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ui.Provider methods take variadic arguments #699
Description
Feature: #698 · Epic: #445 · Plan: docs/plans/ui-at-root.md
All six ui.Provider methods take a single msg string:
func (p *Provider) Error(msg string)
func (p *Provider) Fail(msg string) error
func (p *Provider) Note(msg string)
func (p *Provider) Print(msg string)
func (p *Provider) Succeed(msg string)
func (p *Provider) Warn(msg string)Make them variadic. This is worth doing on its own merits — note("saw", n, "packages") is the natural
way to write it — and it is a hard prerequisite for #698, because the builtin print these methods are
about to replace is variadic.
The contract to match
starlark-go's print (starlark/library.go:799):
- variadic over positional arguments
sepkeyword, defaulting to" "- strings written as-is;
Byteswritten raw; everything else throughwriteValue, i.e. itsrepr - returns
None
Variadic provider methods already work — file.Join(parts ...string) is announced today — so the
signature change needs no bridge work.
Steps
(args ...any)on all six;Fail(args ...any) error- Join the way the builtin does: strings as-is, everything else through the value's Starlark representation
- Decide
sep— a matching keyword parameter, or a documented narrowing. The bridge has a
kwargs map[string]anyconvention (flow.Degradeduses it), so it is available if we want it - Update the method table in
docs/architecture/3.5.16-ui-provider.mdand its status companion - Regenerate; confirm all six still claim
deterministic, so a hermetic planning runtime keeps its output
Verification
ui.note("a", 1, True)renders each argument the way Starlark wouldmake check,make test-race,make test-scenario- Claim check green across
"",darwin,linux,windows
Activity
David-Noble-at-work commentedon Aug 26, 2026
Correction to step 3, after reading the generator.
goastmarks a parameter variadic withvariadic := isLast && isEllipsis(cmd/star/provider/goast/helpers.go:438). Go requires...to be last, so nothing can follow the variadic parameter — there is no signature that is both Go-variadic and carries asepkeyword.The bridge's kwargs sink does not rescue it: it must be last too, and a non-final
[]anyis not marked variadic by that rule. That is whyflow.Degraded'sargs []anyis an ordinary list parameter, not a variadic sink.So step 3 is a fork, not a preference:
sep—Print(args ...any), joined with" "sepfirst — inverts the ergonomics, makesprint("a")bind to the separator. Rejectedgoasta declared variadic sink soPrint(args []any, sep string)is expressible — generator and bridge work, for one keywordSweep result: zero
sep=call sites across every.starfile in the tree. Recommending 1.David-Noble-at-work commentedon Aug 26, 2026
Settled: no
sepkeyword.Print(args ...any), joined with" ". Zerosep=call sites in the tree, so the narrowing costs nothing, and option 3 (teachinggoasta declared variadic sink) stays available if the need ever appears.Rationale from the ruling:
sephas always been dumb.David-Noble-at-work commentedon Aug 26, 2026
Closing: no signature changes.
ui.Providermethods keep(msg string).Two candidate reconciliations with the builtin were considered and both fail:
fmt.Printfsemantics — double interpretation. Starlark's%is an operator that runs before the call, soprint("%s" % name)arrives as a finished string. Printf semantics would re-scan that string for verbs, turning50% offinto50%!o(MISSING)ffwhenever the data contains a%. Go avoids this by makingPrintandPrintfdifferent functions; one function cannot be both. Everyday form:print("100% done")becomes a bug.Variadic space-join — the bridge has already destroyed the types.
fillVariadicSlotrunstoGoInto, so a Go-sideargs ...anyreceives Go natives:Trueasbool,Noneasnil, a list as[]any. Rendering those Go-side givestrue,<nil>,[a b]where Starlark saysTrue,None,["a"]. Faithful output would mean reimplementingwriteValueon the far side of a conversion that already threw the information away.(msg string)is therefore correct rather than a compromise: the script renders withstr()and%— Starlark's own rendering, deterministic by construction — and hands over a finished string. For a configuration language, requiring explicitstr()is a feature.Survey of the tree confirms nothing breaks:
print(fail(Every site passes one string, built with
%,+, or an explicitstr(...).Residual failure, named:
print("a", "b")andprint(42)are legal against the builtin and become errors against us. Nothing in the tree does either, but a Python reflex will produce one. The errors are legible —toGoScalarusesstarlark.AsStringwith no coercion, soprint(42)reportsexpected string, got int. Documenting the one-string contract moved to #700.All remaining work is on #700.