fix: partition child PK/UNIQUE constraints cause perpetual plan drift (#495)

internal/diff/constraint.go

@@ -166,7 +166,12 @@ func constraintsEqual(old, new *ir.Constraint) bool {
 	if old.CheckClause != new.CheckClause {
 		return false
 	}
-	if old.NoInherit != new.NoInherit {
+	// NoInherit (connoinherit) is only meaningful for CHECK constraints where
+	// it controls the NO INHERIT modifier. For PK/UNIQUE/FK/EXCLUDE constraints,
+	// PostgreSQL sets connoinherit inconsistently (e.g. true for a standalone
+	// constraint vs false for one created via PARTITION OF), so comparing it
+	// would cause false diffs on partition children (#495).
+	if old.Type == ir.ConstraintTypeCheck && old.NoInherit != new.NoInherit {
 		return false
 	}
 	if old.ExclusionDefinition != new.ExclusionDefinition {

testdata/diff/create_table/issue_495_partition_constraint_convergence/new.sql

@@ -0,0 +1,8 @@
+CREATE TABLE public.p (
+    band_id integer NOT NULL,
+    geom_id integer NOT NULL,
+    CONSTRAINT p_band_id_geom_id_key UNIQUE (band_id, geom_id)
+) PARTITION BY LIST (band_id);
+
+CREATE TABLE public.p_12 PARTITION OF public.p FOR VALUES IN (12);
+CREATE TABLE public.p_13 PARTITION OF public.p FOR VALUES IN (13);

testdata/diff/create_table/issue_495_partition_constraint_convergence/old.sql

@@ -0,0 +1,22 @@
+-- This represents what the target database looks like after pgschema apply:
+-- partition children created as standalone tables with explicit constraints,
+-- then attached to the parent table.
+CREATE TABLE public.p (
+    band_id integer NOT NULL,
+    geom_id integer NOT NULL,
+    CONSTRAINT p_band_id_geom_id_key UNIQUE (band_id, geom_id)
+) PARTITION BY LIST (band_id);
+
+CREATE TABLE public.p_12 (
+    band_id integer NOT NULL,
+    geom_id integer NOT NULL,
+    CONSTRAINT p_12_band_id_geom_id_key UNIQUE (band_id, geom_id)
+);
+ALTER TABLE public.p ATTACH PARTITION public.p_12 FOR VALUES IN (12);
+
+CREATE TABLE public.p_13 (
+    band_id integer NOT NULL,
+    geom_id integer NOT NULL,
+    CONSTRAINT p_13_band_id_geom_id_key UNIQUE (band_id, geom_id)
+);
+ALTER TABLE public.p ATTACH PARTITION public.p_13 FOR VALUES IN (13);

testdata/diff/create_table/issue_495_partition_constraint_convergence/plan.json

@@ -0,0 +1,9 @@
+{
+  "version": "1.0.0",
+  "pgschema_version": "1.11.1",
+  "created_at": "1970-01-01T00:00:00Z",
+  "source_fingerprint": {
+    "hash": "b52a7d3e192793cd8af86dbf6b990056fa88b14303a29a10bb55048423a811c0"
+  },
+  "groups": null
+}

testdata/diff/create_table/issue_495_partition_constraint_convergence/plan.txt

@@ -0,0 +1 @@
+No changes detected.