Auto merge of rust-lang#131966 - ChrisDenton:bare-link, r=<try>

Allow #[link(kind = "dylib")] without a name

This PR allows `#[link(kind = "dylib")]` without a library name (see the [dllimport RFC](https://rust-lang.github.io/rfcs/1717-dllimport.html) for how this affects `extern {}` blocks).

This will need a lang fcp but I wanted to investigate how feasible this is. I want a bare `kind` to act the same as any other `#[link]` for the purposes of applying (or not) dllimport so it gets added to the same array. However, this then means they need to be filtered out from normal queries. To facilitate this I've added a wrapper type for the `NativeLib` container and a separate query for `is_dllimport`.

try-job: x86_64-msvc
try-job: x86_64-mingw

compiler/rustc_codegen_llvm/src/callee.rs

@@ -142,8 +142,7 @@ pub(crate) fn get_fn<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'t
             // MinGW: For backward compatibility we rely on the linker to decide whether it
             // should use dllimport for functions.
             if cx.use_dll_storage_attrs
-                && let Some(library) = tcx.native_library(instance_def_id)
-                && library.kind.is_dllimport()
+                && tcx.is_dllimport(instance_def_id)
                 && !matches!(tcx.sess.target.env.as_ref(), "gnu" | "uclibc")
             {
                 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);

compiler/rustc_codegen_llvm/src/consts.rs

@@ -358,10 +358,7 @@ impl<'ll> CodegenCx<'ll, '_> {
             }
         }
 
-        if self.use_dll_storage_attrs
-            && let Some(library) = self.tcx.native_library(def_id)
-            && library.kind.is_dllimport()
-        {
+        if self.use_dll_storage_attrs && self.tcx.is_dllimport(def_id) {
             // For foreign (native) libs we know the exact storage type to use.
             unsafe {
                 llvm::LLVMSetDLLStorageClass(g, llvm::DLLStorageClass::DllImport);

compiler/rustc_feature/src/unstable.rs

@@ -377,6 +377,9 @@ declare_features! (
     (unstable, async_fn_track_caller, "1.73.0", Some(110011)),
     /// Allows `for await` loops.
     (unstable, async_for_loop, "1.77.0", Some(118898)),
+    /// Allows `#[link(kind = "dylib")]` without a library name.
+    /// FIXME: put real issue here.
+    (unstable, bare_link_kind, "CURRENT_RUSTC_VERSION", Some(131966)),
     /// Allows using C-variadics.
     (unstable, c_variadic, "1.34.0", Some(44930)),
     /// Allows the use of `#[cfg(<true/false>)]`.

compiler/rustc_metadata/src/native_libs.rs

@@ -9,13 +9,13 @@ use rustc_middle::ty::{List, ParamEnv, ParamEnvAnd, Ty, TyCtxt};
 use rustc_session::Session;
 use rustc_session::config::CrateType;
 use rustc_session::cstore::{
-    DllCallingConvention, DllImport, ForeignModule, NativeLib, PeImportNameType,
+    DllCallingConvention, DllImport, ForeignModule, NativeLib, NativeLibs, PeImportNameType,
 };
 use rustc_session::parse::feature_err;
 use rustc_session::search_paths::PathKind;
 use rustc_session::utils::NativeLibKind;
 use rustc_span::def_id::{DefId, LOCAL_CRATE};
-use rustc_span::symbol::{Symbol, sym};
+use rustc_span::symbol::{Symbol, kw, sym};
 use rustc_target::spec::LinkSelfContainedComponents;
 use rustc_target::spec::abi::Abi;
 
@@ -173,15 +173,15 @@ fn find_bundled_library(
     None
 }
 
-pub(crate) fn collect(tcx: TyCtxt<'_>, LocalCrate: LocalCrate) -> Vec<NativeLib> {
+pub(crate) fn collect(tcx: TyCtxt<'_>, LocalCrate: LocalCrate) -> NativeLibs {
     let mut collector = Collector { tcx, libs: Vec::new() };
     if tcx.sess.opts.unstable_opts.link_directives {
         for module in tcx.foreign_modules(LOCAL_CRATE).values() {
             collector.process_module(module);
         }
     }
     collector.process_command_line();
-    collector.libs
+    collector.libs.into()
 }
 
 pub(crate) fn relevant_lib(sess: &Session, lib: &NativeLib) -> bool {
@@ -191,6 +191,20 @@ pub(crate) fn relevant_lib(sess: &Session, lib: &NativeLib) -> bool {
     }
 }
 
+pub(crate) fn find_by_id<'a, I: Iterator<Item = &'a NativeLib>>(
+    tcx: TyCtxt<'_>,
+    id: DefId,
+    iter: I,
+) -> Option<&'a NativeLib> {
+    iter.filter(|lib| relevant_lib(tcx.sess, lib)).find(|lib| {
+        let Some(fm_id) = lib.foreign_module else {
+            return false;
+        };
+        let map = tcx.foreign_modules(id.krate);
+        map.get(&fm_id).expect("failed to find foreign module").foreign_items.contains(&id)
+    })
+}
+
 struct Collector<'tcx> {
     tcx: TyCtxt<'tcx>,
     libs: Vec<NativeLib>,
@@ -445,10 +459,6 @@ impl<'tcx> Collector<'tcx> {
             if wasm_import_module.is_some() {
                 (name, kind) = (wasm_import_module, Some(NativeLibKind::WasmImportModule));
             }
-            let Some((name, name_span)) = name else {
-                sess.dcx().emit_err(errors::LinkRequiresName { span: m.span });
-                continue;
-            };
 
             // Do this outside of the loop so that `import_name_type` can be specified before `kind`.
             if let Some((_, span)) = import_name_type {
@@ -457,8 +467,25 @@ impl<'tcx> Collector<'tcx> {
                 }
             }
 
+            if kind != Some(NativeLibKind::RawDylib) {
+                for &child_item in foreign_items {
+                    if self.tcx.def_kind(child_item).has_codegen_attrs()
+                        && self.tcx.codegen_fn_attrs(child_item).link_ordinal.is_some()
+                    {
+                        let link_ordinal_attr =
+                            self.tcx.get_attr(child_item, sym::link_ordinal).unwrap();
+                        sess.dcx()
+                            .emit_err(errors::LinkOrdinalRawDylib { span: link_ordinal_attr.span });
+                    }
+                }
+            }
+
             let dll_imports = match kind {
                 Some(NativeLibKind::RawDylib) => {
+                    let Some((name, name_span)) = name else {
+                        sess.dcx().emit_err(errors::LinkRequiresName { span: m.span });
+                        continue;
+                    };
                     if name.as_str().contains('\0') {
                         sess.dcx().emit_err(errors::RawDylibNoNul { span: name_span });
                     }
@@ -473,25 +500,29 @@ impl<'tcx> Collector<'tcx> {
                         })
                         .collect()
                 }
-                _ => {
-                    for &child_item in foreign_items {
-                        if self.tcx.def_kind(child_item).has_codegen_attrs()
-                            && self.tcx.codegen_fn_attrs(child_item).link_ordinal.is_some()
-                        {
-                            let link_ordinal_attr =
-                                self.tcx.get_attr(child_item, sym::link_ordinal).unwrap();
-                            sess.dcx().emit_err(errors::LinkOrdinalRawDylib {
-                                span: link_ordinal_attr.span,
-                            });
-                        }
-                    }
+                _ => Vec::new(),
+            };
 
-                    Vec::new()
-                }
+            // Allow kind of "dylib" or "static" without adding a native lib.
+            let name = if self.tcx.features().bare_link_kind
+                && matches!(kind, Some(NativeLibKind::Dylib { .. } | NativeLibKind::Static { .. }))
+                && items.len() == 1
+            {
+                kw::Empty
+            } else {
+                let Some((name, _)) = name else {
+                    sess.dcx().emit_err(errors::LinkRequiresName { span: m.span });
+                    continue;
+                };
+                name
             };
 
             let kind = kind.unwrap_or(NativeLibKind::Unspecified);
-            let filename = find_bundled_library(name, verbatim, kind, cfg.is_some(), self.tcx);
+            let filename = if !name.is_empty() {
+                find_bundled_library(name, verbatim, kind, cfg.is_some(), self.tcx)
+            } else {
+                None
+            };
             self.libs.push(NativeLib {
                 name,
                 filename,

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -17,6 +17,7 @@ use rustc_middle::ty::fast_reject::SimplifiedType;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_middle::util::Providers;
 use rustc_session::cstore::{CrateStore, ExternCrate};
+use rustc_session::utils::NativeLibKind;
 use rustc_session::{Session, StableCrateId};
 use rustc_span::Span;
 use rustc_span::hygiene::ExpnId;
@@ -437,30 +438,27 @@ provide! { tcx, def_id, other, cdata,
 
 pub(in crate::rmeta) fn provide(providers: &mut Providers) {
     provide_cstore_hooks(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
     providers.queries = rustc_middle::query::Providers {
         allocator_kind: |tcx, ()| CStore::from_tcx(tcx).allocator_kind(),
         alloc_error_handler_kind: |tcx, ()| CStore::from_tcx(tcx).alloc_error_handler_kind(),
         is_private_dep: |_tcx, LocalCrate| false,
         native_library: |tcx, id| {
-            tcx.native_libraries(id.krate)
-                .iter()
-                .filter(|lib| native_libs::relevant_lib(tcx.sess, lib))
-                .find(|lib| {
-                    let Some(fm_id) = lib.foreign_module else {
-                        return false;
-                    };
-                    let map = tcx.foreign_modules(id.krate);
-                    map.get(&fm_id)
-                        .expect("failed to find foreign module")
-                        .foreign_items
-                        .contains(&id)
-                })
+            native_libs::find_by_id(tcx, id, tcx.native_libraries(id.krate).iter())
         },
         native_libraries: native_libs::collect,
         foreign_modules: foreign_modules::collect,
+        is_dllimport: |tcx, id| {
+            native_libs::find_by_id(tcx, id, tcx.native_libraries(id.krate).iter_all_items())
+                .map(|l| {
+                    matches!(
+                        l.kind,
+                        NativeLibKind::Dylib { .. }
+                            | NativeLibKind::RawDylib
+                            | NativeLibKind::Unspecified
+                    )
+                })
+                .unwrap_or(false)
+        },
 
         // Returns a map from a sufficiently visible external item (i.e., an
         // external item that is visible from at least one local module) to a

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1813,7 +1813,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     fn encode_native_libraries(&mut self) -> LazyArray<NativeLib> {
         empty_proc_macro!(self);
         let used_libraries = self.tcx.native_libraries(LOCAL_CRATE);
-        self.lazy_array(used_libraries.iter())
+        self.lazy_array(used_libraries.iter_all_items())
     }
 
     fn encode_foreign_modules(&mut self) -> LazyArray<ForeignModule> {

compiler/rustc_middle/src/query/mod.rs

@@ -35,7 +35,7 @@ use rustc_query_system::query::{QueryCache, QueryMode, QueryState, try_get_cache
 use rustc_session::Limits;
 use rustc_session::config::{EntryFnType, OptLevel, OutputFilenames, SymbolManglingVersion};
 use rustc_session::cstore::{
-    CrateDepKind, CrateSource, ExternCrate, ForeignModule, LinkagePreference, NativeLib,
+    CrateDepKind, CrateSource, ExternCrate, ForeignModule, LinkagePreference, NativeLib, NativeLibs,
 };
 use rustc_session::lint::LintExpectationId;
 use rustc_span::def_id::LOCAL_CRATE;
@@ -406,7 +406,7 @@ rustc_queries! {
     /// These are assembled from the following places:
     /// - `extern` blocks (depending on their `link` attributes)
     /// - the `libs` (`-l`) option
-    query native_libraries(_: CrateNum) -> &'tcx Vec<NativeLib> {
+    query native_libraries(_: CrateNum) -> &'tcx NativeLibs {
         arena_cache
         desc { "looking up the native libraries of a linked crate" }
         separate_provide_extern
@@ -1734,6 +1734,10 @@ rustc_queries! {
         desc { |tcx| "getting the native library for `{}`", tcx.def_path_str(def_id) }
     }
 
+    query is_dllimport(def_id: DefId) -> bool {
+        desc { |tcx| "determining dllimport status of `{}`", tcx.def_path_str(def_id) }
+    }
+
     query inherit_sig_for_delegation_item(def_id: LocalDefId) -> &'tcx [Ty<'tcx>] {
         desc { "inheriting delegation signature" }
     }

compiler/rustc_session/src/cstore.rs

@@ -88,6 +88,31 @@ impl NativeLib {
     }
 }
 
+#[derive(Debug, HashStable_Generic)]
+pub struct NativeLibs {
+    libs: Vec<NativeLib>,
+}
+impl NativeLibs {
+    pub fn iter(&self) -> impl Iterator<Item = &NativeLib> {
+        // Hide entries without a library name.
+        self.iter_all_items().filter(|l| !l.name.is_empty())
+    }
+
+    pub fn iter_all_items(&self) -> impl Iterator<Item = &NativeLib> {
+        self.libs.iter()
+    }
+}
+impl From<Vec<NativeLib>> for NativeLibs {
+    fn from(libs: Vec<NativeLib>) -> Self {
+        Self { libs }
+    }
+}
+impl FromIterator<NativeLib> for NativeLibs {
+    fn from_iter<T: IntoIterator<Item = NativeLib>>(iter: T) -> Self {
+        Self { libs: FromIterator::from_iter(iter) }
+    }
+}
+
 /// Different ways that the PE Format can decorate a symbol name.
 /// From <https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-name-type>
 #[derive(Copy, Clone, Debug, Encodable, Decodable, HashStable_Generic, PartialEq, Eq)]

compiler/rustc_session/src/utils.rs

@@ -70,13 +70,6 @@ impl NativeLibKind {
     pub fn is_statically_included(&self) -> bool {
         matches!(self, NativeLibKind::Static { .. })
     }
-
-    pub fn is_dllimport(&self) -> bool {
-        matches!(
-            self,
-            NativeLibKind::Dylib { .. } | NativeLibKind::RawDylib | NativeLibKind::Unspecified
-        )
-    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]

compiler/rustc_span/src/symbol.rs

@@ -490,6 +490,7 @@ symbols! {
         avx512f,
         await_macro,
         bang,
+        bare_link_kind,
         begin_panic,
         bench,
         bin,

tests/ui/extern/auxiliary/bare_link_kind_cdylib.rs

@@ -0,0 +1,4 @@
+#![crate_type = "cdylib"]
+
+#[no_mangle]
+pub static FOO: u32 = 0xFEDCBA98;

tests/ui/extern/bare_link_kind.rs

@@ -0,0 +1,19 @@
+//@ run-pass
+//@ aux-build:bare_link_kind_cdylib.rs
+
+#![feature(bare_link_kind)]
+
+#[link(kind = "dylib")]
+extern "C" {
+    static FOO: u32;
+}
+
+#[cfg_attr(not(target_env = "msvc"), link(name = "bare_link_kind_cdylib", kind = "dylib"))]
+#[cfg_attr(target_env = "msvc", link(name = "bare_link_kind_cdylib.dll", kind = "dylib"))]
+extern "C" {}
+
+fn main() {
+    unsafe {
+        assert_eq!(FOO, 0xFEDCBA98);
+    }
+}

tests/ui/feature-gates/feature-gate-bare-link-kind.rs

@@ -0,0 +1,6 @@
+#[link(kind = "dylib")] //~ ERROR `#[link]` attribute requires a `name = "string"` argument
+extern "C" {
+    static FOO: u32;
+}
+
+fn main() {}

tests/ui/feature-gates/feature-gate-bare-link-kind.stderr

@@ -0,0 +1,9 @@
+error[E0459]: `#[link]` attribute requires a `name = "string"` argument
+  --> $DIR/feature-gate-bare-link-kind.rs:1:1
+   |
+LL | #[link(kind = "dylib")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^ missing `name` argument
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0459`.