GP import: chord names/diagrams missing entirely when source file has no Diagram Collection

[carochacs]

Repro

Reported against So Far Away (J).gp (GP7/8 tab, likely a community transcription): no chord names or diagrams show anywhere in the highway UI, despite chords clearly being played.

Root cause

Chord name/fingering extraction (_parse_chord_diagrams, lib/gp2rs_gpx.py:719-777 for GP6/7/8; the analogous beat.effect.chord path in lib/gp2rs.py:596-643,1048-1063 for GP3-5) only pulls from the source file's own Diagram Collection — the chord library a person manually builds/names inside Guitar Pro's UI (Properties/Property[@name="DiagramCollection"] for the .gp container). It's applied only on an exact fret-pattern match:

# lib/gp2rs_gpx.py:2025-2033
if fkey not in chord_template_map:
    chord_template_map[fkey] = len(chord_templates)
    _diag = chord_diagram_map.get(fkey)
    chord_templates.append(ChordTemplate(
        name=(_diag['name'] if _diag else ''),
        frets=list(frets_t),
        fingers=(list(_diag['fingers']) if _diag else [-1] * width),
    ))

There's no shape-recognition fallback. This is intentional/documented behavior from the introducing PR (#522 — "Only enriches on exact fret-pattern match; diagram-less charts import identically (blank)", covered by tests/test_gp2rs_gpx.py:1071-1078), but it means any GP file whose author never used GP's separate chord-naming tool imports every chord with a blank name — very common for tab-site transcriptions, which just place notes on the fretboard.

The blank name isn't just a missing label — it hides the entire diagram, name and fret-dots both:

• plugins/highway_3d/screen.js:13862-13867 — the corner chord-diagram HUD box is fully gated on chordTemplateLabel(tmpl) being non-empty:

  const lbl = chordTemplateLabel(tmpl);
  if (lbl && tmpl?.frets) {
      newChord = { name: lbl, frets: tmpl.frets, t: ch.t, t0: ch.t, chDt, nStr };
  }

  tmpl.frets is populated correctly (the real fret pattern actually played) even when name is blank, but the falsy lbl check throws the whole box away.
• plugins/highway_3d/screen.js:12852-12853 — the on-neck gold chord-name label above the strummed shape is similarly gated on chordName truthiness (the wireframe box around the shape itself is not gated and still draws).

What's NOT broken

lib/song.py, the WS wire serializer (chord_template_to_wire, lib/song.py:331-357), and lib/routers/ws_highway.py:724-725 all faithfully carry the blank name through — no data loss/corruption downstream of extraction. The gap is entirely at import time (no fallback) and at the diagram-box render gate (blank name hides fret-dots that are otherwise available).

Existing workaround

The editor plugin (plugins/editor/routes.py:3952-3973) round-trips chordName/displayName/per-string fingers on save, so a user can manually add chord names in the editor's authoring UI after import — not automatic, but available today.

Suggested fix

1. Stop gating the diagram box on lbl truthiness in plugins/highway_3d/screen.js:13862-13867 — show the fret-shape even when unnamed, so users at least see the diagram.
2. Consider a basic standard-chord shape-recognition fallback (keyed by fret pattern + tuning) for common open/barre chords, so files without an authored Diagram Collection still get sensible names.