Tagged path rejects alias mapping keys and drops key anchors #12

New Issue

2026-07-12T12:25:32Z

Mihaela commented

2026-07-12 12:25:32 +00:00

(Migrated from codeberg.org)

Status (2026-07-12)

Open. Disclosed as a known limit while closing #9: the anchors/aliases/styles
round-trip work preserves alias structure in VALUE positions, but a document
using an alias where a mapping key is expected (*b : value, yaml-test-suite
E76Z/26DV) still fails to parse on the Tagged path with expectedScalarKey.
This is pre-existing behavior, not a regression: Tagged.EventComposer's
composeMappingKey accepts only scalar events. The plain parse(_:) path
handles alias keys correctly (see AliasAsMappingKeyTests), so this is a
Tagged-path capability gap only.

Related: an anchored scalar KEY's anchor is registered for later alias
resolution but is not carried on the pair itself, so it does not re-emit
(Tagged.Pair.key is a String, not a node). Same root cause, same fix
surface.

Impact

parseTagged(_:) rejects documents the primary parser accepts whenever an
alias stands in key position, and a round trip through Tagged.Dumper loses
anchors that sit on keys. The corpus round-trip law in
TaggedNodeCorpusRoundTripTests counts these documents as "rejected", so the
gap is visible, not silent.

Work

Widen Tagged.Pair's key from String to a node-carrying representation
(a Tagged.Node or a scalar-plus-properties key type). This is a breaking
change to Tagged.Pair, Tagged.Mapping's subscript, Tagged.Constructor
key handling, and the validator's key-uniqueness check, so it should land
as its own pass, not ride along on another change.
Teach composeMappingKey to accept alias events (resolving through the
anchors table like composeNode does) and to carry key anchors.
Extend Tagged.Dumper.renderBlockPair/renderInline to emit key
properties and alias keys (*a : value).
Extend the corpus round-trip law: E76Z/26DV-shaped fixtures move from
"rejected" to round-tripping with alias-key topology intact.

Part of #8.

## Status (2026-07-12) Open. Disclosed as a known limit while closing #9: the anchors/aliases/styles round-trip work preserves alias structure in VALUE positions, but a document using an alias where a mapping key is expected (`*b : value`, yaml-test-suite E76Z/26DV) still fails to parse on the `Tagged` path with `expectedScalarKey`. This is pre-existing behavior, not a regression: `Tagged.EventComposer`'s `composeMappingKey` accepts only scalar events. The plain `parse(_:)` path handles alias keys correctly (see `AliasAsMappingKeyTests`), so this is a `Tagged`-path capability gap only. Related: an anchored scalar KEY's anchor is registered for later alias resolution but is not carried on the pair itself, so it does not re-emit (`Tagged.Pair.key` is a `String`, not a node). Same root cause, same fix surface. ## Impact `parseTagged(_:)` rejects documents the primary parser accepts whenever an alias stands in key position, and a round trip through `Tagged.Dumper` loses anchors that sit on keys. The corpus round-trip law in `TaggedNodeCorpusRoundTripTests` counts these documents as "rejected", so the gap is visible, not silent. ## Work - Widen `Tagged.Pair`'s key from `String` to a node-carrying representation (a `Tagged.Node` or a scalar-plus-properties key type). This is a breaking change to `Tagged.Pair`, `Tagged.Mapping`'s subscript, `Tagged.Constructor` key handling, and the validator's key-uniqueness check, so it should land as its own pass, not ride along on another change. - Teach `composeMappingKey` to accept alias events (resolving through the anchors table like `composeNode` does) and to carry key anchors. - Extend `Tagged.Dumper.renderBlockPair`/`renderInline` to emit key properties and alias keys (`*a : value`). - Extend the corpus round-trip law: E76Z/26DV-shaped fixtures move from "rejected" to round-tripping with alias-key topology intact. Part of #8.

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Reference: NodetteHQ/PureYAML#12