Move Query to rustc_query_system.

Rename it to QueryStackFrame and document a bit.

compiler/rustc_query_system/src/query/mod.rs

@@ -4,7 +4,7 @@ pub use self::plumbing::*;
 mod job;
 #[cfg(parallel_compiler)]
 pub use self::job::deadlock;
-pub use self::job::{QueryInfo, QueryJob, QueryJobId, QueryJobInfo};
+pub use self::job::{QueryInfo, QueryJob, QueryJobId, QueryJobInfo, QueryMap};
 
 mod caches;
 pub use self::caches::{
@@ -15,24 +15,63 @@ mod config;
 pub use self::config::{QueryAccessors, QueryConfig, QueryDescription};
 
 use crate::dep_graph::{DepNode, DepNodeIndex, HasDepContext, SerializedDepNodeIndex};
-use crate::query::job::QueryMap;
 
-use rustc_data_structures::stable_hasher::HashStable;
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lock;
 use rustc_data_structures::thin_vec::ThinVec;
 use rustc_errors::Diagnostic;
 use rustc_span::def_id::DefId;
+use rustc_span::Span;
+
+/// Description of a frame in the query stack.
+///
+/// This is mostly used in case of cycles for error reporting.
+#[derive(Clone, Debug)]
+pub struct QueryStackFrame {
+    pub name: &'static str,
+    pub description: String,
+    span: Option<Span>,
+    /// This hash is used to deterministically pick
+    /// a query to remove cycles in the parallel compiler.
+    hash: Fingerprint,
+}
+
+impl QueryStackFrame {
+    #[inline]
+    pub fn new(
+        name: &'static str,
+        description: String,
+        span: Option<Span>,
+        hash: Fingerprint,
+    ) -> Self {
+        Self { name, hash, description, span }
+    }
+
+    // FIXME(eddyb) Get more valid `Span`s on queries.
+    #[inline]
+    pub fn default_span(&self, span: Span) -> Span {
+        if !span.is_dummy() {
+            return span;
+        }
+        self.span.unwrap_or(span)
+    }
+}
+
+impl<CTX> HashStable<CTX> for QueryStackFrame {
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        self.hash.hash_stable(hcx, hasher)
+    }
+}
 
 pub trait QueryContext: HasDepContext {
-    type Query: Clone + HashStable<Self::StableHashingContext>;
-
     /// Get string representation from DefPath.
     fn def_path_str(&self, def_id: DefId) -> String;
 
     /// Get the query information from the TLS context.
     fn current_query_job(&self) -> Option<QueryJobId<Self::DepKind>>;
 
-    fn try_collect_active_jobs(&self) -> Option<QueryMap<Self::DepKind, Self::Query>>;
+    fn try_collect_active_jobs(&self) -> Option<QueryMap<Self::DepKind>>;
 
     /// Load data from the on-disk cache.
     fn try_load_from_on_disk_cache(&self, dep_node: &DepNode<Self::DepKind>);