Managing source files and user messages

A real compiler must deal with many files. Usually, the developer calls the compiler with the name of the main compilation unit. This compilation unit can refer to other files, for example, via #include directives in C or import statements in Python or Modula-2. An imported module can import other modules and so on. All these files must be loaded into memory and run through the analysis stages of the compiler. During development, a developer may make syntactical or semantical errors. When detected, an error message, including the source line and a marker, should be printed. At this point, it should be obvious that this essential component is not trivial.

Luckily, LLVM comes with a solution: the llvm::SourceMgr class. A new source file is added to SourceMgr with a call to the AddNewSourceBuffer() method. Alternatively, a file can be loaded with a call to the AddIncludeFile() method. Both methods return an ID to identify the buffer. You use...