rustc: Use `tcx.used_crates(())` more

And explain when it should be used.

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -399,7 +399,7 @@ fn upstream_monomorphizations_provider(
     tcx: TyCtxt<'_>,
     (): (),
 ) -> DefIdMap<UnordMap<GenericArgsRef<'_>, CrateNum>> {
-    let cnums = tcx.crates(());
+    let cnums = tcx.used_crates(());
 
     let mut instances: DefIdMap<UnordMap<_, _>> = Default::default();
 

compiler/rustc_codegen_ssa/src/base.rs

@@ -539,7 +539,7 @@ pub fn collect_debugger_visualizers_transitive(
     tcx.debugger_visualizers(LOCAL_CRATE)
         .iter()
         .chain(
-            tcx.crates(())
+            tcx.used_crates(())
                 .iter()
                 .filter(|&cnum| {
                     let used_crate_source = tcx.used_crate_source(*cnum);
@@ -849,7 +849,7 @@ impl CrateInfo {
         // `compiler_builtins` are always placed last to ensure that they're linked correctly.
         used_crates.extend(compiler_builtins);
 
-        let crates = tcx.crates(());
+        let crates = tcx.used_crates(());
         let n_crates = crates.len();
         let mut info = CrateInfo {
             target_cpu,

compiler/rustc_interface/src/passes.rs

@@ -458,7 +458,7 @@ fn write_out_deps(tcx: TyCtxt<'_>, outputs: &OutputFilenames, out_filenames: &[P
                 }
             }
 
-            for &cnum in tcx.crates(()) {
+            for &cnum in tcx.crates_including_speculative(()) {
                 let source = tcx.used_crate_source(cnum);
                 if let Some((path, _)) = &source.dylib {
                     files.push(escape_dep_filename(&path.display().to_string()));

compiler/rustc_metadata/src/dependency_format.rs

@@ -143,7 +143,7 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
                     && sess.crt_static(Some(ty))
                     && !sess.target.crt_static_allows_dylibs)
             {
-                for &cnum in tcx.crates(()).iter() {
+                for &cnum in tcx.used_crates(()).iter() {
                     if tcx.dep_kind(cnum).macros_only() {
                         continue;
                     }
@@ -164,7 +164,7 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
     // Sweep all crates for found dylibs. Add all dylibs, as well as their
     // dependencies, ensuring there are no conflicts. The only valid case for a
     // dependency to be relied upon twice is for both cases to rely on a dylib.
-    for &cnum in tcx.crates(()).iter() {
+    for &cnum in tcx.used_crates(()).iter() {
         if tcx.dep_kind(cnum).macros_only() {
             continue;
         }
@@ -182,7 +182,7 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
     }
 
     // Collect what we've got so far in the return vector.
-    let last_crate = tcx.crates(()).len();
+    let last_crate = tcx.used_crates(()).len();
     let mut ret = (1..last_crate + 1)
         .map(|cnum| match formats.get(&CrateNum::new(cnum)) {
             Some(&RequireDynamic) => Linkage::Dynamic,
@@ -196,7 +196,7 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
     //
     // If the crate hasn't been included yet and it's not actually required
     // (e.g., it's an allocator) then we skip it here as well.
-    for &cnum in tcx.crates(()).iter() {
+    for &cnum in tcx.used_crates(()).iter() {
         let src = tcx.used_crate_source(cnum);
         if src.dylib.is_none()
             && !formats.contains_key(&cnum)
@@ -284,7 +284,7 @@ fn add_library(
 
 fn attempt_static(tcx: TyCtxt<'_>, unavailable: &mut Vec<CrateNum>) -> Option<DependencyList> {
     let all_crates_available_as_rlib = tcx
-        .crates(())
+        .used_crates(())
         .iter()
         .copied()
         .filter_map(|cnum| {
@@ -305,7 +305,7 @@ fn attempt_static(tcx: TyCtxt<'_>, unavailable: &mut Vec<CrateNum>) -> Option<De
     // All crates are available in an rlib format, so we're just going to link
     // everything in explicitly so long as it's actually required.
     let mut ret = tcx
-        .crates(())
+        .used_crates(())
         .iter()
         .map(|&cnum| match tcx.dep_kind(cnum) {
             CrateDepKind::Explicit => Linkage::Static,

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

@@ -435,7 +435,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
             // traversal, but not globally minimal across all crates.
             let bfs_queue = &mut VecDeque::new();
 
-            for &cnum in tcx.crates(()) {
+            for &cnum in tcx.crates_including_speculative(()) {
                 // Ignore crates without a corresponding local `extern crate` item.
                 if tcx.missing_extern_crate_item(cnum) {
                     continue;
@@ -505,7 +505,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
             tcx.arena
                 .alloc_slice(&CStore::from_tcx(tcx).crate_dependencies_in_postorder(LOCAL_CRATE))
         },
-        crates: |tcx, ()| {
+        crates_including_speculative: |tcx, ()| {
             // The list of loaded crates is now frozen in query cache,
             // so make sure cstore is not mutably accessed from here on.
             tcx.untracked().cstore.freeze();

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1898,7 +1898,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
         let deps = self
             .tcx
-            .crates(())
+            .crates_including_speculative(())
             .iter()
             .map(|&cnum| {
                 let dep = CrateDep {

compiler/rustc_middle/src/hir/map/mod.rs

@@ -1016,7 +1016,7 @@ pub(super) fn crate_hash(tcx: TyCtxt<'_>, _: LocalCrate) -> Svh {
     let krate = tcx.hir_crate(());
     let hir_body_hash = krate.opt_hir_hash.expect("HIR hash missing while computing crate hash");
 
-    let upstream_crates = upstream_crates(tcx);
+    let upstream_crates = upstream_crates_for_hashing(tcx);
 
     let resolutions = tcx.resolutions(());
 
@@ -1085,9 +1085,9 @@ pub(super) fn crate_hash(tcx: TyCtxt<'_>, _: LocalCrate) -> Svh {
     Svh::new(crate_hash)
 }
 
-fn upstream_crates(tcx: TyCtxt<'_>) -> Vec<(StableCrateId, Svh)> {
+fn upstream_crates_for_hashing(tcx: TyCtxt<'_>) -> Vec<(StableCrateId, Svh)> {
     let mut upstream_crates: Vec<_> = tcx
-        .crates(())
+        .crates_including_speculative(())
         .iter()
         .map(|&cnum| {
             let stable_crate_id = tcx.stable_crate_id(cnum);

compiler/rustc_middle/src/query/mod.rs

@@ -1860,13 +1860,22 @@ rustc_queries! {
         eval_always
         desc { "calculating the stability index for the local crate" }
     }
-    query crates(_: ()) -> &'tcx [CrateNum] {
+    /// All loaded crates, including those loaded purely for doc links or diagnostics.
+    /// (Diagnostics include lints, so speculatively loaded crates may occur in successful
+    /// compilation even without doc links.)
+    /// Should be used when encoding crate metadata (and therefore when generating crate hash,
+    /// depinfo and similar things), to avoid dangling crate references in other encoded data,
+    /// like source maps.
+    /// May also be used for diagnostics - if we are loading a crate anyway we can suggest some
+    /// items from it as well.
+    /// But otherwise, `used_crates` should generally be used.
+    query crates_including_speculative(_: ()) -> &'tcx [CrateNum] {
         eval_always
         desc { "fetching all foreign CrateNum instances" }
     }
-    // Crates that are loaded non-speculatively (not for diagnostics or doc links).
-    // FIXME: This is currently only used for collecting lang items, but should be used instead of
-    // `crates` in most other cases too.
+    /// Crates that are loaded non-speculatively (not for diagnostics or doc links).
+    /// Should be used to maintain observable language behavior, for example when collecting lang
+    /// items or impls from all crates, or collecting libraries to link.
     query used_crates(_: ()) -> &'tcx [CrateNum] {
         eval_always
         desc { "fetching `CrateNum`s for all crates loaded non-speculatively" }

compiler/rustc_middle/src/ty/context.rs

@@ -1611,7 +1611,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     pub fn all_traits(self) -> impl Iterator<Item = DefId> + 'tcx {
         iter::once(LOCAL_CRATE)
-            .chain(self.crates(()).iter().copied())
+            .chain(self.used_crates(()).iter().copied())
             .flat_map(move |cnum| self.traits(cnum).iter().copied())
     }
 

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -3258,7 +3258,7 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
     let queue = &mut Vec::new();
     let mut seen_defs: DefIdSet = Default::default();
 
-    for &cnum in tcx.crates(()).iter() {
+    for &cnum in tcx.crates_including_speculative(()).iter() {
         let def_id = cnum.as_def_id();
 
         // Ignore crates that are not direct dependencies.

compiler/rustc_middle/src/ty/trait_def.rs

@@ -205,7 +205,7 @@ pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> Trait
     // Traits defined in the current crate can't have impls in upstream
     // crates, so we don't bother querying the cstore.
     if !trait_id.is_local() {
-        for &cnum in tcx.crates(()).iter() {
+        for &cnum in tcx.used_crates(()).iter() {
             for &(impl_def_id, simplified_self_ty) in
                 tcx.implementations_of_trait((cnum, trait_id)).iter()
             {
@@ -247,7 +247,7 @@ pub(super) fn incoherent_impls_provider(
     let mut impls = Vec::new();
 
     let mut res = Ok(());
-    for cnum in iter::once(LOCAL_CRATE).chain(tcx.crates(()).iter().copied()) {
+    for cnum in iter::once(LOCAL_CRATE).chain(tcx.used_crates(()).iter().copied()) {
         let incoherent_impls = match tcx.crate_incoherent_impls((cnum, simp)) {
             Ok(impls) => impls,
             Err(e) => {

compiler/rustc_passes/src/diagnostic_items.rs

@@ -82,7 +82,7 @@ fn all_diagnostic_items(tcx: TyCtxt<'_>, (): ()) -> DiagnosticItems {
     let mut items = DiagnosticItems::default();
 
     // Collect diagnostic items in other crates.
-    for &cnum in tcx.crates(()).iter().chain(std::iter::once(&LOCAL_CRATE)) {
+    for &cnum in tcx.crates_including_speculative(()).iter().chain(std::iter::once(&LOCAL_CRATE)) {
         for (&name, &def_id) in &tcx.diagnostic_items(cnum).name_to_id {
             collect_item(tcx, &mut items, name, def_id);
         }

compiler/rustc_passes/src/stability.rs

@@ -1020,7 +1020,7 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
         // stabilization diagnostic, but it can be avoided when there are no
         // `remaining_lib_features`.
         let mut all_implications = remaining_implications.clone();
-        for &cnum in tcx.crates(()) {
+        for &cnum in tcx.used_crates(()) {
             all_implications
                 .extend_unord(tcx.stability_implications(cnum).items().map(|(k, v)| (*k, *v)));
         }
@@ -1033,7 +1033,7 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
             &all_implications,
         );
 
-        for &cnum in tcx.crates(()) {
+        for &cnum in tcx.used_crates(()) {
             if remaining_lib_features.is_empty() && remaining_implications.is_empty() {
                 break;
             }

compiler/rustc_passes/src/weak_lang_items.rs

@@ -68,7 +68,7 @@ fn verify(tcx: TyCtxt<'_>, items: &lang_items::LanguageItems) {
     }
 
     let mut missing = FxHashSet::default();
-    for &cnum in tcx.crates(()).iter() {
+    for &cnum in tcx.used_crates(()).iter() {
         for &item in tcx.missing_lang_items(cnum).iter() {
             missing.insert(item);
         }

compiler/rustc_smir/src/rustc_smir/context.rs

@@ -126,7 +126,7 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         let mut tables = self.0.borrow_mut();
         let tcx = tables.tcx;
         iter::once(LOCAL_CRATE)
-            .chain(tables.tcx.crates(()).iter().copied())
+            .chain(tables.tcx.used_crates(()).iter().copied())
             .flat_map(|cnum| tcx.trait_impls_in_crate(cnum).iter())
             .map(|impl_def_id| tables.impl_def(*impl_def_id))
             .collect()
@@ -201,14 +201,19 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
 
     fn external_crates(&self) -> Vec<stable_mir::Crate> {
         let tables = self.0.borrow();
-        tables.tcx.crates(()).iter().map(|crate_num| smir_crate(tables.tcx, *crate_num)).collect()
+        tables
+            .tcx
+            .used_crates(())
+            .iter()
+            .map(|crate_num| smir_crate(tables.tcx, *crate_num))
+            .collect()
     }
 
     fn find_crates(&self, name: &str) -> Vec<stable_mir::Crate> {
         let tables = self.0.borrow();
         let crates: Vec<stable_mir::Crate> = [LOCAL_CRATE]
             .iter()
-            .chain(tables.tcx.crates(()).iter())
+            .chain(tables.tcx.used_crates(()).iter())
             .filter_map(|crate_num| {
                 let crate_name = tables.tcx.crate_name(*crate_num).to_string();
                 (name == crate_name).then(|| smir_crate(tables.tcx, *crate_num))

src/librustdoc/clean/types.rs

@@ -1937,7 +1937,7 @@ impl PrimitiveType {
             let mut primitive_locations = FxHashMap::default();
             // NOTE: technically this misses crates that are only passed with `--extern` and not loaded when checking the crate.
             // This is a degenerate case that I don't plan to support.
-            for &crate_num in tcx.crates(()) {
+            for &crate_num in tcx.crates_including_speculative(()) {
                 let e = ExternalCrate { crate_num };
                 let crate_name = e.name(tcx);
                 debug!(?crate_num, ?crate_name);

src/librustdoc/core.rs

@@ -347,7 +347,7 @@ pub(crate) fn run_global_ctxt(
         show_coverage,
     };
 
-    for cnum in tcx.crates(()) {
+    for cnum in tcx.crates_including_speculative(()) {
         crate::visit_lib::lib_embargo_visit_item(&mut ctxt, cnum.as_def_id());
     }
 

src/librustdoc/formats/cache.rs

@@ -155,7 +155,7 @@ impl Cache {
 
         // Cache where all our extern crates are located
         // FIXME: this part is specific to HTML so it'd be nice to remove it from the common code
-        for &crate_num in tcx.crates(()) {
+        for &crate_num in tcx.crates_including_speculative(()) {
             let e = ExternalCrate { crate_num };
 
             let name = e.name(tcx);

src/librustdoc/passes/collect_trait_impls.rs

@@ -47,7 +47,7 @@ pub(crate) fn collect_trait_impls(mut krate: Crate, cx: &mut DocContext<'_>) ->
     // External trait impls.
     {
         let _prof_timer = tcx.sess.prof.generic_activity("build_extern_trait_impls");
-        for &cnum in tcx.crates(()) {
+        for &cnum in tcx.crates_including_speculative(()) {
             for &impl_def_id in tcx.trait_impls_in_crate(cnum) {
                 cx.with_param_env(impl_def_id, |cx| {
                     inline::build_impl(cx, impl_def_id, None, &mut new_items_external);

src/librustdoc/scrape_examples.rs

@@ -283,7 +283,7 @@ pub(crate) fn run(
         // Collect CrateIds corresponding to provided target crates
         // If two different versions of the crate in the dependency tree, then examples will be collected from both.
         let all_crates = tcx
-            .crates(())
+            .crates_including_speculative(())
             .iter()
             .chain([&LOCAL_CRATE])
             .map(|crate_num| (crate_num, tcx.crate_name(*crate_num)))

src/tools/clippy/clippy_utils/src/lib.rs

@@ -647,7 +647,7 @@ fn item_children_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: Symbol) -> Vec<Re
 /// This function is expensive and should be used sparingly.
 pub fn def_path_res(cx: &LateContext<'_>, path: &[&str]) -> Vec<Res> {
     fn find_crates(tcx: TyCtxt<'_>, name: Symbol) -> impl Iterator<Item = DefId> + '_ {
-        tcx.crates(())
+        tcx.crates_including_speculative(())
             .iter()
             .copied()
             .filter(move |&num| tcx.crate_name(num) == name)

src/tools/miri/src/helpers.rs

@@ -126,7 +126,7 @@ fn try_resolve_did(tcx: TyCtxt<'_>, path: &[&str], namespace: Option<Namespace>)
     // the one in the sysroot and the one locally built by `cargo test`.)
     // FIXME: can we prefer the one from the sysroot?
     'crates: for krate in
-        tcx.crates(()).iter().filter(|&&krate| tcx.crate_name(krate).as_str() == crate_name)
+        tcx.used_crates(()).iter().filter(|&&krate| tcx.crate_name(krate).as_str() == crate_name)
     {
         let mut cur_item = DefId { krate: *krate, index: CRATE_DEF_INDEX };
         // Go over the modules.
@@ -1365,7 +1365,7 @@ pub fn get_local_crates(tcx: TyCtxt<'_>) -> Vec<CrateNum> {
         .map(|crates| crates.split(',').map(|krate| krate.to_string()).collect::<Vec<_>>())
         .unwrap_or_default();
     let mut local_crates = Vec::new();
-    for &crate_num in tcx.crates(()) {
+    for &crate_num in tcx.crates_including_speculative(()) {
         let name = tcx.crate_name(crate_num);
         let name = name.as_str();
         if local_crate_names.iter().any(|local_name| local_name == name) {

tests/ui/extern-flag/empty-extern-arg.stderr

@@ -1,13 +1,6 @@
 error: extern location for std does not exist: 
 
-error: `#[panic_handler]` function required, but not found
-
-error: unwinding panics are not supported without std
-   |
-   = help: using nightly cargo, use -Zbuild-std with panic="abort" to avoid unwinding
-   = note: since the core library is usually precompiled with panic="unwind", rebuilding your crate with panic="abort" may not be enough to fix the problem
-
 error: requires `sized` lang_item
 
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors