proc/variables: bugfix: nil pointer with interfaces to functions

Fixes #325

_fixtures/testvariables3.go

@@ -25,6 +25,13 @@ func afunc(x int) int {
 	return x + 2
 }
 
+func afunc1(x int) {
+}
+
+func afunc2() int {
+	return 0
+}
+
 type functype func(int) int
 
 func (a *astruct) Error() string {
@@ -125,6 +132,8 @@ func main() {
 	recursive1 := dstruct{}
 	recursive1.x = &recursive1
 	var iface5 interface{} = &recursive1
+	var iface2fn1 interface{} = afunc1
+	var iface2fn2 interface{} = afunc2
 
 	var amb1 = 1
 	runtime.Breakpoint()
@@ -132,5 +141,5 @@ func main() {
 		fmt.Println(amb1)
 	}
 	runtime.Breakpoint()
-	fmt.Println(i1, i2, i3, p1, amb1, s1, s3, a1, p2, p3, s2, as1, str1, f1, fn1, fn2, nilslice, nilptr, ch1, chnil, m1, mnil, m2, m3, up1, i4, i5, i6, err1, err2, errnil, iface1, iface2, ifacenil, arr1, parr, cpx1, const1, iface3, iface4, recursive1, recursive1.x, iface5)
+	fmt.Println(i1, i2, i3, p1, amb1, s1, s3, a1, p2, p3, s2, as1, str1, f1, fn1, fn2, nilslice, nilptr, ch1, chnil, m1, mnil, m2, m3, up1, i4, i5, i6, err1, err2, errnil, iface1, iface2, ifacenil, arr1, parr, cpx1, const1, iface3, iface4, recursive1, recursive1.x, iface5, iface2fn1, iface2fn2)
 }

proc/proc_test.go

@@ -1063,3 +1063,17 @@ func TestIssue316(t *testing.T) {
 		assertNoError(err, t, "EvalVariable()")
 	})
 }
+
+func TestIssue325(t *testing.T) {
+	// nil pointer dereference when evaluating interfaces to function pointers
+	withTestProcess("testvariables3", t, func(p *Process, fixture protest.Fixture) {
+		assertNoError(p.Continue(), t, "Continue()")
+		iface2fn1v, err := evalVariable(p, "iface2fn1")
+		assertNoError(err, t, "EvalVariable()")
+		t.Logf("iface2fn1: %v\n", iface2fn1v)
+
+		iface2fn2v, err := evalVariable(p, "iface2fn2")
+		assertNoError(err, t, "EvalVariable()")
+		t.Logf("iface2fn2: %v\n", iface2fn2v)
+	})
+}

proc/types.go

@@ -98,8 +98,10 @@ func (dbp *Process) expandPackagesInType(expr ast.Expr) {
 		for i := range e.Params.List {
 			dbp.expandPackagesInType(e.Params.List[i].Type)
 		}
-		for i := range e.Results.List {
-			dbp.expandPackagesInType(e.Results.List[i].Type)
+		if e.Results != nil {
+			for i := range e.Results.List {
+				dbp.expandPackagesInType(e.Results.List[i].Type)
+			}
 		}
 	case *ast.MapType:
 		dbp.expandPackagesInType(e.Key)