fix(generate): send falsy optional values as present and match variant tags by own property

[marc0olo]

Part of the naming and encoding chain.

Behaviour

This PR changes what goes on the wire — a fix rather than an API change: no type changes, and a canister relying on the old behaviour was relying on a bug. No BREAKING CHANGE footer for that reason.

you write	you mean	before	after
{ count: 0n }	present, value 0	[] — absent	[0n]
{ count: undefined }	absent	[]	[]
decoding any variant		a tag named constructor, toString, valueOf, … matched every value and won	decodes correctly
a candid type named Object	shadowed the global the conversions call	escaped — Object_; a method of that name is unchanged

An opt nat carries two independent things: whether there is a value, and what it is. 0 is a perfectly good nat, so present with value 0 is not absent — but the old code answered the first question by testing the second for truthiness. Setting a field to 0n and omitting it produced identical bytes, so 0, false and "" could not be sent at all. A canister that was receiving nothing for those fields now receives what the caller asked to send.

null counts as absent alongside undefined, symmetric with decoding, which yields null for a bare opt and undefined for a record field. opt null stays ambiguous — present-with-null and absent are indistinguishable in any JavaScript mapping, as before.

Snapshot churn is 42 lines over 7 files, all of it the optional-field encoding (the example fixture repeated across the wasm-generate matrix). Variants whose tags are not inherited property names are untouched.

Why

Both were well-formed TypeScript that computed the wrong answer, which is why parsing, typechecking and snapshots all passed over them. Optional fields were tested for truthiness (value.count ? … : …). Variant tags were matched with in, which walks the prototype chain, so a tag named constructor matched whatever the value held and the first such tag won outright.

Reviewer note. in does double duty: runtime test and the narrowing TypeScript uses to discriminate the variant union. Replacing it with Object.hasOwn outright costs the member access inside each arm and the exhaustiveness of the last one, and churns every snapshot. So an own-property test is conjoined only for the twelve names in gets wrong — redundant at runtime, since in is implied by it — and the last arm asserts never only where a conjunction was needed. It is spelled Object.prototype.hasOwnProperty.call(value, name) rather than Object.hasOwn, which is ES2022: the wrapper ships into someone else's build, bundlers do not polyfill built-in methods, and going through Object.prototype also survives a decoded object carrying its own hasOwnProperty. Object is escaped through MODULE_NAMES rather than KEYWORDS: the keyword table also shapes method keys, so it would have renamed a method named Object while the wire call kept the name.

Testing

tests/conversion-runtime.test.ts runs the generated conversions instead of reading them — nothing else in the suite would have caught either bug, since the output was valid, typechecked and wrong. The tests fail against the previous generator, with expected [] to deeply equal [ 0n ] and expected 'toString' to be 'plain'. They cover the three encoding paths separately — record field, variant payload and bare opt argument — and execute the conversion of a candid type named Object, which is what proves the escaped declaration leaves the global reachable.

[Copilot]

🔵 Needs a closer look

Moderate unresolved issues remain around variant payload coverage and shared Object identifier escaping.

Pull request overview

Fixes generated TypeScript conversions so falsy optional values remain present and variant decoding ignores inherited properties.

Changes:

• Uses explicit presence checks for optional values.
• Adds own-property validation for variant tags.
• Adds runtime regression coverage and updates snapshots.

File summaries

File	Reviewed change
tests/snapshots/wasm-generate/typescript/example/example.ts.snapshot	Updated generated optional encoding snapshot.
tests/snapshots/wasm-generate/typescript-root-export/example/example.ts.snapshot	Updated generated optional encoding snapshot.
tests/snapshots/wasm-generate/root-export/example/example.ts.snapshot	Updated generated optional encoding snapshot.
tests/snapshots/wasm-generate/no-root-export/example/example.ts.snapshot	Updated generated optional encoding snapshot.
tests/snapshots/generate/variant_payload_tags/variant_payload_tags.ts.snapshot	Updated variant payload encoding snapshot.
tests/snapshots/generate/example/example.ts.snapshot	Updated optional encoding snapshot.
tests/snapshots/generate/conversion_encoding/declarations/conversion_encoding.did.js.snapshot	Updated generated JavaScript declarations.
tests/snapshots/generate/conversion_encoding/declarations/conversion_encoding.did.d.ts.snapshot	Updated generated TypeScript declarations.
tests/snapshots/generate/conversion_encoding/conversion_encoding.ts.snapshot	Updated generated conversion wrapper snapshot.
tests/generate.test.ts	Registers the conversion encoding fixture.
tests/conversion-runtime.test.ts	Executes regression cases; variant payload coverage for present 0n and absent values remains needed.
tests/assets/conversion_encoding.did	Adds optional and variant regression types.
src/core/generate/rs/src/bindings/typescript_native/utils.rs	Adds Object to shared keyword protection, which risks renaming generated APIs and should be separated from property-name escaping.
src/core/generate/rs/src/bindings/typescript_native/conversion_functions_generator.rs	Corrects optional encoding and variant tag handling.

Review details

Suppressed comments (2)

src/core/generate/rs/src/bindings/typescript_native/conversion_functions_generator.rs:948

• The new runtime regression test exercises optional primitive fields on a record, but not this separate discriminated-variant payload path. A variant { payload : opt nat } could therefore regress to the old truthiness check while the suite still passes; please execute the generated variant conversion with a present 0n payload and assert that it emits [0n] (and retains the absent case).

                                test: Box::new(self.field_is_present(
                                    param_name,
                                    &field_name,
                                    field_access.clone(),
                                )),

src/core/generate/rs/src/bindings/typescript_native/utils.rs:404

• Adding Object to this shared KEYWORDS list also feeds get_ident_guarded, which is used for generated service method/interface names (compile_wrapper.rs:441 and new_typescript_native_types.rs:1003). A valid Candid method named Object (and a service basename object) therefore changes from Object to Object_, while the actor call still targets .Object; this introduces a generated API/name change not described by the PR. Please keep the global protection needed by Object.hasOwn separate from property-name escaping, or reference the global without reserving Object.

    "Object",

• Files reviewed: 14/14 changed files
• Comments generated: 0
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

No unresolved blocking issues were identified.

Review details

• Files reviewed: 20/20 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟡 Changes recommended

A critical unresolved variant-tag matching issue remains for inherited properties outside the hard-coded list.

Get a fresh assessment by requesting another Copilot review.

Review details

• Files reviewed: 20/20 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

No unresolved review issues remain, and the regression coverage addresses the corrected behavior.

Review details

• Files reviewed: 20/20 changed files
• Comments generated: 0 new
• Review effort level: Lite

[marc0olo]

Force-pushed as part of a stack-wide rebase. This PR's own diff is unchanged — nothing to re-review here.

Only #175, #187 and #188 changed content in this round: a nested option reached through a type alias took the single-option path, so opt Inner with type Inner = opt Cfg was declared and converted unlike the opt opt Cfg it is. #187 fixes it for standalone types and record fields, #188 for variant payloads, and #175 corrects a doc comment that promised more than it did.

Comparing this PR's commit patch before and after the rebase, with context and ignoring index lines, gives a byte-identical diff.

[marc0olo]

Superseded by #197 for the optional-value encoding (0, false and "" sent as present). The own-property matching of inherited tag names (constructor, toString) is dropped as not realistic.