reflect: add FuncOf function

This also involves adding functions to typelinks along with a minor
change to ensure they are sorted correctly.

Change-Id: I054a79b6498a634cbccce17579f52c299733c2cf
Reviewed-on: https://go-review.googlesource.com/1996
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/reflect/all_test.go

@@ -3663,6 +3663,67 @@ func TestMapOfGCValues(t *testing.T) {
 	}
 }
 
+func TestTypelinksSorted(t *testing.T) {
+	var last string
+	for i, n := range TypeLinks() {
+		if n < last {
+			t.Errorf("typelinks not sorted: %q [%d] > %q [%d]", last, i-1, n, i)
+		}
+		last = n
+	}
+}
+
+func TestFuncOf(t *testing.T) {
+	// check construction and use of type not in binary
+	type K string
+	type V float64
+
+	fn := func(args []Value) []Value {
+		if len(args) != 1 {
+			t.Errorf("args == %v, want exactly one arg", args)
+		} else if args[0].Type() != TypeOf(K("")) {
+			t.Errorf("args[0] is type %v, want %v", args[0].Type, TypeOf(K("")))
+		} else if args[0].String() != "gopher" {
+			t.Errorf("args[0] = %q, want %q", args[0].String(), "gopher")
+		}
+		return []Value{ValueOf(V(3.14))}
+	}
+	v := MakeFunc(FuncOf([]Type{TypeOf(K(""))}, []Type{TypeOf(V(0))}, false), fn)
+
+	outs := v.Call([]Value{ValueOf(K("gopher"))})
+	if len(outs) != 1 {
+		t.Fatalf("v.Call returned %v, want exactly one result", outs)
+	} else if outs[0].Type() != TypeOf(V(0)) {
+		t.Fatalf("c.Call[0] is type %v, want %v", outs[0].Type, TypeOf(V(0)))
+	}
+	f := outs[0].Float()
+	if f != 3.14 {
+		t.Errorf("constructed func returned %f, want %f", f, 3.14)
+	}
+
+	// check that types already in binary are found
+	type T1 int
+	testCases := []struct {
+		in, out  []Type
+		variadic bool
+		want     interface{}
+	}{
+		{in: []Type{TypeOf(T1(0))}, want: (func(T1))(nil)},
+		{in: []Type{TypeOf(int(0))}, want: (func(int))(nil)},
+		{in: []Type{SliceOf(TypeOf(int(0)))}, variadic: true, want: (func(...int))(nil)},
+		{in: []Type{TypeOf(int(0))}, out: []Type{TypeOf(false)}, want: (func(int) bool)(nil)},
+		{in: []Type{TypeOf(int(0))}, out: []Type{TypeOf(false), TypeOf("")}, want: (func(int) (bool, string))(nil)},
+	}
+	for _, tt := range testCases {
+		checkSameType(t, Zero(FuncOf(tt.in, tt.out, tt.variadic)).Interface(), tt.want)
+	}
+
+	// check that variadic requires last element be a slice.
+	FuncOf([]Type{TypeOf(1), TypeOf(""), SliceOf(TypeOf(false))}, nil, true)
+	shouldPanic(func() { FuncOf([]Type{TypeOf(0), TypeOf(""), TypeOf(false)}, nil, true) })
+	shouldPanic(func() { FuncOf(nil, nil, true) })
+}
+
 type B1 struct {
 	X int
 	Y int