Fix formatter blank line and over-indent for union template argument

[oha-4]

Fixes #11009

Problem

When a union expression is used directly as one of multiple template arguments and the argument list is long enough to wrap, tsp format inserts a blank line before the union and indents its leading-| variants one level deeper than the sibling arguments:

model Picked
  is PickProperties<
    Sample,

      | "alpha"
      | "bravo"
      ...
  >;

Fix

printTemplateParameters already emits a softline + an indent level before each argument in a multi-argument list. printUnion was also emitting its own leading line + indent (+ align(2)), so the two stacked, producing the blank line and the extra indentation level.

printUnion now detects when the union is a direct argument of a multi-argument template reference (isInMultiTemplateArgumentList) and, in that case, lets the surrounding argument list control the line break and indentation. Result:

model Picked
  is PickProperties<
    Sample,
    | "alpha"
    | "bravo"
    ...
  >;

The standalone/value-position cases (e.g. alias X = "a" | "b" | ...) and the single-template-argument (shouldHug) case are unchanged, since there the surrounding context does not supply the line break/indent.

Tests

• Added a regression test for the multi-argument case (Formatter adds a blank line and over-indents a union used as a template argument #11009) and a test pinning the single-argument behavior in formatter.test.ts.
• Reformatted two committed http-client-java test fixtures that contained the buggy output (whitespace only; no semantic change).
• pnpm prettier --check "**/*.tsp", formatter test suite, tsc, and eslint all pass.

[oha-4]

@microsoft-github-policy-service agree

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npm i https://pkg.pr.new/@typespec/compiler@11010

commit: 4daeb1b

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@typespec/compiler - fix ✏️

Fix formatter inserting a blank line and over-indenting a union expression used directly as one of multiple template arguments (e.g. PickProperties<Source, "a" | "b">)

[timotheeguerin]

Thanks for the contribution, I think there is also a regression this introduce in the formatting, i'll also need to see the effect this has on all of azure specs though it does seem like a good thing to fix

[oha-4]

Thanks for the careful review — you're right, fixed in 4daeb1b6b. The previous change dropped align(2) from the variants, which de-indented the nested template.

And to your question: this does follow prettier's union printer — indent-or-not depends on the parent (shouldIndent, union-type.js#L23-L38), but the per-variant align(2) is kept regardless (#L49-L56). I'd wrongly tied them together; now align(2) is unconditional, so a breaking variant stays aligned under its | , matching your screenshot. Added a regression test for it too.

[timotheeguerin]

to dig a little more on this loop, as you pointed out the indent in typescript printer depends on the parent, which we have above, but I don't fully see how the type reference is involved here. Do we really need that loop, is thre maybe then some test missing to showcase those scenarios?

[oha-4]

Thanks, that's a great catch — you're right, the loop was unnecessary. A TemplateArgument only ever exists inside TypeReference.arguments (the sole TemplateArgumentNode[] in the AST), so the owning TypeReference is always the next ancestor. I've replaced the loop with a direct getParentNode(1) check in 02007f6.

We still need the TypeReference itself (not just the parent) to read the argument count: a single argument hugs (no list indent, so the union keeps its own), while multiple arguments indent the list — that's the case the fix targets. Both are covered by the existing single-/multi-arg tests, and all 205 formatter tests still pass.