Rollup merge of #66018 - pnkfelix:issue-64872-revert-64324, r=alexcri…

…chton

Revert PR 64324: dylibs export generics again (for now)

As discussed on PR #65781, this is a targeted attempt to undo the main semantic change from PR #64324, by putting `dylib` back in the set of crate types that export generic symbols.

The main reason to do this is that PR #64324 had unanticipated side-effects that caused bugs like #64872, and in the opinion of @alexcrichton and myself, the impact of #64872 is worse than #64319.

In other words, it is better for us, in the short term, to reopen #64319 as currently unfixed for now than to introduce new bugs like #64872.

Fix #64872

Reopen #64319

src/librustc/ty/context.rs

@@ -1514,8 +1514,14 @@ impl<'tcx> TyCtxt<'tcx> {
                 CrateType::Executable |
                 CrateType::Staticlib  |
                 CrateType::ProcMacro  |
-                CrateType::Dylib      |
                 CrateType::Cdylib     => false,
+
+                // 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.
+                CrateType::Dylib      => true,
+
                 CrateType::Rlib       => true,
             }
         })

src/librustc_codegen_ssa/back/linker.rs

@@ -14,7 +14,6 @@ use rustc::middle::dependency_format::Linkage;
 use rustc::session::Session;
 use rustc::session::config::{self, CrateType, OptLevel, DebugInfo,
                              LinkerPluginLto, Lto};
-use rustc::middle::exported_symbols::ExportedSymbol;
 use rustc::ty::TyCtxt;
 use rustc_target::spec::{LinkerFlavor, LldFlavor};
 use rustc_serialize::{json, Encoder};
@@ -1112,20 +1111,10 @@ fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
                     continue;
                 }
 
-                // Do not export generic symbols from upstream crates in linked
-                // artifact (notably the `dylib` crate type). The main reason
-                // for this is that `symbol_name` is actually wrong for generic
-                // symbols because it guesses the name we'd give them locally
-                // rather than the name it has upstream (depending on
-                // `share_generics` settings and such).
-                //
-                // To fix that issue we just say that linked artifacts, aka
-                // `dylib`s, never export generic symbols and they aren't
-                // available to downstream crates. (the not available part is
-                // handled elsewhere).
-                if let ExportedSymbol::Generic(..) = symbol {
-                    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());
             }

src/librustc_metadata/cstore_impl.rs

@@ -9,7 +9,6 @@ use rustc::ty::query::QueryConfig;
 use rustc::middle::cstore::{CrateSource, CrateStore, DepKind, EncodedMetadata, NativeLibraryKind};
 use rustc::middle::exported_symbols::ExportedSymbol;
 use rustc::middle::stability::DeprecationEntry;
-use rustc::middle::dependency_format::Linkage;
 use rustc::hir::def;
 use rustc::hir;
 use rustc::session::{CrateDisambiguator, Session};
@@ -235,26 +234,11 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     used_crate_source => { Lrc::new(cdata.source.clone()) }
 
     exported_symbols => {
-        let mut syms = cdata.exported_symbols(tcx);
-
-        // When linked into a dylib crates don't export their generic symbols,
-        // so if that's happening then we can't load upstream monomorphizations
-        // from this crate.
-        let formats = tcx.dependency_formats(LOCAL_CRATE);
-        let remove_generics = formats.iter().any(|(_ty, list)| {
-            match list.get(def_id.krate.as_usize() - 1) {
-                Some(Linkage::IncludedFromDylib) | Some(Linkage::Dynamic) => true,
-                _ => false,
-            }
-        });
-        if remove_generics {
-            syms.retain(|(sym, _threshold)| {
-                match sym {
-                    ExportedSymbol::Generic(..) => false,
-                    _ => return true,
-                }
-            });
-        }
+        let syms = cdata.exported_symbols(tcx);
+
+        // 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.
 
         Arc::new(syms)
     }

src/test/run-make-fulldeps/symbol-visibility/Makefile

@@ -79,12 +79,12 @@ all:
 	# Check that a Rust dylib exports its monomorphic functions, including generics this time
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_c_function_from_rust_dylib)" -eq "1" ]
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_rust_function_from_rust_dylib)" -eq "1" ]
-	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_generic_function_from_rust_dylib)" -eq "0" ]
+	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_generic_function_from_rust_dylib)" -eq "1" ]
 
 	# Check that a Rust dylib exports the monomorphic functions from its dependencies
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_c_function_from_rlib)" -eq "1" ]
 	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_rust_function_from_rlib)" -eq "1" ]
-	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_generic_function_from_rlib)" -eq "0" ]
+	[ "$$($(NM) $(TMPDIR)/$(RDYLIB_NAME) | grep -c public_generic_function_from_rlib)" -eq "1" ]
 
 	# Check that an executable does not export any dynamic symbols
 	[ "$$($(NM) $(TMPDIR)/$(EXE_NAME) | grep -c public_c_function_from_rlib)" -eq "0" ]

src/test/ui/cross-crate/issue-64872/auxiliary/a_def_obj.rs

@@ -0,0 +1,16 @@
+// compile-flags: -C debuginfo=2
+
+// no-prefer-dynamic
+#![crate_type = "rlib"]
+
+pub trait Object { fn method(&self) { } }
+
+impl Object for u32 { }
+impl Object for () { }
+impl<T> Object for &T { }
+
+pub fn unused() {
+    let ref u = 0_u32;
+    let _d = &u as &dyn crate::Object;
+    _d.method()
+}

src/test/ui/cross-crate/issue-64872/auxiliary/b_reexport_obj.rs

@@ -0,0 +1,7 @@
+// compile-flags: -C debuginfo=2 -C prefer-dynamic
+
+#![crate_type="dylib"]
+
+extern crate a_def_obj;
+
+pub use a_def_obj::Object;

src/test/ui/cross-crate/issue-64872/auxiliary/c_another_vtable_for_obj.rs

@@ -0,0 +1,12 @@
+// no-prefer-dynamic
+// compile-flags: -C debuginfo=2
+#![crate_type="rlib"]
+
+extern crate b_reexport_obj;
+use b_reexport_obj::Object;
+
+pub fn another_dyn_debug() {
+    let ref u = 1_u32;
+    let _d = &u as &dyn crate::Object;
+    _d.method()
+}

src/test/ui/cross-crate/issue-64872/auxiliary/d_chain_of_rlibs_and_dylibs.rs

@@ -0,0 +1,9 @@
+// compile-flags: -C debuginfo=2 -C prefer-dynamic
+
+#![crate_type="rlib"]
+
+extern crate c_another_vtable_for_obj;
+
+pub fn chain() {
+    c_another_vtable_for_obj::another_dyn_debug();
+}

src/test/ui/cross-crate/issue-64872/issue-64872.rs

@@ -0,0 +1,17 @@
+// run-pass
+
+// note that these aux-build directives must be in this order: the
+// later crates depend on the earlier ones. (The particular bug that
+// is being exercised here used to exhibit itself during the build of
+// `chain_of_rlibs_and_dylibs.dylib`)
+
+// aux-build:a_def_obj.rs
+// aux-build:b_reexport_obj.rs
+// aux-build:c_another_vtable_for_obj.rs
+// aux-build:d_chain_of_rlibs_and_dylibs.rs
+
+extern crate d_chain_of_rlibs_and_dylibs;
+
+pub fn main() {
+    d_chain_of_rlibs_and_dylibs::chain();
+}