improve diagnostics for const eval query overflow

Author: mzacho

compiler/rustc_query_impl/src/plumbing.rs

@@ -27,7 +27,7 @@ use rustc_query_system::query::{
     QueryCache, QueryConfig, QueryContext, QueryJobId, QueryMap, QuerySideEffects, QueryStackFrame,
     force_query,
 };
-use rustc_query_system::{LayoutOfDepth, QueryOverflow};
+use rustc_query_system::{QueryOverflow, QueryOverflowNote};
 use rustc_serialize::{Decodable, Encodable};
 use rustc_session::Limit;
 use rustc_span::def_id::LOCAL_CRATE;
@@ -154,12 +154,10 @@ impl QueryContext for QueryCtxt<'_> {
 
     fn depth_limit_error(self, job: QueryJobId) {
         let mut span = None;
-        let mut layout_of_depth = None;
-        if let Some((info, depth)) =
-            job.try_find_layout_root(self.collect_active_jobs(), dep_kinds::layout_of)
-        {
+        let mut note = None;
+        if let Some((info, depth)) = job.try_find_dep_kind_root(self.collect_active_jobs()) {
             span = Some(info.job.span);
-            layout_of_depth = Some(LayoutOfDepth { desc: info.query.description, depth });
+            note = Some(QueryOverflowNote { desc: info.query.description, depth });
         }
 
         let suggested_limit = match self.recursion_limit() {
@@ -169,7 +167,7 @@ impl QueryContext for QueryCtxt<'_> {
 
         self.sess.dcx().emit_fatal(QueryOverflow {
             span,
-            layout_of_depth,
+            note,
             suggested_limit,
             crate_name: self.crate_name(LOCAL_CRATE),
         });

compiler/rustc_query_system/messages.ftl

@@ -21,7 +21,7 @@ query_system_increment_compilation = internal compiler error: encountered increm
 query_system_increment_compilation_note1 = Please follow the instructions below to create a bug report with the provided information
 query_system_increment_compilation_note2 = See <https://github.com/rust-lang/rust/issues/84970> for more information
 
-query_system_layout_of_depth = query depth increased by {$depth} when {$desc}
+query_system_overflow_note = query depth increased by {$depth} when {$desc}
 
 query_system_query_overflow = queries overflow the depth limit!
     .help = consider increasing the recursion limit by adding a `#![recursion_limit = "{$suggested_limit}"]` attribute to your crate (`{$crate_name}`)

compiler/rustc_query_system/src/error.rs

@@ -84,14 +84,14 @@ pub struct QueryOverflow {
     #[primary_span]
     pub span: Option<Span>,
     #[subdiagnostic]
-    pub layout_of_depth: Option<LayoutOfDepth>,
+    pub note: Option<QueryOverflowNote>,
     pub suggested_limit: Limit,
     pub crate_name: Symbol,
 }
 
 #[derive(Subdiagnostic)]
-#[note(query_system_layout_of_depth)]
-pub struct LayoutOfDepth {
+#[note(query_system_overflow_note)]
+pub struct QueryOverflowNote {
     pub desc: String,
     pub depth: usize,
 }

compiler/rustc_query_system/src/lib.rs

@@ -16,7 +16,7 @@ pub mod ich;
 pub mod query;
 mod values;
 
-pub use error::{HandleCycleError, LayoutOfDepth, QueryOverflow};
+pub use error::{HandleCycleError, QueryOverflow, QueryOverflowNote};
 pub use values::Value;
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }

compiler/rustc_query_system/src/query/job.rs

@@ -15,7 +15,7 @@ use rustc_span::{DUMMY_SP, Span};
 use crate::dep_graph::DepContext;
 use crate::error::CycleStack;
 use crate::query::plumbing::CycleError;
-use crate::query::{DepKind, QueryContext, QueryStackFrame};
+use crate::query::{QueryContext, QueryStackFrame};
 
 /// Represents a span and a query key.
 #[derive(Clone, Debug)]
@@ -136,18 +136,16 @@ impl QueryJobId {
 
     #[cold]
     #[inline(never)]
-    pub fn try_find_layout_root(
-        &self,
-        query_map: QueryMap,
-        layout_of_kind: DepKind,
-    ) -> Option<(QueryJobInfo, usize)> {
-        let mut last_layout = None;
-        let mut current_id = Some(*self);
-        let mut depth = 0;
+    pub fn try_find_dep_kind_root(&self, query_map: QueryMap) -> Option<(QueryJobInfo, usize)> {
+        let mut depth = 1;
+        let info = query_map.get(&self).unwrap();
+        let dep_kind = info.query.dep_kind;
+        let mut current_id = info.job.parent;
+        let mut last_layout = Some((info.clone(), depth));
 
         while let Some(id) = current_id {
             let info = query_map.get(&id).unwrap();
-            if info.query.dep_kind == layout_of_kind {
+            if info.query.dep_kind == dep_kind {
                 depth += 1;
                 last_layout = Some((info.clone(), depth));
             }

tests/ui/generic-const-items/recursive.rs

@@ -1,12 +1,11 @@
-// FIXME(generic_const_items): This leads to a stack overflow in the compiler!
-//@ known-bug: unknown
-//@ ignore-test
+//@ build-fail
 
 #![feature(generic_const_items)]
 #![allow(incomplete_features)]
+#![recursion_limit = "15"]
 
 const RECUR<T>: () = RECUR::<(T,)>;
 
 fn main() {
-    let _ = RECUR::<()>;
+    let _ = RECUR::<()>; //~ ERROR: queries overflow the depth limit!
 }

tests/ui/generic-const-items/recursive.stderr

@@ -0,0 +1,11 @@
+error: queries overflow the depth limit!
+  --> $DIR/recursive.rs:10:13
+   |
+LL |     let _ = RECUR::<()>;
+   |             ^^^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "30"]` attribute to your crate (`recursive`)
+   = note: query depth increased by 17 when simplifying constant for the type system `RECUR`
+
+error: aborting due to 1 previous error
+