fix(filters): qualify model columns to avoid ambiguity with joins

Qualify plain model columns with the main table alias in resolvespec
filters so preload joins no longer cause SQLSTATE 42702, and accept
<table>.<column> from clients in resolvespec and restheadspec instead
of silently dropping the filter. Add join/preload tests for
resolvespec, restheadspec and funcspec.

pkg/common/qualify_column_test.go

@@ -0,0 +1,55 @@
+package common
+
+import "testing"
+
+type qualifyModel struct {
+	ID   int64  `bun:"id,pk"`
+	Name string `bun:"name"`
+}
+
+func TestQualifyModelColumn(t *testing.T) {
+	m := qualifyModel{}
+	cases := []struct{ alias, col, want string }{
+		{"t", "name", `"t"."name"`},
+		{"t", "NAME", `"t"."NAME"`},
+		{"t", "missing", "missing"},
+		{"t", "data->>'x'", "data->>'x'"},
+		{"t", "rel.name", "rel.name"},
+		{"", "name", "name"},
+	}
+	for _, c := range cases {
+		if got := QualifyModelColumn(m, c.alias, c.col); got != c.want {
+			t.Errorf("Qualify(%q,%q) = %q, want %q", c.alias, c.col, got, c.want)
+		}
+	}
+	if got := QualifyModelColumn(nil, "t", "name"); got != "name" {
+		t.Errorf("nil model: %q", got)
+	}
+}
+
+func TestStripMainTablePrefix(t *testing.T) {
+	m := qualifyModel{}
+	cases := []struct{ col, want string }{
+		{"province_state.name", "name"},
+		{`"province_state"."name"`, "name"},
+		{"PROVINCE_STATE.name", "name"},
+		{"rel_rid_country.name", "rel_rid_country.name"},
+		{"province_state.missing", "province_state.missing"},
+		{"name", "name"},
+	}
+	for _, c := range cases {
+		if got := StripMainTablePrefix(m, c.col, "province_state"); got != c.want {
+			t.Errorf("Strip(%q) = %q, want %q", c.col, got, c.want)
+		}
+	}
+}
+
+func TestStripMainTablePrefix_ValidatorKeepsFilter(t *testing.T) {
+	m := qualifyModel{}
+	filters := []FilterOption{{Column: "province_state.name", Operator: "eq", Value: "x"}}
+	StripMainTablePrefixFromFilters(m, filters, "province_state")
+	out := NewColumnValidator(m).FilterRequestOptions(RequestOptions{Filters: filters})
+	if len(out.Filters) != 1 || out.Filters[0].Column != "name" {
+		t.Fatalf("filters = %+v", out.Filters)
+	}
+}