typescript/sync: tuples and type literals from checker.typeToTypeNode print multi-line (SingleLine flag lost) #64991

🔎 Search Terms

typeToTypeNode multiline, printNode single line, EmitFlags SingleLine api, typescript/sync printer, typeToTypeNode tuple printed on several lines

🕗 Version & Regression Information

• This changed between versions 6.0.2 (classic API) and 7.1.0-dev.20261027.1 (typescript/sync, gitHead 49e6983)
• not the same as [api] Add back missing: setEmitFlags and addSynthetic*Comment #64429 - that one asks for setEmitFlags on nodes the caller builds. here the checker builds the nodes, and the 6.0 node builder marks them single-line itself

⏯ Playground Link

n/a - needs the typescript/sync API

💻 Code

// input.ts
export type Shape = { tuple: [Date, number]; obj: { a: string } };

// repro.mjs - node 24.18, typescript@7.1.0-dev.20261027.1
import path from 'node:path';
import { API } from 'typescript/sync';

const entry = path.resolve('input.ts');
const api = new API({ cwd: process.cwd() });
const program = api.createProgram([entry], { strict: true });
const checker = program.getProject().checker;
const sourceFile = program.getSourceFile(entry);
const alias = sourceFile.statements.find(s => s.name?.text === 'Shape');
const shape = checker.getDeclaredTypeOfSymbol(checker.getSymbolAtLocation(alias.name));
for (const prop of checker.getPropertiesOfType(shape)) {
    const type = checker.getTypeOfSymbol(prop);
    const node = checker.typeToTypeNode(type, sourceFile, 0);
    console.log(`--- ${prop.name}`);
    console.log('printNode:');
    console.log(api.printer.printNode(node));
    console.log(`typeToString: ${checker.typeToString(type)}`);
}
api.close();

🙁 Actual behavior

--- tuple
printNode:
[
    Date,
    number
]
typeToString: [Date, number]
--- obj
printNode:
{
    a: string;
}
typeToString: { a: string; }

the same script on 6.0.2 (ts.createProgram, ts.createPrinter().printNode(ts.EmitHint.Unspecified, node, sourceFile)) prints [Date, number] and { a: string; }

🙂 Expected behavior

printNode gives [Date, number] and { a: string; } on one line, like 6.0 and like typeToString

Additional information about the issue

we generate a big .ts file of request/response types from typeToTypeNode output and are moving the generator from the 6.0 API to typescript/sync. this is the one difference we can't work around - every tuple and inline object type from the checker now takes several lines, and on one of our services ~14.5k of the 16k lines of the generated file change

as far as we can see the node encoder only sends multiLine for blocks and object/array literals (getNodeCommonData in dist/api/node/encoder.generated.js), and PrintNodeOptions only has preserveSourceNewlines, neverAsciiEscape and terminateUnterminatedLiterals, so the client can't ask for single-line. keeping the node builder's single-line flag on these nodes, or a printer option, would both do it for us