Rollup merge of #124976 - petrochenkov:usedcrates, r=oli-obk

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

And explain when it should be used.

Addresses comments from https://github.com/rust-lang/rust/pull/121167.

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) => {