genbindings: reorder ctors to put (QWidget* parent) version first

cmd/genbindings/main.go

@@ -161,6 +161,7 @@ func generate(packageName string, srcDirs []string, clangBin, cflagsCombined, ou
 		astTransformChildClasses(parsed) // must be first
 		astTransformOptional(parsed)
 		astTransformOverloads(parsed)
+		astTransformConstructorOrder(parsed)
 		atr.Process(parsed)
 
 		// Update global state tracker (AFTER astTransformChildClasses)

cmd/genbindings/transformctors.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"sort"
+)
+
+// astTransformConstructorOrder creates a canonical ordering for constructors
+// where the 0th entry is any entry taking solely a QWidget* parameter.
+// This is so that UIC can safely assume this for types.
+// @ref https://github.com/mappu/miqt/issues/46
+func astTransformConstructorOrder(parsed *CppParsedHeader) {
+
+	// QFoo(QWidget* parent);
+	checkIsDefaultCtor := func(candidate CppMethod) bool {
+		return len(candidate.Parameters) == 1 &&
+			candidate.Parameters[0].ParameterType == "QWidget" &&
+			candidate.Parameters[0].Pointer
+	}
+
+	// Iterate all classes
+	for i, c := range parsed.Classes {
+
+		// Sort
+		sort.SliceStable(c.Ctors, func(i, j int) bool {
+			ic := checkIsDefaultCtor(c.Ctors[i])
+			jc := checkIsDefaultCtor(c.Ctors[j])
+
+			if ic && !jc {
+				return true
+			}
+			return false
+		})
+
+		// Persist mutation
+		parsed.Classes[i] = c
+
+	}
+}