actually test always_zero hasher

.forgejo/workflows/test.yml

@@ -59,3 +59,4 @@ jobs:
       - run: cargo build --tests --features=unstable-doc
       - run: cargo test --doc --features=unstable-doc
       - run: cargo doc --features=unstable-doc
+      - run: FAYALITE_TEST_HASHER=always_zero cargo test --test=module --features=unstable-doc,unstable-test-hasher

Cargo.lock

@@ -2,18 +2,6 @@
 # It is not intended for manual editing.
 version = 3
 
-[[package]]
-name = "ahash"
-version = "0.8.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "77c3a9648d43b9cd48db467b3f87fdd6e146bcc88ab0180006cef2179fe11d01"
-dependencies = [
- "cfg-if",
- "once_cell",
- "version_check",
- "zerocopy",
-]
-
 [[package]]
 name = "allocator-api2"
 version = "0.2.16"
@@ -365,6 +353,12 @@ version = "0.5.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d674e81391d1e1ab681a28d99df07927c6d4aa5b027d7da16ba32d1d21ecd99"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "funty"
 version = "2.0.0"
@@ -400,12 +394,13 @@ checksum = "d2fabcfbdc87f4758337ca535fb41a6d701b65693ce38287d856d1674551ec9b"
 
 [[package]]
 name = "hashbrown"
-version = "0.14.3"
+version = "0.15.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "290f1a1d9242c78d09ce40a5e87e7554ee637af1351968159f4952f028f75604"
+checksum = "bf151400ff0baff5465007dd2f3e717f3fe502074ca563069ce3a6629d07b289"
 dependencies = [
- "ahash",
  "allocator-api2",
+ "equivalent",
+ "foldhash",
 ]
 
 [[package]]
@@ -431,9 +426,9 @@ checksum = "ce23b50ad8242c51a442f3ff322d56b02f08852c77e4c0b4d3fd684abc89c683"
 
 [[package]]
 name = "indexmap"
-version = "2.5.0"
+version = "2.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "68b900aa2f7301e21c36462b170ee99994de34dff39a4a6a528e80e7376d07e5"
+checksum = "cea70ddb795996207ad57735b50c5982d8844f38ba9ee5f1aedcfb708a2aa11e"
 dependencies = [
  "equivalent",
  "hashbrown",
@@ -524,11 +519,14 @@ dependencies = [
 
 [[package]]
 name = "petgraph"
-version = "0.6.5"
-source = "git+https://github.com/programmerjake/petgraph.git?rev=258ea8071209a924b73fe96f9f87a3b7b45cbc9f#258ea8071209a924b73fe96f9f87a3b7b45cbc9f"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a98c6720655620a521dcc722d0ad66cd8afd5d86e34a89ef691c50b7b24de06"
 dependencies = [
  "fixedbitset",
+ "hashbrown",
  "indexmap",
+ "serde",
 ]
 
 [[package]]
@@ -893,23 +891,3 @@ checksum = "05f360fc0b24296329c78fda852a1e9ae82de9cf7b27dae4b7f62f118f77b9ed"
 dependencies = [
  "tap",
 ]
-
-[[package]]
-name = "zerocopy"
-version = "0.7.32"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "74d4d3961e53fa4c9a25a8637fc2bfaf2595b3d3ae34875568a5cf64787716be"
-dependencies = [
- "zerocopy-derive",
-]
-
-[[package]]
-name = "zerocopy-derive"
-version = "0.7.32"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9ce1b18ccd8e73a9321186f97e46f9f04b778851177567b1975109d26a08d2a6"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn",
-]

Cargo.toml

@@ -23,14 +23,13 @@ blake3 = { version = "1.5.4", features = ["serde"] }
 clap = { version = "4.5.9", features = ["derive", "env", "string"] }
 ctor = "0.2.8"
 eyre = "0.6.12"
-hashbrown = "0.14.3"
+hashbrown = "0.15.2"
 indexmap = { version = "2.5.0", features = ["serde"] }
 jobslot = "0.2.19"
 num-bigint = "0.4.6"
 num-traits = "0.2.16"
 os_pipe = "1.2.1"
-# TODO: switch back to crates.io once petgraph accepts PR #684 and releases a new version
-petgraph = { git = "https://github.com/programmerjake/petgraph.git", rev = "258ea8071209a924b73fe96f9f87a3b7b45cbc9f" }
+petgraph = "0.8.1"
 prettyplease = "0.2.20"
 proc-macro2 = "1.0.83"
 quote = "1.0.36"

crates/fayalite/Cargo.toml

@@ -40,6 +40,7 @@ fayalite-visit-gen.workspace = true
 
 [features]
 unstable-doc = []
+unstable-test-hasher = []
 
 [package.metadata.docs.rs]
 features = ["unstable-doc"]

crates/fayalite/src/bundle.rs

@@ -14,9 +14,9 @@ use crate::{
         impl_match_variant_as_self, CanonicalType, MatchVariantWithoutScope, OpaqueSimValue,
         StaticType, Type, TypeProperties, TypeWithDeref,
     },
+    util::HashMap,
 };
 use bitvec::{slice::BitSlice, vec::BitVec};
-use hashbrown::HashMap;
 use serde::{Deserialize, Serialize};
 use std::{fmt, marker::PhantomData};
 
@@ -160,7 +160,7 @@ impl Default for BundleTypePropertiesBuilder {
 impl Bundle {
     #[track_caller]
     pub fn new(fields: Interned<[BundleField]>) -> Self {
-        let mut name_indexes = HashMap::with_capacity(fields.len());
+        let mut name_indexes = HashMap::with_capacity_and_hasher(fields.len(), Default::default());
         let mut field_offsets = Vec::with_capacity(fields.len());
         let mut type_props_builder = BundleTypePropertiesBuilder::new();
         for (index, &BundleField { name, flipped, ty }) in fields.iter().enumerate() {

crates/fayalite/src/cli.rs

@@ -258,7 +258,7 @@ pub struct VerilogArgs {
         default_value = "firtool",
         env = "FIRTOOL",
         value_hint = ValueHint::CommandName,
-        value_parser = OsStringValueParser::new().try_map(which::which)
+        value_parser = OsStringValueParser::new().try_map(which)
     )]
     pub firtool: PathBuf,
     #[arg(long)]
@@ -428,6 +428,13 @@ impl clap::Args for FormalAdjustArgs {
     }
 }
 
+fn which(v: std::ffi::OsString) -> which::Result<PathBuf> {
+    #[cfg(not(miri))]
+    return which::which(v);
+    #[cfg(miri)]
+    return Ok(Path::new("/").join(v));
+}
+
 #[derive(Parser, Clone)]
 #[non_exhaustive]
 pub struct FormalArgs {
@@ -438,7 +445,7 @@ pub struct FormalArgs {
         default_value = "sby",
         env = "SBY",
         value_hint = ValueHint::CommandName,
-        value_parser = OsStringValueParser::new().try_map(which::which)
+        value_parser = OsStringValueParser::new().try_map(which)
     )]
     pub sby: PathBuf,
     #[arg(long)]

crates/fayalite/src/enum_.rs

@@ -19,9 +19,9 @@ use crate::{
         CanonicalType, MatchVariantAndInactiveScope, OpaqueSimValue, StaticType, Type,
         TypeProperties,
     },
+    util::HashMap,
 };
 use bitvec::{order::Lsb0, slice::BitSlice, view::BitView};
-use hashbrown::HashMap;
 use serde::{Deserialize, Serialize};
 use std::{convert::Infallible, fmt, iter::FusedIterator, sync::Arc};
 
@@ -193,7 +193,8 @@ impl Default for EnumTypePropertiesBuilder {
 impl Enum {
     #[track_caller]
     pub fn new(variants: Interned<[EnumVariant]>) -> Self {
-        let mut name_indexes = HashMap::with_capacity(variants.len());
+        let mut name_indexes =
+            HashMap::with_capacity_and_hasher(variants.len(), Default::default());
         let mut type_props_builder = EnumTypePropertiesBuilder::new();
         for (index, EnumVariant { name, ty }) in variants.iter().enumerate() {
             if let Some(old_index) = name_indexes.insert(*name, index) {

crates/fayalite/src/expr.rs

@@ -274,6 +274,17 @@ pub struct Expr<T: Type> {
 
 impl<T: Type + fmt::Debug> fmt::Debug for Expr<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        #[cfg(debug_assertions)]
+        {
+            let Self {
+                __enum,
+                __ty,
+                __flow,
+            } = self;
+            let expr_ty = __ty.canonical();
+            let enum_ty = __enum.to_expr().__ty;
+            assert_eq!(expr_ty, enum_ty, "expr ty mismatch:\nExpr {{\n__enum: {__enum:?},\n__ty: {__ty:?},\n__flow: {__flow:?}\n}}");
+        }
         self.__enum.fmt(f)
     }
 }

crates/fayalite/src/firrtl.rs

@@ -36,12 +36,11 @@ use crate::{
     ty::{CanonicalType, Type},
     util::{
         const_str_array_is_strictly_ascending, BitSliceWriteWithBase, DebugAsRawString,
-        GenericConstBool,
+        GenericConstBool, HashMap, HashSet,
     },
 };
 use bitvec::slice::BitSlice;
 use clap::value_parser;
-use hashbrown::{HashMap, HashSet};
 use num_traits::Signed;
 use serde::Serialize;
 use std::{
@@ -2622,7 +2621,7 @@ fn export_impl(
             indent_depth: &indent_depth,
             indent: "    ",
         },
-        seen_modules: HashSet::new(),
+        seen_modules: HashSet::default(),
         unwritten_modules: VecDeque::new(),
         global_ns,
         module: ModuleState::default(),

crates/fayalite/src/intern.rs

@@ -1,9 +1,9 @@
 // SPDX-License-Identifier: LGPL-3.0-or-later
 // See Notices.txt for copyright information
 #![allow(clippy::type_complexity)]
-use crate::intern::type_map::TypeIdMap;
+use crate::{intern::type_map::TypeIdMap, util::DefaultBuildHasher};
 use bitvec::{ptr::BitPtr, slice::BitSlice, vec::BitVec};
-use hashbrown::{hash_map::RawEntryMut, HashMap, HashTable};
+use hashbrown::HashTable;
 use serde::{Deserialize, Serialize};
 use std::{
     any::{Any, TypeId},
@@ -17,7 +17,7 @@ use std::{
     sync::{Mutex, RwLock},
 };
 
-pub mod type_map;
+mod type_map;
 
 pub trait LazyInternedTrait<T: ?Sized + Send + Sync + 'static>: Send + Sync + Any {
     fn get(&self) -> Interned<T>;
@@ -316,8 +316,13 @@ pub trait Intern: Any + Send + Sync {
     }
 }
 
+struct InternerState<T: ?Sized + 'static + Send + Sync> {
+    table: HashTable<&'static T>,
+    hasher: DefaultBuildHasher,
+}
+
 pub struct Interner<T: ?Sized + 'static + Send + Sync> {
-    map: Mutex<HashMap<&'static T, ()>>,
+    state: Mutex<InternerState<T>>,
 }
 
 impl<T: ?Sized + 'static + Send + Sync> Interner<T> {
@@ -330,7 +335,10 @@ impl<T: ?Sized + 'static + Send + Sync> Interner<T> {
 impl<T: ?Sized + 'static + Send + Sync> Default for Interner<T> {
     fn default() -> Self {
         Self {
-            map: Default::default(),
+            state: Mutex::new(InternerState {
+                table: HashTable::new(),
+                hasher: Default::default(),
+            }),
         }
     }
 }
@@ -341,17 +349,16 @@ impl<T: ?Sized + 'static + Send + Sync + Hash + Eq + ToOwned> Interner<T> {
         alloc: F,
         value: Cow<'_, T>,
     ) -> Interned<T> {
-        let mut map = self.map.lock().unwrap();
-        let hasher = map.hasher().clone();
-        let hash = hasher.hash_one(&*value);
-        let inner = match map.raw_entry_mut().from_hash(hash, |k| **k == *value) {
-            RawEntryMut::Occupied(entry) => *entry.key(),
-            RawEntryMut::Vacant(entry) => {
-                *entry
-                    .insert_with_hasher(hash, alloc(value), (), |k| hasher.hash_one(&**k))
-                    .0
-            }
-        };
+        let mut state = self.state.lock().unwrap();
+        let InternerState { table, hasher } = &mut *state;
+        let inner = *table
+            .entry(
+                hasher.hash_one(&*value),
+                |k| **k == *value,
+                |k| hasher.hash_one(&**k),
+            )
+            .or_insert_with(|| alloc(value))
+            .get();
         Interned { inner }
     }
 }
@@ -742,7 +749,7 @@ pub trait MemoizeGeneric: 'static + Send + Sync + Hash + Eq + Copy {
     fn get_cow(self, input: Self::InputCow<'_>) -> Self::Output {
         static TYPE_ID_MAP: TypeIdMap = TypeIdMap::new();
         let map: &RwLock<(
-            hashbrown::hash_map::DefaultHashBuilder,
+            DefaultBuildHasher,
             HashTable<(Self, Self::InputOwned, Self::Output)>,
         )> = TYPE_ID_MAP.get_or_insert_default();
         fn hash_eq_key<'a, 'b, T: MemoizeGeneric>(

crates/fayalite/src/module.rs

@@ -24,10 +24,10 @@ use crate::{
     sim::{ExternModuleSimGenerator, ExternModuleSimulation},
     source_location::SourceLocation,
     ty::{CanonicalType, Type},
-    util::ScopedRef,
+    util::{HashMap, HashSet, ScopedRef},
     wire::{IncompleteWire, Wire},
 };
-use hashbrown::{hash_map::Entry, HashMap, HashSet};
+use hashbrown::hash_map::Entry;
 use num_bigint::BigInt;
 use std::{
     cell::RefCell,
@@ -1498,7 +1498,7 @@ impl TargetState {
                         .collect(),
                 },
                 CanonicalType::PhantomConst(_) => TargetStateInner::Decomposed {
-                    subtargets: HashMap::new(),
+                    subtargets: HashMap::default(),
                 },
                 CanonicalType::Array(ty) => TargetStateInner::Decomposed {
                     subtargets: (0..ty.len())
@@ -1864,7 +1864,7 @@ impl<T: BundleType> Module<T> {
         AssertValidityState {
             module: self.canonical(),
             blocks: vec![],
-            target_states: HashMap::with_capacity(64),
+            target_states: HashMap::with_capacity_and_hasher(64, Default::default()),
         }
         .assert_validity();
     }
@@ -2125,8 +2125,8 @@ impl ModuleBuilder {
                         incomplete_declarations: vec![],
                         stmts: vec![],
                     }],
-                    annotations_map: HashMap::new(),
-                    memory_map: HashMap::new(),
+                    annotations_map: HashMap::default(),
+                    memory_map: HashMap::default(),
                 },
             }),
         };
@@ -2136,7 +2136,7 @@ impl ModuleBuilder {
             impl_: RefCell::new(ModuleBuilderImpl {
                 body,
                 io: vec![],
-                io_indexes: HashMap::new(),
+                io_indexes: HashMap::default(),
                 module_annotations: vec![],
             }),
         };

crates/fayalite/src/module/transform/deduce_resets.rs

@@ -24,8 +24,9 @@ use crate::{
     },
     prelude::*,
     reset::{ResetType, ResetTypeDispatch},
+    util::{HashMap, HashSet},
 };
-use hashbrown::{hash_map::Entry, HashMap, HashSet};
+use hashbrown::hash_map::Entry;
 use num_bigint::BigInt;
 use petgraph::unionfind::UnionFind;
 use std::{fmt, marker::PhantomData};
@@ -2251,9 +2252,9 @@ pub fn deduce_resets(
     fallback_to_sync_reset: bool,
 ) -> Result<Interned<Module<Bundle>>, DeduceResetsError> {
     let mut state = State {
-        modules_added_to_graph: HashSet::new(),
-        substituted_modules: HashMap::new(),
-        expr_resets: HashMap::new(),
+        modules_added_to_graph: HashSet::default(),
+        substituted_modules: HashMap::default(),
+        expr_resets: HashMap::default(),
         reset_graph: ResetGraph::default(),
         fallback_to_sync_reset,
     };

crates/fayalite/src/module/transform/simplify_enums.rs

@@ -18,10 +18,10 @@ use crate::{
     },
     source_location::SourceLocation,
     ty::{CanonicalType, Type},
+    util::HashMap,
     wire::Wire,
 };
 use core::fmt;
-use hashbrown::HashMap;
 
 #[derive(Debug)]
 pub enum SimplifyEnumsError {
@@ -965,8 +965,8 @@ pub fn simplify_enums(
     kind: SimplifyEnumsKind,
 ) -> Result<Interned<Module<Bundle>>, SimplifyEnumsError> {
     module.fold(&mut State {
-        enum_types: HashMap::new(),
-        replacement_mem_ports: HashMap::new(),
+        enum_types: HashMap::default(),
+        replacement_mem_ports: HashMap::default(),
         kind,
         module_state_stack: vec![],
     })

crates/fayalite/src/module/transform/simplify_memories.rs

@@ -14,11 +14,10 @@ use crate::{
     },
     source_location::SourceLocation,
     ty::{CanonicalType, Type},
-    util::MakeMutSlice,
+    util::{HashMap, MakeMutSlice},
     wire::Wire,
 };
 use bitvec::{slice::BitSlice, vec::BitVec};
-use hashbrown::HashMap;
 use std::{
     convert::Infallible,
     fmt::Write,
@@ -897,7 +896,7 @@ impl Folder for State {
             module,
             ModuleState {
                 output_module: None,
-                memories: HashMap::new(),
+                memories: HashMap::default(),
             },
         );
         let mut this = PushedState::push_module(self, module);

crates/fayalite/src/sim.rs

@@ -41,10 +41,9 @@ use crate::{
         value::SimValue,
     },
     ty::StaticType,
-    util::{BitSliceWriteWithBase, DebugAsDisplay},
+    util::{BitSliceWriteWithBase, DebugAsDisplay, HashMap, HashSet},
 };
 use bitvec::{bits, order::Lsb0, slice::BitSlice, vec::BitVec, view::BitView};
-use hashbrown::{HashMap, HashSet};
 use num_bigint::BigInt;
 use num_traits::{Signed, Zero};
 use petgraph::{
@@ -580,8 +579,9 @@ impl Assignments {
             big_slots,
         }) = self.slot_readers();
         AssignmentsElements {
-            node_indexes: HashMap::with_capacity(
+            node_indexes: HashMap::with_capacity_and_hasher(
                 self.assignments().len() + small_slots.len() + big_slots.len(),
+                Default::default(),
             ),
             nodes: self.node_references(),
             edges: self.edge_references(),
@@ -1022,6 +1022,16 @@ impl VisitMap<AssignmentOrSlotIndex> for AssignmentsVisitMap {
             AssignmentOrSlotIndex::BigSlot(slot) => self.slots.contains(slot),
         }
     }
+
+    fn unvisit(&mut self, n: AssignmentOrSlotIndex) -> bool {
+        match n {
+            AssignmentOrSlotIndex::AssignmentIndex(assignment_index) => {
+                mem::replace(&mut self.assignments[assignment_index], false)
+            }
+            AssignmentOrSlotIndex::SmallSlot(slot) => self.slots.remove(slot),
+            AssignmentOrSlotIndex::BigSlot(slot) => self.slots.remove(slot),
+        }
+    }
 }
 
 impl Visitable for Assignments {
@@ -1676,18 +1686,18 @@ impl Compiler {
             insns: Insns::new(),
             original_base_module,
             base_module,
-            modules: HashMap::new(),
+            modules: HashMap::default(),
             extern_modules: Vec::new(),
-            compiled_values: HashMap::new(),
-            compiled_exprs: HashMap::new(),
-            compiled_exprs_to_values: HashMap::new(),
-            decl_conditions: HashMap::new(),
-            compiled_values_to_dyn_array_indexes: HashMap::new(),
-            compiled_value_bool_dest_is_small_map: HashMap::new(),
+            compiled_values: HashMap::default(),
+            compiled_exprs: HashMap::default(),
+            compiled_exprs_to_values: HashMap::default(),
+            decl_conditions: HashMap::default(),
+            compiled_values_to_dyn_array_indexes: HashMap::default(),
+            compiled_value_bool_dest_is_small_map: HashMap::default(),
             assignments: Assignments::default(),
             clock_triggers: Vec::new(),
-            compiled_value_to_clock_trigger_map: HashMap::new(),
-            enum_discriminants: HashMap::new(),
+            compiled_value_to_clock_trigger_map: HashMap::default(),
+            enum_discriminants: HashMap::default(),
             registers: Vec::new(),
             traces: SimTraces(Vec::new()),
             memories: Vec::new(),
@@ -5976,8 +5986,8 @@ impl SimulationModuleState {
     fn new(base_targets: impl IntoIterator<Item = (Target, CompiledValue<CanonicalType>)>) -> Self {
         let mut retval = Self {
             base_targets: Vec::new(),
-            uninitialized_ios: HashMap::new(),
-            io_targets: HashMap::new(),
+            uninitialized_ios: HashMap::default(),
+            io_targets: HashMap::default(),
             did_initial_settle: false,
         };
         for (base_target, value) in base_targets {
@@ -6207,7 +6217,7 @@ impl Default for EarliestWaitTargets {
         Self {
             settle: false,
             instant: None,
-            changes: HashMap::new(),
+            changes: HashMap::default(),
         }
     }
 }
@@ -6217,14 +6227,14 @@ impl EarliestWaitTargets {
         Self {
             settle: true,
             instant: None,
-            changes: HashMap::new(),
+            changes: HashMap::default(),
         }
     }
     fn instant(instant: SimInstant) -> Self {
         Self {
             settle: false,
             instant: Some(instant),
-            changes: HashMap::new(),
+            changes: HashMap::default(),
         }
     }
     fn len(&self) -> usize {

crates/fayalite/src/sim/interpreter.rs

@@ -7,10 +7,9 @@ use crate::{
     intern::{Intern, Interned, Memoize},
     source_location::SourceLocation,
     ty::CanonicalType,
-    util::get_many_mut,
+    util::{get_many_mut, HashMap, HashSet},
 };
 use bitvec::{boxed::BitBox, slice::BitSlice};
-use hashbrown::{HashMap, HashSet};
 use num_bigint::BigInt;
 use num_traits::{One, Signed, ToPrimitive, Zero};
 use std::{

crates/fayalite/src/sim/vcd.rs

@@ -14,9 +14,10 @@ use crate::{
         TraceModuleIO, TraceReg, TraceSInt, TraceScalar, TraceScalarId, TraceScope, TraceSyncReset,
         TraceUInt, TraceWire, TraceWriter, TraceWriterDecls,
     },
+    util::HashMap,
 };
 use bitvec::{order::Lsb0, slice::BitSlice};
-use hashbrown::{hash_map::Entry, HashMap};
+use hashbrown::hash_map::Entry;
 use std::{
     fmt::{self, Write as _},
     io, mem,

crates/fayalite/src/source_location.rs

@@ -2,9 +2,8 @@
 // See Notices.txt for copyright information
 use crate::{
     intern::{Intern, Interned},
-    util::DebugAsDisplay,
+    util::{DebugAsDisplay, HashMap},
 };
-use hashbrown::HashMap;
 use std::{cell::RefCell, fmt, num::NonZeroUsize, panic, path::Path};
 
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -97,7 +96,7 @@ impl NormalizeFilesForTestsState {
     fn new() -> Self {
         Self {
             test_position: panic::Location::caller(),
-            file_pattern_matches: HashMap::new(),
+            file_pattern_matches: HashMap::default(),
         }
     }
 }
@@ -143,7 +142,7 @@ impl From<&'_ panic::Location<'_>> for SourceLocation {
                         map.entry_ref(file)
                             .or_insert_with(|| NormalizedFileForTestState {
                                 file_name_id: NonZeroUsize::new(len + 1).unwrap(),
-                                positions_map: HashMap::new(),
+                                positions_map: HashMap::default(),
                             });
                     file_str = m.generate_file_name(file_state.file_name_id);
                     file = &file_str;

crates/fayalite/src/testing.rs

@@ -3,9 +3,9 @@
 use crate::{
     cli::{FormalArgs, FormalMode, FormalOutput, RunPhase},
     firrtl::ExportOptions,
+    util::HashMap,
 };
 use clap::Parser;
-use hashbrown::HashMap;
 use serde::Deserialize;
 use std::{
     fmt::Write,
@@ -87,7 +87,7 @@ fn get_assert_formal_target_path(test_name: &dyn std::fmt::Display) -> PathBuf {
     let index = *DIRS
         .lock()
         .unwrap()
-        .get_or_insert_with(HashMap::new)
+        .get_or_insert_with(HashMap::default)
         .entry_ref(&dir)
         .and_modify(|v| *v += 1)
         .or_insert(0);

crates/fayalite/src/util.rs

@@ -8,6 +8,16 @@ mod const_usize;
 mod misc;
 mod scoped_ref;
 pub(crate) mod streaming_read_utf8;
+mod test_hasher;
+
+// allow easily switching the hasher crate-wide for testing
+#[cfg(feature = "unstable-test-hasher")]
+pub type DefaultBuildHasher = test_hasher::DefaultBuildHasher;
+#[cfg(not(feature = "unstable-test-hasher"))]
+pub(crate) type DefaultBuildHasher = hashbrown::DefaultHashBuilder;
+
+pub(crate) type HashMap<K, V> = hashbrown::HashMap<K, V, DefaultBuildHasher>;
+pub(crate) type HashSet<T> = hashbrown::HashSet<T, DefaultBuildHasher>;
 
 #[doc(inline)]
 pub use const_bool::{ConstBool, ConstBoolDispatch, ConstBoolDispatchTag, GenericConstBool};

crates/fayalite/src/util/test_hasher.rs

@@ -0,0 +1,240 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+#![cfg(feature = "unstable-test-hasher")]
+
+use std::{
+    fmt::Write as _,
+    hash::{BuildHasher, Hash, Hasher},
+    io::Write as _,
+    marker::PhantomData,
+    sync::LazyLock,
+};
+
+type BoxDynHasher = Box<dyn Hasher + Send + Sync>;
+type BoxDynBuildHasher = Box<dyn DynBuildHasherTrait + Send + Sync>;
+type BoxDynMakeBuildHasher = Box<dyn Fn() -> BoxDynBuildHasher + Send + Sync>;
+
+trait TryGetDynBuildHasher: Copy {
+    type Type;
+    fn try_get_make_build_hasher(self) -> Option<BoxDynMakeBuildHasher>;
+}
+
+impl<T> TryGetDynBuildHasher for PhantomData<T> {
+    type Type = T;
+    fn try_get_make_build_hasher(self) -> Option<BoxDynMakeBuildHasher> {
+        None
+    }
+}
+
+impl<T: Default + BuildHasher<Hasher: Send + Sync + 'static> + Send + Sync + 'static + Clone>
+    TryGetDynBuildHasher for &'_ PhantomData<T>
+{
+    type Type = T;
+    fn try_get_make_build_hasher(self) -> Option<BoxDynMakeBuildHasher> {
+        Some(Box::new(|| Box::<DynBuildHasher<T>>::default()))
+    }
+}
+
+#[derive(Default, Clone)]
+struct DynBuildHasher<T>(T);
+
+trait DynBuildHasherTrait: BuildHasher<Hasher = BoxDynHasher> {
+    fn clone_dyn_build_hasher(&self) -> BoxDynBuildHasher;
+}
+
+impl<BH: BuildHasher<Hasher: Send + Sync + 'static>> BuildHasher for DynBuildHasher<BH> {
+    type Hasher = BoxDynHasher;
+
+    fn build_hasher(&self) -> Self::Hasher {
+        Box::new(self.0.build_hasher())
+    }
+
+    fn hash_one<T: Hash>(&self, x: T) -> u64 {
+        self.0.hash_one(x)
+    }
+}
+
+impl<BH> DynBuildHasherTrait for DynBuildHasher<BH>
+where
+    Self: Clone + BuildHasher<Hasher = BoxDynHasher> + Send + Sync + 'static,
+{
+    fn clone_dyn_build_hasher(&self) -> BoxDynBuildHasher {
+        Box::new(self.clone())
+    }
+}
+
+pub struct DefaultBuildHasher(BoxDynBuildHasher);
+
+impl Clone for DefaultBuildHasher {
+    fn clone(&self) -> Self {
+        DefaultBuildHasher(self.0.clone_dyn_build_hasher())
+    }
+}
+
+const ENV_VAR_NAME: &'static str = "FAYALITE_TEST_HASHER";
+
+struct EnvVarValue {
+    key: &'static str,
+    try_get_make_build_hasher: fn() -> Option<BoxDynMakeBuildHasher>,
+    description: &'static str,
+}
+
+macro_rules! env_var_value {
+    (
+        key: $key:literal,
+        build_hasher: $build_hasher:ty,
+        description: $description:literal,
+    ) => {
+        EnvVarValue {
+            key: $key,
+            try_get_make_build_hasher: || {
+                // use rust method resolution to detect if $build_hasher is usable
+                // (e.g. hashbrown's hasher won't be usable without the right feature enabled)
+                (&PhantomData::<DynBuildHasher<$build_hasher>>).try_get_make_build_hasher()
+            },
+            description: $description,
+        }
+    };
+}
+
+#[derive(Default)]
+struct AlwaysZeroHasher;
+
+impl Hasher for AlwaysZeroHasher {
+    fn write(&mut self, _bytes: &[u8]) {}
+    fn finish(&self) -> u64 {
+        0
+    }
+}
+
+const ENV_VAR_VALUES: &'static [EnvVarValue] = &[
+    env_var_value! {
+        key: "std",
+        build_hasher: std::hash::RandomState,
+        description: "use std::hash::RandomState",
+    },
+    env_var_value! {
+        key: "hashbrown",
+        build_hasher: hashbrown::DefaultHashBuilder,
+        description: "use hashbrown's DefaultHashBuilder",
+    },
+    env_var_value! {
+        key: "always_zero",
+        build_hasher: std::hash::BuildHasherDefault<AlwaysZeroHasher>,
+        description: "use a hasher that always returns 0 for all hashes,\n    \
+        this is useful for checking that PartialEq impls are correct",
+    },
+];
+
+fn report_bad_env_var(msg: impl std::fmt::Display) -> ! {
+    let mut msg = format!("{ENV_VAR_NAME}: {msg}\n");
+    for &EnvVarValue {
+        key,
+        try_get_make_build_hasher,
+        description,
+    } in ENV_VAR_VALUES
+    {
+        let availability = match try_get_make_build_hasher() {
+            Some(_) => "available",
+            None => "unavailable",
+        };
+        writeln!(msg, "{key}: ({availability})\n    {description}").expect("can't fail");
+    }
+    std::io::stderr()
+        .write_all(msg.as_bytes())
+        .expect("should be able to write to stderr");
+    std::process::abort();
+}
+
+impl Default for DefaultBuildHasher {
+    fn default() -> Self {
+        static DEFAULT_FN: LazyLock<BoxDynMakeBuildHasher> = LazyLock::new(|| {
+            let var = std::env::var_os(ENV_VAR_NAME);
+            let var = var.as_deref().unwrap_or("std".as_ref());
+            for &EnvVarValue {
+                key,
+                try_get_make_build_hasher,
+                description: _,
+            } in ENV_VAR_VALUES
+            {
+                if var.as_encoded_bytes().eq_ignore_ascii_case(key.as_bytes()) {
+                    return try_get_make_build_hasher().unwrap_or_else(|| {
+                        report_bad_env_var(format_args!(
+                            "unavailable hasher: {key} (is the appropriate feature enabled?)"
+                        ));
+                    });
+                }
+            }
+            report_bad_env_var(format_args!("unrecognized hasher: {var:?}"));
+        });
+        Self(DEFAULT_FN())
+    }
+}
+
+pub struct DefaultHasher(BoxDynHasher);
+
+impl BuildHasher for DefaultBuildHasher {
+    type Hasher = DefaultHasher;
+
+    fn build_hasher(&self) -> Self::Hasher {
+        DefaultHasher(self.0.build_hasher())
+    }
+}
+
+impl Hasher for DefaultHasher {
+    fn finish(&self) -> u64 {
+        self.0.finish()
+    }
+
+    fn write(&mut self, bytes: &[u8]) {
+        self.0.write(bytes)
+    }
+
+    fn write_u8(&mut self, i: u8) {
+        self.0.write_u8(i)
+    }
+
+    fn write_u16(&mut self, i: u16) {
+        self.0.write_u16(i)
+    }
+
+    fn write_u32(&mut self, i: u32) {
+        self.0.write_u32(i)
+    }
+
+    fn write_u64(&mut self, i: u64) {
+        self.0.write_u64(i)
+    }
+
+    fn write_u128(&mut self, i: u128) {
+        self.0.write_u128(i)
+    }
+
+    fn write_usize(&mut self, i: usize) {
+        self.0.write_usize(i)
+    }
+
+    fn write_i8(&mut self, i: i8) {
+        self.0.write_i8(i)
+    }
+
+    fn write_i16(&mut self, i: i16) {
+        self.0.write_i16(i)
+    }
+
+    fn write_i32(&mut self, i: i32) {
+        self.0.write_i32(i)
+    }
+
+    fn write_i64(&mut self, i: i64) {
+        self.0.write_i64(i)
+    }
+
+    fn write_i128(&mut self, i: i128) {
+        self.0.write_i128(i)
+    }
+
+    fn write_isize(&mut self, i: isize) {
+        self.0.write_isize(i)
+    }
+}

crates/fayalite/tests/ui/simvalue_is_not_internable.rs

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+
+//! check that SimValue can't be interned, since equality may ignore types
+
+use fayalite::{
+    intern::{Intern, Interned},
+    sim::value::SimValue,
+};
+
+fn f(v: SimValue<()>) -> Interned<SimValue<()>> {
+    Intern::intern_sized(v)
+}
+
+fn main() {}

crates/fayalite/tests/ui/simvalue_is_not_internable.stderr

@@ -0,0 +1,178 @@
+error[E0277]: `Cell<util::alternating_cell::State>` cannot be shared between threads safely
+  --> tests/ui/simvalue_is_not_internable.rs:11:26
+   |
+11 | fn f(v: SimValue<()>) -> Interned<SimValue<()>> {
+   |                          ^^^^^^^^^^^^^^^^^^^^^^ `Cell<util::alternating_cell::State>` cannot be shared between threads safely
+   |
+   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`, which is required by `SimValue<()>: Sync`
+   = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`
+note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
+  --> src/util/alternating_cell.rs
+   |
+   | pub(crate) struct AlternatingCell<T: ?Sized> {
+   |                   ^^^^^^^^^^^^^^^
+note: required because it appears within the type `SimValue<()>`
+  --> src/sim/value.rs
+   |
+   | pub struct SimValue<T: Type> {
+   |            ^^^^^^^^
+note: required by a bound in `fayalite::intern::Interned`
+  --> src/intern.rs
+   |
+   | pub struct Interned<T: ?Sized + 'static + Send + Sync> {
+   |                                                  ^^^^ required by this bound in `Interned`
+
+error[E0277]: `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
+  --> tests/ui/simvalue_is_not_internable.rs:11:26
+   |
+11 | fn f(v: SimValue<()>) -> Interned<SimValue<()>> {
+   |                          ^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
+   |
+   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`, which is required by `SimValue<()>: Sync`
+note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
+  --> src/util/alternating_cell.rs
+   |
+   | pub(crate) struct AlternatingCell<T: ?Sized> {
+   |                   ^^^^^^^^^^^^^^^
+note: required because it appears within the type `SimValue<()>`
+  --> src/sim/value.rs
+   |
+   | pub struct SimValue<T: Type> {
+   |            ^^^^^^^^
+note: required by a bound in `fayalite::intern::Interned`
+  --> src/intern.rs
+   |
+   | pub struct Interned<T: ?Sized + 'static + Send + Sync> {
+   |                                                  ^^^^ required by this bound in `Interned`
+
+error[E0277]: the trait bound `SimValue<()>: Intern` is not satisfied
+  --> tests/ui/simvalue_is_not_internable.rs:12:26
+   |
+12 |     Intern::intern_sized(v)
+   |     -------------------- ^ the trait `Hash` is not implemented for `SimValue<()>`, which is required by `SimValue<()>: Intern`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `Intern`:
+             BitSlice
+             [T]
+             str
+   = note: required for `SimValue<()>` to implement `Intern`
+
+error[E0277]: the trait bound `SimValue<()>: Intern` is not satisfied
+  --> tests/ui/simvalue_is_not_internable.rs:12:26
+   |
+12 |     Intern::intern_sized(v)
+   |     -------------------- ^ the trait `std::cmp::Eq` is not implemented for `SimValue<()>`, which is required by `SimValue<()>: Intern`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `Intern`:
+             BitSlice
+             [T]
+             str
+   = note: required for `SimValue<()>` to implement `Intern`
+
+error[E0277]: `Cell<util::alternating_cell::State>` cannot be shared between threads safely
+  --> tests/ui/simvalue_is_not_internable.rs:12:26
+   |
+12 |     Intern::intern_sized(v)
+   |     -------------------- ^ `Cell<util::alternating_cell::State>` cannot be shared between threads safely
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`, which is required by `SimValue<()>: Sync`
+   = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`
+note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
+  --> src/util/alternating_cell.rs
+   |
+   | pub(crate) struct AlternatingCell<T: ?Sized> {
+   |                   ^^^^^^^^^^^^^^^
+note: required because it appears within the type `SimValue<()>`
+  --> src/sim/value.rs
+   |
+   | pub struct SimValue<T: Type> {
+   |            ^^^^^^^^
+note: required by a bound in `intern_sized`
+  --> src/intern.rs
+   |
+   | pub trait Intern: Any + Send + Sync {
+   |                                ^^^^ required by this bound in `Intern::intern_sized`
+   |     fn intern(&self) -> Interned<Self>;
+   |     fn intern_sized(self) -> Interned<Self>
+   |        ------------ required by a bound in this associated function
+
+error[E0277]: `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
+  --> tests/ui/simvalue_is_not_internable.rs:12:26
+   |
+12 |     Intern::intern_sized(v)
+   |     -------------------- ^ `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`, which is required by `SimValue<()>: Sync`
+note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
+  --> src/util/alternating_cell.rs
+   |
+   | pub(crate) struct AlternatingCell<T: ?Sized> {
+   |                   ^^^^^^^^^^^^^^^
+note: required because it appears within the type `SimValue<()>`
+  --> src/sim/value.rs
+   |
+   | pub struct SimValue<T: Type> {
+   |            ^^^^^^^^
+note: required by a bound in `intern_sized`
+  --> src/intern.rs
+   |
+   | pub trait Intern: Any + Send + Sync {
+   |                                ^^^^ required by this bound in `Intern::intern_sized`
+   |     fn intern(&self) -> Interned<Self>;
+   |     fn intern_sized(self) -> Interned<Self>
+   |        ------------ required by a bound in this associated function
+
+error[E0277]: `Cell<util::alternating_cell::State>` cannot be shared between threads safely
+  --> tests/ui/simvalue_is_not_internable.rs:12:5
+   |
+12 |     Intern::intern_sized(v)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ `Cell<util::alternating_cell::State>` cannot be shared between threads safely
+   |
+   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`, which is required by `SimValue<()>: Sync`
+   = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`
+note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
+  --> src/util/alternating_cell.rs
+   |
+   | pub(crate) struct AlternatingCell<T: ?Sized> {
+   |                   ^^^^^^^^^^^^^^^
+note: required because it appears within the type `SimValue<()>`
+  --> src/sim/value.rs
+   |
+   | pub struct SimValue<T: Type> {
+   |            ^^^^^^^^
+note: required by a bound in `fayalite::intern::Interned`
+  --> src/intern.rs
+   |
+   | pub struct Interned<T: ?Sized + 'static + Send + Sync> {
+   |                                                  ^^^^ required by this bound in `Interned`
+
+error[E0277]: `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
+  --> tests/ui/simvalue_is_not_internable.rs:12:5
+   |
+12 |     Intern::intern_sized(v)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
+   |
+   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`, which is required by `SimValue<()>: Sync`
+note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
+  --> src/util/alternating_cell.rs
+   |
+   | pub(crate) struct AlternatingCell<T: ?Sized> {
+   |                   ^^^^^^^^^^^^^^^
+note: required because it appears within the type `SimValue<()>`
+  --> src/sim/value.rs
+   |
+   | pub struct SimValue<T: Type> {
+   |            ^^^^^^^^
+note: required by a bound in `fayalite::intern::Interned`
+  --> src/intern.rs
+   |
+   | pub struct Interned<T: ?Sized + 'static + Send + Sync> {
+   |                                                  ^^^^ required by this bound in `Interned`