ASTImporter is part of Clang's core library, the AST library. There are cases when we have to work with more than one AST contexts, but we would like to view the set of the ASTs as if they were one big AST resulting from the parsing of all files together. ASTImporter imports nodes of an AST context into another AST context. Existing clients of the ASTImporter library are Cross Translation Unit (CTU) static analysis and the LLDB expression parser. CTU static analysis imports a definition of a function if its definition is found in another translation unit (TU). This way the analysis can breach out from the single TU limitation. LLDB’s "expr" command parses a user-defined expression, creates an ASTContext for that and then imports the missing definitions from the AST what we got from the debug information (DWARF, etc).
