docs(wiki): digest mdl/visitor — two new pages and the first re-sync

[ako]

Stacked on #359. The whole chain — #356 → #357 → #358 → #359 → this — is still open against a main that has moved on; they want landing in order.

27 of the 28 mdl/visitor findings (96%). Two new pages, and one re-sync — the first any wiki page has had since the initial synthesis on 2026-05-24, which was the point of building the trigger.

page	findings
expression-translation-drift	13	new
misleading-diagnostics	6	new
visitor-wiring-gaps	—	re-synced

expression-translation-drift

Deliberately kept distinct from platform-semantics-gaps. There, the MDL is illegal Mendix. Here the MDL is correct, the emitted Mendix expression is well-formed, and it says something else.

The worst instance is the quietest: an additive chain rebuilt with its operators reordered, so a microflow computed a different number than its source said — mxcli check, mx check and the build all green, and the corruption in the stored document rather than in the description. Nothing downstream can catch it, because the output is a valid expression; strings on the .mxunit is what showed the swap.

Three ways meaning is lost — a literal changes type, an operator changes (/ is division in most languages and member navigation in Mendix), a function resolves to the wrong overload (contains/find exist as both string functions and list operations). Plus the ANTLR trap behind the standard fix: GetText() excludes hidden tokens and a source-interval slice includes them, so preserving raw source inherits every comment in that span — which is how a -- comment ended up inside a Mendix expression.

misleading-diagnostics

Graded above "the message could be clearer", because a missing hint costs a minute and a wrong one costs however long the reader spends acting on it. In the reported cases they blamed their quoting, renamed an attribute that was fine, or concluded a construct was unsupported.

A hint's precision matters more than its coverage: the "unescaped apostrophe" hint matched any short lowercase word, so it fired on every genuine parse error at on, in, as, to, by. And key the hint off the source line, not the parser message — a misplaced index clause errors on the index name, so the message never contains the word index and no message-matching hint can fire.

The re-sync

visitor-wiring-gaps described one size of gap. The findings show three:

• a field — the original case, a doc comment or an OR REPLACE flag lost;
• a structure — ELSIF arms dropped, because Mendix has no native elsif and each arm must be lowered into a nested if;
• a whole statement — one that parses, exits 0, prints nothing and dispatches to nothing. It presents as an empty result ("this page has no content") rather than as a missing feature, which is exactly what lets it survive.

Also added: the neighbouring failure where a field is wired to the wrong thing — a delete-behaviour keyword storing a different behaviour, a dollar-quoted SQL body overwritten by a parameter default. Those report success and change the model's meaning, where an unwired field merely loses it.

sources: narrowed from the findings directory to the specific shard, last-synced refreshed, wiki-links normalised.

The digest, complete for the five largest areas

area	findings	covered
mdl/executor	248	83%
cmd/mxcli	95	92%
mdl/backend	83	99%
mdl/grammar	53	92%
mdl/visitor	28	96%

25 pattern pages, up from 3. Every sources: path and every [[wiki-link]] across all of them verified to resolve.

🤖 Generated with Claude Code