Auto merge of #86143 - bjorn3:revert_revert_merge_crate_disambiguator, r=michaelwoerister

Reland "Merge CrateDisambiguator into StableCrateId"

Reverts https://github.com/rust-lang/rust/pull/85891 as this revert of #85804 made perf even worse.

r? `@Mark-Simulacrum`

compiler/rustc_span/src/crate_disambiguator.rs

@@ -1,35 +0,0 @@
-// This is here because `rustc_session` wants to refer to it,
-// and so does `rustc_hir`, but `rustc_hir` shouldn't refer to `rustc_session`.
-
-use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::{base_n, impl_stable_hash_via_hash};
-
-use std::fmt;
-
-/// Hash value constructed out of all the `-C metadata` arguments passed to the
-/// compiler. Together with the crate-name forms a unique global identifier for
-/// the crate.
-#[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Clone, Copy, Encodable, Decodable)]
-pub struct CrateDisambiguator(Fingerprint);
-
-impl CrateDisambiguator {
-    pub fn to_fingerprint(self) -> Fingerprint {
-        self.0
-    }
-}
-
-impl fmt::Display for CrateDisambiguator {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
-        let (a, b) = self.0.as_value();
-        let as_u128 = a as u128 | ((b as u128) << 64);
-        f.write_str(&base_n::encode(as_u128, base_n::CASE_INSENSITIVE))
-    }
-}
-
-impl From<Fingerprint> for CrateDisambiguator {
-    fn from(fingerprint: Fingerprint) -> CrateDisambiguator {
-        CrateDisambiguator(fingerprint)
-    }
-}
-
-impl_stable_hash_via_hash!(CrateDisambiguator);

compiler/rustc_span/src/def_id.rs

@@ -1,4 +1,3 @@
-use crate::crate_disambiguator::CrateDisambiguator;
 use crate::HashStableContext;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
@@ -127,26 +126,51 @@ impl Borrow<Fingerprint> for DefPathHash {
     }
 }
 
-/// A [StableCrateId] is a 64 bit hash of `(crate-name, crate-disambiguator)`. It
-/// is to [CrateNum] what [DefPathHash] is to [DefId]. It is stable across
-/// compilation sessions.
+/// A [StableCrateId] is a 64 bit hash of the crate name combined with all
+/// `-Cmetadata` arguments. It is to [CrateNum] what [DefPathHash] is to
+/// [DefId]. It is stable across compilation sessions.
 ///
 /// Since the ID is a hash value there is a (very small) chance that two crates
 /// end up with the same [StableCrateId]. The compiler will check for such
 /// collisions when loading crates and abort compilation in order to avoid
 /// further trouble.
-#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug, Encodable, Decodable)]
+#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
+#[derive(HashStable_Generic, Encodable, Decodable)]
 pub struct StableCrateId(u64);
 
 impl StableCrateId {
+    pub fn to_u64(self) -> u64 {
+        self.0
+    }
+
     /// Computes the stable ID for a crate with the given name and
-    /// disambiguator.
-    pub fn new(crate_name: &str, crate_disambiguator: CrateDisambiguator) -> StableCrateId {
+    /// `-Cmetadata` arguments.
+    pub fn new(crate_name: &str, is_exe: bool, mut metadata: Vec<String>) -> StableCrateId {
         use std::hash::Hash;
+        use std::hash::Hasher;
 
         let mut hasher = StableHasher::new();
         crate_name.hash(&mut hasher);
-        crate_disambiguator.hash(&mut hasher);
+
+        // We don't want the stable crate id to dependent on the order
+        // -C metadata arguments, so sort them:
+        metadata.sort();
+        // Every distinct -C metadata value is only incorporated once:
+        metadata.dedup();
+
+        hasher.write(b"metadata");
+        for s in &metadata {
+            // Also incorporate the length of a metadata string, so that we generate
+            // different values for `-Cmetadata=ab -Cmetadata=c` and
+            // `-Cmetadata=a -Cmetadata=bc`
+            hasher.write_usize(s.len());
+            hasher.write(s.as_bytes());
+        }
+
+        // Also incorporate crate type, so that we don't get symbol conflicts when
+        // linking against a library of the same name, if this is an executable.
+        hasher.write(if is_exe { b"exe" } else { b"lib" });
+
         StableCrateId(hasher.finish())
     }
 }

compiler/rustc_span/src/lib.rs

@@ -45,8 +45,6 @@ pub mod lev_distance;
 mod span_encoding;
 pub use span_encoding::{Span, DUMMY_SP};
 
-pub mod crate_disambiguator;
-
 pub mod symbol;
 pub use symbol::{sym, Symbol};