Code Generation

The code generator converts the Mist AST into Rust source code directly — no intermediate representation.

Key files

• src/lib.rs — RustCodegen struct with output buffer, indentation tracking, Mapping for position translation
• src/top_level.rs — Generates Rust for top-level items (structs, enums, traits, functions, impls, imports, type aliases, const/static)
• src/statement.rs — Generates Rust for statements and blocks
• src/expr.rs — Generates Rust for expressions (literals, paths, binary ops, closures, arrays, prefix/postfix)
• src/class_decl.rs — Class-specific code generation (struct + vtable + impl blocks + Deref)

Codegen Design

The RustCodegen maintains:

• A string output buffer
• An indent level (4 spaces per level)
• A Mapping that records (RustMap, MistMap) pairs for source position remapping
• A current position tracker (RustMap(line, column))

Generation follows the GenRust trait:

pub trait GenRust {
    fn gen_rust(&self, ctx: &mut Context, cg: &mut RustCodegen);
}

And GetRust for simple string-returning types:

pub trait GetRust {
    fn get_rust(&self) -> String;
}

The Context carries optional expression path information for class super / Super resolution.

Class Codegen

Classes are the most complex codegen path. ClassProcessedData analyzes a class declaration and emits:

1. Struct declaration — struct ClassName<G> { pub _super: Parent, pub field1: T1, ... } (or _vptr for root classes)
2. Vtable constants — Index constants __FN_METHOD and a __V_TABLE static array of function pointers. For inherited classes, parent vtable entries are copied and overridden entries replaced.
3. Constructor — pub fn new(...) -> Self that creates an uninitialized instance via MaybeUninit, sets the vtable pointer, writes field defaults, calls self.constructor(...), and returns this
4. Method trampolines — Public methods with self get wrapper functions __m_method stored in the vtable, plus virtual dispatch methods
5. Override support — Methods marked override are validated at compile time via generated test code
6. Deref impls — impl Deref<Target = Parent> for Child and DerefMut for inherited classes
7. Impl declarations — Inner impl blocks are rewritten to use the self type