package wax

Changelog

This is the changelog for the wax / wax-lib opam packages. dune-release reads the top entry's version and notes when cutting an opam release (see RELEASING.md). The VS Code extension keeps its own changelog, editors/vscode/CHANGELOG.md; the tree-sitter grammar keeps none, and both are versioned independently of the toolchain.

0.2.0

Language

• The final ; of a block is now optional. Writing it still does not discard the statement's value, and the formatter keeps emitting the canonical trailing ;.
• New parenthesized type ascription (e : t). It asserts a type instead of converting to it: the operand's type must already be a subtype of t, the expression compiles to nothing, and an ascription that does not hold is a compile-time error. Use it to pin a literal's width, or to widen a reference without a runtime cast.
• The compilation-hints proposal is supported and preserved through every conversion, with no feature flag: #[freq = n], #[never_opt], #[always_opt] and #[targets(f: 0.73, …)] prefixing an expression, and #[priority = n], #[optimization = n] and #[run_once] on a function.
• A hole _ is now rejected, with an explanation, as a match scrutinee, a dispatch index or a while condition. Those positions desugar to a nested block, where a hole draws from the block's own stack and could never pick up the intended value.
• custom-descriptors follows two upstream rule changes: a type and its descriptor must agree on finality, and the "L" subtyping rule is gone. Exact allocation types are now gated on the feature as well.
• compact-import-section treats the text form as authoritative for import layout. A Wax import "m" { … } block (or a WAT (import "m" (item …) …) group) lowers to a compact entry, a one-item block flattens to a plain import, and imports written separately are never merged. A binary input, which has no authorial layout, still gets its runs of same-module imports coalesced. The shared-type text form cannot bind identifiers, so a group whose items carry names takes the one-type-per-item form and the binary encoder restores the shared-type encoding.
• A module name annotation is rejected inside a #[if] / (@if) conditional, since the name applies in every configuration.
• A branch-hint annotation is accepted on a folded operand in WAT.

Command line

• New --faithful: decompile without the stream-reshaping recoveries, so a WAT or Wasm module converted to Wax recompiles with the same reachable instruction structure. Wax output only. The new Round-Tripping page states the contract and the few inert divergences that remain.
• --desugar now synthesizes the declarative element segment that Wax's lenient reader lets a module omit, so the output passes strict spec validation, including after resolving conditionals with -D. The metadata.code.* hint annotations are real WebAssembly text and are kept.
• --error-format human appends the warning's -W name to the header (Warning [unused-local]:). With json, a diagnostic carrying a machine-applicable fix gained an edit object, and syntax errors now emit hint, related and edit like every other diagnostic.
• --source-map is rejected as a usage error when the input is a Wasm binary, which carries no source to map.
• New developer --debug categories width-check and width-record, self checks on the decompiler's numeric-width recording.

Warnings

• unused-field and unused-import now ask reachability from the module's roots rather than the mere presence of a reference, so a dead cycle of mutually recursive functions or types is reported. They span every named index space: functions, globals, memories, tables, tags, types, and passive data and element segments.
• New unnecessary-mut (shown by default): a module-defined, non-exported global declared mutable that no assignment ever targets, so it could be a const.
• New confusable-unicode (shown by default): a "Trojan Source" bidirectional control character in a string the module carries (an export or import name, a string literal, a data segment), which can make the source read differently than it runs.
• New suggestion group, hidden by default and reported at a distinct Suggestion severity, each entry carrying a machine-applicable rewrite: compound-assignment (x = x + e to x += e), field-punning ({x: x} to {x}) and redundant-annotation (a type the inference already pins).
• dead-code also reports a #[if] / (@if) branch that no configuration can select.
• Quick-fix edits are attached to unused-local, unused-label, precedence and redundant casts, so editors can offer them.
• cast-always-fails reports only the innermost cast of a chain, where the fix belongs.
• Fewer false positives: float arithmetic identities, x - x on floats, any/extern conversions, a leading sign on a constant operand, and SIMD vector methods now classified as effect-free. Constant expressions are linted too, not just function bodies.

Diagnostics

• Parser error messages are regenerated by stele, a message generator vendored with the repository, and are golden-tested. They name the construct under repair, underline the right token, and fall back to hand-written wording for the states heuristics cannot serve.
• Syntax errors carry a structured payload, and a parse that recovery repairs by inserting a token (a missing ; or operand) offers that insertion as a fix.
• Better locations throughout: br_table targets, block parameters and results, a missing block argument, the arms of an if and of a structured try, the intrinsic name in an arity error, a non-function callee at the call site, a missing ; at the end of the previous lexeme.
• A duplicate binding, export or dispatch arm now reports where the previous one was.
• Error cascades are cut: a failed cast, a failed arithmetic operand, a local whose declared type is unresolved, and a chained or nested type error each report once instead of at every level.

Editors

• Machine-applicable suggestions are served as textDocument/codeAction quick fixes over LSP, mirroring the VS Code code-action provider.
• Contextual type completion: value and heap types in Wax, and types in WAT buffers.

Fixes

• Silent miscompilations in both directions of the Wax/Wasm conversion, most of them numeric-width drift: a decompiled expression could recompile at a different width than the original opcode stated. The decompiler now records the type each source opcode states and the type checker pins any value that would otherwise come back at the wrong width.
• A shadowing let's initializer is kept in the outer scope.
• A call through a struct's function-pointer field is no longer rejected when the field's name is also a built-in method's (copy, length, switch, a SIMD lane operation). The type checker chose the intrinsic by name and argument count, while the lowering had always chosen by the receiver's type. Field names come from the name section, so a decompiled module could carry one and produce Wax that did not compile back.
• Conditional modules: entities referenced only inside an (@if) body are converted, imports are hoisted, and every configuration is checked as a whole rather than through a separate specializer.
• A memory's minimum is derived from its custom page size.
• A bare (type N) blocktype naming an implicit type resolves.
• Generated labels no longer clash with dispatch and match arm labels.
• Crash on become of a binary intrinsic method, plus several crashes and a hang in typer error recovery.
• Writing a large Wasm binary no longer overflows the stack, and lowering nested calls no longer blows up exponentially.
• Inputs that were wrongly accepted are now rejected: a br_on_cast flags byte outside 0..3, overlong tag bytes, degenerate import groups, a non-finite or over-long hint payload, a br value that violates the block's result type, and a table with a non-nullable element type written with an inline element list, whose active segment fills the table at instantiation but leaves the table itself without a default. An out-of-f32-range float literal takes type f64.
• A decompiled block (do, if, loop, try) whose value is left on the stack for a later statement keeps its result type. Two annotations that were each redundant on their own — the block's result, and the cast pinning the same type — were both dropped, and the Wax that came out no longer compiled.
• Decompiled dead code no longer gains a ref.cast, or a stray extern.convert_any, on the way back. The decompiler pins the type of an operand it cannot see, and those pins were landing on a neighbouring value instead of on the hole they were meant for, where they turned into real instructions. Affected a ref.cast into the extern hierarchy, both extern/any conversions, a call_ref callee, a field or element access receiver, array.len and i31.get_s.
• A conditionally-compiled module no longer defeats the decompiler's type pins. Where a pin sat over a value whose type the decompiler could not read, behind an #[if] it could take a value one of the branches had pushed — producing Wax that either did not compile back or gained a stray extern.convert_any.
• Output fixes: an empty blocktype uses the 0x40 shorthand, funcidx element segments encode (ref func) rather than funcref, an empty name-section entry names nothing, and data strings are split at word boundaries.
• Formatting fixes: an empty block body beside a following clause, rec groups and catch arms always broken across lines, (do &t { x; }[0] = 1), and more faithful preservation of comments and of annotations the tokenizer does not interpret.

Performance

• The pretty-printer streams straight to the output channel instead of building a document tree, and an in-house Printer replaces Format throughout.
• An O(n²) in the binary-to-text path is gone, trivia tables are keyed on byte offsets, and several hot traversals are allocation-free.

Library

• wax-lib depends on cmdliner, and now needs menhir 20260122 or later: the parser and its error messages are built with options that release introduced.
• Driver.to_binary reports a failed lowering (a conditional that survived specialization, an unresolved reference) as a located diagnostic instead of letting an exception escape to the embedder.
• The embedding API can turn the unused-declaration warnings off.
• Parsing and Parser_error_runtime moved to lib-utils, Naming to lib-conversion.

Documentation

• A browser playground: write Wax, see the WAT and the diagnostics live, with no install.
• A wax agent skill under skills/wax/, for coding assistants that read the SKILL.md format (npx skills add ocsigen/wax).
• opam install wax is documented now that both packages are in opam-repository.

0.1.0

• Initial release of the Wax toolchain: bidirectional conversion between Wax, WebAssembly text (WAT), and WebAssembly binary, with formatting, type checking, a language server, and the supporting libraries (wax-lib).