The Zig compiler has implemented incremental compilation, a feature that significantly speeds up rebuild times. This allows the compiler to identify changed functions and declarations, recompile only that specific code, and patch the output binary directly. This has transformed Zig's rebuild process from a proof-of-concept to a daily tool for the core team, enabling changes in complex applications within milliseconds.

The process begins with file processing, where source files are parsed into an Abstract Syntax Tree (AST) and then converted into Zig Intermediate Representation (ZIR). This stage is embarrassingly parallel and ZIR can be efficiently cached to disk. Changes to a file only trigger recompilation if the file's content has changed, making this part of the pipeline nearly instantaneous.

The more challenging aspect is semantic analysis, which includes type checking and comptime evaluation. Zig's design has been optimized for incremental compilation by breaking down analysis into 'analysis units.' These units represent aspects like type layouts, declaration types, constant values, and runtime function bodies. By modeling dependencies between these units, the compiler can precisely determine which parts need re-analysis when changes occur, drastically reducing build times for modified code. This advanced feature is expected to be fully available in Zig 0.17.0.