Type inference for dynamic programming languages is an important yet challenging task. By leveraging the natural language information of existing human annotations, deep neural networks outperform other traditional techniques and become the state-of-the-art (SOTA) in this task. However, they are facing some new challenges, such as fixed type set, type drift, type correctness, and composite type prediction. To mitigate the challenges, in this paper, we propose a hybrid type inference framework named HiTyper, which integrates static inference into deep learning (DL) models for more accurate type prediction. Specifically, HiTyper creates a new syntax graph for each program, called type graph, illustrating the type flow among all variables in the program. Based on the type graph, HiTyper statically infers the types of the variables with appropriate static constraints. HiTyper then adopts a SOTA DL model to predict the types of other variables that cannot be inferred statically, during which process a type correction algorithm is employed to validate and correct the types recommended by the DL model. Extensive experiments show that HiTyper outperforms the SOTA DL approach by 12.7% in terms of top-1 F1-score. Moreover, HiTyper filters out 50.6% of incorrect candidate types recommended by the SOTA DL model, indicating that HiTyper could improve the correctness of predicted types. Case studies also demonstrate the capability of HiTyper in alleviating the fixed type set issue, and in handling type drift and complicated types such as composite data types.
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