Compute query::Providers almost entirely at compile-time.

src/librustc_codegen_llvm/attributes.rs

@@ -342,7 +342,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
     }
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     providers.supported_target_features = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
         if tcx.sess.opts.actually_rustdoc {
@@ -360,7 +360,7 @@ pub fn provide(providers: &mut Providers) {
     provide_extern(providers);
 }
 
-pub fn provide_extern(providers: &mut Providers) {
+pub const fn provide_extern(providers: &mut Providers) {
     providers.wasm_import_module_map = |tcx, cnum| {
         // Build up a map from DefId to a `NativeLib` structure, where
         // `NativeLib` internally contains information about

src/librustc_codegen_llvm/lib.rs

@@ -7,6 +7,8 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
 #![feature(const_cstr_unchecked)]
+#![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![feature(crate_visibility_modifier)]
 #![feature(extern_types)]
 #![feature(in_band_lifetimes)]

src/librustc_codegen_ssa/back/symbol_export.rs

@@ -366,7 +366,7 @@ fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_>, def_id: DefId) -> b
     }
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     providers.reachable_non_generics = reachable_non_generics_provider;
     providers.is_reachable_non_generic = is_reachable_non_generic_provider_local;
     providers.exported_symbols = exported_symbols_provider_local;
@@ -375,7 +375,7 @@ pub fn provide(providers: &mut Providers) {
     providers.upstream_drop_glue_for = upstream_drop_glue_for_provider;
 }
 
-pub fn provide_extern(providers: &mut Providers) {
+pub const fn provide_extern(providers: &mut Providers) {
     providers.is_reachable_non_generic = is_reachable_non_generic_provider_extern;
     providers.upstream_monomorphizations_for = upstream_monomorphizations_for_provider;
 }

src/librustc_codegen_ssa/base.rs

@@ -852,7 +852,7 @@ impl CrateInfo {
     }
 }
 
-pub fn provide_both(providers: &mut Providers) {
+pub const fn provide_both(providers: &mut Providers) {
     providers.backend_optimization_level = |tcx, cratenum| {
         let for_speed = match tcx.sess.opts.optimize {
             // If globally no optimisation is done, #[optimize] has no effect.

src/librustc_codegen_ssa/lib.rs

@@ -1,6 +1,8 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
+#![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![feature(try_blocks)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
@@ -138,12 +140,12 @@ pub struct CodegenResults {
     pub crate_info: CrateInfo,
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     crate::back::symbol_export::provide(providers);
     crate::base::provide_both(providers);
 }
 
-pub fn provide_extern(providers: &mut Providers) {
+pub const fn provide_extern(providers: &mut Providers) {
     crate::back::symbol_export::provide_extern(providers);
     crate::base::provide_both(providers);
 }

src/librustc_interface/lib.rs

@@ -1,5 +1,7 @@
 #![feature(bool_to_option)]
 #![feature(box_syntax)]
+#![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![feature(set_stdio)]
 #![feature(nll)]
 #![feature(generator_trait)]
@@ -14,6 +16,7 @@ mod queries;
 pub mod util;
 
 pub use interface::{run_compiler, Config};
+pub use passes::{DEFAULT_EXTERN_QUERY_PROVIDERS, DEFAULT_QUERY_PROVIDERS};
 pub use queries::Queries;
 
 #[cfg(test)]

src/librustc_interface/passes.rs

@@ -19,6 +19,7 @@ use rustc_middle::arena::Arena;
 use rustc_middle::dep_graph::DepGraph;
 use rustc_middle::middle;
 use rustc_middle::middle::cstore::{CrateStore, MetadataLoader, MetadataLoaderDyn};
+use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::steal::Steal;
 use rustc_middle::ty::{self, GlobalCtxt, ResolverOutputs, TyCtxt};
 use rustc_mir as mir;
@@ -719,31 +720,49 @@ pub fn prepare_outputs(
     Ok(outputs)
 }
 
-pub fn default_provide(providers: &mut ty::query::Providers) {
-    providers.analysis = analysis;
-    proc_macro_decls::provide(providers);
-    plugin::build::provide(providers);
-    rustc_middle::hir::provide(providers);
-    mir::provide(providers);
-    mir_build::provide(providers);
-    rustc_privacy::provide(providers);
-    typeck::provide(providers);
-    ty::provide(providers);
-    traits::provide(providers);
-    rustc_passes::provide(providers);
-    rustc_resolve::provide(providers);
-    rustc_traits::provide(providers);
-    rustc_ty::provide(providers);
-    rustc_metadata::provide(providers);
-    rustc_lint::provide(providers);
-    rustc_symbol_mangling::provide(providers);
-    rustc_codegen_ssa::provide(providers);
-}
+pub const DEFAULT_QUERY_PROVIDERS: Providers = {
+    // FIXME(eddyb) the `const fn` shouldn't be needed, but mutable references
+    // were disallowed in constants even when not escaping as `&'static mut T`.
+    const fn default_providers() -> Providers {
+        let mut providers = &mut Providers::EMPTY;
+
+        providers.analysis = analysis;
+        proc_macro_decls::provide(providers);
+        plugin::build::provide(providers);
+        rustc_middle::hir::provide(providers);
+        mir::provide(providers);
+        mir_build::provide(providers);
+        rustc_privacy::provide(providers);
+        typeck::provide(providers);
+        ty::provide(providers);
+        traits::provide(providers);
+        rustc_passes::provide(providers);
+        rustc_resolve::provide(providers);
+        rustc_traits::provide(providers);
+        rustc_ty::provide(providers);
+        rustc_metadata::provide(providers);
+        rustc_lint::provide(providers);
+        rustc_symbol_mangling::provide(providers);
+        rustc_codegen_ssa::provide(providers);
+
+        *providers
+    }
+    default_providers()
+};
 
-pub fn default_provide_extern(providers: &mut ty::query::Providers) {
-    rustc_metadata::provide_extern(providers);
-    rustc_codegen_ssa::provide_extern(providers);
-}
+pub const DEFAULT_EXTERN_QUERY_PROVIDERS: Providers = {
+    // FIXME(eddyb) the `const fn` shouldn't be needed, but mutable references
+    // were disallowed in constants even when not escaping as `&'static mut T`.
+    const fn default_extern_providers() -> Providers {
+        let providers = &mut DEFAULT_QUERY_PROVIDERS;
+
+        rustc_metadata::provide_extern(providers);
+        rustc_codegen_ssa::provide_extern(providers);
+
+        *providers
+    }
+    default_extern_providers()
+};
 
 pub struct QueryContext<'tcx>(&'tcx GlobalCtxt<'tcx>);
 
@@ -780,12 +799,11 @@ pub fn create_global_ctxt<'tcx>(
     let query_result_on_disk_cache = rustc_incremental::load_query_result_cache(sess);
 
     let codegen_backend = compiler.codegen_backend();
-    let mut local_providers = ty::query::Providers::default();
-    default_provide(&mut local_providers);
+    let mut local_providers = DEFAULT_QUERY_PROVIDERS;
     codegen_backend.provide(&mut local_providers);
 
-    let mut extern_providers = local_providers;
-    default_provide_extern(&mut extern_providers);
+    let mut extern_providers = DEFAULT_EXTERN_QUERY_PROVIDERS;
+    codegen_backend.provide(&mut extern_providers);
     codegen_backend.provide_extern(&mut extern_providers);
 
     if let Some(callback) = compiler.override_queries {

src/librustc_interface/proc_macro_decls.rs

@@ -35,6 +35,6 @@ impl<'v> ItemLikeVisitor<'v> for Finder {
     fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem<'_>) {}
 }
 
-pub(crate) fn provide(providers: &mut Providers) {
+pub(crate) const fn provide(providers: &mut Providers) {
     *providers = Providers { proc_macro_decls_static, ..*providers };
 }

src/librustc_lint/levels.rs

@@ -571,6 +571,6 @@ impl<'tcx> intravisit::Visitor<'tcx> for LintLevelMapBuilder<'_, 'tcx> {
     }
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     providers.lint_levels = lint_levels;
 }

src/librustc_lint/lib.rs

@@ -29,6 +29,8 @@
 #![cfg_attr(test, feature(test))]
 #![feature(bool_to_option)]
 #![feature(box_syntax)]
+#![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![feature(crate_visibility_modifier)]
 #![feature(iter_order_by)]
 #![feature(never_type)]
@@ -88,7 +90,7 @@ pub use rustc_session::lint::Level::{self, *};
 pub use rustc_session::lint::{BufferedEarlyLint, FutureIncompatibleInfo, Lint, LintId};
 pub use rustc_session::lint::{LintArray, LintPass};
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     levels::provide(providers);
     *providers = Providers { lint_mod, ..*providers };
 }

src/librustc_metadata/lib.rs

@@ -1,5 +1,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
+#![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![feature(core_intrinsics)]
 #![feature(crate_visibility_modifier)]
 #![feature(drain_filter)]

src/librustc_metadata/rmeta/decoder/cstore_impl.rs

@@ -30,7 +30,7 @@ use std::any::Any;
 macro_rules! provide {
     (<$lt:tt> $tcx:ident, $def_id:ident, $other:ident, $cdata:ident,
       $($name:ident => $compute:block)*) => {
-        pub fn provide_extern(providers: &mut Providers) {
+        pub const fn provide_extern(providers: &mut Providers) {
             $(fn $name<$lt>(
                 $tcx: TyCtxt<$lt>,
                 def_id_arg: ty::query::query_keys::$name<$lt>,
@@ -240,7 +240,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     crate_extern_paths => { cdata.source().paths().cloned().collect() }
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     // FIXME(#44234) - almost all of these queries have no sub-queries and
     // therefore no actual inputs, they're just reading tables calculated in
     // resolve! Does this work? Unsure! That's what the issue is about

src/librustc_middle/hir/map/mod.rs

@@ -1067,6 +1067,6 @@ fn hir_id_to_string(map: &Map<'_>, id: HirId) -> String {
     }
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     providers.def_kind = |tcx, def_id| tcx.hir().def_kind(def_id.expect_local());
 }

src/librustc_middle/hir/mod.rs

@@ -62,7 +62,7 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     providers.parent_module_from_def_id = |tcx, id| {
         let hir = tcx.hir();
         hir.local_def_id(hir.get_module_parent_node(hir.as_local_hir_id(id)))

src/librustc_middle/lib.rs

@@ -29,6 +29,7 @@
 #![feature(box_syntax)]
 #![cfg_attr(bootstrap, feature(const_if_match))]
 #![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![feature(const_panic)]
 #![feature(const_transmute)]
 #![feature(core_intrinsics)]

src/librustc_middle/ty/context.rs

@@ -2699,7 +2699,7 @@ fn ptr_eq<T, U>(t: *const T, u: *const U) -> bool {
     t as *const () == u as *const ()
 }
 
-pub fn provide(providers: &mut ty::query::Providers) {
+pub const fn provide(providers: &mut ty::query::Providers) {
     providers.in_scope_traits_map = |tcx, id| tcx.gcx.trait_map.get(&id);
     providers.module_exports = |tcx, id| tcx.gcx.export_map.get(&id).map(|v| &v[..]);
     providers.crate_name = |tcx, id| {

src/librustc_middle/ty/erase_regions.rs

@@ -1,7 +1,7 @@
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::{self, Ty, TyCtxt, TypeFlags};
 
-pub(super) fn provide(providers: &mut ty::query::Providers) {
+pub(super) const fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers { erase_regions_ty, ..*providers };
 }
 

src/librustc_middle/ty/layout.rs

@@ -210,7 +210,7 @@ fn layout_raw<'tcx>(
     })
 }
 
-pub fn provide(providers: &mut ty::query::Providers) {
+pub const fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers { layout_raw, ..*providers };
 }
 

src/librustc_middle/ty/mod.rs

@@ -2966,7 +2966,7 @@ pub fn is_impl_trait_defn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
     None
 }
 
-pub fn provide(providers: &mut ty::query::Providers) {
+pub const fn provide(providers: &mut ty::query::Providers) {
     context::provide(providers);
     erase_regions::provide(providers);
     layout::provide(providers);

src/librustc_middle/ty/query/plumbing.rs

@@ -496,11 +496,6 @@ macro_rules! define_queries_inner {
             tcx: $tcx,
             input: ($(([$($modifiers)*] [$name] [$($K)*] [$V]))*)
         }
-
-        impl Copy for Providers {}
-        impl Clone for Providers {
-            fn clone(&self) -> Self { *self }
-        }
     }
 }
 
@@ -565,14 +560,19 @@ macro_rules! define_provider_struct {
             $(pub $name: for<$tcx> fn(TyCtxt<$tcx>, $K) -> $R,)*
         }
 
-        impl Default for Providers {
-            fn default() -> Self {
+        impl Copy for Providers {}
+        impl Clone for Providers {
+            fn clone(&self) -> Self { *self }
+        }
+
+        impl Providers {
+            pub const EMPTY: Self = {
                 $(fn $name<$tcx>(_: TyCtxt<$tcx>, key: $K) -> $R {
                     bug!("`tcx.{}({:?})` unsupported by its crate",
                          stringify!($name), key);
                 })*
                 Providers { $($name),* }
-            }
+            };
         }
     };
 }

src/librustc_middle/util/bug.rs

@@ -47,6 +47,6 @@ pub fn trigger_delay_span_bug(tcx: TyCtxt<'_>, key: rustc_hir::def_id::DefId) {
     );
 }
 
-pub fn provide(providers: &mut crate::ty::query::Providers) {
+pub const fn provide(providers: &mut crate::ty::query::Providers) {
     *providers = crate::ty::query::Providers { trigger_delay_span_bug, ..*providers };
 }

src/librustc_mir/borrow_check/mod.rs

@@ -86,7 +86,7 @@ crate struct Upvar {
 
 const DEREF_PROJECTION: &[PlaceElem<'_>; 1] = &[ProjectionElem::Deref];
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     *providers = Providers { mir_borrowck, ..*providers };
 }
 

src/librustc_mir/const_eval/fn_queries.rs

@@ -156,7 +156,7 @@ fn const_fn_is_allowed_fn_ptr(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
         && tcx.lookup_const_stability(def_id).map(|stab| stab.allow_const_fn_ptr).unwrap_or(false)
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     *providers = Providers {
         is_const_fn_raw,
         is_const_impl_raw: |tcx, def_id| is_const_impl_raw(tcx, def_id.expect_local()),

src/librustc_mir/lib.rs

@@ -12,6 +12,7 @@ Rust MIR: a lowered representation of Rust.
 #![feature(const_fn)]
 #![cfg_attr(bootstrap, feature(const_if_match))]
 #![cfg_attr(bootstrap, feature(const_loop))]
+#![feature(const_mut_refs)]
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]
@@ -47,7 +48,7 @@ pub mod util;
 
 use rustc_middle::ty::query::Providers;
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     borrow_check::provide(providers);
     const_eval::provide(providers);
     shim::provide(providers);

src/librustc_mir/monomorphize/partitioning.rs

@@ -994,7 +994,7 @@ fn collect_and_partition_mono_items(
     (tcx.arena.alloc(mono_items), codegen_units)
 }
 
-pub fn provide(providers: &mut Providers) {
+pub const fn provide(providers: &mut Providers) {
     providers.collect_and_partition_mono_items = collect_and_partition_mono_items;
 
     providers.is_codegened_item = |tcx, def_id| {