Auto merge of rust-lang#136226 - tgross35:builtins-is-private-dep, r=<try>

Inject `compiler_builtins` during postprocessing rather than via AST

`compiler_builtins` is currently injected into the AST as `extern crate compiler_builtins as _`. This has made gating via diagnostics difficult because it appears in the crate graph as a non-private dependency, and there isn't an easy way to differentiate between the injected AST and user-specified `extern crate compiler_builtins`.

Resolve this by injecting `compiler_builtins` during postprocessing rather than early in the AST. Most of the time this isn't even needed because it shows up in `std` or `core`'s crate graph, but injection is still needed to ensure `#![no_core]` works correctly.

A similar change was attempted at [1] but this encountered errors building `proc_macro` and `rustc-std-workspace-std`. Similar failures showed up while working on this patch, which were traced back to `compiler_builtins` showing up in the graph twice (once via dependency and once via injection). This is resolved by not injecting if a `#![compiler_builtins]` crate already exists.

[1]: rust-lang#113634

try-job: dist-x86_64-linux
try-job: x86_64-gnu-distcheck
try-job: x86_64-msvc-1
try-job: x86_64-rust-for-linux
try-job: test-various

Author: bors

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -19,16 +19,12 @@ pub fn inject(
     let edition = sess.psess.edition;
 
     // the first name in this list is the crate name of the crate with the prelude
-    let names: &[Symbol] = if attr::contains_name(pre_configured_attrs, sym::no_core) {
+    let name: Symbol = if attr::contains_name(pre_configured_attrs, sym::no_core) {
         return 0;
     } else if attr::contains_name(pre_configured_attrs, sym::no_std) {
-        if attr::contains_name(pre_configured_attrs, sym::compiler_builtins) {
-            &[sym::core]
-        } else {
-            &[sym::core, sym::compiler_builtins]
-        }
+        sym::core
     } else {
-        &[sym::std]
+        sym::std
     };
 
     let expn_id = resolver.expansion_for_ast_pass(
@@ -43,36 +39,16 @@ pub fn inject(
     let ecfg = ExpansionConfig::default("std_lib_injection".to_string(), features);
     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
 
-    // .rev() to preserve ordering above in combination with insert(0, ...)
-    for &name in names.iter().rev() {
-        let ident_span = if edition >= Edition2018 { span } else { call_site };
-        let item = if name == sym::compiler_builtins {
-            // compiler_builtins is a private implementation detail. We only
-            // need to insert it into the crate graph for linking and should not
-            // expose any of its public API.
-            //
-            // FIXME(#113634) We should inject this during post-processing like
-            // we do for the panic runtime, profiler runtime, etc.
-            cx.item(
-                span,
-                Ident::new(kw::Underscore, ident_span),
-                thin_vec![],
-                ast::ItemKind::ExternCrate(Some(name)),
-            )
-        } else {
-            cx.item(
-                span,
-                Ident::new(name, ident_span),
-                thin_vec![cx.attr_word(sym::macro_use, span)],
-                ast::ItemKind::ExternCrate(None),
-            )
-        };
-        krate.items.insert(0, item);
-    }
+    let ident_span = if edition >= Edition2018 { span } else { call_site };
 
-    // The crates have been injected, the assumption is that the first one is
-    // the one with the prelude.
-    let name = names[0];
+    let item = cx.item(
+        span,
+        Ident::new(name, ident_span),
+        thin_vec![cx.attr_word(sym::macro_use, span)],
+        ast::ItemKind::ExternCrate(None),
+    );
+
+    krate.items.insert(0, item);
 
     let root = (edition == Edition2015).then_some(kw::PathRoot);
 
@@ -88,6 +64,7 @@ pub fn inject(
         .map(|&symbol| Ident::new(symbol, span))
         .collect();
 
+    // Inject the relevant crate's prelude.
     let use_item = cx.item(
         span,
         Ident::empty(),

compiler/rustc_metadata/messages.ftl

@@ -47,6 +47,9 @@ metadata_crate_dep_rustc_driver =
 metadata_crate_location_unknown_type =
     extern location for {$crate_name} is of an unknown type: {$path}
 
+metadata_crate_not_compiler_builtins =
+    the crate `{$crate_name}` resolved as `compiler_builtins` but is not `#![compiler_builtins]`
+
 metadata_crate_not_panic_runtime =
     the crate `{$crate_name}` is not a panic runtime
 

compiler/rustc_metadata/src/creader.rs

@@ -142,6 +142,7 @@ impl<'a> std::fmt::Debug for CrateDump<'a> {
             writeln!(fmt, "  cnum: {cnum}")?;
             writeln!(fmt, "  hash: {}", data.hash())?;
             writeln!(fmt, "  reqd: {:?}", data.dep_kind())?;
+            writeln!(fmt, "  priv: {:?}", data.is_private_dep())?;
             let CrateSource { dylib, rlib, rmeta } = data.source();
             if let Some(dylib) = dylib {
                 writeln!(fmt, "  dylib: {}", dylib.0.display())?;
@@ -157,6 +158,43 @@ impl<'a> std::fmt::Debug for CrateDump<'a> {
     }
 }
 
+/// Reason that a crate is being sourced as a dependency.
+#[derive(Clone, Copy)]
+enum CrateOrigin<'a> {
+    /// This crate was a dependency of another crate.
+    Dependency {
+        dep_root: &'a CratePaths,
+        /// Dependency info about this crate.
+        dep: &'a CrateDep,
+    },
+    /// Injected by `rustc`.
+    Injected,
+    /// An extern that has been provided with the `force` option.
+    ForcedExtern,
+    /// Part of the extern prelude.
+    ExternPrelude,
+    /// Provided by `extern crate foo`.
+    AstExtern,
+}
+
+impl<'a> CrateOrigin<'a> {
+    /// Return the dependency root, if any.
+    fn dep_root(&self) -> Option<&'a CratePaths> {
+        match self {
+            CrateOrigin::Dependency { dep_root, .. } => Some(dep_root),
+            _ => None,
+        }
+    }
+
+    /// Return dependency information, if any.
+    fn dep(&self) -> Option<&'a CrateDep> {
+        match self {
+            CrateOrigin::Dependency { dep, .. } => Some(dep),
+            _ => None,
+        }
+    }
+}
+
 impl CStore {
     pub fn from_tcx(tcx: TyCtxt<'_>) -> FreezeReadGuard<'_, CStore> {
         FreezeReadGuard::map(tcx.untracked().cstore.read(), |cstore| {
@@ -404,7 +442,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         &self,
         name: Symbol,
         private_dep: Option<bool>,
-        dep_root: Option<&CratePaths>,
+        origin: CrateOrigin<'_>,
     ) -> bool {
         // Standard library crates are never private.
         if STDLIB_STABLE_CRATES.contains(&name) {
@@ -414,10 +452,14 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
 
         let extern_private = self.sess.opts.externs.get(name.as_str()).map(|e| e.is_private_dep);
 
+        if matches!(origin, CrateOrigin::Injected) {
+            return true;
+        }
+
         // Any descendants of `std` should be private. These crates are usually not marked
         // private in metadata, so we ignore that field.
         if extern_private.is_none()
-            && let Some(dep) = dep_root
+            && let Some(dep) = origin.dep_root()
             && STDLIB_STABLE_CRATES.contains(&dep.name)
         {
             return true;
@@ -435,7 +477,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
     fn register_crate(
         &mut self,
         host_lib: Option<Library>,
-        dep_root: Option<&CratePaths>,
+        origin: CrateOrigin<'_>,
         lib: Library,
         dep_kind: CrateDepKind,
         name: Symbol,
@@ -447,7 +489,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         let Library { source, metadata } = lib;
         let crate_root = metadata.get_root();
         let host_hash = host_lib.as_ref().map(|lib| lib.metadata.get_root().hash());
-        let private_dep = self.is_private_dep(name, private_dep, dep_root);
+        let private_dep = self.is_private_dep(name, private_dep, origin);
 
         // Claim this crate number and cache it
         let feed = self.cstore.intern_stable_crate_id(&crate_root, self.tcx)?;
@@ -463,7 +505,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         // Maintain a reference to the top most crate.
         // Stash paths for top-most crate locally if necessary.
         let crate_paths;
-        let dep_root = if let Some(dep_root) = dep_root {
+        let dep_root = if let Some(dep_root) = origin.dep_root() {
             dep_root
         } else {
             crate_paths = CratePaths::new(crate_root.name(), source.clone());
@@ -571,17 +613,23 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         name: Symbol,
         span: Span,
         dep_kind: CrateDepKind,
+        origin: CrateOrigin<'_>,
     ) -> Option<CrateNum> {
         self.used_extern_options.insert(name);
-        match self.maybe_resolve_crate(name, dep_kind, None) {
+        match self.maybe_resolve_crate(name, dep_kind, origin) {
             Ok(cnum) => {
                 self.cstore.set_used_recursively(cnum);
                 Some(cnum)
             }
             Err(err) => {
                 debug!("failed to resolve crate {} {:?}", name, dep_kind);
-                let missing_core =
-                    self.maybe_resolve_crate(sym::core, CrateDepKind::Explicit, None).is_err();
+                let missing_core = self
+                    .maybe_resolve_crate(
+                        sym::core,
+                        CrateDepKind::Explicit,
+                        CrateOrigin::ExternPrelude,
+                    )
+                    .is_err();
                 err.report(self.sess, span, missing_core);
                 None
             }
@@ -592,15 +640,15 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         &'b mut self,
         name: Symbol,
         mut dep_kind: CrateDepKind,
-        dep_of: Option<(&'b CratePaths, &'b CrateDep)>,
+        origin: CrateOrigin<'b>,
     ) -> Result<CrateNum, CrateError> {
         info!("resolving crate `{}`", name);
         if !name.as_str().is_ascii() {
             return Err(CrateError::NonAsciiName(name));
         }
 
-        let dep_root = dep_of.map(|d| d.0);
-        let dep = dep_of.map(|d| d.1);
+        let dep_root = origin.dep_root();
+        let dep = origin.dep();
         let hash = dep.map(|d| d.hash);
         let host_hash = dep.map(|d| d.host_hash).flatten();
         let extra_filename = dep.map(|d| &d.extra_filename[..]);
@@ -638,12 +686,12 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
 
         match result {
             (LoadResult::Previous(cnum), None) => {
-                info!("library for `{}` was loaded previously", name);
+                info!("library for `{}` was loaded previously, cnum {cnum}", name);
                 // When `private_dep` is none, it indicates the directly dependent crate. If it is
                 // not specified by `--extern` on command line parameters, it may be
                 // `private-dependency` when `register_crate` is called for the first time. Then it must be updated to
                 // `public-dependency` here.
-                let private_dep = self.is_private_dep(name, private_dep, dep_root);
+                let private_dep = self.is_private_dep(name, private_dep, origin);
                 let data = self.cstore.get_crate_data_mut(cnum);
                 if data.is_proc_macro_crate() {
                     dep_kind = CrateDepKind::MacrosOnly;
@@ -654,7 +702,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
             }
             (LoadResult::Loaded(library), host_library) => {
                 info!("register newly loaded library for `{}`", name);
-                self.register_crate(host_library, dep_root, library, dep_kind, name, private_dep)
+                self.register_crate(host_library, origin, library, dep_kind, name, private_dep)
             }
             _ => panic!(),
         }
@@ -730,7 +778,10 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
                 CrateDepKind::MacrosOnly => CrateDepKind::MacrosOnly,
                 _ => dep.kind,
             };
-            let cnum = self.maybe_resolve_crate(dep.name, dep_kind, Some((dep_root, &dep)))?;
+            let cnum = self.maybe_resolve_crate(dep.name, dep_kind, CrateOrigin::Dependency {
+                dep_root,
+                dep: &dep,
+            })?;
             crate_num_map.push(cnum);
         }
 
@@ -824,7 +875,9 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         };
         info!("panic runtime not found -- loading {}", name);
 
-        let Some(cnum) = self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit) else {
+        let Some(cnum) =
+            self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit, CrateOrigin::Injected)
+        else {
             return;
         };
         let data = self.cstore.get_crate_data(cnum);
@@ -853,7 +906,9 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         info!("loading profiler");
 
         let name = Symbol::intern(&self.sess.opts.unstable_opts.profiler_runtime);
-        let Some(cnum) = self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit) else {
+        let Some(cnum) =
+            self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit, CrateOrigin::Injected)
+        else {
             return;
         };
         let data = self.cstore.get_crate_data(cnum);
@@ -966,12 +1021,54 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
             if entry.force {
                 let name_interned = Symbol::intern(name);
                 if !self.used_extern_options.contains(&name_interned) {
-                    self.resolve_crate(name_interned, DUMMY_SP, CrateDepKind::Explicit);
+                    self.resolve_crate(
+                        name_interned,
+                        DUMMY_SP,
+                        CrateDepKind::Explicit,
+                        CrateOrigin::ForcedExtern,
+                    );
                 }
             }
         }
     }
 
+    /// Inject the `compiler_builtins` crate if it is not already in the graph.
+    fn inject_compiler_builtins(&mut self, krate: &ast::Crate) {
+        // `compiler_builtins` does not get extern builtins, nor do `#![no_core]` crates
+        if attr::contains_name(&krate.attrs, sym::compiler_builtins)
+            || attr::contains_name(&krate.attrs, sym::no_core)
+        {
+            info!("`compiler_builtins` unneeded");
+            return;
+        }
+
+        // If a `#![compiler_builtins]` crate already exists, avoid injecting it twice. This is
+        // the common case since usually it appears as a dependency of `std` or `core`.
+        for (cnum, cmeta) in self.cstore.iter_crate_data() {
+            if cmeta.is_compiler_builtins() {
+                info!("`compiler_builtins` already exists (cnum = {cnum}); skipping injection");
+                return;
+            }
+        }
+
+        // Allow builtins to remain unresolved, which will just mean linker errors if the
+        // relevant symbols aren't otherwise provided.
+        let Ok(cnum) = self.maybe_resolve_crate(
+            sym::compiler_builtins,
+            CrateDepKind::Implicit,
+            CrateOrigin::Injected,
+        ) else {
+            info!("`compiler_builtins` not resolved");
+            return;
+        };
+
+        // Sanity check that the loaded crate is `#![compiler_builtins]`
+        let cmeta = self.cstore.get_crate_data(cnum);
+        if !cmeta.is_compiler_builtins() {
+            self.dcx().emit_err(errors::CrateNotCompilerBuiltins { crate_name: cmeta.name() });
+        }
+    }
+
     fn inject_dependency_if(
         &mut self,
         krate: CrateNum,
@@ -1081,6 +1178,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
     }
 
     pub fn postprocess(&mut self, krate: &ast::Crate) {
+        self.inject_compiler_builtins(krate);
         self.inject_forced_externs();
         self.inject_profiler_runtime();
         self.inject_allocator_crate(krate);
@@ -1092,6 +1190,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         info!("{:?}", CrateDump(self.cstore));
     }
 
+    /// Process an `extern crate foo` AST node.
     pub fn process_extern_crate(
         &mut self,
         item: &ast::Item,
@@ -1117,7 +1216,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
                     CrateDepKind::Explicit
                 };
 
-                let cnum = self.resolve_crate(name, item.span, dep_kind)?;
+                let cnum = self.resolve_crate(name, item.span, dep_kind, CrateOrigin::AstExtern)?;
 
                 let path_len = definitions.def_path(def_id).data.len();
                 self.cstore.update_extern_crate(cnum, ExternCrate {
@@ -1133,7 +1232,8 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
     }
 
     pub fn process_path_extern(&mut self, name: Symbol, span: Span) -> Option<CrateNum> {
-        let cnum = self.resolve_crate(name, span, CrateDepKind::Explicit)?;
+        let cnum =
+            self.resolve_crate(name, span, CrateDepKind::Explicit, CrateOrigin::ExternPrelude)?;
 
         self.cstore.update_extern_crate(cnum, ExternCrate {
             src: ExternCrateSource::Path,
@@ -1147,7 +1247,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
     }
 
     pub fn maybe_process_path_extern(&mut self, name: Symbol) -> Option<CrateNum> {
-        self.maybe_resolve_crate(name, CrateDepKind::Explicit, None).ok()
+        self.maybe_resolve_crate(name, CrateDepKind::Explicit, CrateOrigin::ExternPrelude).ok()
     }
 }