1 //! Validates all used crates and extern libraries and loads their metadata
3 use crate::locator::{CrateLocator, CratePaths};
4 use crate::rmeta::{CrateDep, CrateMetadata, CrateNumMap, CrateRoot, MetadataBlob};
6 use rustc::hir::map::Definitions;
7 use rustc::middle::cstore::DepKind;
8 use rustc::middle::cstore::{CrateSource, ExternCrate, ExternCrateSource, MetadataLoaderDyn};
9 use rustc::session::config;
10 use rustc::session::search_paths::PathKind;
11 use rustc::session::{CrateDisambiguator, Session};
12 use rustc::ty::TyCtxt;
13 use rustc_data_structures::svh::Svh;
14 use rustc_data_structures::sync::Lrc;
15 use rustc_errors::struct_span_err;
16 use rustc_expand::base::SyntaxExtension;
17 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
18 use rustc_index::vec::IndexVec;
19 use rustc_span::edition::Edition;
20 use rustc_span::symbol::{sym, Symbol};
21 use rustc_span::{Span, DUMMY_SP};
22 use rustc_target::spec::{PanicStrategy, TargetTriple};
25 use syntax::expand::allocator::{global_allocator_spans, AllocatorKind};
27 use log::{debug, info, log_enabled};
28 use proc_macro::bridge::client::ProcMacro;
34 metas: IndexVec<CrateNum, Option<Lrc<CrateMetadata>>>,
35 injected_panic_runtime: Option<CrateNum>,
36 /// This crate needs an allocator and either provides it itself, or finds it in a dependency.
37 /// If the above is true, then this field denotes the kind of the found allocator.
38 allocator_kind: Option<AllocatorKind>,
39 /// This crate has a `#[global_allocator]` item.
40 has_global_allocator: bool,
43 pub struct CrateLoader<'a> {
44 // Immutable configuration.
46 metadata_loader: &'a MetadataLoaderDyn,
47 local_crate_name: Symbol,
52 pub enum LoadedMacro {
53 MacroDef(ast::Item, Edition),
54 ProcMacro(SyntaxExtension),
57 crate struct Library {
58 pub source: CrateSource,
59 pub metadata: MetadataBlob,
68 LocatorError(CrateLocator<'a>),
71 impl<'a> LoadError<'a> {
72 fn report(self) -> ! {
74 LoadError::LocatorError(locator) => locator.report_errs(),
79 fn dump_crates(cstore: &CStore) {
80 info!("resolved crates:");
81 cstore.iter_crate_data(|cnum, data| {
82 info!(" name: {}", data.name());
83 info!(" cnum: {}", cnum);
84 info!(" hash: {}", data.hash());
85 info!(" reqd: {:?}", data.dep_kind());
86 let CrateSource { dylib, rlib, rmeta } = data.source();
87 dylib.as_ref().map(|dl| info!(" dylib: {}", dl.0.display()));
88 rlib.as_ref().map(|rl| info!(" rlib: {}", rl.0.display()));
89 rmeta.as_ref().map(|rl| info!(" rmeta: {}", rl.0.display()));
94 crate fn from_tcx(tcx: TyCtxt<'_>) -> &CStore {
95 tcx.cstore_as_any().downcast_ref::<CStore>().expect("`tcx.cstore` is not a `CStore`")
98 fn alloc_new_crate_num(&mut self) -> CrateNum {
99 self.metas.push(None);
100 CrateNum::new(self.metas.len() - 1)
103 crate fn get_crate_data(&self, cnum: CrateNum) -> &CrateMetadata {
106 .unwrap_or_else(|| panic!("Failed to get crate data for {:?}", cnum))
109 fn set_crate_data(&mut self, cnum: CrateNum, data: CrateMetadata) {
110 assert!(self.metas[cnum].is_none(), "Overwriting crate metadata entry");
111 self.metas[cnum] = Some(Lrc::new(data));
114 crate fn iter_crate_data(&self, mut f: impl FnMut(CrateNum, &CrateMetadata)) {
115 for (cnum, data) in self.metas.iter_enumerated() {
116 if let Some(data) = data {
122 fn push_dependencies_in_postorder(&self, deps: &mut Vec<CrateNum>, cnum: CrateNum) {
123 if !deps.contains(&cnum) {
124 let data = self.get_crate_data(cnum);
125 for &dep in data.dependencies().iter() {
127 self.push_dependencies_in_postorder(deps, dep);
135 crate fn crate_dependencies_in_postorder(&self, cnum: CrateNum) -> Vec<CrateNum> {
136 let mut deps = Vec::new();
137 if cnum == LOCAL_CRATE {
138 self.iter_crate_data(|cnum, _| self.push_dependencies_in_postorder(&mut deps, cnum));
140 self.push_dependencies_in_postorder(&mut deps, cnum);
145 fn crate_dependencies_in_reverse_postorder(&self, cnum: CrateNum) -> Vec<CrateNum> {
146 let mut deps = self.crate_dependencies_in_postorder(cnum);
151 crate fn injected_panic_runtime(&self) -> Option<CrateNum> {
152 self.injected_panic_runtime
155 crate fn allocator_kind(&self) -> Option<AllocatorKind> {
159 crate fn has_global_allocator(&self) -> bool {
160 self.has_global_allocator
164 impl<'a> CrateLoader<'a> {
167 metadata_loader: &'a MetadataLoaderDyn,
168 local_crate_name: &str,
173 local_crate_name: Symbol::intern(local_crate_name),
175 // We add an empty entry for LOCAL_CRATE (which maps to zero) in
176 // order to make array indices in `metas` match with the
177 // corresponding `CrateNum`. This first entry will always remain
179 metas: IndexVec::from_elem_n(None, 1),
180 injected_panic_runtime: None,
181 allocator_kind: None,
182 has_global_allocator: false,
187 pub fn cstore(&self) -> &CStore {
191 pub fn into_cstore(self) -> CStore {
195 fn existing_match(&self, name: Symbol, hash: Option<Svh>, kind: PathKind) -> Option<CrateNum> {
197 self.cstore.iter_crate_data(|cnum, data| {
198 if data.name() != name {
203 Some(hash) if hash == data.hash() => {
211 // When the hash is None we're dealing with a top-level dependency
212 // in which case we may have a specification on the command line for
213 // this library. Even though an upstream library may have loaded
214 // something of the same name, we have to make sure it was loaded
215 // from the exact same location as well.
217 // We're also sure to compare *paths*, not actual byte slices. The
218 // `source` stores paths which are normalized which may be different
219 // from the strings on the command line.
220 let source = self.cstore.get_crate_data(cnum).source();
221 if let Some(entry) = self.sess.opts.externs.get(&name.as_str()) {
222 // Only use `--extern crate_name=path` here, not `--extern crate_name`.
223 if let Some(mut files) = entry.files() {
225 let l = fs::canonicalize(l).ok();
226 source.dylib.as_ref().map(|p| &p.0) == l.as_ref()
227 || source.rlib.as_ref().map(|p| &p.0) == l.as_ref()
235 // Alright, so we've gotten this far which means that `data` has the
236 // right name, we don't have a hash, and we don't have a --extern
237 // pointing for ourselves. We're still not quite yet done because we
238 // have to make sure that this crate was found in the crate lookup
239 // path (this is a top-level dependency) as we don't want to
240 // implicitly load anything inside the dependency lookup path.
241 let prev_kind = source
244 .or(source.rlib.as_ref())
245 .or(source.rmeta.as_ref())
246 .expect("No sources for crate")
248 if kind.matches(prev_kind) {
255 fn verify_no_symbol_conflicts(&self, span: Span, root: &CrateRoot<'_>) {
256 // Check for (potential) conflicts with the local crate
257 if self.local_crate_name == root.name()
258 && self.sess.local_crate_disambiguator() == root.disambiguator()
264 "the current crate is indistinguishable from one of its \
265 dependencies: it has the same crate-name `{}` and was \
266 compiled with the same `-C metadata` arguments. This \
267 will result in symbol conflicts between the two.",
273 // Check for conflicts with any crate loaded so far
274 self.cstore.iter_crate_data(|_, other| {
275 if other.name() == root.name() && // same crate-name
276 other.disambiguator() == root.disambiguator() && // same crate-disambiguator
277 other.hash() != root.hash()
284 "found two different crates with name `{}` that are \
285 not distinguished by differing `-C metadata`. This \
286 will result in symbol conflicts between the two.",
296 host_lib: Option<Library>,
297 root: Option<&CratePaths>,
303 let _prof_timer = self.sess.prof.generic_activity("metadata_register_crate");
305 let Library { source, metadata } = lib;
306 let crate_root = metadata.get_root();
307 let host_hash = host_lib.as_ref().map(|lib| lib.metadata.get_root().hash());
308 self.verify_no_symbol_conflicts(span, &crate_root);
311 self.sess.opts.externs.get(&name.as_str()).map(|e| e.is_private_dep).unwrap_or(false);
313 info!("register crate `{}` (private_dep = {})", crate_root.name(), private_dep);
315 // Claim this crate number and cache it
316 let cnum = self.cstore.alloc_new_crate_num();
318 // Maintain a reference to the top most crate.
319 // Stash paths for top-most crate locally if necessary.
321 let root = if let Some(root) = root {
324 crate_paths = CratePaths::new(crate_root.name(), source.clone());
328 let cnum_map = self.resolve_crate_deps(root, &crate_root, &metadata, cnum, span, dep_kind);
330 let raw_proc_macros = if crate_root.is_proc_macro_crate() {
332 let (dlsym_source, dlsym_root) = match &host_lib {
333 Some(host_lib) => (&host_lib.source, {
334 temp_root = host_lib.metadata.get_root();
337 None => (&source, &crate_root),
339 let dlsym_dylib = dlsym_source.dylib.as_ref().expect("no dylib for a proc-macro crate");
340 Some(self.dlsym_proc_macros(&dlsym_dylib.0, dlsym_root.disambiguator(), span))
345 self.cstore.set_crate_data(
364 fn load_proc_macro<'b>(
366 locator: &mut CrateLocator<'b>,
368 ) -> Option<(LoadResult, Option<Library>)>
372 // Use a new crate locator so trying to load a proc macro doesn't affect the error
374 let mut proc_macro_locator = locator.clone();
376 // Try to load a proc macro
377 proc_macro_locator.is_proc_macro = Some(true);
379 // Load the proc macro crate for the target
380 let (locator, target_result) = if self.sess.opts.debugging_opts.dual_proc_macros {
381 proc_macro_locator.reset();
382 let result = match self.load(&mut proc_macro_locator)? {
383 LoadResult::Previous(cnum) => return Some((LoadResult::Previous(cnum), None)),
384 LoadResult::Loaded(library) => Some(LoadResult::Loaded(library)),
386 locator.hash = locator.host_hash;
387 // Use the locator when looking for the host proc macro crate, as that is required
388 // so we want it to affect the error message
391 (&mut proc_macro_locator, None)
394 // Load the proc macro crate for the host
397 locator.is_proc_macro = Some(true);
398 locator.target = &self.sess.host;
399 locator.triple = TargetTriple::from_triple(config::host_triple());
400 locator.filesearch = self.sess.host_filesearch(path_kind);
402 let host_result = self.load(locator)?;
404 Some(if self.sess.opts.debugging_opts.dual_proc_macros {
405 let host_result = match host_result {
406 LoadResult::Previous(..) => {
407 panic!("host and target proc macros must be loaded in lock-step")
409 LoadResult::Loaded(library) => library,
411 (target_result.unwrap(), Some(host_result))
417 fn resolve_crate<'b>(
422 dep: Option<(&'b CratePaths, &'b CrateDep)>,
424 self.maybe_resolve_crate(name, span, dep_kind, dep).unwrap_or_else(|err| err.report())
427 fn maybe_resolve_crate<'b>(
431 mut dep_kind: DepKind,
432 dep: Option<(&'b CratePaths, &'b CrateDep)>,
433 ) -> Result<CrateNum, LoadError<'b>> {
434 info!("resolving crate `{}`", name);
435 let (root, hash, host_hash, extra_filename, path_kind) = match dep {
436 Some((root, dep)) => (
440 Some(&dep.extra_filename[..]),
441 PathKind::Dependency,
443 None => (None, None, None, None, PathKind::Crate),
445 let result = if let Some(cnum) = self.existing_match(name, hash, path_kind) {
446 (LoadResult::Previous(cnum), None)
448 info!("falling back to a load");
449 let mut locator = CrateLocator::new(
451 self.metadata_loader,
460 Some(false), // is_proc_macro
463 self.load(&mut locator)
466 dep_kind = DepKind::UnexportedMacrosOnly;
467 self.load_proc_macro(&mut locator, path_kind)
469 .ok_or_else(move || LoadError::LocatorError(locator))?
473 (LoadResult::Previous(cnum), None) => {
474 let data = self.cstore.get_crate_data(cnum);
475 if data.is_proc_macro_crate() {
476 dep_kind = DepKind::UnexportedMacrosOnly;
478 data.update_dep_kind(|data_dep_kind| cmp::max(data_dep_kind, dep_kind));
481 (LoadResult::Loaded(library), host_library) => {
482 Ok(self.register_crate(host_library, root, span, library, dep_kind, name))
488 fn load(&self, locator: &mut CrateLocator<'_>) -> Option<LoadResult> {
489 let library = locator.maybe_load_library_crate()?;
491 // In the case that we're loading a crate, but not matching
492 // against a hash, we could load a crate which has the same hash
493 // as an already loaded crate. If this is the case prevent
494 // duplicates by just using the first crate.
496 // Note that we only do this for target triple crates, though, as we
497 // don't want to match a host crate against an equivalent target one
499 let root = library.metadata.get_root();
500 if locator.triple == self.sess.opts.target_triple {
501 let mut result = LoadResult::Loaded(library);
502 self.cstore.iter_crate_data(|cnum, data| {
503 if data.name() == root.name() && root.hash() == data.hash() {
504 assert!(locator.hash.is_none());
505 info!("load success, going to previous cnum: {}", cnum);
506 result = LoadResult::Previous(cnum);
511 Some(LoadResult::Loaded(library))
515 fn update_extern_crate(&self, cnum: CrateNum, extern_crate: ExternCrate) {
516 let cmeta = self.cstore.get_crate_data(cnum);
517 if cmeta.update_extern_crate(extern_crate) {
518 // Propagate the extern crate info to dependencies if it was updated.
519 let extern_crate = ExternCrate { dependency_of: cnum, ..extern_crate };
520 for &dep_cnum in cmeta.dependencies().iter() {
521 self.update_extern_crate(dep_cnum, extern_crate);
526 // Go through the crate metadata and load any crates that it references
527 fn resolve_crate_deps(
530 crate_root: &CrateRoot<'_>,
531 metadata: &MetadataBlob,
536 debug!("resolving deps of external crate");
537 if crate_root.is_proc_macro_crate() {
538 return CrateNumMap::new();
541 // The map from crate numbers in the crate we're resolving to local crate numbers.
542 // We map 0 and all other holes in the map to our parent crate. The "additional"
543 // self-dependencies should be harmless.
544 std::iter::once(krate)
545 .chain(crate_root.decode_crate_deps(metadata).map(|dep| {
547 "resolving dep crate {} hash: `{}` extra filename: `{}`",
548 dep.name, dep.hash, dep.extra_filename
550 if dep.kind == DepKind::UnexportedMacrosOnly {
553 let dep_kind = match dep_kind {
554 DepKind::MacrosOnly => DepKind::MacrosOnly,
557 self.resolve_crate(dep.name, span, dep_kind, Some((root, &dep)))
562 fn dlsym_proc_macros(
565 disambiguator: CrateDisambiguator,
567 ) -> &'static [ProcMacro] {
568 use crate::dynamic_lib::DynamicLibrary;
571 // Make sure the path contains a / or the linker will search for it.
572 let path = env::current_dir().unwrap().join(path);
573 let lib = match DynamicLibrary::open(Some(&path)) {
575 Err(err) => self.sess.span_fatal(span, &err),
578 let sym = self.sess.generate_proc_macro_decls_symbol(disambiguator);
580 let sym = match lib.symbol(&sym) {
582 Err(err) => self.sess.span_fatal(span, &err),
584 *(sym as *const &[ProcMacro])
587 // Intentionally leak the dynamic library. We can't ever unload it
588 // since the library can make things that will live arbitrarily long.
589 std::mem::forget(lib);
594 fn inject_panic_runtime(&mut self, krate: &ast::Crate) {
595 // If we're only compiling an rlib, then there's no need to select a
596 // panic runtime, so we just skip this section entirely.
598 self.sess.crate_types.borrow().iter().any(|ct| *ct != config::CrateType::Rlib);
600 info!("panic runtime injection skipped, only generating rlib");
604 // If we need a panic runtime, we try to find an existing one here. At
605 // the same time we perform some general validation of the DAG we've got
606 // going such as ensuring everything has a compatible panic strategy.
608 // The logic for finding the panic runtime here is pretty much the same
609 // as the allocator case with the only addition that the panic strategy
610 // compilation mode also comes into play.
611 let desired_strategy = self.sess.panic_strategy();
612 let mut runtime_found = false;
613 let mut needs_panic_runtime = attr::contains_name(&krate.attrs, sym::needs_panic_runtime);
615 self.cstore.iter_crate_data(|cnum, data| {
616 needs_panic_runtime = needs_panic_runtime || data.needs_panic_runtime();
617 if data.is_panic_runtime() {
618 // Inject a dependency from all #![needs_panic_runtime] to this
619 // #![panic_runtime] crate.
620 self.inject_dependency_if(cnum, "a panic runtime", &|data| {
621 data.needs_panic_runtime()
623 runtime_found = runtime_found || data.dep_kind() == DepKind::Explicit;
627 // If an explicitly linked and matching panic runtime was found, or if
628 // we just don't need one at all, then we're done here and there's
629 // nothing else to do.
630 if !needs_panic_runtime || runtime_found {
634 // By this point we know that we (a) need a panic runtime and (b) no
635 // panic runtime was explicitly linked. Here we just load an appropriate
636 // default runtime for our panic strategy and then inject the
639 // We may resolve to an already loaded crate (as the crate may not have
640 // been explicitly linked prior to this) and we may re-inject
641 // dependencies again, but both of those situations are fine.
643 // Also note that we have yet to perform validation of the crate graph
644 // in terms of everyone has a compatible panic runtime format, that's
645 // performed later as part of the `dependency_format` module.
646 let name = match desired_strategy {
647 PanicStrategy::Unwind => Symbol::intern("panic_unwind"),
648 PanicStrategy::Abort => Symbol::intern("panic_abort"),
650 info!("panic runtime not found -- loading {}", name);
652 let cnum = self.resolve_crate(name, DUMMY_SP, DepKind::Implicit, None);
653 let data = self.cstore.get_crate_data(cnum);
655 // Sanity check the loaded crate to ensure it is indeed a panic runtime
656 // and the panic strategy is indeed what we thought it was.
657 if !data.is_panic_runtime() {
658 self.sess.err(&format!("the crate `{}` is not a panic runtime", name));
660 if data.panic_strategy() != desired_strategy {
661 self.sess.err(&format!(
662 "the crate `{}` does not have the panic \
665 desired_strategy.desc()
669 self.cstore.injected_panic_runtime = Some(cnum);
670 self.inject_dependency_if(cnum, "a panic runtime", &|data| data.needs_panic_runtime());
673 fn inject_profiler_runtime(&mut self) {
674 if self.sess.opts.debugging_opts.profile || self.sess.opts.cg.profile_generate.enabled() {
675 info!("loading profiler");
677 let name = Symbol::intern("profiler_builtins");
678 let cnum = self.resolve_crate(name, DUMMY_SP, DepKind::Implicit, None);
679 let data = self.cstore.get_crate_data(cnum);
681 // Sanity check the loaded crate to ensure it is indeed a profiler runtime
682 if !data.is_profiler_runtime() {
683 self.sess.err(&format!(
684 "the crate `profiler_builtins` is not \
691 fn inject_allocator_crate(&mut self, krate: &ast::Crate) {
692 self.cstore.has_global_allocator = match &*global_allocator_spans(krate) {
693 [span1, span2, ..] => {
695 .struct_span_err(*span2, "cannot define multiple global allocators")
696 .span_label(*span2, "cannot define a new global allocator")
697 .span_label(*span1, "previous global allocator is defined here")
701 spans => !spans.is_empty(),
704 // Check to see if we actually need an allocator. This desire comes
705 // about through the `#![needs_allocator]` attribute and is typically
706 // written down in liballoc.
707 let mut needs_allocator = attr::contains_name(&krate.attrs, sym::needs_allocator);
708 self.cstore.iter_crate_data(|_, data| {
709 needs_allocator = needs_allocator || data.needs_allocator();
711 if !needs_allocator {
715 // At this point we've determined that we need an allocator. Let's see
716 // if our compilation session actually needs an allocator based on what
718 let all_rlib = self.sess.crate_types.borrow().iter().all(|ct| match *ct {
719 config::CrateType::Rlib => true,
726 // Ok, we need an allocator. Not only that but we're actually going to
727 // create an artifact that needs one linked in. Let's go find the one
728 // that we're going to link in.
730 // First up we check for global allocators. Look at the crate graph here
731 // and see what's a global allocator, including if we ourselves are a
733 let mut global_allocator =
734 self.cstore.has_global_allocator.then(|| Symbol::intern("this crate"));
735 self.cstore.iter_crate_data(|_, data| {
736 if !data.has_global_allocator() {
739 match global_allocator {
740 Some(other_crate) => {
741 self.sess.err(&format!(
742 "the `#[global_allocator]` in {} \
743 conflicts with global \
749 None => global_allocator = Some(data.name()),
752 if global_allocator.is_some() {
753 self.cstore.allocator_kind = Some(AllocatorKind::Global);
757 // Ok we haven't found a global allocator but we still need an
758 // allocator. At this point our allocator request is typically fulfilled
759 // by the standard library, denoted by the `#![default_lib_allocator]`
761 let mut has_default = attr::contains_name(&krate.attrs, sym::default_lib_allocator);
762 self.cstore.iter_crate_data(|_, data| {
763 if data.has_default_lib_allocator() {
770 "no global memory allocator found but one is \
771 required; link to std or \
772 add `#[global_allocator]` to a static item \
773 that implements the GlobalAlloc trait.",
776 self.cstore.allocator_kind = Some(AllocatorKind::Default);
779 fn inject_dependency_if(
783 needs_dep: &dyn Fn(&CrateMetadata) -> bool,
785 // don't perform this validation if the session has errors, as one of
786 // those errors may indicate a circular dependency which could cause
787 // this to stack overflow.
788 if self.sess.has_errors() {
792 // Before we inject any dependencies, make sure we don't inject a
793 // circular dependency by validating that this crate doesn't
794 // transitively depend on any crates satisfying `needs_dep`.
795 for dep in self.cstore.crate_dependencies_in_reverse_postorder(krate) {
796 let data = self.cstore.get_crate_data(dep);
797 if needs_dep(&data) {
798 self.sess.err(&format!(
799 "the crate `{}` cannot depend \
800 on a crate that needs {}, but \
802 self.cstore.get_crate_data(krate).name(),
809 // All crates satisfying `needs_dep` do not explicitly depend on the
810 // crate provided for this compile, but in order for this compilation to
811 // be successfully linked we need to inject a dependency (to order the
812 // crates on the command line correctly).
813 self.cstore.iter_crate_data(|cnum, data| {
814 if !needs_dep(data) {
818 info!("injecting a dep from {} to {}", cnum, krate);
819 data.add_dependency(krate);
823 pub fn postprocess(&mut self, krate: &ast::Crate) {
824 self.inject_profiler_runtime();
825 self.inject_allocator_crate(krate);
826 self.inject_panic_runtime(krate);
828 if log_enabled!(log::Level::Info) {
829 dump_crates(&self.cstore);
833 pub fn process_extern_crate(
836 definitions: &Definitions,
839 ast::ItemKind::ExternCrate(orig_name) => {
841 "resolving extern crate stmt. ident: {} orig_name: {:?}",
842 item.ident, orig_name
844 let name = match orig_name {
846 crate::validate_crate_name(
853 None => item.ident.name,
855 let dep_kind = if attr::contains_name(&item.attrs, sym::no_link) {
856 DepKind::UnexportedMacrosOnly
861 let cnum = self.resolve_crate(name, item.span, dep_kind, None);
863 let def_id = definitions.opt_local_def_id(item.id).unwrap();
864 let path_len = definitions.def_path(def_id.index).data.len();
865 self.update_extern_crate(
868 src: ExternCrateSource::Extern(def_id),
871 dependency_of: LOCAL_CRATE,
880 pub fn process_path_extern(&mut self, name: Symbol, span: Span) -> CrateNum {
881 let cnum = self.resolve_crate(name, span, DepKind::Explicit, None);
883 self.update_extern_crate(
886 src: ExternCrateSource::Path,
888 // to have the least priority in `update_extern_crate`
889 path_len: usize::max_value(),
890 dependency_of: LOCAL_CRATE,
897 pub fn maybe_process_path_extern(&mut self, name: Symbol, span: Span) -> Option<CrateNum> {
898 self.maybe_resolve_crate(name, span, DepKind::Explicit, None).ok()