JS: a test spec can opt into the style its own source is written in

[knutwannheden]

A JS test fixture indented with tabs comes back indented with four spaces from any recipe that formats, so the expectation cannot be written the way the file reads:

before:  function f() {\n\tconst x = 1;\n}
after:   function f() {\n    const x = 1;\n}

This is the documented style resolution — constructor styles, then NamedStyles markers on the source file, then IntelliJ defaults — working as specified. A bare javascript()/typescript() spec carries no style marker, so it lands on the defaults. Instrumenting AutoformatVisitor confirms it: the source file is found, markers:[], useTabCharacter=false, indentSize=4. The style-marker code lives only in the npm() generator, which samples all specs together; a spec standing on its own never reaches it.

Declaring a style was already possible, but only by hand-building a NamedStyles marker and overriding the spec's parser. withDetectedStyle samples the file and attaches what it finds, wired per spec:

spec.rewriteRun({
    ...typescript("function f() {\n\tconst x = 1;\n\treturn x;\n}\n"),
    beforeRecipe: withDetectedStyle
})

Why opt-in

Applying it to every spec was the first version and is wrong. Java is the reference: RewriteTest has no style handling at all, and a test asks for one with spec.parser(JavaParser.fromJavaVersion().styles(...)). That makes the existing JS behaviour symmetric rather than broken — npm() ≈ project parsing and autodetects, a bare spec ≈ a bare Java test and does not. Automatic detection also changes what 9 existing tests are measured against, 8 of them in format.test.ts, which feed deliberately messy input and assert canonical output; autodetecting from that input is self-defeating.

Full detection rather than indentation alone, since an explicit opt-in is a request for the file's style, and no guard against an existing marker, since a caller that asks should get what it asked for.

Tests

One test, a spec opting into its own style keeps the tabs it is written with, pins the whole path — sample, attach, getStyle lookup, formatter. It fails without the beforeRecipe line (tabs become four spaces), so it catches a marker the lookup cannot find as well as a detector that reads the wrong indent. autodetect.test.ts covers the detector's output but never that the marker is consumed. Full JS suite: 1629 passed, 0 failed, no existing test moved.