Feature idea: composite IEC 81346 structure identifiers (=plant+location-prefix)

[ispyisail]

Checked: is this already done?

Partially, and the parts that exist don't connect to each other. IEC 81346's three structure-identifier aspects each have some representation in QET today, but they're three disconnected pieces of data rather than one composite reference designation.

What exists today, and where it stops short

• "=" (functional/installation aspect) and "+" (location aspect): both exist as diagram-level fields — TitleBlockProperties::plant/locmach (titleblockproperties.h:58-59), keyed as DIA_PLANT/DIA_LOCMACH (qetinformation.h:103-104), with UI labels that literally say tr("Installation (=)") / tr("Localisation (+)") (qetinformation.cpp:240-241) — the IEC 81346 notation is already named correctly in the UI. But grepping every use of DIA_PLANT/DIA_LOCMACH across the codebase, the only hits are the key-list registration and that tooltip string — these diagram-level values are never read anywhere else. They're not substituted into any formula, and they're never consulted as a default for an element's own plant/location.
• Element-level "=" / "+": separately, %{plant}/plant-and-locmach-typed NumStrategy parts are functional — substituted into formulas (assignvariables.cpp:218,585-588) and usable in element auto-numbering. But an element's own plant/locmach info is independent of the diagram's — nothing inherits the folio-level "=" / "+" default down to elements placed on it, so every element needs these typed in individually even when an entire folio (or the whole project) shares one installation/location.
• "-" (product/component aspect): the classic single-letter reference-designation prefix (K for a relay, Q for a breaker, etc.) already exists and is functional — Element::setPrefix()/m_prefix, populated via autonum::elementPrefixForLocation() (assignvariables.cpp:642-658) and used throughout auto-numbering.
• No composite identifier: nowhere in the codebase do these three aspects get concatenated into one proper IEC 81346 structure identifier (=E1+A2-K3-style). Each is a separate field/formula token; there's no builder that combines plant + locmach + prefix + number into a single reference designation string.

Proposed scope

• Have an element's plant/locmach fall back to the containing diagram's DIA_PLANT/DIA_LOCMACH when the element's own value is empty, the same three-tier priority (manual element value → [structural default] → folio value) already discussed and agreed on in principle in the original terminal-block-generator forum thread, just never implemented for these two fields specifically.
• Add a combined structure-identifier formula token (e.g. %{structure_id} or similar) that assembles =<plant>+<locmach>-<prefix><number> from the pieces above using standard IEC 81346 separator characters, so labels/titleblocks can show the full reference designation as one value instead of the user manually concatenating the existing separate %{plant}/%{locmach}/prefix/number tokens by hand in every formula that wants one.
• Leave deeper multi-level/hierarchical aspects (nested sub-installations, =E1.1+A2.3-style dotted structure) out of scope for a first pass — the flat single-level case covers the immediate gap and matches what's already partially wired up.

Happy to build this if the scope above sounds right.

[ispyisail]

Status: in progress — PR #648: #648