Auto merge of rust-lang#100748 - SparrowLii:query_depth, r=cjgillot

add `depth_limit` in `QueryVTable` to avoid entering a new tcx in `layout_of`

Fixes rust-lang#49735
Updates rust-lang#48685

The `layout_of` query needs to check whether it overflows the depth limit, and the current implementation needs to create a new `ImplicitCtxt` inside `layout_of`. However, `start_query` will already create a new `ImplicitCtxt`, so we can check the depth limit in `start_query`.

We can tell whether we need to check the depth limit simply by whether the return value of `to_debug_str` of the query is `layout_of`. But I think adding the `depth_limit` field in `QueryVTable` may be more elegant and more scalable.

Author: bors

compiler/rustc_macros/src/query.rs

@@ -106,9 +106,12 @@ struct QueryModifiers {
     /// Generate a dep node based on the dependencies of the query
     anon: Option<Ident>,
 
-    // Always evaluate the query, ignoring its dependencies
+    /// Always evaluate the query, ignoring its dependencies
     eval_always: Option<Ident>,
 
+    /// Whether the query has a call depth limit
+    depth_limit: Option<Ident>,
+
     /// Use a separate query provider for local and extern crates
     separate_provide_extern: Option<Ident>,
 
@@ -126,6 +129,7 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
     let mut no_hash = None;
     let mut anon = None;
     let mut eval_always = None;
+    let mut depth_limit = None;
     let mut separate_provide_extern = None;
     let mut remap_env_constness = None;
 
@@ -194,6 +198,8 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
             try_insert!(anon = modifier);
         } else if modifier == "eval_always" {
             try_insert!(eval_always = modifier);
+        } else if modifier == "depth_limit" {
+            try_insert!(depth_limit = modifier);
         } else if modifier == "separate_provide_extern" {
             try_insert!(separate_provide_extern = modifier);
         } else if modifier == "remap_env_constness" {
@@ -215,6 +221,7 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
         no_hash,
         anon,
         eval_always,
+        depth_limit,
         separate_provide_extern,
         remap_env_constness,
     })
@@ -365,6 +372,10 @@ pub fn rustc_queries(input: TokenStream) -> TokenStream {
         if let Some(eval_always) = &modifiers.eval_always {
             attributes.push(quote! { (#eval_always) });
         };
+        // Pass on the depth_limit modifier
+        if let Some(depth_limit) = &modifiers.depth_limit {
+            attributes.push(quote! { (#depth_limit) });
+        };
         // Pass on the separate_provide_extern modifier
         if let Some(separate_provide_extern) = &modifiers.separate_provide_extern {
             attributes.push(quote! { (#separate_provide_extern) });

compiler/rustc_middle/src/query/mod.rs

@@ -1309,6 +1309,7 @@ rustc_queries! {
     query layout_of(
         key: ty::ParamEnvAnd<'tcx, Ty<'tcx>>
     ) -> Result<ty::layout::TyAndLayout<'tcx>, ty::layout::LayoutError<'tcx>> {
+        depth_limit
         desc { "computing layout of `{}`", key.value }
         remap_env_constness
     }

compiler/rustc_middle/src/ty/context.rs

@@ -1857,8 +1857,8 @@ pub mod tls {
         /// This is updated by `JobOwner::start` in `ty::query::plumbing` when executing a query.
         pub diagnostics: Option<&'a Lock<ThinVec<Diagnostic>>>,
 
-        /// Used to prevent layout from recursing too deeply.
-        pub layout_depth: usize,
+        /// Used to prevent queries from calling too deeply.
+        pub query_depth: usize,
 
         /// The current dep graph task. This is used to add dependencies to queries
         /// when executing them.
@@ -1872,7 +1872,7 @@ pub mod tls {
                 tcx,
                 query: None,
                 diagnostics: None,
-                layout_depth: 0,
+                query_depth: 0,
                 task_deps: TaskDepsRef::Ignore,
             }
         }

compiler/rustc_middle/src/ty/layout.rs

@@ -229,49 +229,38 @@ fn layout_of<'tcx>(
     tcx: TyCtxt<'tcx>,
     query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
 ) -> Result<TyAndLayout<'tcx>, LayoutError<'tcx>> {
-    ty::tls::with_related_context(tcx, move |icx| {
-        let (param_env, ty) = query.into_parts();
-        debug!(?ty);
-
-        if !tcx.recursion_limit().value_within_limit(icx.layout_depth) {
-            tcx.sess.fatal(&format!("overflow representing the type `{}`", ty));
+    let (param_env, ty) = query.into_parts();
+    debug!(?ty);
+
+    let param_env = param_env.with_reveal_all_normalized(tcx);
+    let unnormalized_ty = ty;
+
+    // FIXME: We might want to have two different versions of `layout_of`:
+    // One that can be called after typecheck has completed and can use
+    // `normalize_erasing_regions` here and another one that can be called
+    // before typecheck has completed and uses `try_normalize_erasing_regions`.
+    let ty = match tcx.try_normalize_erasing_regions(param_env, ty) {
+        Ok(t) => t,
+        Err(normalization_error) => {
+            return Err(LayoutError::NormalizationFailure(ty, normalization_error));
         }
+    };
 
-        // Update the ImplicitCtxt to increase the layout_depth
-        let icx = ty::tls::ImplicitCtxt { layout_depth: icx.layout_depth + 1, ..icx.clone() };
-
-        ty::tls::enter_context(&icx, |_| {
-            let param_env = param_env.with_reveal_all_normalized(tcx);
-            let unnormalized_ty = ty;
-
-            // FIXME: We might want to have two different versions of `layout_of`:
-            // One that can be called after typecheck has completed and can use
-            // `normalize_erasing_regions` here and another one that can be called
-            // before typecheck has completed and uses `try_normalize_erasing_regions`.
-            let ty = match tcx.try_normalize_erasing_regions(param_env, ty) {
-                Ok(t) => t,
-                Err(normalization_error) => {
-                    return Err(LayoutError::NormalizationFailure(ty, normalization_error));
-                }
-            };
-
-            if ty != unnormalized_ty {
-                // Ensure this layout is also cached for the normalized type.
-                return tcx.layout_of(param_env.and(ty));
-            }
+    if ty != unnormalized_ty {
+        // Ensure this layout is also cached for the normalized type.
+        return tcx.layout_of(param_env.and(ty));
+    }
 
-            let cx = LayoutCx { tcx, param_env };
+    let cx = LayoutCx { tcx, param_env };
 
-            let layout = cx.layout_of_uncached(ty)?;
-            let layout = TyAndLayout { ty, layout };
+    let layout = cx.layout_of_uncached(ty)?;
+    let layout = TyAndLayout { ty, layout };
 
-            cx.record_layout_for_printing(layout);
+    cx.record_layout_for_printing(layout);
 
-            sanity_check_layout(&cx, &layout);
+    sanity_check_layout(&cx, &layout);
 
-            Ok(layout)
-        })
-    })
+    Ok(layout)
 }
 
 pub struct LayoutCx<'tcx, C> {

compiler/rustc_query_impl/src/plumbing.rs

@@ -96,19 +96,24 @@ impl QueryContext for QueryCtxt<'_> {
     fn start_query<R>(
         &self,
         token: QueryJobId,
+        depth_limit: bool,
         diagnostics: Option<&Lock<ThinVec<Diagnostic>>>,
         compute: impl FnOnce() -> R,
     ) -> R {
         // The `TyCtxt` stored in TLS has the same global interner lifetime
         // as `self`, so we use `with_related_context` to relate the 'tcx lifetimes
         // when accessing the `ImplicitCtxt`.
         tls::with_related_context(**self, move |current_icx| {
+            if depth_limit && !self.recursion_limit().value_within_limit(current_icx.query_depth) {
+                self.depth_limit_error();
+            }
+
             // Update the `ImplicitCtxt` to point to our new query job.
             let new_icx = ImplicitCtxt {
                 tcx: **self,
                 query: Some(token),
                 diagnostics,
-                layout_depth: current_icx.layout_depth,
+                query_depth: current_icx.query_depth + depth_limit as usize,
                 task_deps: current_icx.task_deps,
             };
 
@@ -210,6 +215,18 @@ macro_rules! is_eval_always {
     };
 }
 
+macro_rules! depth_limit {
+    ([]) => {{
+        false
+    }};
+    ([(depth_limit) $($rest:tt)*]) => {{
+        true
+    }};
+    ([$other:tt $($modifiers:tt)*]) => {
+        depth_limit!([$($modifiers)*])
+    };
+}
+
 macro_rules! hash_result {
     ([]) => {{
         Some(dep_graph::hash_result)
@@ -349,6 +366,7 @@ macro_rules! define_queries {
                 QueryVTable {
                     anon: is_anon!([$($modifiers)*]),
                     eval_always: is_eval_always!([$($modifiers)*]),
+                    depth_limit: depth_limit!([$($modifiers)*]),
                     dep_kind: dep_graph::DepKind::$name,
                     hash_result: hash_result!([$($modifiers)*]),
                     handle_cycle_error: |tcx, mut error| handle_cycle_error!([$($modifiers)*][tcx, error]),

compiler/rustc_query_system/src/query/config.rs

@@ -23,6 +23,7 @@ pub struct QueryVTable<CTX: QueryContext, K, V> {
     pub anon: bool,
     pub dep_kind: CTX::DepKind,
     pub eval_always: bool,
+    pub depth_limit: bool,
     pub cache_on_disk: bool,
 
     pub compute: fn(CTX::DepContext, K) -> V,

compiler/rustc_query_system/src/query/mod.rs

@@ -14,7 +14,7 @@ pub use self::caches::{
 mod config;
 pub use self::config::{QueryConfig, QueryDescription, QueryVTable};
 
-use crate::dep_graph::{DepNodeIndex, HasDepContext, SerializedDepNodeIndex};
+use crate::dep_graph::{DepContext, DepNodeIndex, HasDepContext, SerializedDepNodeIndex};
 
 use rustc_data_structures::sync::Lock;
 use rustc_data_structures::thin_vec::ThinVec;
@@ -119,7 +119,12 @@ pub trait QueryContext: HasDepContext {
     fn start_query<R>(
         &self,
         token: QueryJobId,
+        depth_limit: bool,
         diagnostics: Option<&Lock<ThinVec<Diagnostic>>>,
         compute: impl FnOnce() -> R,
     ) -> R;
+
+    fn depth_limit_error(&self) {
+        self.dep_context().sess().fatal("queries overflow the depth limit!");
+    }
 }

compiler/rustc_query_system/src/query/plumbing.rs

@@ -381,7 +381,9 @@ where
     // Fast path for when incr. comp. is off.
     if !dep_graph.is_fully_enabled() {
         let prof_timer = tcx.dep_context().profiler().query_provider();
-        let result = tcx.start_query(job_id, None, || query.compute(*tcx.dep_context(), key));
+        let result = tcx.start_query(job_id, query.depth_limit, None, || {
+            query.compute(*tcx.dep_context(), key)
+        });
         let dep_node_index = dep_graph.next_virtual_depnode_index();
         prof_timer.finish_with_query_invocation_id(dep_node_index.into());
         return (result, dep_node_index);
@@ -394,7 +396,7 @@ where
 
         // The diagnostics for this query will be promoted to the current session during
         // `try_mark_green()`, so we can ignore them here.
-        if let Some(ret) = tcx.start_query(job_id, None, || {
+        if let Some(ret) = tcx.start_query(job_id, false, None, || {
             try_load_from_disk_and_cache_in_memory(tcx, &key, &dep_node, query)
         }) {
             return ret;
@@ -404,18 +406,20 @@ where
     let prof_timer = tcx.dep_context().profiler().query_provider();
     let diagnostics = Lock::new(ThinVec::new());
 
-    let (result, dep_node_index) = tcx.start_query(job_id, Some(&diagnostics), || {
-        if query.anon {
-            return dep_graph.with_anon_task(*tcx.dep_context(), query.dep_kind, || {
-                query.compute(*tcx.dep_context(), key)
-            });
-        }
+    let (result, dep_node_index) =
+        tcx.start_query(job_id, query.depth_limit, Some(&diagnostics), || {
+            if query.anon {
+                return dep_graph.with_anon_task(*tcx.dep_context(), query.dep_kind, || {
+                    query.compute(*tcx.dep_context(), key)
+                });
+            }
 
-        // `to_dep_node` is expensive for some `DepKind`s.
-        let dep_node = dep_node_opt.unwrap_or_else(|| query.to_dep_node(*tcx.dep_context(), &key));
+            // `to_dep_node` is expensive for some `DepKind`s.
+            let dep_node =
+                dep_node_opt.unwrap_or_else(|| query.to_dep_node(*tcx.dep_context(), &key));
 
-        dep_graph.with_task(dep_node, *tcx.dep_context(), key, query.compute, query.hash_result)
-    });
+            dep_graph.with_task(dep_node, *tcx.dep_context(), key, query.compute, query.hash_result)
+        });
 
     prof_timer.finish_with_query_invocation_id(dep_node_index.into());