Pin the shipped shape: every path, each category's format, each column's datatype and nullability

shape_test.go

@@ -0,0 +1,68 @@
+package fejkdata
+
+import (
+	"os"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+const shapePin = "testdata/shipped_shape.txt"
+
+// TestShippedShapeIsPinned pins what a version promises about the shipped data (see
+// the README's Versioning): every path, each category's format, and each record
+// column's datatype and nullability. REPIN=1 rewrites the pin.
+func TestShippedShapeIsPinned(t *testing.T) {
+	f, err := New(WithSeed(1))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := shippedShape(f)
+	if os.Getenv("REPIN") == "1" {
+		if err := os.WriteFile(shapePin, []byte(got), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return
+	}
+	want, err := os.ReadFile(shapePin)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != string(want) {
+		t.Fatalf("the shipped shape differs from %s: a removed, renamed or retyped line is a breaking change; add the CHANGELOG.md entry, then repin with REPIN=1", shapePin)
+	}
+}
+
+// shippedShape lists every path Fake accepts, one per line. A category-level template
+// carries its format, and each of its columns its datatype and whether it may be null.
+func shippedShape(f *Generator) string {
+	facts := map[string]string{}
+	var walk func(prefix string, n node)
+	walk = func(prefix string, n node) {
+		switch n := n.(type) {
+		case *folder:
+			for _, name := range sortedNames(n.children) {
+				walk(join(prefix, name), n.children[name])
+			}
+		case *template:
+			facts[prefix] = "\tformat " + strconv.Quote(n.format)
+			if _, columns, err := recordOf(n); err == nil {
+				for _, c := range columns {
+					fact := "\t" + c.DataType.String()
+					if _, nullable := columnItems(n.fields[c.Name]); nullable {
+						fact += " null"
+					}
+					facts[join(prefix, c.Name)] = fact
+				}
+			}
+		}
+	}
+	for _, name := range sortedNames(f.categories) {
+		walk(name, f.categories[name])
+	}
+	var b strings.Builder
+	for _, p := range f.List() {
+		b.WriteString(p + facts[p] + "\n")
+	}
+	return b.String()
+}