fix: parser hangs when a bracket isn't closed (#1005) (#1029)

Co-authored-by: harrisbisset <hb233@st-andrews.ac.uk>
Co-authored-by: Harris Bisset <harrisbisset@gmail.com>
Co-authored-by: Adrian Hesketh <adrianhesketh@hushmail.com>

parser/v2/goexpression/parse_test.go

@@ -354,6 +354,18 @@ var expressionTests = []testInput{
 		name:  "string concat",
 		input: `direction + "newest"`,
 	},
+	{
+		name: "function call",
+		input: `SplitRule(types.GroupMember{
+    UserID:   uuid.NewString(),
+    Username: "user me",
+}, []types.GroupMember{
+    {
+    UserID:   uuid.NewString(),
+    Username: "user 1",
+    },
+})`,
+	},
 }
 
 func TestExpression(t *testing.T) {

parser/v2/goexpression/scanner.go

@@ -82,6 +82,16 @@ func (ep *ExpressionParser) Insert(
 	defer func() {
 		ep.Previous = tok
 	}()
+
+	// If we've reach the end of the file, terminate reading.
+	if tok == token.EOF {
+		// If the EOF was reached, but we're not at the top level, we must have an unbalanced expression.
+		if !ep.isTopLevel() {
+			return true, ErrUnbalanced{ep.Stack.Pop()}
+		}
+		return true, nil
+	}
+
 	// Handle function literals e.g. func() { fmt.Println("Hello") }
 	// By pushing the current depth onto the stack, we prevent stopping
 	// until we've closed the function.

parser/v2/templelementparser_test.go

@@ -449,3 +449,36 @@ func TestTemplElementExpressionParser(t *testing.T) {
 		})
 	}
 }
+
+func TestTemplElementExpressionParserFailures(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name: "templelement: missing closing brace",
+			input: `@SplitRule(types.GroupMember{
+    UserID:   uuid.NewString(),
+    Username: "user me",
+}, []types.GroupMember{
+    {
+    UserID:   uuid.NewString(),
+    Username: "user 1",
+    },
+`,
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			input := parse.NewInput(tt.input)
+			_, ok, err := templElementExpression.Parse(input)
+			if err == nil {
+				t.Fatalf("expected an error")
+			}
+			if ok {
+				t.Fatalf("expected a failure")
+			}
+		})
+	}
+}