bind, bind/java: support generating exceptional constructors

In Go type constructors can often return an error type too
beside an instance of the type being created. This is useful
in cases where the parameters might be wrong and instantiaion
cannot succeed. This CL extends the Java generator so that
these methods are also converted into class constructors that
also can throw.

Change-Id: I5e531eec126904a026767a8503968255b9fd833b
Reviewed-on: https://go-review.googlesource.com/31184
Reviewed-by: Elias Naur <elias.naur@gmail.com>

bind/gen.go

@@ -175,13 +175,14 @@ func (g *Generator) Init() {
 	}
 }
 
-// constructorType returns the type T for a function on the form
+// constructorType returns the type T for a function of the forms:
 //
-// func NewT(...) *T
+// func NewT...(...) *T
+// func NewT...(...) (*T, error)
 func (g *Generator) constructorType(f *types.Func) *types.TypeName {
 	sig := f.Type().(*types.Signature)
 	res := sig.Results()
-	if res.Len() != 1 {
+	if res.Len() != 1 && !(res.Len() == 2 && isErrorType(res.At(1).Type())) {
 		return nil
 	}
 	rt := res.At(0).Type()

bind/genjava.go

@@ -941,6 +941,7 @@ func (g *JavaGen) genJNIConstructor(f *types.Func, sName string) {
 		return
 	}
 	sig := f.Type().(*types.Signature)
+	res := sig.Results()
 
 	g.Printf("JNIEXPORT jobject JNICALL\n")
 	g.Printf("Java_%s_%s_%s(JNIEnv *env, jclass clazz", g.jniPkgName(), sName, java.JNIMangle("__"+f.Name()))
@@ -956,8 +957,12 @@ func (g *JavaGen) genJNIConstructor(f *types.Func, sName string) {
 		name := g.paramName(params, i)
 		g.genJavaToC(name, params.At(i).Type(), modeTransient)
 	}
-	// Constructors always have one result parameter, a *T.
-	g.Printf("int32_t refnum = proxy%s__%s(", g.pkgPrefix, f.Name())
+	// Constructors always return a mandatory *T and an optional error
+	if res.Len() == 1 {
+		g.Printf("int32_t refnum = proxy%s__%s(", g.pkgPrefix, f.Name())
+	} else {
+		g.Printf("struct proxy%s__%s_return res = proxy%s__%s(", g.pkgPrefix, f.Name(), g.pkgPrefix, f.Name())
+	}
 	for i := 0; i < params.Len(); i++ {
 		if i > 0 {
 			g.Printf(", ")
@@ -968,6 +973,12 @@ func (g *JavaGen) genJNIConstructor(f *types.Func, sName string) {
 	for i := 0; i < params.Len(); i++ {
 		g.genRelease(g.paramName(params, i), params.At(i).Type(), modeTransient)
 	}
+	// Extract multi returns and handle errors
+	if res.Len() == 2 {
+		g.Printf("int32_t refnum = res.r0;\n")
+		g.genCToJava("_err", "res.r1", res.At(1).Type(), modeRetained)
+		g.Printf("go_seq_maybe_throw_exception(env, _err);\n")
+	}
 	// Pass no proxy class so that the Seq.Ref is returned instead.
 	g.Printf("return go_seq_from_refnum(env, refnum, NULL, NULL);\n")
 	g.Outdent()

bind/java/SeqTest.java

@@ -530,12 +530,27 @@ public class SeqTest extends InstrumentationTestCase {
   public void testConstructor() {
     Interface i = new Concrete();
     i.f();
+
     S2 s = new S2(1, 2);
     assertEquals("new S2().sum", 3.0, s.sum());
     assertEquals("new S2().tryTwoStrings", "gostring", s.tryTwoStrings("go", "string"));
-	new S3();
-	S4 s4 = new S4(123);
-	assertEquals("Constructor argument", 123, s4.getI());
+
+	  new S3();
+
+	  S4 s4 = new S4(123);
+	  assertEquals("Constructor argument", 123, s4.getI());
+
+    s4 = new S4(123.456);
+    assertEquals("Overloaded constructor argument", 123, s4.getI());
+
+    s4 = new S4(false);
+    assertEquals("Exceptional constructor", 0, s4.getI());
+
+    try {
+      s4 = new S4(true);
+      fail("Constructor error wasn't caught");
+    } catch (Exception e) {
+    }
   }
 
   public void testEmptyError() {

bind/testpkg/testpkg.go

@@ -558,3 +558,14 @@ type S4 struct {
 func NewS4WithInt(i int) *S4 {
 	return &S4{i}
 }
+
+func NewS4WithFloat(f float64) *S4 {
+	return &S4{int(f)}
+}
+
+func NewS4WithBoolAndError(b bool) (*S4, error) {
+	if b {
+		return nil, errors.New("some error")
+	}
+	return new(S4), nil
+}