Reuse metadata file from work products.

Author: cjgillot

Cargo.lock

@@ -3995,6 +3995,7 @@ dependencies = [
  "rustc_fs_util",
  "rustc_hir",
  "rustc_hir_pretty",
+ "rustc_incremental",
  "rustc_index",
  "rustc_macros",
  "rustc_middle",

compiler/rustc_metadata/Cargo.toml

@@ -19,6 +19,7 @@ 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_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -2260,7 +2260,28 @@ 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.dcx().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,
@@ -2274,6 +2295,10 @@ pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path) {
         join(|| prefetch_mir(tcx), || tcx.exported_symbols(LOCAL_CRATE));
     }
 
+    tcx.dep_graph.with_task(dep_node, tcx, path, encode_metadata_impl, None);
+}
+
+fn encode_metadata_impl(tcx: TyCtxt<'_>, path: &Path) {
     let mut encoder = opaque::FileEncoder::new(path)
         .unwrap_or_else(|err| tcx.dcx().emit_fatal(FailCreateFileEncoder { err }));
     encoder.emit_raw_bytes(METADATA_HEADER);

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -140,6 +140,7 @@ 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.
@@ -157,6 +158,12 @@ pub(crate) fn make_compile_mono_item<'tcx>(
     DepNode::construct(tcx, dep_kinds::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, dep_kinds::Metadata, &())
+}
+
 pub trait DepNodeExt: Sized {
     /// Extracts the DefId corresponding to this DepNode. This will work
     /// if two conditions are met:

compiler/rustc_middle/src/dep_graph/mod.rs

@@ -8,7 +8,7 @@ use crate::ty::{self, TyCtxt};
 mod dep_node;
 
 pub use dep_node::{DepKind, DepNode, DepNodeExt, dep_kinds, label_strs};
-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 use rustc_query_system::dep_graph::debug::{DepNodeFilter, EdgeFilter};
 pub use rustc_query_system::dep_graph::{
     DepContext, DepGraphQuery, DepNodeIndex, Deps, SerializedDepGraph, SerializedDepNodeIndex,

compiler/rustc_middle/src/ty/context.rs

@@ -3171,6 +3171,10 @@ impl<'tcx> TyCtxt<'tcx> {
         self.resolver_for_lowering_raw(()).0
     }
 
+    pub fn metadata_dep_node(self) -> crate::dep_graph::DepNode {
+        crate::dep_graph::make_metadata(self)
+    }
+
     /// Given an `impl_id`, return the trait it implements.
     /// Return `None` if this is an inherent impl.
     pub fn impl_trait_ref(

compiler/rustc_query_impl/src/plumbing.rs

@@ -859,6 +859,17 @@ macro_rules! define_queries {
                 }
             }
 
+            pub(crate) 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,
+                    name: &"Metadata",
+                }
+            }
+
             $(pub(crate) fn $name<'tcx>()-> DepKindStruct<'tcx> {
                 $crate::plumbing::query_callback::<query_impl::$name::QueryType<'tcx>>(
                     is_anon!([$($modifiers)*]),