Auto merge of #94079 - petrochenkov:cstr, r=joshtriplett

library: Move `CStr` to libcore, and `CString` to liballoc

Closes #46736

Interesting points:
- Stability:
    - To make `CStr(ing)` from libcore/liballoc unusable without enabling features I had to make these structures unstable, and reexport them from libstd using stable type aliases instead of `pub use` reexports. (Because stability of `use` items is not checked.)
- Relying on target ABI in libcore is ok:
    - #94079 (comment)
- `trait CStrExt` (UPDATE: used only in `cfg(bootstrap)` mode, otherwise lang items are used instead)
    - #94079 (comment)
- `strlen`
    - #94079 (comment)

Otherwise it's just a code move + some minor hackery usual for liballoc in `cfg(test)` mode.

Cargo.lock

@@ -731,9 +731,9 @@ dependencies = [
 
 [[package]]
 name = "compiler_builtins"
-version = "0.1.70"
+version = "0.1.71"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "80873f979f0a344a4ade87c2f70d9ccf5720b83b10c97ec7cd745895d021e85a"
+checksum = "163437f05ca8f29d7e9128ea728dedf5eb620e445fbca273641d3a3050305f23"
 dependencies = [
  "cc",
  "rustc-std-workspace-core",

compiler/rustc_hir/src/lang_items.rs

@@ -326,6 +326,8 @@ language_item_table! {
     Range,                   sym::Range,               range_struct,               Target::Struct,         GenericRequirement::None;
     RangeToInclusive,        sym::RangeToInclusive,    range_to_inclusive_struct,  Target::Struct,         GenericRequirement::None;
     RangeTo,                 sym::RangeTo,             range_to_struct,            Target::Struct,         GenericRequirement::None;
+
+    CStr,                    sym::CStr,                c_str,                      Target::Struct,         GenericRequirement::None;
 }
 
 pub enum GenericRequirement {

compiler/rustc_metadata/src/creader.rs

@@ -417,6 +417,7 @@ impl<'a> CrateLoader<'a> {
 
         let crate_metadata = CrateMetadata::new(
             self.sess,
+            &self.cstore,
             metadata,
             crate_root,
             raw_proc_macros,

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1,6 +1,6 @@
 // Decoding metadata from a single crate's metadata
 
-use crate::creader::CrateMetadataRef;
+use crate::creader::{CStore, CrateMetadataRef};
 use crate::rmeta::table::{FixedSizeEncoding, Table};
 use crate::rmeta::*;
 
@@ -1737,6 +1737,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 impl CrateMetadata {
     crate fn new(
         sess: &Session,
+        cstore: &CStore,
         blob: MetadataBlob,
         root: CrateRoot<'static>,
         raw_proc_macros: Option<&'static [ProcMacro]>,
@@ -1752,11 +1753,6 @@ impl CrateMetadata {
             .decode((&blob, sess))
             .map(|trait_impls| (trait_impls.trait_id, trait_impls.impls))
             .collect();
-        let incoherent_impls = root
-            .incoherent_impls
-            .decode((&blob, sess))
-            .map(|incoherent_impls| (incoherent_impls.self_ty, incoherent_impls.impls))
-            .collect();
         let alloc_decoding_state =
             AllocDecodingState::new(root.interpret_alloc_index.decode(&blob).collect());
         let dependencies = Lock::new(cnum_map.iter().cloned().collect());
@@ -1765,11 +1761,11 @@ impl CrateMetadata {
         // that does not copy any data. It just does some data verification.
         let def_path_hash_map = root.def_path_hash_map.decode(&blob);
 
-        CrateMetadata {
+        let mut cdata = CrateMetadata {
             blob,
             root,
             trait_impls,
-            incoherent_impls,
+            incoherent_impls: Default::default(),
             raw_proc_macros,
             source_map_import_info: OnceCell::new(),
             def_path_hash_map,
@@ -1786,7 +1782,17 @@ impl CrateMetadata {
             hygiene_context: Default::default(),
             def_key_cache: Default::default(),
             def_path_hash_cache: Default::default(),
-        }
+        };
+
+        // Need `CrateMetadataRef` to decode `DefId`s in simplified types.
+        cdata.incoherent_impls = cdata
+            .root
+            .incoherent_impls
+            .decode(CrateMetadataRef { cdata: &cdata, cstore })
+            .map(|incoherent_impls| (incoherent_impls.self_ty, incoherent_impls.impls))
+            .collect();
+
+        cdata
     }
 
     crate fn dependencies(&self) -> LockGuard<'_, Vec<CrateNum>> {

compiler/rustc_typeck/src/check/method/probe.rs

@@ -644,7 +644,11 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 self.assemble_inherent_impl_candidates_for_type(p.def_id());
             }
             ty::Adt(def, _) => {
-                self.assemble_inherent_impl_candidates_for_type(def.did());
+                let def_id = def.did();
+                self.assemble_inherent_impl_candidates_for_type(def_id);
+                if Some(def_id) == self.tcx.lang_items().c_str() {
+                    self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty);
+                }
             }
             ty::Foreign(did) => {
                 self.assemble_inherent_impl_candidates_for_type(did);

compiler/rustc_typeck/src/coherence/inherent_impls.rs

@@ -55,7 +55,12 @@ impl<'tcx> ItemLikeVisitor<'_> for InherentCollect<'tcx> {
         let self_ty = self.tcx.type_of(item.def_id);
         match *self_ty.kind() {
             ty::Adt(def, _) => {
-                self.check_def_id(item, def.did());
+                let def_id = def.did();
+                if !def_id.is_local() && Some(def_id) == self.tcx.lang_items().c_str() {
+                    self.check_primitive_impl(item.def_id, self_ty, items, ty.span)
+                } else {
+                    self.check_def_id(item, def_id);
+                }
             }
             ty::Foreign(did) => {
                 self.check_def_id(item, did);