Practical scope recovery using bridge parsing

Interactive development environments (IDEs) increase programmer productivity, but unfortunately also the burden on language implementors since sophisticated tool support is expected even for small domain-specific languages. Our goal is to alleviate that burden, by generating IDEs from high-level language specifications using the JastAdd meta-compiler system. This puts increased tension on scope recovery in parsers, since at least a partial AST is required by the system to perform static analysis, such as name completion and context sensitive search. In this paper we present a novel recovery algorithm called bridge parsing, which provides a light-weight recovery mechanism that complements existing parsing recovery techniques. An initial phase recovers nesting structure in source files making them easier to process by existing parsers. This enables batch parser generators with existing grammars to be used in an interactive setting with minor or no modifications. We have implemented bridge parsing in a generic extensible IDE for JastAdd based compilers. It is independent of parsing technology, which we validate by showing how it improves recovery in a set of typical interactive editing scenarios for three parser generators: ANTLR (LL(variable lookahead) parsers), LPG (LALR(k) parsers), and Beaver (LALR(1) parsers). ANTLR and LPG both contain sophisticated support for error recovery, while Beaver requires manual error productions. Bridge parsing complements these techniques and yields better recovery for all these tools with only minimal changes to existing grammars