motoko (moc)

• feat: M0218 ("redundant stable keyword") now ships a machine-applicable edit, so mops check --fix removes the explicit stable keyword on fields of a persistent actor (#6175).

• feat: Permitting destructuring patterns against actor types — let { foo } = a, func g({foo} : actor T) {}, etc. (#6149).

• feat: /// @deprecated M0235 <message> — the caffeine deprecation warning (M0235) can now carry a free-text message, rendered as a note: sub-diagnostic at every use site. M0154 free-text deprecation messages now render the same way (#6153).

• perf: Multi-value Wasm codegen is now on by default, --no-experimental-multi-value flag disables (if not desired) (#6165).

• bugfix: M0237 (implicit argument can be omitted) only fires now when the suggested removal preserves the same type instantiation. Previously the edit could be rejected (M0098) (#6166).

• bugfix: M0236 dot-notation suggestion no longer fires for literal receivers — the lit.f() rewrite could misparse (-1.1.isNaN() → -(1.1.isNaN())), mis-lex (0xff.abs as a hex float), or fail to type-check when it lost a literal coercion (Blob.isEmpty("\00") → "\00".isEmpty()) (#6173).

• bugfix: M0236 dot-notation suggestion no longer fires when the receiver cannot be inferred or would infer to a different type causing the call to resolve to a different function (#6177).

• bugfix: Implicit argument derivation now resolves type variables that occur only in a covariant result position (e.g. JSON-style decoders Text -> ?T). Previously such a variable was solved to None (bottom), so the implicit had to be passed explicitly (#6186).

• bugfix: Diagnostic columns now count Unicode codepoints (matching editor displays and rustc), and JSON diagnostics gain byte_start/byte_end for encoding-independent edit anchors. Previously mops check --fix over-deleted on multi-byte lines (e.g. Char.toNat32('京') trimmed the trailing )) (#6168).

motoko (moc)

• feat: Structural implicit derivation for records and tuples via __record and __tuple combiners. Per-field results are lazy thunks, enabling short-circuiting for operations like compare (#5903).

• feat: --experimental-multi-value flag enables function-level multi-value Wasm codegen. Off by default (#6113).

motoko (moc)

• bugfix: M0236 dot-notation suggestion no longer fires when the receiver argument is not already a postfix expression (e.g. Nat.toText((x * a + b) % c)). The compiler used to print the suggestion as (<expr>).toText(...) but emit no machine-applicable edits, leaving mops check --fix with nothing to do; suggesting (complex).f() over Module.f(complex) is also a debatable style change. Trivial-receiver cases (variables, literals, calls) are unaffected (#6144).

motoko (moc)

• bugfix: Split stable-signature compatibility error M0169 — the "previous version does not contain the stable variable required by the migration function" case now reports as new code M0263, leaving M0169 strictly for the "stable variable would be implicitly discarded" (data-loss) case. The two scenarios have different fixes and now have distinct codes (#6134).

motoko (moc)

• feat: Implicit argument derivation — the compiler can derive implicit arguments from functions that themselves have implicit parameters (e.g., compare for [Nat] from Array.compare<Nat> + Nat.compare). Works transitively and is depth-limited via --implicit-derivation-depth (#5966).

• feat: and-patterns — p1 and p2 matches when both legs match, binding from both (#6049).

• bugfix: M0236 dot-notation auto-fix on unparenthesized single-argument calls (e.g. List.reverse b) no longer rewrites them into a bare function reference (b.reverse), which silently turned a call into a no-op; the suggestion now produces b.reverse() (#6096).

motoko (moc)

• feat: Add null-coalescing operator ?? (#5722).
  e1 ?? e2 evaluates to the unwrapped contents of e1 when e1 is ?v,
  otherwise to e2. The right-hand side is evaluated lazily (short-circuit).
  For example, opt ?? defaultValue replaces the verbose
  switch opt { case (?v) v; case null defaultValue }.
  The right-hand side may be a block (e.g. opt ?? { let x = 1; x }),
  a do-block, or a Prim.trap for fail-fast unwrapping. Because { ... }
  on the right is parsed as a block, a bare record literal must be wrapped
  in extra braces or parentheses, e.g. opt ?? ({ x = 0 }) or
  opt ?? {{ x = 0 }}.

• perf: Compile enhanced multi-migration chains as per-step functions instead of one deeply-nested inlined expression, avoiding the wasm-function complexity limit hit by long chains (#6065).

• bugfix: Preserve GC-only roots (blob deduplication table, migration functions list) across graph-copy upgrades, and defer actor type compatibility checks to ICStableRead so enhanced multi-migration chains with multiple pending steps are accepted (#5993).

• bugfix: Clearer error when installing a Motoko canister over a non-Motoko or otherwise incompatible canister (#6044).

motoko (moc)

• feat: expose caller attributes feature through primitives (#5970).

• bugfix: Fix moc.js resolution of relative flag paths (e.g. --enhanced-migration, --actor-idl): resolve against the project root (via new setProjectRoot API) instead of the source file's directory, matching native moc behavior. The language server should call setProjectRoot(path) before processing files (#6015).

motoko (moc)

• bugfix: Resolve relative paths in moc.js flags (e.g. --enhanced-migration, --actor-idl) against the source file's directory, fixing "not a directory" errors when these flags are passed with relative paths via the language server (#6002).