Make sure that all upstream generics get re-exported from Rust dylibs.

src/librustc/middle/exported_symbols.rs

@@ -32,7 +32,9 @@ pub enum ExportedSymbol<'tcx> {
 }
 
 impl<'tcx> ExportedSymbol<'tcx> {
-    pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> ty::SymbolName {
+    /// This is the symbol name of an instance if it is instantiated in the
+    /// local crate.
+    pub fn symbol_name_for_local_instance(&self, tcx: TyCtxt<'tcx>) -> ty::SymbolName {
         match *self {
             ExportedSymbol::NonGeneric(def_id) => tcx.symbol_name(ty::Instance::mono(tcx, def_id)),
             ExportedSymbol::Generic(def_id, substs) => {
@@ -50,9 +52,22 @@ impl<'tcx> ExportedSymbol<'tcx> {
                 }
                 ExportedSymbol::Generic(..) | ExportedSymbol::NoDefId(_) => cmp::Ordering::Less,
             },
-            ExportedSymbol::Generic(..) => match *other {
+            ExportedSymbol::Generic(self_def_id, self_substs) => match *other {
                 ExportedSymbol::NonGeneric(_) => cmp::Ordering::Greater,
-                ExportedSymbol::Generic(..) => self.symbol_name(tcx).cmp(&other.symbol_name(tcx)),
+                ExportedSymbol::Generic(other_def_id, other_substs) => {
+                    // We compare the symbol names because they are cached as query
+                    // results which makes them relatively cheap to access repeatedly.
+                    //
+                    // It might be even faster to build a local cache of stable IDs
+                    // for sorting. Exported symbols are really only sorted once
+                    // in order to make the `exported_symbols` query result stable.
+                    let self_symbol_name =
+                        tcx.symbol_name(ty::Instance::new(self_def_id, self_substs));
+                    let other_symbol_name =
+                        tcx.symbol_name(ty::Instance::new(other_def_id, other_substs));
+
+                    self_symbol_name.cmp(&other_symbol_name)
+                }
                 ExportedSymbol::NoDefId(_) => cmp::Ordering::Less,
             },
             ExportedSymbol::NoDefId(self_symbol_name) => match *other {

src/librustc/query/mod.rs

@@ -557,6 +557,9 @@ rustc_queries! {
             desc { |tcx| "generating MIR shim for `{}`", tcx.def_path_str(key.def_id()) }
         }
 
+        /// The `symbol_name` query provides the symbol name for calling a
+        /// given instance from the local crate. In particular, it will also
+        /// look up the correct symbol name of instances from upstream crates.
         query symbol_name(key: ty::Instance<'tcx>) -> ty::SymbolName {
             no_force
             desc { "computing the symbol for `{}`", key }
@@ -971,6 +974,11 @@ rustc_queries! {
     }
 
     Linking {
+        /// The list of symbols exported from the given crate.
+        ///
+        /// - All names contained in `exported_symbols(cnum)` are guaranteed to
+        ///   correspond to a publicly visible symbol in `cnum` machine code.
+        /// - The `exported_symbols` sets of different crates do not intersect.
         query exported_symbols(_: CrateNum)
             -> Arc<Vec<(ExportedSymbol<'tcx>, SymbolExportLevel)>> {
             desc { "exported_symbols" }

src/librustc_codegen_ssa/back/linker.rs

@@ -1103,7 +1103,11 @@ fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
     let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
     for &(symbol, level) in tcx.exported_symbols(LOCAL_CRATE).iter() {
         if level.is_below_threshold(export_threshold) {
-            symbols.push(symbol.symbol_name(tcx).to_string());
+            symbols.push(symbol_export::symbol_name_for_instance_in_crate(
+                tcx,
+                symbol,
+                LOCAL_CRATE,
+            ));
         }
     }
 
@@ -1124,12 +1128,7 @@ fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
                     continue;
                 }
 
-                // FIXME rust-lang/rust#64319, rust-lang/rust#64872:
-                // We want to block export of generics from dylibs,
-                // but we must fix rust-lang/rust#65890 before we can
-                // do that robustly.
-
-                symbols.push(symbol.symbol_name(tcx).to_string());
+                symbols.push(symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum));
             }
         }
     }

src/librustc_codegen_ssa/back/symbol_export.rs

@@ -8,6 +8,7 @@ use rustc::ty::query::Providers;
 use rustc::ty::subst::SubstsRef;
 use rustc::ty::Instance;
 use rustc::ty::{SymbolName, TyCtxt};
+use rustc_codegen_utils::symbol_names;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
@@ -358,3 +359,32 @@ fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel
         SymbolExportLevel::Rust
     }
 }
+
+/// This is the symbol name of the given instance instantiated in a specific crate.
+pub fn symbol_name_for_instance_in_crate<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    symbol: ExportedSymbol<'tcx>,
+    instantiating_crate: CrateNum,
+) -> String {
+    // If this is something instantiated in the local crate then we might
+    // already have cached the name as a query result.
+    if instantiating_crate == LOCAL_CRATE {
+        return symbol.symbol_name_for_local_instance(tcx).to_string();
+    }
+
+    // This is something instantiated in an upstream crate, so we have to use
+    // the slower (because uncached) version of computing the symbol name.
+    match symbol {
+        ExportedSymbol::NonGeneric(def_id) => symbol_names::symbol_name_for_instance_in_crate(
+            tcx,
+            Instance::mono(tcx, def_id),
+            instantiating_crate,
+        ),
+        ExportedSymbol::Generic(def_id, substs) => symbol_names::symbol_name_for_instance_in_crate(
+            tcx,
+            Instance::new(def_id, substs),
+            instantiating_crate,
+        ),
+        ExportedSymbol::NoDefId(symbol_name) => symbol_name.to_string(),
+    }
+}

src/librustc_codegen_ssa/back/write.rs

@@ -2,7 +2,7 @@ use super::command::Command;
 use super::link::{self, get_linker, remove};
 use super::linker::LinkerInfo;
 use super::lto::{self, SerializedModule};
-use super::symbol_export::ExportedSymbols;
+use super::symbol_export::{symbol_name_for_instance_in_crate, ExportedSymbols};
 use crate::{
     CachedModuleCodegen, CodegenResults, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind,
     RLIB_BYTECODE_EXTENSION,
@@ -956,7 +956,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
             let symbols = tcx
                 .exported_symbols(cnum)
                 .iter()
-                .map(|&(s, lvl)| (s.symbol_name(tcx).to_string(), lvl))
+                .map(|&(s, lvl)| (symbol_name_for_instance_in_crate(tcx, s, cnum), lvl))
                 .collect();
             Arc::new(symbols)
         };

src/librustc_codegen_utils/symbol_names.rs

@@ -91,8 +91,9 @@ use rustc::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc::mir::mono::{InstantiationMode, MonoItem};
 use rustc::session::config::SymbolManglingVersion;
 use rustc::ty::query::Providers;
+use rustc::ty::subst::SubstsRef;
 use rustc::ty::{self, Instance, TyCtxt};
-use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_hir::Node;
 
 use rustc_span::symbol::Symbol;
@@ -102,15 +103,70 @@ use log::debug;
 mod legacy;
 mod v0;
 
+/// This function computes the symbol name for the given `instance` and the
+/// given instantiating crate. That is, if you know that instance X is
+/// instantiated in crate Y, this is the symbol name this instance would have.
+pub fn symbol_name_for_instance_in_crate(
+    tcx: TyCtxt<'tcx>,
+    instance: Instance<'tcx>,
+    instantiating_crate: CrateNum,
+) -> String {
+    compute_symbol_name(tcx, instance, || instantiating_crate)
+}
+
 pub fn provide(providers: &mut Providers<'_>) {
-    *providers = Providers {
-        symbol_name: |tcx, instance| ty::SymbolName { name: symbol_name(tcx, instance) },
+    *providers = Providers { symbol_name: symbol_name_provider, ..*providers };
+}
 
-        ..*providers
-    };
+// The `symbol_name` query provides the symbol name for calling a given
+// instance from the local crate. In particular, it will also look up the
+// correct symbol name of instances from upstream crates.
+fn symbol_name_provider(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> ty::SymbolName {
+    let symbol_name = compute_symbol_name(tcx, instance, || {
+        // This closure determines the instantiating crate for instances that
+        // need an instantiating-crate-suffix for their symbol name, in order
+        // to differentiate between local copies.
+        //
+        // For generics we might find re-usable upstream instances. For anything
+        // else we rely on their being a local copy available.
+
+        if is_generic(instance.substs) {
+            let def_id = instance.def_id();
+
+            if !def_id.is_local() && tcx.sess.opts.share_generics() {
+                // If we are re-using a monomorphization from another crate,
+                // we have to compute the symbol hash accordingly.
+                let upstream_monomorphizations = tcx.upstream_monomorphizations_for(def_id);
+
+                upstream_monomorphizations
+                    .and_then(|monos| monos.get(&instance.substs).cloned())
+                    // If there is no instance available upstream, there'll be
+                    // one in the current crate.
+                    .unwrap_or(LOCAL_CRATE)
+            } else {
+                // For generic functions defined in the current crate, there
+                // can be no upstream instances. Also, if we don't share
+                // generics, we'll instantiate a local copy too.
+                LOCAL_CRATE
+            }
+        } else {
+            // For non-generic things that need to avoid naming conflicts, we
+            // always instantiate a copy in the local crate.
+            LOCAL_CRATE
+        }
+    });
+
+    ty::SymbolName { name: Symbol::intern(&symbol_name) }
 }
 
-fn symbol_name(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Symbol {
+/// Computes the symbol name for the given instance. This function will call
+/// `compute_instantiating_crate` if it needs to factor the instantiating crate
+/// into the symbol name.
+fn compute_symbol_name(
+    tcx: TyCtxt<'tcx>,
+    instance: Instance<'tcx>,
+    compute_instantiating_crate: impl FnOnce() -> CrateNum,
+) -> String {
     let def_id = instance.def_id();
     let substs = instance.substs;
 
@@ -121,11 +177,11 @@ fn symbol_name(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Symbol {
     if def_id.is_local() {
         if tcx.plugin_registrar_fn(LOCAL_CRATE) == Some(def_id) {
             let disambiguator = tcx.sess.local_crate_disambiguator();
-            return Symbol::intern(&tcx.sess.generate_plugin_registrar_symbol(disambiguator));
+            return tcx.sess.generate_plugin_registrar_symbol(disambiguator);
         }
         if tcx.proc_macro_decls_static(LOCAL_CRATE) == Some(def_id) {
             let disambiguator = tcx.sess.local_crate_disambiguator();
-            return Symbol::intern(&tcx.sess.generate_proc_macro_decls_symbol(disambiguator));
+            return tcx.sess.generate_proc_macro_decls_symbol(disambiguator);
         }
     }
 
@@ -162,29 +218,28 @@ fn symbol_name(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Symbol {
             || !tcx.wasm_import_module_map(def_id.krate).contains_key(&def_id)
         {
             if let Some(name) = attrs.link_name {
-                return name;
+                return name.to_string();
             }
-            return tcx.item_name(def_id);
+            return tcx.item_name(def_id).to_string();
         }
     }
 
     if let Some(name) = attrs.export_name {
         // Use provided name
-        return name;
+        return name.to_string();
     }
 
     if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
         // Don't mangle
-        return tcx.item_name(def_id);
+        return tcx.item_name(def_id).to_string();
     }
 
-    let is_generic = substs.non_erasable_generics().next().is_some();
     let avoid_cross_crate_conflicts =
         // If this is an instance of a generic function, we also hash in
         // the ID of the instantiating crate. This avoids symbol conflicts
         // in case the same instances is emitted in two crates of the same
         // project.
-        is_generic ||
+        is_generic(substs) ||
 
         // If we're dealing with an instance of a function that's inlined from
         // another crate but we're marking it as globally shared to our
@@ -197,25 +252,8 @@ fn symbol_name(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Symbol {
             _ => false,
         };
 
-    let instantiating_crate = if avoid_cross_crate_conflicts {
-        Some(if is_generic {
-            if !def_id.is_local() && tcx.sess.opts.share_generics() {
-                // If we are re-using a monomorphization from another crate,
-                // we have to compute the symbol hash accordingly.
-                let upstream_monomorphizations = tcx.upstream_monomorphizations_for(def_id);
-
-                upstream_monomorphizations
-                    .and_then(|monos| monos.get(&substs).cloned())
-                    .unwrap_or(LOCAL_CRATE)
-            } else {
-                LOCAL_CRATE
-            }
-        } else {
-            LOCAL_CRATE
-        })
-    } else {
-        None
-    };
+    let instantiating_crate =
+        if avoid_cross_crate_conflicts { Some(compute_instantiating_crate()) } else { None };
 
     // Pick the crate responsible for the symbol mangling version, which has to:
     // 1. be stable for each instance, whether it's being defined or imported
@@ -232,10 +270,12 @@ fn symbol_name(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Symbol {
         tcx.symbol_mangling_version(mangling_version_crate)
     };
 
-    let mangled = match mangling_version {
+    match mangling_version {
         SymbolManglingVersion::Legacy => legacy::mangle(tcx, instance, instantiating_crate),
         SymbolManglingVersion::V0 => v0::mangle(tcx, instance, instantiating_crate),
-    };
+    }
+}
 
-    Symbol::intern(&mangled)
+fn is_generic(substs: SubstsRef<'_>) -> bool {
+    substs.non_erasable_generics().next().is_some()
 }