'tcx> {
+                DepKindStruct {
+                    is_anon: false,
+                    is_eval_always: false,
+                    fingerprint_style: FingerprintStyle::Unit,
+                    force_from_dep_node: None,
+                    try_load_from_on_disk_cache: None,
+                }
+            }
+
             $(pub(crate) fn $name<'tcx>()-> DepKindStruct<'tcx> {
                 $crate::plumbing::query_callback::<query_impl::$name::QueryType<'tcx>>(
                     is_anon!([$($modifiers)*]),