Compiler-directed Migrating API Callsite of Client Code

API developers evolve software libraries to fix bugs, add new features, or refactor code, but the evolution can introduce API-breaking changes (e.g., API renaming). To benefit from such evolution, the programmers of client projects have to repetitively upgrade the callsites of libraries, since API-breaking changes introduce many compilation errors. It is tedious and error-prone to resolve such errors, especially when programmers are often unfamiliar with the API usages of newer versions. To migrate client code, the prior approaches either mine API mappings or learn edit scripts, but both the research lines have inherent limitations. For example, mappings alone cannot handle complex cases, and there is no sufficient source (e.g., migration commits) for learning edit scripts. In this paper, we propose a new research direction. When a library is replaced with a newer version, each type of API-breaking change introduces a type of compilation error. For example, renaming the name of an API method causes undefined-method errors at its callsites. Based on this observation, we propose to resolve errors that are introduced by migration, according to their locations and types that are reported by compilers. In this way, a migration tool can incrementally migrate complex cases, even without any change examples. Towards this direction, we propose the first approach, called LibCatch. It defines 14 migration operators, and in a compiler-directed way, it exploits the combinations of migration operators to generate migration solutions, until its predefined criteria are satisfied. We conducted two evaluations. In the first evaluation, we use LibCatch to handle 123 migration tasks. LibCatch reduced migration-related compilation errors for 92.7% of tasks, and eliminated such errors for 32.4% of tasks. We inspect the tasks whose errors are eliminated, and find that 33.9% of them produce identical edits to manual migration edits. In the second evaluation, we use two tools and LibCatch to migrate 15 real client projects in the wild. LibCatch resolved all compilation errors of 7 projects, and reduced the compilation errors of 6 other projects to no more than two errors. As a comparison, the compared two tools reduced the compilation errors of only 1 project.