Update features list

docs/feature-checklist.md

@@ -4,137 +4,200 @@ which is available for use under [MIT](https://github.com/verus-lang/verus/blob/
 license.
 -->
 
-**Last Updated: 2025-04-10**
+**Last Updated: 2026-06-18**
+
+Status reflects concrete execution against the Rust UI test suite. Many limitations trace back to a
+single missing component: an **address model** (a representation of addresses in memory). Types whose
+values own heap-allocated data (`Box`, `Vec`, etc.) additionally need dynamic (heap)
+allocation of that data, built on the address model. **A _Supported_ label can be followed by an
+address-model caveat** (e.g. references work, but not references into heap/static data, which are not modeled yet). Therefore, please read
+the *Notes* for a full description of the supported features.
+Such dependencies are flagged in bold as **Requires the address model** / **Requires heap allocation**.
 
 ## Items
-|Feature|Status|
-|-------|------|
-|Functions, methods, associated functions|Supported|
-|Associated constants|Not supported|
-|Structs|Partially supported|
-|Enums|Partially supported|
-|Const functions|Not supported|
-|Async functions|Not supported|
-|Macros|N/A (MIR)|
-|Type aliases|Not supported|
-|Const items|Not supported|
-|Static items|Not supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|Functions, methods, associated functions|Supported|indirect calls through a stored function pointer: see Function pointer types|
+|Associated constants|Supported||
+|Structs|Partially supported|construction and field access work; decoding reordered/padded layouts from raw bytes not yet|
+|Enums|Partially supported|construction and matching work; decoding with-field / niche-encoded variants from raw bytes not yet|
+|Const functions|Supported||
+|Async functions|Not supported|desugars to coroutines (also not supported)|
+|Macros|N/A (MIR)||
+|Type aliases|Supported|resolved before MIR|
+|Const items|Supported|value constants work; **Requires the address model** for constants holding references into data (`&str`, `&[T]`)|
+|Static items|Not supported|**Requires the address model**|
 
 ## Struct/enum definitions
-|Feature|Status|
-|-------|------|
-|Type parameters|Not supported|
-|Where clauses|Not supported|
-|Lifetime parameters|Not supported|
-|Const generics|Not supported|
-|Custom discriminants| Supported|
-|Public / private fields|N/A (MIR)|
+|Feature|Status|Notes|
+|-------|------|-----|
+|Type parameters|Supported|monomorphized before MIR|
+|Where clauses|Supported|resolved at type-check|
+|Lifetime parameters|Supported|erased in MIR|
+|Const generics|Supported|monomorphized; complex `generic_const_exprs` (unstable) not yet (see `impl` types)|
+|Custom discriminants|Supported||
+|Public / private fields|N/A (MIR)||
 
 ## Expressions and Statements
-|Feature|Status|
-|-------|------|
-|Variables, assignment, mutable variables|Supported|
-|`if`, `else`|Supported|
-|Patterns, `match`, `if let`, match guards|Supported|
-|Block expressions|Supported|
-|Items|Supported|
-|`loop`, `while`|Supported|
-|`for`|Not supported (`Range` not supported)|
-|`?`|Supported|
-|Async blocks|Not supported|
-|`await`|Not supported|
-|Unsafe blocks|Supported|
-|`&`|Supported|
-|`&mut`, place expressions|Supported|
-|`==`, `!=`|Supported|
-|Type cast (`as`)|Partially supported|
-|Compound assigments (`+=`, etc.)|Supported|
-|Array expressions|Not supported|
-|Range expressions|Not supported|
-|Index expressions|Not supported (Arrays not supported)|
-|Tuple expressions|Supported|
-|Struct/enum constructors|Not supported|
-|Field access|Supported|
-|Function and method calls|Supported|
-|Closures|Supported|
-|Labels, break, continue|Supported|
-|Return statements|Supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|Variables, assignment, mutable variables|Supported||
+|`if`, `else`|Supported||
+|Patterns, `match`, `if let`, match guards|Supported|slice rest-patterns (`[head, tail @ ..]`) not yet|
+|Block expressions|Supported||
+|Items|Supported||
+|`loop`, `while`|Supported||
+|`for`|Supported|desugars to iterators|
+|`?`|Supported||
+|Async blocks|Not supported|desugars to coroutines (also not supported)|
+|`await`|Not supported|desugars to coroutines (also not supported)|
+|Unsafe blocks|Supported||
+|`&`|Supported||
+|`&mut`, place expressions|Supported||
+|`==`, `!=`|Supported||
+|Type cast (`as`)|Partially supported|numeric and pointer casts work; **Requires the address model** for integer↔pointer casts; float casts not yet|
+|Compound assigments (`+=`, etc.)|Supported||
+|Array expressions|Supported|including multi-dimensional|
+|Range expressions|Supported||
+|Index expressions|Supported|element indexing works; range-indexing into a sub-slice: see Patterns|
+|Tuple expressions|Supported||
+|Struct/enum constructors|Supported||
+|Field access|Supported|union cross-field access: see Unions|
+|Function and method calls|Supported|indirect calls through a stored function pointer: see Function pointer types|
+|Closures|Supported||
+|Labels, break, continue|Supported||
+|Return statements|Supported||
 
 ## Integer arithmetic
-|Feature|Status|
-|-------|------|
-|Arithmetic for unsigned|Supported|
-|Arithmetic for signed (`+`, `-`, `*`, `/`, `%`)|Supported|
-|Bitwise operations (`&`, `\|`, `!`, `>>`, `<<`)|Supported|
-|Arch-dependent types (`usize`, `isize`)|Not supported (fixed width) |
+|Feature|Status|Notes|
+|-------|------|-----|
+|Arithmetic for unsigned|Supported||
+|Arithmetic for signed (`+`, `-`, `*`, `/`, `%`)|Supported||
+|Bitwise operations (`&`, `\|`, `!`, `>>`, `<<`)|Supported||
+|Arch-dependent types (`usize`, `isize`)|Not supported (fixed width)|`usize`/`isize` work as fixed 64-bit|
 
 ## Types and standard library functionality
-|Feature|Status|
-|-------|------|
-|Integer types|Supported|
-|`bool`|Supported|
-|Strings|Not supported|
-|`Vec`|Not supported|
-|`Option` / `Result`|Supported|
-|Floating point|Not supported|
-|Slices|Not supported|
-|Arrays|Not supported|
-|Pointers|Not supported|
-|References (`&`)|Supported|
-|Mutable references (`&mut`)|Supported|
-|Never type (`!`)|Not supported|
-|Function pointer types|Not supported|
-|Closure types|Supported|
-|Trait objects (`dyn`)|Not supported|
-|`impl` types|Not supported|
-|`Cell`, `RefCell`|Not supported|
-|Iterators|Not supported|
-|`HashMap`|Not supported|
-|Smart pointers (`Box`, `Rc`, `Arc`)|Not supported|
-|`Pin`|Not supported|
-|Hardware intrinsics|Not supported|
-|Printing, I/O|Not supported|
-|Panic-unwinding|Not supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|Integer types|Supported||
+|`bool`|Supported||
+|`char`|Not supported|char values not yet modeled|
+|Strings|Not supported|`str` not yet; `String` **Requires heap allocation**|
+|`Vec`|Not supported|**Requires heap allocation**|
+|`Option` / `Result`|Supported|construction and matching work; decoding niche/with-field variants from raw bytes not yet (see Enums)|
+|Floating point|Not supported|float decoding and arithmetic not yet implemented|
+|Slices|Partially supported|indexing and `split_at` work; slice rest-patterns and fat-pointer length metadata not yet|
+|Arrays|Partially supported|indexing and multi-dimensional arrays work; slice rest-patterns (`[head, tail @ ..]`) not yet|
+|Pointers|Partially supported|place-based pointers partly work (some pointer casts still produce thunks and fail); **Requires the address model** for integer↔pointer casts|
+|References (`&`)|Supported|references to stack data work; **Requires the address model** for references to constant/static/heap data|
+|Mutable references (`&mut`)|Supported|references to stack data work; **Requires the address model** for references to constant/static/heap data|
+|Never type (`!`)|Not supported||
+|Function pointer types|Partially supported|passing a function or closure as an argument works; calling indirectly through a stored function pointer not yet|
+|Closure types|Supported|`dyn Fn` dispatch: see Trait objects|
+|Coroutines / generators|Not supported|underlies async|
+|Trait objects (`dyn`)|Not supported|needs dynamic dispatch via vtables; `Box<dyn>` also **Requires heap allocation**|
+|`impl` types|Partially supported|return-position and argument `impl Trait` work; some opaque-type cases not yet|
+|`Cell`, `RefCell`|Partially supported|`Cell` works; `RefCell` (borrow tracking) not yet|
+|Iterators|Supported||
+|`HashMap`|Not supported|**Requires heap allocation**|
+|Smart pointers (`Box`, `Rc`, `Arc`)|Not supported|**Requires heap allocation**|
+|`Pin`|Not supported||
+|Hardware intrinsics|Partially supported|several implemented; many (including SIMD) not yet|
+|Printing, I/O|Not supported||
+|Panic-unwinding|Not supported|panics that abort are detected; unwinding / `catch_unwind` not yet|
 
 ## Traits
-|Feature|Status|
-|-------|------|
-|User-defined traits|Supported|
-|Default implementations|Supported|
-|Trait bounds on trait declarations|Supported|
-|Traits with type arguments|Supported|
-|Associated types|Supported|
-|Generic associated types|Supported|
-|Higher-ranked trait bounds|Supported|
-|`Clone`|Supported|
-|Marker traits (`Copy`)|Supported|
-|Marker traits (`Send`, `Sync`)|Not supported|
-|Standard traits (`Hash`, `Debug`)|Not supported|
-|User-defined destructors (`Drop`)|Not supported|
-|`Sized` (`size_of`, `align_of`)|Not supported|
-|`Deref`, `DerefMut`|Not supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|User-defined traits|Supported||
+|Default implementations|Supported||
+|Trait bounds on trait declarations|Supported||
+|Traits with type arguments|Supported||
+|Associated types|Supported||
+|Generic associated types|Supported||
+|Higher-ranked trait bounds|Supported||
+|`Clone`|Supported||
+|Marker traits (`Copy`)|Supported||
+|Marker traits (`Send`, `Sync`)|Not supported|markers erased in MIR; meaningful only with concurrency which is not supported|
+|Standard traits (`Hash`, `Debug`)|Not supported|formatting / hashing machinery not implemented|
+|User-defined destructors (`Drop`)|Not supported|destructors do not run (Drop is a no-op); control flow continues|
+|`Sized` (`size_of`, `align_of`)|Supported|`size_of_val` on unsized types: see Hardware intrinsics|
+|`Deref`, `DerefMut`|Partially supported|user `Deref`/`DerefMut` impls work; `Box`/`Rc` deref **Requires heap allocation**|
 
 ## Multi-threading
-|Feature|Status|
-|-------|------|
-|`Mutex`, `RwLock` (from standard library)|Not supported
-|Verified lock implementations|Not supported
-|Atomics|Not supported|
-|`spawn` and `join`|Not supported|
-|Interior mutability|Not supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|`Mutex`, `RwLock` (from standard library)|Not supported|**Requires heap allocation** and concurrency|
+|Verified lock implementations|Not supported||
+|Atomics|Not supported||
+|`spawn` and `join`|Not supported|no threading model|
+|Interior mutability|Partially supported|`Cell` works; `RefCell` not yet (see Cell/RefCell)|
 
 ## Unsafe
-|Feature|Status|
-|-------|------|
-|Raw pointers|Not supported|
-|Transmute|Not supported|
-|Unions|Not supported|
-|`UnsafeCell`|Not supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|Raw pointers|Partially supported|place-based pointers partly work (some pointer casts still produce thunks and fail); **Requires the address model** for integer↔pointer casts|
+|Transmute|Partially supported|byte / wrapper / enum transmutes work; **Requires the address model** for transmutes involving pointer/address values|
+|Unions|Partially supported|reading the field last written works; cross-field type-punning not yet|
+|`UnsafeCell`|Not supported|**Requires the address model**: direct use fails on a pointer-alignment check; `Cell`, built on it, works (see Cell/RefCell)|
+|FFI / `extern` functions|Not supported|external functions have no MIR body to execute|
 
 ## Crates and code organization
-|Feature|Status|
-|-------|------|
-|Multi-crate projects|Partially supported|
-|Verified crate + unverified crates|Not supported|
-|Modules|Supported|
-|rustdoc|Not supported|
+|Feature|Status|Notes|
+|-------|------|-----|
+|Multi-crate projects|Partially supported||
+|Verified crate + unverified crates|Not supported||
+|Modules|Supported||
+|rustdoc|Not supported||
+
+## Methodology and evidence
+
+The statuses above were derived from three sources, cross-checked:
+
+1. A full run of the Rust **UI test suite** under the LLVM (concrete) backend (~2888 tests).
+2. The repository's **integration tests**: the curated `prove-rs` suite (each `*-fail.rs` is *expected* to fail), the `decode-value` cases, and `verify-rust-std`.
+3. **Targeted checks**: small programs run directly to probe a specific feature.
+
+A feature is only marked **Supported** when it both has a passing test that exercises it *and* no failing
+test has it as the **root cause**. Distinguishing "root cause" from "where execution stops" matters: a test
+often gets stuck far from the real problem (e.g. an arithmetic test that fails only because it prints its
+result). To attribute correctly we **tracked thunks** (when the semantics cannot yet rewrite an evaluation it
+records it as a *thunk*, noting where that thunk was created) and traced each failure back to the thunk that
+caused it. This allows us to say that a feature works while its nominal-category failures are due to *other*
+unsupported features.
+
+In the table below, *Passing* gives tests that exercise the feature and succeed (integration tests are under
+`kmir/src/tests/integration/data/`, UI tests under `tests/ui/`). *Failures attributed to* gives, for the
+not-fully-passing rows, representative failing tests in the same area with the **other** feature their failure
+actually traces to. UI directories are nominal groupings, so a directory rarely passes entirely even when the
+named feature works. A few directories do pass entirely, noted as such.
+
+| Row | Status | Passing | Failures attributed to |
+|-----|--------|---------|-----------------------|
+| Iterators | Supported | `iterator-simple`, `iter_next_1/2/3`, `iter-eq-copied-take-dereftruncate`; `tests/ui/iterators/iter-map-fold-type-length` | `iter-sum-overflow` → panic-unwinding; `iter-count-overflow` → loop-to-2⁶⁴ timeout; `iter-range` → printing |
+| Arrays | Partially supported | `array_match`, `array_write`, `array_nest_compare` (nested `[[u16;3];2]`); `tests/ui/array-slice-vec/{array_const_index-2,copy-out-of-array-1}` | own gap: `tests/ui/array-slice-vec/{subslice-patterns-const-eval,vec-matching-fold}` (slice rest-patterns). Other fails → heap (`box-of-array-of-drop-1`) |
+| Slices | Partially supported | `slice-split-at` | same slice rest-pattern gap as Arrays |
+| `for` / Range / Index / Struct-enum constructors | Supported | `struct`, `enum`; `tests/ui/structs-enums/{class-methods,borrow-tuple-fields}`; `for`/range via `iterator-simple` + targeted `1..5` checks | `tests/ui/structs-enums/class-cast-to-trait` → heap (Vec alloc); `align-struct` → unimplemented `min_align_of_val` intrinsic |
+| Type/lifetime/const generics, where clauses | Supported | monomorphized/erased before MIR; 284 generics / 106 lifetimes / 46 const-generics passing UI tests, e.g. `tests/ui/generics/generic-fn-twice`, `tests/ui/lifetimes/issue-84604`, `tests/ui/const-generics/const-arg-in-fn` | `tests/ui/const-generics` fails → heap/transmute and unimplemented `generic_const_exprs` (`OpaqueCast`) |
+| Associated constants | Supported | `tests/ui/associated-consts/{assoc-const,associated-const-const-eval}` (19 passing in dir, 1 fail) | `associated-const-in-global-const` → constant-into-allocation (address model) |
+| Const functions | Supported | run like normal functions; `tests/ui/const-generics/min_const_generics/const_fn_in_generics`, targeted `const fn` checks |  |
+| Type aliases | Supported | resolved before MIR; `tests/ui/type-alias-enum-variants/` (both tests pass) |  |
+| Const items | Supported | value constants work (targeted `const C: u32` checks; no dedicated UI dir); constants holding references into data (`&str`, `&[T]`) need the address model |  |
+| Function pointer types | Partially supported | fn-item/closure-as-argument: `488-support-function-pointer-calls` | calling indirectly through a stored/cast function pointer not yet (the `tests/ui/` indirect-call failures) |
+| `impl` types | Partially supported | `tests/ui/impl-trait/{closure-in-impl-trait-arg,example-st}`, targeted `impl Fn`/`impl Into` | `equality-rpass` → `OpaqueCast`/`Subtype` projection; others → heap/transmute |
+| Transmute | Partially supported | `transmute-bytes`, `transmute_transparent_wrapper_up/down`, `transmute-u8-to-enum`; `tests/ui/transmute/` (passes wholesale) | own gap: `transmute-maybe-uninit-fail`; pointer/address-typed transmutes → address model |
+| Unions | Partially supported | `tests/ui/union/{union-derive-rpass,union-inherent-method,union-backcomp}` | own gap: `union-pat-refutability`, `union-const-eval-field` (cross-field punning); `union-align` → unimplemented `min_align_of_val` |
+| `Cell` / Interior mutability | Partially supported | `Cell`: `interior-mut2` (no dedicated UI dir) | `RefCell`: `interior-mut-fail` (borrow tracking) |
+| Raw pointers / Pointers | Partially supported | place-based: `offset_read`, `pointer-cast` | `raw-ptr-cast-fail` → pointer-alignment check / `ptr as usize` (address model) |
+| `Sized` (`size_of`, `align_of`) | Supported | `align_and_size` (all integer widths; no dedicated UI dir) |  |
+| `Deref`/`DerefMut` | Partially supported | user impls: `tests/ui/autoref-autoderef/autoderef-privacy` | `Box`/`Rc` deref → heap |
+| Hardware intrinsics | Partially supported | `intrinsics` (rotate_left, bswap, ctpop, ctlz_nonzero); `tests/ui/intrinsics/{intrinsic-assume,intrinsic-raw_eq-const}` | `const-eval-select-x86_64` → SIMD; `intrinsic-alignment` → unimplemented `pref_align_of` |
+| Smart pointers (`Box`/`Rc`/`Arc`) | Not supported |  | `box_heap_alloc-fail` (expected fail) → heap |
+| Static items | Not supported |  | `volatile_load_static-fail`, `volatile_store_static-fail` (expected fail) → address model |
+| `UnsafeCell` | Not supported |  | `interior-mut3-fail` (expected fail) → pointer-alignment / address model |
+| Floating point | Not supported |  | `verify-rust-std/0011-floats-ints` (`to_int_unchecked` parked); no passing float test |
+| Enums (decode of with-field/niche variants) | Partially supported | fieldless variants decode fine (`enum-direct-tag-decode`) | `decode-value` SKIP: `enum-1-variant-1-field`, `enum-option-nonzero-none`, … (with-field/niche decode) |
+| Strings | Not supported |  | `decode-value` SKIP `str` |
+| `char` | Not supported |  | no `char` value representation (decode rule unimplemented); only size/alignment known |
+| Coroutines / generators | Not supported |  | `tests/ui/coroutine/` (all 33 fail, e.g. `addassign-yield`) → `aggregateKindCoroutine` unhandled |
+| FFI / `extern` functions | Not supported |  | external functions have no MIR body (e.g. `tests/ui/abi/anon-extern-mod`) |