Initial support for dynamically linked crates

compiler/rustc_ast_lowering/src/item.rs

@@ -1240,7 +1240,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
             // create a fake body so that the entire rest of the compiler doesn't have to deal with
             // this as a special case.
             return self.lower_fn_body(decl, contract, |this| {
-                if attrs.iter().any(|a| a.name_or_empty() == sym::rustc_intrinsic) {
+                if attrs.iter().any(|a| a.name_or_empty() == sym::rustc_intrinsic)
+                    || this.tcx.is_sdylib_interface_build()
+                {
                     let span = this.lower_span(span);
                     let empty_block = hir::Block {
                         hir_id: this.next_id(),

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -82,6 +82,8 @@ struct AstValidator<'a> {
     /// Used to ban explicit safety on foreign items when the extern block is not marked as unsafe.
     extern_mod_safety: Option<Safety>,
 
+    is_sdylib_interface: bool,
+
     lint_buffer: &'a mut LintBuffer,
 }
 
@@ -926,7 +928,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 
                 let is_intrinsic =
                     item.attrs.iter().any(|a| a.name_or_empty() == sym::rustc_intrinsic);
-                if body.is_none() && !is_intrinsic {
+                if body.is_none() && !is_intrinsic && !self.is_sdylib_interface {
                     self.dcx().emit_err(errors::FnWithoutBody {
                         span: item.span,
                         replace_span: self.ending_semi_or_hi(item.span),
@@ -1423,7 +1425,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     });
                 }
                 AssocItemKind::Fn(box Fn { body, .. }) => {
-                    if body.is_none() {
+                    if body.is_none() && !self.is_sdylib_interface {
                         self.dcx().emit_err(errors::AssocFnWithoutBody {
                             span: item.span,
                             replace_span: self.ending_semi_or_hi(item.span),
@@ -1673,6 +1675,7 @@ pub fn check_crate(
     sess: &Session,
     features: &Features,
     krate: &Crate,
+    is_sdylib_interface: bool,
     lints: &mut LintBuffer,
 ) -> bool {
     let mut validator = AstValidator {
@@ -1684,6 +1687,7 @@ pub fn check_crate(
         outer_impl_trait: None,
         disallow_tilde_const: Some(TildeConstReason::Item),
         extern_mod_safety: None,
+        is_sdylib_interface,
         lint_buffer: lints,
     };
     visit::walk_crate(&mut validator, krate);

compiler/rustc_ast_pretty/src/pprust/mod.rs

@@ -7,7 +7,9 @@ use std::borrow::Cow;
 use rustc_ast as ast;
 use rustc_ast::token::{Nonterminal, Token, TokenKind};
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
-pub use state::{AnnNode, Comments, PpAnn, PrintState, State, print_crate};
+pub use state::{
+    AnnNode, Comments, PpAnn, PrintState, State, print_crate, print_crate_as_interface,
+};
 
 pub fn nonterminal_to_string(nt: &Nonterminal) -> String {
     State::new().nonterminal_to_string(nt)

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -221,6 +221,7 @@ pub struct State<'a> {
     pub s: pp::Printer,
     comments: Option<Comments<'a>>,
     ann: &'a (dyn PpAnn + 'a),
+    is_sdylib_interface: bool,
 }
 
 const INDENT_UNIT: isize = 4;
@@ -236,10 +237,39 @@ pub fn print_crate<'a>(
     is_expanded: bool,
     edition: Edition,
     g: &AttrIdGenerator,
+) -> String {
+    let mut s = State {
+        s: pp::Printer::new(),
+        comments: Some(Comments::new(sm, filename, input)),
+        ann,
+        is_sdylib_interface: false,
+    };
+
+    print_crate_inner(&mut s, krate, is_expanded, edition, g);
+
+    s.ann.post(&mut s, AnnNode::Crate(krate));
+    s.s.eof()
+}
+
+pub fn print_crate_as_interface(
+    krate: &ast::Crate,
+    edition: Edition,
+    g: &AttrIdGenerator,
 ) -> String {
     let mut s =
-        State { s: pp::Printer::new(), comments: Some(Comments::new(sm, filename, input)), ann };
+        State { s: pp::Printer::new(), comments: None, ann: &NoAnn, is_sdylib_interface: true };
 
+    print_crate_inner(&mut s, krate, false, edition, g);
+    s.s.eof()
+}
+
+fn print_crate_inner<'a>(
+    s: &mut State<'a>,
+    krate: &ast::Crate,
+    is_expanded: bool,
+    edition: Edition,
+    g: &AttrIdGenerator,
+) {
     if is_expanded && !krate.attrs.iter().any(|attr| attr.has_name(sym::no_core)) {
         // We need to print `#![no_std]` (and its feature gate) so that
         // compiling pretty-printed source won't inject libstd again.
@@ -277,8 +307,6 @@ pub fn print_crate<'a>(
         s.print_item(item);
     }
     s.print_remaining_comments();
-    s.ann.post(&mut s, AnnNode::Crate(krate));
-    s.s.eof()
 }
 
 /// Should two consecutive tokens be printed with a space between them?
@@ -1093,7 +1121,7 @@ impl<'a> PrintState<'a> for State<'a> {
 
 impl<'a> State<'a> {
     pub fn new() -> State<'a> {
-        State { s: pp::Printer::new(), comments: None, ann: &NoAnn }
+        State { s: pp::Printer::new(), comments: None, ann: &NoAnn, is_sdylib_interface: false }
     }
 
     fn commasep_cmnt<T, F, G>(&mut self, b: Breaks, elts: &[T], mut op: F, mut get_span: G)

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -150,6 +150,10 @@ impl<'a> State<'a> {
 
     /// Pretty-prints an item.
     pub(crate) fn print_item(&mut self, item: &ast::Item) {
+        if self.is_sdylib_interface && item.span.is_dummy() {
+            // Do not print prelude for interface files.
+            return;
+        }
         self.hardbreak_if_not_bol();
         self.maybe_print_comment(item.span.lo());
         self.print_outer_attributes(&item.attrs);
@@ -670,6 +674,12 @@ impl<'a> State<'a> {
             self.nbsp();
             self.print_contract(contract);
         }
+        if self.is_sdylib_interface {
+            self.word(";");
+            self.end(); // end inner head-block
+            self.end(); // end outer head-block
+            return;
+        }
         if let Some(body) = body {
             self.nbsp();
             self.print_block_with_attrs(body, attrs);

compiler/rustc_codegen_gcc/src/back/lto.rs

@@ -44,7 +44,11 @@ use crate::{GccCodegenBackend, GccContext, SyncContext, to_gcc_opt_level};
 
 pub fn crate_type_allows_lto(crate_type: CrateType) -> bool {
     match crate_type {
-        CrateType::Executable | CrateType::Dylib | CrateType::Staticlib | CrateType::Cdylib => true,
+        CrateType::Executable
+        | CrateType::Dylib
+        | CrateType::Staticlib
+        | CrateType::Cdylib
+        | CrateType::Sdylib => true,
         CrateType::Rlib | CrateType::ProcMacro => false,
     }
 }

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -41,7 +41,8 @@ fn crate_type_allows_lto(crate_type: CrateType) -> bool {
         | CrateType::Dylib
         | CrateType::Staticlib
         | CrateType::Cdylib
-        | CrateType::ProcMacro => true,
+        | CrateType::ProcMacro
+        | CrateType::Sdylib => true,
         CrateType::Rlib => false,
     }
 }

compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs

@@ -95,7 +95,11 @@ pub(crate) fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool {
     // in the `.debug_gdb_scripts` section. For that reason, we make sure that the
     // section is only emitted for leaf crates.
     let embed_visualizers = cx.tcx.crate_types().iter().any(|&crate_type| match crate_type {
-        CrateType::Executable | CrateType::Dylib | CrateType::Cdylib | CrateType::Staticlib => {
+        CrateType::Executable
+        | CrateType::Dylib
+        | CrateType::Cdylib
+        | CrateType::Staticlib
+        | CrateType::Sdylib => {
             // These are crate types for which we will embed pretty printers since they
             // are treated as leaf crates.
             true

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1050,9 +1050,10 @@ fn link_natively(
                 strip_with_external_utility(sess, stripcmd, out_filename, &["--strip-debug"])
             }
             // Per the manpage, `-x` is the maximum safe strip level for dynamic libraries. (#93988)
-            (Strip::Symbols, CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro) => {
-                strip_with_external_utility(sess, stripcmd, out_filename, &["-x"])
-            }
+            (
+                Strip::Symbols,
+                CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro | CrateType::Sdylib,
+            ) => strip_with_external_utility(sess, stripcmd, out_filename, &["-x"]),
             (Strip::Symbols, _) => {
                 strip_with_external_utility(sess, stripcmd, out_filename, &["--strip-all"])
             }
@@ -1240,8 +1241,10 @@ fn add_sanitizer_libraries(
     // which should be linked to both executables and dynamic libraries.
     // Everywhere else the runtimes are currently distributed as static
     // libraries which should be linked to executables only.
-    if matches!(crate_type, CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro)
-        && !(sess.target.is_like_osx || sess.target.is_like_msvc)
+    if matches!(
+        crate_type,
+        CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro | CrateType::Sdylib
+    ) && !(sess.target.is_like_osx || sess.target.is_like_msvc)
     {
         return;
     }
@@ -1935,6 +1938,7 @@ fn add_late_link_args(
     codegen_results: &CodegenResults,
 ) {
     let any_dynamic_crate = crate_type == CrateType::Dylib
+        || crate_type == CrateType::Sdylib
         || codegen_results.crate_info.dependency_formats.iter().any(|(ty, list)| {
             *ty == crate_type && list.iter().any(|&linkage| linkage == Linkage::Dynamic)
         });

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1814,7 +1814,7 @@ pub(crate) fn linked_symbols(
     crate_type: CrateType,
 ) -> Vec<(String, SymbolExportKind)> {
     match crate_type {
-        CrateType::Executable | CrateType::Cdylib | CrateType::Dylib => (),
+        CrateType::Executable | CrateType::Cdylib | CrateType::Dylib | CrateType::Sdylib => (),
         CrateType::Staticlib | CrateType::ProcMacro | CrateType::Rlib => {
             return Vec::new();
         }

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -29,7 +29,7 @@ fn crate_export_threshold(crate_type: CrateType) -> SymbolExportLevel {
         CrateType::Executable | CrateType::Staticlib | CrateType::ProcMacro | CrateType::Cdylib => {
             SymbolExportLevel::C
         }
-        CrateType::Rlib | CrateType::Dylib => SymbolExportLevel::Rust,
+        CrateType::Rlib | CrateType::Dylib | CrateType::Sdylib => SymbolExportLevel::Rust,
     }
 }
 
@@ -45,7 +45,7 @@ pub fn crates_export_threshold(crate_types: &[CrateType]) -> SymbolExportLevel {
 }
 
 fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<SymbolExportInfo> {
-    if !tcx.sess.opts.output_types.should_codegen() {
+    if !tcx.sess.opts.output_types.should_codegen() && !tcx.is_sdylib_interface_build() {
         return Default::default();
     }
 
@@ -173,7 +173,7 @@ fn exported_symbols_provider_local(
     tcx: TyCtxt<'_>,
     _: LocalCrate,
 ) -> &[(ExportedSymbol<'_>, SymbolExportInfo)] {
-    if !tcx.sess.opts.output_types.should_codegen() {
+    if !tcx.sess.opts.output_types.should_codegen() && !tcx.is_sdylib_interface_build() {
         return &[];
     }
 

compiler/rustc_codegen_ssa/src/base.rs

@@ -1024,7 +1024,7 @@ impl CrateInfo {
         }
 
         let embed_visualizers = tcx.crate_types().iter().any(|&crate_type| match crate_type {
-            CrateType::Executable | CrateType::Dylib | CrateType::Cdylib => {
+            CrateType::Executable | CrateType::Dylib | CrateType::Cdylib | CrateType::Sdylib => {
                 // These are crate types for which we invoke the linker and can embed
                 // NatVis visualizers.
                 true

compiler/rustc_driver_impl/src/lib.rs

@@ -56,8 +56,8 @@ use rustc_metadata::locator;
 use rustc_middle::ty::TyCtxt;
 use rustc_parse::{new_parser_from_file, new_parser_from_source_str, unwrap_or_emit_fatal};
 use rustc_session::config::{
-    CG_OPTIONS, ErrorOutputType, Input, OptionDesc, OutFileName, OutputType, UnstableOptions,
-    Z_OPTIONS, nightly_options, parse_target_triple,
+    CG_OPTIONS, CrateType, ErrorOutputType, Input, OptionDesc, OutFileName, OutputType,
+    UnstableOptions, Z_OPTIONS, nightly_options, parse_target_triple,
 };
 use rustc_session::getopts::{self, Matches};
 use rustc_session::lint::{Lint, LintId};
@@ -358,6 +358,8 @@ pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send))
 
             passes::write_dep_info(tcx);
 
+            passes::write_interface(tcx);
+
             if sess.opts.output_types.contains_key(&OutputType::DepInfo)
                 && sess.opts.output_types.len() == 1
             {
@@ -794,6 +796,7 @@ fn print_crate_info(
                 let supported_crate_types = CRATE_TYPES
                     .iter()
                     .filter(|(_, crate_type)| !invalid_output_for_target(&sess, *crate_type))
+                    .filter(|(_, crate_type)| *crate_type != CrateType::Sdylib)
                     .map(|(crate_type_sym, _)| *crate_type_sym)
                     .collect::<BTreeSet<_>>();
                 for supported_crate_type in supported_crate_types {

compiler/rustc_feature/src/builtin_attrs.rs

@@ -506,6 +506,11 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         naked_functions, experimental!(naked)
     ),
 
+    gated!(
+        export, Normal, template!(Word), WarnFollowing,
+        EncodeCrossCrate::Yes, experimental!(export)
+    ),
+
     // Testing:
     gated!(
         test_runner, CrateLevel, template!(List: "path"), ErrorFollowing,

compiler/rustc_feature/src/unstable.rs

@@ -209,6 +209,8 @@ declare_features! (
     (internal, compiler_builtins, "1.13.0", None),
     /// Allows writing custom MIR
     (internal, custom_mir, "1.65.0", None),
+    /// Allows using `#[export]` which indicates that an item is exportable.
+    (internal, export, "CURRENT_RUSTC_VERSION", None),
     /// Outputs useful `assert!` messages
     (unstable, generic_assert, "1.63.0", None),
     /// Allows using the `rust-intrinsic`'s "ABI".

compiler/rustc_interface/src/passes.rs

@@ -29,10 +29,11 @@ use rustc_resolve::Resolver;
 use rustc_session::config::{CrateType, Input, OutFileName, OutputFilenames, OutputType};
 use rustc_session::cstore::Untracked;
 use rustc_session::output::{collect_crate_types, filename_for_input};
+use rustc_session::parse::feature_err;
 use rustc_session::search_paths::PathKind;
 use rustc_session::{Limit, Session};
 use rustc_span::{
-    ErrorGuaranteed, FileName, SourceFileHash, SourceFileHashAlgorithm, Span, Symbol, sym,
+    DUMMY_SP, ErrorGuaranteed, FileName, SourceFileHash, SourceFileHashAlgorithm, Span, Symbol, sym,
 };
 use rustc_target::spec::PanicStrategy;
 use rustc_trait_selection::traits;
@@ -235,6 +236,7 @@ fn configure_and_expand(
             sess,
             features,
             &krate,
+            tcx.is_sdylib_interface_build(),
             resolver.lint_buffer(),
         )
     });
@@ -251,6 +253,9 @@ fn configure_and_expand(
             sess.dcx().emit_err(errors::MixedProcMacroCrate);
         }
     }
+    if crate_types.contains(&CrateType::Sdylib) && !tcx.features().export() {
+        feature_err(sess, sym::export, DUMMY_SP, "`sdylib` crate type is unstable").emit();
+    }
 
     if is_proc_macro_crate && sess.panic_strategy() == PanicStrategy::Abort {
         sess.dcx().emit_warn(errors::ProcMacroCratePanicAbort);
@@ -715,6 +720,27 @@ pub fn write_dep_info(tcx: TyCtxt<'_>) {
     }
 }
 
+pub fn write_interface<'tcx>(tcx: TyCtxt<'tcx>) {
+    if !tcx.crate_types().contains(&rustc_session::config::CrateType::Sdylib)
+        || tcx.is_sdylib_interface_build()
+    {
+        return;
+    }
+    let _timer = tcx.sess.timer("write_interface");
+    let (_, krate) = &*tcx.resolver_for_lowering().borrow();
+
+    let krate = rustc_ast_pretty::pprust::print_crate_as_interface(
+        krate,
+        tcx.sess.psess.edition,
+        &tcx.sess.psess.attr_id_generator,
+    );
+    let export_output = tcx.output_filenames(()).interface_path();
+    let mut file = fs::File::create_buffered(export_output).unwrap();
+    if let Err(err) = write!(file, "{}", krate) {
+        tcx.dcx().fatal(format!("error writing interface file: {}", err));
+    }
+}
+
 pub static DEFAULT_QUERY_PROVIDERS: LazyLock<Providers> = LazyLock::new(|| {
     let providers = &mut Providers::default();
     providers.analysis = analysis;
@@ -883,6 +909,10 @@ fn run_required_analyses(tcx: TyCtxt<'_>) {
                 CStore::from_tcx(tcx).report_unused_deps(tcx);
             },
             {
+                if tcx.crate_types().contains(&CrateType::Sdylib) {
+                    tcx.ensure_ok().exportable_items(LOCAL_CRATE);
+                    tcx.ensure_ok().stable_order_of_exportable_impls(LOCAL_CRATE);
+                }
                 tcx.par_hir_for_each_module(|module| {
                     tcx.ensure_ok().check_mod_loops(module);
                     tcx.ensure_ok().check_mod_attrs(module);