BuildListColumn's per-attribute binder calls used the generic "column
items"/"column values"/"column onchange"/"column onclick" context
strings from the initial slice — indistinguishable when a list has
several columns of the same type. Route every column-attribute binder
call (text items/colors/onclick, check values/onchange, icon
values/onclick) through the ColumnContext helper item 2 introduced, so
every throw message reads column[N] type="..." attr. ValidateIconKind
gains an optional context parameter (default "iconkind" for the
existing non-column call sites — <icon>, <button icon>, <list icons>,
none of which changed message-wise beyond wording) so the column
iconkind check can identify its own column too.
Updated all twelve column-throw tests in MarkupListColumnsTests to
assert Assert.Contains on the distinguishing phrase: the ten
attribute-specific ones now check column[0] type="..." attr; the
unknown-<column type> and combined-with-legacy-attribute tests keep
(and, for the type one, add to) their existing distinguishing
assertions. Confirmed each attribute-specific assertion is meaningful
by first running the malformed-colors case against the pre-fix
"column colors must be..." message (mismatch), then landing the
production change alongside the rest.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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