[Harsh Vardhan Chauhan (1-DARK)]

Fixes #64991

Problem

With typescript/sync/async, checker.typeToTypeNode(...) results printed via api.printer.printNode(...) come out across several lines:

[
    Date,
    number
]

whereas checker.typeToString and the 6.0 API give [Date, number] / { a: string; }.

Cause

The node builder marks tuple types, type literals (and a few other nodes: mapped types, empty type literals, string literals in type position, pseudo-type-builder results) with EFSingleLine / EFNoAsciiEscaping. Those flags live in the node builder's EmitContext, not on the node. The API encoder only serialized the node, and printNode decoded it into a fresh printer with no emit flags, so the default multi-line layout was used.

Fix

Carry the two printer hints across the API boundary:

• ast/nodeflags.go: add NodeFlagsEmitSingleLine (bit 29) and NodeFlagsEmitNoAsciiEscaping (bit 30). They are transport-only and never set by the parser/binder.
• api/encoder: new EncodeNodeWithEmitContext; when given an emit context it sets those bits in each node's flags (without mutating the nodes).
• checker/printer.go: TypeToTypeNodeWithEmitContext and SignatureToSignatureDeclarationWithEmitContext return the builder's emit context alongside the node.
• api/session.go: typeToTypeNode and signatureToSignatureDeclaration encode with that context; printNode converts the bits back into emit flags before printing.
• Regenerated enums/nodeFlags.* and enum_values_generated.go.

No client-facing API changes. Because the hint travels in node.flags, it survives the client re-encoding the node for printNode. FlagsMultilineObjectLiterals is respected (the builder doesn't set the flag in that case, so nothing is sent), and hand-written multi-line type literals are unaffected.

Alternatives considered

• A PrintNodeOptions flag (e.g. singleLine): works, but would flatten every type literal/tuple in the tree, including user-written ones, and requires callers to opt in to what 6.0 did by default.
• Per-kind commonData bits in the encoder: more explicit, but needs generator and TS node class changes. Happy to switch to that if preferred.

Tests

• Go: TestPrintNodeRestoresEmitFlags (encode with emit context → decode → print; with and without the hint).
• JS: new sync/async API test printing typeToTypeNode results for { tuple: [Date, number]; obj: { a: string } } and asserting they equal typeToString.
• npx hereby test: 168642 tests passed. hereby lint and hereby check:format are clean. Sync/async API tests: 727/727.

Notes

• Note: node.flags for builder-produced nodes seen from JS now includes bit 29/30 when set.
• AI disclosure: this patch was authored with an AI coding agent (pi). I have reviewed it, understand it, and will respond to review feedback myself.

[Copilot]

🟡 Changes recommended

The new tests lack non-ASCII round-trip coverage for EFNoAsciiEscaping, so regressions in transporting or restoring that hint would go undetected.

1 open issue

• Add non-ASCII round-trip coverage for transported hints · New

1 file not reviewed

• tsc/internal/api/enum_values_generated.go: Generated file

What changed in this PR

Preserves node-builder printer hints across the TypeScript API boundary, addressing #64991 so checker-generated tuples and type literals retain their single-line formatting.

Changes:

• Transports single-line and no-ASCII-escaping hints through node flags.
• Returns emit contexts from checker builders and restores hints before printing.
• Adds Go round-trip coverage and sync/async API formatting tests.

File	Description
tsc/​internal/​checker/​printer.go	Adds builder methods that return emit contexts.
tsc/​internal/​ast/​nodeflags.go	Defines transport flags for printer hints.
tsc/​internal/​api/​session.go	Encodes builder hints and restores them for printing.
tsc/​internal/​api/​printnode_emitflags_test.go	Tests single-line hints through encoding and decoding.
tsc/​internal/​api/​enum_values_generated.go	Registers the new generated enum values.
tsc/​internal/​api/​encoder/​encoder.go	Serializes emit hints without mutating nodes.
packages/​typescript/​test/​sync/​api.test.ts	Tests single-line formatting through the sync API.
packages/​typescript/​test/​async/​api.test.ts	Tests single-line formatting through the async API.
packages/​typescript/​enums/​nodeFlags.js	Adds runtime enum values for transported hints.
packages/​typescript/​enums/​nodeFlags.d.ts	Adds corresponding enum declarations.

_{Review effort: Balanced}

[Harsh Vardhan Chauhan (1-DARK)]

Good catch, thanks. Added TestPrintNodeRestoresNoAsciiEscaping: a synthesized "é" literal round-trips verbatim with EFNoAsciiEscaping and as "\u00E9" without it. I also confirmed it fails if the encoder stops setting NodeFlagsEmitNoAsciiEscaping.

[Copilot]

🟢 Approval recommended

No active review issues were identified for the change preserving printer hints across the TypeScript API boundary.

1 open issue

• Add non-ASCII round-trip coverage for transported hints

1 file not reviewed

• tsc/internal/api/enum_values_generated.go: Generated file

_{Review effort: Balanced}