bind: preserve no-arg Java constructors

When the Java class parser began culling unused constructors, the
logic for determining whether a given Java class has a no-arg
constructor broke when the no-arg constructor is culled. Add
an explicit field for tracking the no-arg constructor property.

Change-Id: Ib68929ae1108bd6fa1fd23de1d134332eb0d97a2
Reviewed-on: https://go-review.googlesource.com/29875
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

bind/genjava.go

@@ -34,8 +34,8 @@ type javaClassInfo struct {
 	// All Java classes and interfaces this class extends and implements.
 	supers  []*java.Class
 	methods map[string]*java.Func
-	// Does the extended class include a noarg constructor
-	hasNoargCon bool
+	// Does the class need a default no-arg constructor
+	genNoargCon bool
 	// Constructors for the type, on the form
 	// func New<Type>(...) *Type
 	cons []*types.Func
@@ -57,7 +57,7 @@ func (g *JavaGen) Init(classes []*java.Class) {
 		}
 		inf := &javaClassInfo{
 			methods:     make(map[string]*java.Func),
-			hasNoargCon: true, // java.lang.Object has a noarg constructor
+			genNoargCon: true, // java.lang.Object has a no-arg constructor
 		}
 		for _, n := range classes {
 			cls := g.clsMap[n]
@@ -76,13 +76,7 @@ func (g *JavaGen) Init(classes []*java.Class) {
 					g.errorf("%s embeds final Java class %s", s.obj, cls.Name)
 				}
 				inf.extends = cls
-				inf.hasNoargCon = false
-				for _, f := range cls.Funcs {
-					if f.Constructor && len(f.Params) == 0 {
-						inf.hasNoargCon = true
-						break
-					}
-				}
+				inf.genNoargCon = cls.HasNoArgCon
 			}
 		}
 		g.jstructs[s.obj] = inf
@@ -91,6 +85,8 @@ func (g *JavaGen) Init(classes []*java.Class) {
 		if t := g.constructorType(f); t != nil {
 			jinf := g.jstructs[t]
 			if jinf != nil {
+				sig := f.Type().(*types.Signature)
+				jinf.genNoargCon = jinf.genNoargCon && sig.Params().Len() > 0
 				jinf.cons = append(jinf.cons, f)
 			}
 		}
@@ -181,7 +177,7 @@ func (g *JavaGen) genStruct(s structInfo) {
 			}
 			g.genConstructor(f, n)
 		}
-		if jinf.hasNoargCon {
+		if jinf.genNoargCon {
 			// Generate constructor for Go instantiated instances.
 			g.Printf("%s(Seq.Ref ref) { this.ref = ref; }\n\n", n)
 			// Generate default no-arg constructor
@@ -1279,7 +1275,7 @@ func (g *JavaGen) GenC() error {
 		if jinf, ok := g.jstructs[s.obj]; ok {
 			// Leave the class and constructor NULL for Java classes with no
 			// default constructor.
-			if !jinf.hasNoargCon {
+			if !jinf.genNoargCon {
 				continue
 			}
 		}
@@ -1328,7 +1324,7 @@ func (g *JavaGen) GenC() error {
 			for _, f := range jinf.cons {
 				g.genJNIConstructor(f, sName)
 			}
-			if jinf.hasNoargCon {
+			if jinf.genNoargCon {
 				g.Printf("JNIEXPORT jobject JNICALL\n")
 				g.Printf("Java_%s_%s_%s(JNIEnv *env, jclass clazz) {\n", g.jniPkgName(), sName, java.JNIMangle("__New"))
 				g.Indent()

bind/testdata/classes.java.c.golden

@@ -125,6 +125,9 @@ Java_go_java_Java__1init(JNIEnv *env, jclass _unused) {
     clazz = (*env)->FindClass(env, "go/java/Future");
     proxy_class_java_Future = (*env)->NewGlobalRef(env, clazz);
     proxy_class_java_Future_cons = (*env)->GetMethodID(env, clazz, "<init>", "(Lgo/Seq$Ref;)V");
+    clazz = (*env)->FindClass(env, "go/java/Object");
+    proxy_class_java_Object = (*env)->NewGlobalRef(env, clazz);
+    proxy_class_java_Object_cons = (*env)->GetMethodID(env, clazz, "<init>", "(Lgo/Seq$Ref;)V");
     clazz = (*env)->FindClass(env, "go/java/Runnable");
     proxy_class_java_Runnable = (*env)->NewGlobalRef(env, clazz);
     proxy_class_java_Runnable_cons = (*env)->GetMethodID(env, clazz, "<init>", "(Lgo/Seq$Ref;)V");
@@ -207,6 +210,12 @@ Java_go_java_InputStream_getInputStream(JNIEnv *env, jobject this) {
     return _r0;
 }
 
+JNIEXPORT jobject JNICALL
+Java_go_java_Object__1_1New(JNIEnv *env, jclass clazz) {
+    int32_t refnum = new_java_Object();
+    return go_seq_from_refnum(env, refnum, NULL, NULL);
+}
+
 JNIEXPORT void JNICALL
 Java_go_java_Object_setObject(JNIEnv *env, jobject this, jobject v) {
     int32_t o = go_seq_to_refnum(env, this);

bind/testdata/classes.java.golden

@@ -75,6 +75,12 @@ public final class Object extends java.lang.Object implements Seq.GoObject {
     
     private final Seq.Ref ref;
     
+    Object(Seq.Ref ref) { this.ref = ref; }
+    
+    public Object() { this.ref = __New(); }
+    
+    private static native Seq.Ref __New();
+    
     @Override public final int incRefnum() {
     	int refnum = ref.refnum;
     	Seq.incGoRef(refnum);

bind/testpkg/javapkg/classes.go

@@ -145,3 +145,7 @@ func NewJavaObject() lang.Object {
 func NewJavaInteger() lang.Integer {
 	return Integer.New_I(42)
 }
+
+type NoargConstructor struct {
+	util.BitSet // An otherwise unused class with a no-arg constructor
+}

internal/importers/java/java.go

@@ -46,6 +46,8 @@ type Class struct {
 	Abstract   bool
 	Interface  bool
 	Throwable  bool
+	// Whether the class has a no-arg constructor
+	HasNoArgCon bool
 }
 
 // Func is a Java static function or method or constructor.
@@ -444,8 +446,12 @@ func (j *importer) scanClass(s *bufio.Scanner, name string) (*Class, error) {
 	if err != nil {
 		return nil, err
 	}
-	if len(cls.Supers) == 0 && name != "java.lang.Object" {
-		cls.Supers = append(cls.Supers, "java.lang.Object")
+	if len(cls.Supers) == 0 {
+		if name == "java.lang.Object" {
+			cls.HasNoArgCon = true
+		} else {
+			cls.Supers = append(cls.Supers, "java.lang.Object")
+		}
 	}
 	cls.JNIName = JNIMangle(cls.Name)
 	clsElems := strings.Split(cls.Name, ".")
@@ -503,6 +509,7 @@ func (j *importer) scanClass(s *bufio.Scanner, name string) (*Class, error) {
 				f.Final = final
 				f.Constructor = f.Name == cls.FindName
 				if f.Constructor {
+					cls.HasNoArgCon = cls.HasNoArgCon || len(f.Params) == 0
 					f.Public = f.Public && !cls.Abstract
 					f.Name = "new"
 					f.Ret = &Type{Class: name, Kind: Object}