Remove special-cased stable hashing for HIR module

compiler/rustc_hir/src/hir.rs

@@ -2484,7 +2484,7 @@ impl FnRetTy<'_> {
     }
 }
 
-#[derive(Encodable, Debug)]
+#[derive(Encodable, Debug, HashStable_Generic)]
 pub struct Mod<'hir> {
     /// A span from the first token past `{` to the last token until `}`.
     /// For `mod foo;`, the inner span ranges from the first token

compiler/rustc_hir/src/stable_hash_impls.rs

@@ -2,7 +2,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHas
 
 use crate::hir::{
     AttributeMap, BodyId, Crate, Expr, ForeignItem, ForeignItemId, ImplItem, ImplItemId, Item,
-    ItemId, Mod, OwnerNodes, TraitCandidate, TraitItem, TraitItemId, Ty, VisibilityKind,
+    ItemId, OwnerNodes, TraitCandidate, TraitItem, TraitItemId, Ty, VisibilityKind,
 };
 use crate::hir_id::{HirId, ItemLocalId};
 use rustc_span::def_id::DefPathHash;
@@ -16,7 +16,6 @@ pub trait HashStableContext:
     fn hash_hir_id(&mut self, _: HirId, hasher: &mut StableHasher);
     fn hash_body_id(&mut self, _: BodyId, hasher: &mut StableHasher);
     fn hash_reference_to_item(&mut self, _: HirId, hasher: &mut StableHasher);
-    fn hash_hir_mod(&mut self, _: &Mod<'_>, hasher: &mut StableHasher);
     fn hash_hir_expr(&mut self, _: &Expr<'_>, hasher: &mut StableHasher);
     fn hash_hir_ty(&mut self, _: &Ty<'_>, hasher: &mut StableHasher);
     fn hash_hir_visibility_kind(&mut self, _: &VisibilityKind<'_>, hasher: &mut StableHasher);
@@ -132,12 +131,6 @@ impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for TraitItemId {
     }
 }
 
-impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Mod<'_> {
-    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
-        hcx.hash_hir_mod(self, hasher)
-    }
-}
-
 impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Expr<'_> {
     fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
         hcx.hash_hir_expr(self, hasher)

compiler/rustc_query_system/src/ich/impls_hir.rs

@@ -3,8 +3,7 @@
 
 use crate::ich::hcx::BodyResolver;
 use crate::ich::{NodeIdHashingMode, StableHashingContext};
-use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hir as hir;
 use std::mem;
 
@@ -47,28 +46,6 @@ impl<'ctx> rustc_hir::HashStableContext for StableHashingContext<'ctx> {
         })
     }
 
-    #[inline]
-    fn hash_hir_mod(&mut self, module: &hir::Mod<'_>, hasher: &mut StableHasher) {
-        let hcx = self;
-        let hir::Mod { inner: ref inner_span, ref item_ids } = *module;
-
-        inner_span.hash_stable(hcx, hasher);
-
-        // Combining the `DefPathHash`s directly is faster than feeding them
-        // into the hasher. Because we use a commutative combine, we also don't
-        // have to sort the array.
-        let item_ids_hash = item_ids
-            .iter()
-            .map(|id| {
-                let def_path_hash = id.to_stable_hash_key(hcx);
-                def_path_hash.0
-            })
-            .fold(Fingerprint::ZERO, |a, b| a.combine_commutative(b));
-
-        item_ids.len().hash_stable(hcx, hasher);
-        item_ids_hash.hash_stable(hcx, hasher);
-    }
-
     fn hash_hir_expr(&mut self, expr: &hir::Expr<'_>, hasher: &mut StableHasher) {
         self.while_hashing_hir_bodies(true, |hcx| {
             let hir::Expr { hir_id: _, ref span, ref kind } = *expr;

src/test/incremental/hash-module-order.rs

@@ -0,0 +1,28 @@
+// revisions: rpass1 rpass2
+// compile-flags: -Z incremental-ignore-spans -Z query-dep-graph
+
+// Tests that module hashing depends on the order of the items
+// (since the order is exposed through `Mod.item_ids`).
+// Changing the order of items (while keeping `Span`s the same)
+// should still result in `hir_owner` being invalidated.
+// Note that it's possible to keep the spans unchanged using
+// a proc-macro (e.g. producing the module via `quote!`)
+// but we use `-Z incremental-ignore-spans` for simplicity
+
+#![feature(rustc_attrs)]
+
+#[cfg(rpass1)]
+#[rustc_clean(cfg="rpass1",except="hir_owner")]
+mod foo {
+    struct First;
+    struct Second;
+}
+
+#[cfg(rpass2)]
+#[rustc_clean(cfg="rpass2",except="hir_owner")]
+mod foo {
+    struct Second;
+    struct First;
+}
+
+fn main() {}