Skip placeholder synthesis for unapplied-family use sites

When a constraint references a family unapplied (passed as a
higher-kinded argument, e.g. @CanUpgradeLedgerTables LedgerState@),
the FamilyApp at the use site has no args. The placeholder
synthesizer would emit @LedgerState = ?@ — informationless beyond
the family name itself, which the family node already shows on its
own. Skip these empty-args use sites so the family node sits in the
graph cleanly without a tautological placeholder hanging off it.

Concretizing the bare reference to e.g. @LedgerState (ShelleyBlock
proto era) mk@ would require constraint-solver-like propagation
across the constraint set (matching @l ~ LedgerState (ShelleyBlock
proto era)@ from elsewhere) — work GHC does at typecheck time but
that we don't preserve in the dump.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

diff --git a/data/viewer.js b/data/viewer.js
index 8986cc0ab3c778869255e0ddc8523afbb48c303b..4920e0d5e56e868714b74e63e92d86d1bc6b1fb1 100644 (file)
--- a/data/viewer.js
+++ b/data/viewer.js
@@ -788,6 +788,13 @@
         if (!anyRelevant) {
           const useSites = collectFamilyAppArgs(args, fa);
           for (const ua of useSites) {
+            // Skip placeholder synthesis when the family is referenced
+            // *unapplied* (passed as a higher-kinded argument: e.g.
+            // `CanUpgradeLedgerTables LedgerState`). The use-site args
+            // are empty, so the placeholder would say `Family = ?`
+            // — informationless beyond the family name itself, which
+            // the family node already shows.
+            if (!ua || ua.length === 0) continue;
             const synFi = {
               fiFamily: fa,
               fiArgs: ua,