This repository is the main source code for the Rust programming language compiler (rustc) and its standard library. It is a monorepo containing the compiler, standard library (core, alloc, std), and development tools (clippy linter, miri interpreter, rustfmt formatter, rust-analyzer, rustdoc documentation generator). The compiler is implemented as a collection of Rust crates under compiler/, each handling a specific phase: lexing, parsing, AST construction, HIR lowering, type inference, borrow checking, MIR optimization, and code generation (LLVM, GCC, Cranelift backends). The architecture is modular with well-defined interfaces between phases, enabling incremental compilation and separate development of backends. The primary entry point is compiler/rustc/src/main.rs, which drives the compilation pipeline. Source code flows through the lexer, parser, AST, HIR, MIR, and finally to code generation. The borrow checker (rustc_borrowck) performs region-based static analysis for memory safety. The type inference engine (rustc_infer) handles complex type relationships including generics, traits, and higher-ranked types. The MIR optimization framework (rustc_mir_transform) applies numerous passes such as constant propagation, dead store elimination, and GVN. External dependencies include LLVM for the primary code generation backend, libgccjit for the GCC backend, and various system libraries for platform-specific functionality. The standard library provides OS abstractions, synchronization primitives, I/O, and collections. The repository also includes extensive test suites (tests/) covering compiler diagnostics, code generation, optimization, and tool behavior.