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An informal guide to reading and working on the rustc compiler. ================================================================== If you wish to expand on this document, or have a more experienced Rust contributor add anything else to it, please get in touch: https://github.com/mozilla/rust/wiki/Note-development-policy ("Communication" subheading) or file a bug: https://github.com/mozilla/rust/issues Your concerns are probably the same as someone else's. High-level concepts =================== Rustc consists of the following subdirectories: front/ - front-end: attributes, conditional compilation middle/ - middle-end: name resolution, typechecking, LLVM code generation back/ - back-end: linking and ABI metadata/ - serializer and deserializer for data required by separate compilation driver/ - command-line processing, main() entrypoint util/ - ubiquitous types and helper functions lib/ - bindings to LLVM The files concerned purely with syntax -- that is, the AST, parser, pretty-printer, lexer, macro expander, and utilities for traversing ASTs -- are in a separate crate called "syntax", whose files are in ./../libsyntax if the parent directory of front/, middle/, back/, and so on is . . The entry-point for the compiler is main() in driver/rustc.rs, and this file sequences the various parts together. The 3 central data structures: ------------------------------ #1: ../libsyntax/ast.rs defines the AST. The AST is treated as immutable after parsing, but it depends on mutable context data structures (mainly hash maps) to give it meaning. - Many -- though not all -- nodes within this data structure are wrapped in the type spanned<T>, meaning that the front-end has marked the input coordinates of that node. The member .node is the data itself, the member .span is the input location (file, line, column; both low and high). - Many other nodes within this data structure carry a def_id. These nodes represent the 'target' of some name reference elsewhere in the tree. When the AST is resolved, by middle/resolve.rs, all names wind up acquiring a def that they point to. So anything that can be pointed-to by a name winds up with a def_id. #2: middle/ty.rs defines the datatype sty. This is the type that represents types after they have been resolved and normalized by the middle-end. The typeck phase converts every ast type to a ty::sty, and the latter is used to drive later phases of compilation. Most variants in the ast::ty tag have a corresponding variant in the ty::sty tag. #3: lib/llvm.rs defines the exported types ValueRef, TypeRef, BasicBlockRef, and several others. Each of these is an opaque pointer to an LLVM type, manipulated through the lib::llvm interface. Control and information flow within the compiler: ------------------------------------------------- - main() in driver/rustc.rs assumes control on startup. Options are parsed, platform is detected, etc. - libsyntax/parse/parser.rs parses the input files and produces an AST that represents the input crate. - Multiple middle-end passes (middle/resolve.rs, middle/typeck.rs) analyze the semantics of the resulting AST. Each pass generates new information about the AST and stores it in various environment data structures. The driver passes environments to each compiler pass that needs to refer to them. - Finally middle/trans.rs translates the Rust AST to LLVM bitcode in a type-directed way. When it's finished synthesizing LLVM values, rustc asks LLVM to write them out in some form (.bc, .o) and possibly run the system linker.