Don't use HasDepContext in DepGraph::with_task

The need for a `HasDepContext` impl on tuples can be avoided by passing the
query vtable as part of an argument tuple instead.

Author: Zalathar

compiler/rustc_middle/src/dep_graph/graph.rs

@@ -252,17 +252,17 @@ impl DepGraph {
     }
 
     #[inline(always)]
-    pub fn with_task<'tcx, Ctxt: HasDepContext<'tcx>, A: Debug, R>(
+    pub fn with_task<'tcx, A: Debug, R>(
         &self,
-        key: DepNode,
-        cx: Ctxt,
-        arg: A,
-        task: fn(Ctxt, A) -> R,
+        dep_node: DepNode,
+        tcx: TyCtxt<'tcx>,
+        task_arg: A,
+        task_fn: fn(tcx: TyCtxt<'tcx>, task_arg: A) -> R,
         hash_result: Option<fn(&mut StableHashingContext<'_>, &R) -> Fingerprint>,
     ) -> (R, DepNodeIndex) {
         match self.data() {
-            Some(data) => data.with_task(key, cx, arg, task, hash_result),
-            None => (task(cx, arg), self.next_virtual_depnode_index()),
+            Some(data) => data.with_task(dep_node, tcx, task_arg, task_fn, hash_result),
+            None => (task_fn(tcx, task_arg), self.next_virtual_depnode_index()),
         }
     }
 
@@ -294,66 +294,50 @@ impl DepGraphData {
     /// prevent implicit 'leaks' of tracked state into the task (which
     /// could then be read without generating correct edges in the
     /// dep-graph -- see the [rustc dev guide] for more details on
-    /// the dep-graph). To this end, the task function gets exactly two
-    /// pieces of state: the context `cx` and an argument `arg`. Both
-    /// of these bits of state must be of some type that implements
-    /// `DepGraphSafe` and hence does not leak.
-    ///
-    /// The choice of two arguments is not fundamental. One argument
-    /// would work just as well, since multiple values can be
-    /// collected using tuples. However, using two arguments works out
-    /// to be quite convenient, since it is common to need a context
-    /// (`cx`) and some argument (e.g., a `DefId` identifying what
-    /// item to process).
+    /// the dep-graph).
     ///
-    /// For cases where you need some other number of arguments:
-    ///
-    /// - If you only need one argument, just use `()` for the `arg`
-    ///   parameter.
-    /// - If you need 3+ arguments, use a tuple for the
-    ///   `arg` parameter.
+    /// Therefore, the task function takes a `TyCtxt`, plus exactly one
+    /// additional argument, `task_arg`. The additional argument type can be
+    /// `()` if no argument is needed, or a tuple if multiple arguments are
+    /// needed.
     ///
     /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/queries/incremental-compilation.html
     #[inline(always)]
-    pub fn with_task<'tcx, Ctxt: HasDepContext<'tcx>, A: Debug, R>(
+    pub fn with_task<'tcx, A: Debug, R>(
         &self,
-        key: DepNode,
-        cx: Ctxt,
-        arg: A,
-        task: fn(Ctxt, A) -> R,
+        dep_node: DepNode,
+        tcx: TyCtxt<'tcx>,
+        task_arg: A,
+        task_fn: fn(tcx: TyCtxt<'tcx>, task_arg: A) -> R,
         hash_result: Option<fn(&mut StableHashingContext<'_>, &R) -> Fingerprint>,
     ) -> (R, DepNodeIndex) {
         // If the following assertion triggers, it can have two reasons:
         // 1. Something is wrong with DepNode creation, either here or
         //    in `DepGraph::try_mark_green()`.
         // 2. Two distinct query keys get mapped to the same `DepNode`
         //    (see for example #48923).
-        self.assert_dep_node_not_yet_allocated_in_current_session(
-            cx.dep_context().sess,
-            &key,
-            || {
-                format!(
-                    "forcing query with already existing `DepNode`\n\
-                 - query-key: {arg:?}\n\
-                 - dep-node: {key:?}"
-                )
-            },
-        );
+        self.assert_dep_node_not_yet_allocated_in_current_session(tcx.sess, &dep_node, || {
+            format!(
+                "forcing query with already existing `DepNode`\n\
+                 - query-key: {task_arg:?}\n\
+                 - dep-node: {dep_node:?}"
+            )
+        });
 
-        let with_deps = |task_deps| with_deps(task_deps, || task(cx, arg));
-        let (result, edges) = if cx.dep_context().is_eval_always(key.kind) {
+        let with_deps = |task_deps| with_deps(task_deps, || task_fn(tcx, task_arg));
+        let (result, edges) = if tcx.is_eval_always(dep_node.kind) {
             (with_deps(TaskDepsRef::EvalAlways), EdgesVec::new())
         } else {
             let task_deps = Lock::new(TaskDeps::new(
                 #[cfg(debug_assertions)]
-                Some(key),
+                Some(dep_node),
                 0,
             ));
             (with_deps(TaskDepsRef::Allow(&task_deps)), task_deps.into_inner().reads)
         };
 
         let dep_node_index =
-            self.hash_result_and_alloc_node(cx.dep_context(), key, edges, &result, hash_result);
+            self.hash_result_and_alloc_node(tcx, dep_node, edges, &result, hash_result);
 
         (result, dep_node_index)
     }

compiler/rustc_middle/src/dep_graph/mod.rs

@@ -34,12 +34,6 @@ impl<'tcx> HasDepContext<'tcx> for TyCtxt<'tcx> {
     }
 }
 
-impl<'tcx, T: HasDepContext<'tcx>, Q: Copy> HasDepContext<'tcx> for (T, Q) {
-    fn dep_context(&self) -> TyCtxt<'tcx> {
-        self.0.dep_context()
-    }
-}
-
 /// Describes the contents of the fingerprint generated by a given query.
 ///
 /// This is mainly for determining whether and how we can reconstruct a key

compiler/rustc_query_impl/src/execution.rs

@@ -473,9 +473,9 @@ fn execute_job_incr<'tcx, C: QueryCache, const FLAGS: QueryFlags>(
         // Call the query provider.
         dep_graph_data.with_task(
             dep_node,
-            (tcx, query),
-            key,
-            |(tcx, query), key| query.invoke_provider(tcx, key),
+            tcx,
+            (query, key),
+            |tcx, (query, key)| query.invoke_provider(tcx, key),
             query.hash_result(),
         )
     });

compiler/rustc_query_impl/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(try_blocks)]
 // tidy-alphabetical-end
 
+use std::fmt;
 use std::marker::ConstParamTy;
 
 use rustc_data_structures::sync::AtomicU64;
@@ -76,6 +77,14 @@ impl<'tcx, C: QueryCache, const FLAGS: QueryFlags> Clone
     }
 }
 
+impl<'tcx, C: QueryCache, const FLAGS: QueryFlags> fmt::Debug
+    for SemiDynamicQueryDispatcher<'tcx, C, FLAGS>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.name())
+    }
+}
+
 impl<'tcx, C: QueryCache, const FLAGS: QueryFlags> SemiDynamicQueryDispatcher<'tcx, C, FLAGS> {
     #[inline(always)]
     fn name(self) -> &'static str {