API - DocumentRegistry - sourceFile.scriptTarget can possibly be undefined

[dsherret]

Low priority issue, but the following is possible which can lead to errors when using the compiler API.

TypeScript Version: 3.1.0-dev.20180818

Search Terms: DocumentRegistry, languageVersion undefined

Code

import * as ts from "typescript";

const registry = ts.createDocumentRegistry();
const sourceFile = registry.acquireDocument("/file.ts", {}, ts.ScriptSnapshot.fromString(""), "1");

console.log(sourceFile.languageVersion); // undefined, but languageVersion is not nullable

Caused by the non-null assertion here.

Expected behavior: Not sure. Probably it should default to ScriptTarget.Latest or the compiler options should pass through the function that sets the default values.

Actual behavior: languageVersion is undefined because it was not set on the compiler options.

Related issues: Maybe #18217 covers this already.

[dsherret]

I can fix this if you'd like. Just let me know what the expected behaviour should be.

[RyanCavanaugh]

@sheetalkamat @rbuckton opinions on expected behavior?

[sheetalkamat]

I think we need to change https://github.com/Microsoft/TypeScript/blob/master/src/services/documentRegistry.ts#L187 to

const scriptTarget = scriptKind === ScriptKind.JSON ? ScriptTarget.JSON : compilationSettings.target ||  ScriptTarget.ES5;

[dsherret]

@sheetalkamat thanks! Opened a PR with ES5.

I took a look around the code and it defaults to ES3 in program.ts though. Maybe we should do the same here? What's the rationale for choosing one or the other?

[sheetalkamat]

Language service defaults to ES5 while tsc defaults to ES3