Add `#[rustc_clean(loaded_from_disk)]` to assert loading of query result

Currently, you can use `#[rustc_clean]` to assert to that a particular
query (technically, a `DepNode`) is green or red. However, a green
`DepNode` does not mean that the query result was actually deserialized
from disk - we might have never re-run a query that needed the result.

Some incremental tests are written as regression tests for ICEs that
occured during query result decoding. Using
`#[rustc_clean(loaded_from_disk="typeck")]`, you can now assert
that the result of a particular query (e.g. `typeck`) was actually
loaded from disk, in addition to being green.

5 files changed, 64 insertions, 3 deletions

diff --git a/compiler/rustc_incremental/src/persist/dirty_clean.rs b/compiler/rustc_incremental/src/persist/dirty_clean.rs
index 7ac00b4609a..88795679943 100644
--- a/compiler/rustc_incremental/src/persist/dirty_clean.rs
+++ b/compiler/rustc_incremental/src/persist/dirty_clean.rs
@@ -9,6 +9,13 @@
 //! - `#[rustc_clean(cfg="rev2")]` same as above, except that the
 //!   fingerprints must be the SAME (along with all other fingerprints).
 //!
+//! - `#[rustc_clean(cfg="rev2", loaded_from_disk='typeck")]` asserts that
+//!   the query result for `DepNode::typeck(X)` was actually
+//!   loaded from disk (not just marked green). This can be useful
+//!   to ensure that a test is actually exercising the deserialization
+//!   logic for a particular query result. This can be combined with
+//!   `except`
+//!
 //! Errors are reported if we are in the suitable configuration but
 //! the required condition is not met.
 
@@ -28,6 +35,7 @@ use rustc_span::Span;
 use std::iter::FromIterator;
 use std::vec::Vec;
 
+const LOADED_FROM_DISK: Symbol = sym::loaded_from_disk;
 const EXCEPT: Symbol = sym::except;
 const CFG: Symbol = sym::cfg;
 
@@ -124,6 +132,7 @@ type Labels = FxHashSet<String>;
 struct Assertion {
     clean: Labels,
     dirty: Labels,
+    loaded_from_disk: Labels,
 }
 
 pub fn check_dirty_clean_annotations(tcx: TyCtxt<'_>) {
@@ -174,6 +183,7 @@ impl<'tcx> DirtyCleanVisitor<'tcx> {
     fn assertion_auto(&mut self, item_id: LocalDefId, attr: &Attribute) -> Assertion {
         let (name, mut auto) = self.auto_labels(item_id, attr);
         let except = self.except(attr);
+        let loaded_from_disk = self.loaded_from_disk(attr);
         for e in except.iter() {
             if !auto.remove(e) {
                 let msg = format!(
@@ -183,7 +193,19 @@ impl<'tcx> DirtyCleanVisitor<'tcx> {
                 self.tcx.sess.span_fatal(attr.span, &msg);
             }
         }
-        Assertion { clean: auto, dirty: except }
+        Assertion { clean: auto, dirty: except, loaded_from_disk }
+    }
+
+    /// `loaded_from_disk=` attribute value
+    fn loaded_from_disk(&self, attr: &Attribute) -> Labels {
+        for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
+            if item.has_name(LOADED_FROM_DISK) {
+                let value = expect_associated_value(self.tcx, &item);
+                return self.resolve_labels(&item, value);
+            }
+        }
+        // If `loaded_from_disk=` is not specified, don't assert anything
+        Labels::default()
     }
 
     /// `except=` attribute value
@@ -332,6 +354,18 @@ impl<'tcx> DirtyCleanVisitor<'tcx> {
         }
     }
 
+    fn assert_loaded_from_disk(&self, item_span: Span, dep_node: DepNode) {
+        debug!("assert_loaded_from_disk({:?})", dep_node);
+
+        if !self.tcx.dep_graph.debug_was_loaded_from_disk(dep_node) {
+            let dep_node_str = self.dep_node_str(&dep_node);
+            self.tcx.sess.span_err(
+                item_span,
+                &format!("`{}` should have been loaded from disk but it was not", dep_node_str),
+            );
+        }
+    }
+
     fn check_item(&mut self, item_id: LocalDefId, item_span: Span) {
         let def_path_hash = self.tcx.def_path_hash(item_id.to_def_id());
         for attr in self.tcx.get_attrs(item_id.to_def_id()).iter() {
@@ -348,6 +382,10 @@ impl<'tcx> DirtyCleanVisitor<'tcx> {
                 let dep_node = DepNode::from_label_string(self.tcx, &label, def_path_hash).unwrap();
                 self.assert_dirty(item_span, dep_node);
             }
+            for label in assertion.loaded_from_disk {
+                let dep_node = DepNode::from_label_string(self.tcx, &label, def_path_hash).unwrap();
+                self.assert_loaded_from_disk(item_span, dep_node);
+            }
         }
     }
 }
@@ -382,7 +420,7 @@ fn check_config(tcx: TyCtxt<'_>, attr: &Attribute) -> bool {
             let value = expect_associated_value(tcx, &item);
             debug!("check_config: searching for cfg {:?}", value);
             cfg = Some(config.contains(&(value, None)));
-        } else if !item.has_name(EXCEPT) {
+        } else if !(item.has_name(EXCEPT) || item.has_name(LOADED_FROM_DISK)) {
             tcx.sess.span_err(attr.span, &format!("unknown item `{}`", item.name_or_empty()));
         }
     }
diff --git a/compiler/rustc_query_system/src/dep_graph/graph.rs b/compiler/rustc_query_system/src/dep_graph/graph.rs
index a8be1ca34c0..7bc3fd718e0 100644
--- a/compiler/rustc_query_system/src/dep_graph/graph.rs
+++ b/compiler/rustc_query_system/src/dep_graph/graph.rs
@@ -88,6 +88,11 @@ struct DepGraphData<K: DepKind> {
     previous_work_products: FxHashMap<WorkProductId, WorkProduct>,
 
     dep_node_debug: Lock<FxHashMap<DepNode<K>, String>>,
+
+    /// Used by incremental compilation tests to assert that
+    /// a particular query result was decoded from disk
+    /// (not just marked green)
+    debug_loaded_from_disk: Lock<FxHashSet<DepNode<K>>>,
 }
 
 pub fn hash_result<R>(hcx: &mut StableHashingContext<'_>, result: &R) -> Fingerprint
@@ -135,6 +140,7 @@ impl<K: DepKind> DepGraph<K> {
                 processed_side_effects: Default::default(),
                 previous: prev_graph,
                 colors: DepNodeColorMap::new(prev_graph_node_count),
+                debug_loaded_from_disk: Default::default(),
             })),
             virtual_dep_node_index: Lrc::new(AtomicU32::new(0)),
         }
@@ -438,6 +444,14 @@ impl<K: DepKind> DepGraph<K> {
         &self.data.as_ref().unwrap().previous_work_products
     }
 
+    pub fn mark_debug_loaded_from_disk(&self, dep_node: DepNode<K>) {
+        self.data.as_ref().unwrap().debug_loaded_from_disk.lock().insert(dep_node);
+    }
+
+    pub fn debug_was_loaded_from_disk(&self, dep_node: DepNode<K>) -> bool {
+        self.data.as_ref().unwrap().debug_loaded_from_disk.lock().contains(&dep_node)
+    }
+
     #[inline(always)]
     pub fn register_dep_node_debug_str<F>(&self, dep_node: DepNode<K>, debug_str_gen: F)
     where
diff --git a/compiler/rustc_query_system/src/query/plumbing.rs b/compiler/rustc_query_system/src/query/plumbing.rs
index b08db39e245..33732f9df73 100644
--- a/compiler/rustc_query_system/src/query/plumbing.rs
+++ b/compiler/rustc_query_system/src/query/plumbing.rs
@@ -519,6 +519,10 @@ where
         prof_timer.finish_with_query_invocation_id(dep_node_index.into());
 
         if let Some(result) = result {
+            if unlikely!(tcx.dep_context().sess().opts.debugging_opts.query_dep_graph) {
+                dep_graph.mark_debug_loaded_from_disk(*dep_node)
+            }
+
             let prev_fingerprint = tcx
                 .dep_context()
                 .dep_graph()
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 51a7a2644f6..84cf8878af8 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -788,6 +788,7 @@ symbols! {
         literal,
         llvm_asm,
         load,
+        loaded_from_disk,
         local,
         local_inner_macros,
         log10f32,
diff --git a/src/test/incremental/change_private_fn/struct_point.rs b/src/test/incremental/change_private_fn/struct_point.rs
index 1791c089cfa..d57267adc6b 100644
--- a/src/test/incremental/change_private_fn/struct_point.rs
+++ b/src/test/incremental/change_private_fn/struct_point.rs
@@ -51,7 +51,11 @@ pub mod point {
 pub mod fn_calls_methods_in_same_impl {
     use point::Point;
 
-    #[rustc_clean(cfg="cfail2")]
+    // The cached result should actually be loaded from disk
+    // (not just marked green) - for example, `DeadVisitor`
+    // always runs during compilation as a "pass", and loads
+    // the typeck results for bodies.
+    #[rustc_clean(cfg="cfail2", loaded_from_disk="typeck")]
     pub fn check() {
         let x = Point { x: 2.0, y: 2.0 };
         x.distance_from_origin();