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Compiler Frontends and Source Plugins

pd-vm keeps the built-in frontend surface focused on RustScript (.rss). Additional source languages are provided by crates that implement the SourcePlugin trait and pass themselves through CompileSourceFileOptions.

The compatibility JavaScript and Lua frontends live outside this repository in:

  • pd-vm-compat-frontends

Built-in RustScript (.rss)

Supported syntax and features:

  • Statements: use, fn, pub fn, let, assignment, indexed/member assignment, if/else, while, C-style for, break, continue.
  • Expressions: literals (int, float, bool, string, null), arithmetic (+ - * / %), logical (! && ||), comparison (== != < >), function calls, closures (|...| expr), if-expression form (if cond => { ... } else => { ... }), match expressions.
  • Match patterns: int/string/null literals, wildcard _, None, non-null binding patterns Some(name), and type constructors Some(TypeName) / Option::Some(TypeName).
  • Collections: array literal [], brace literals for arrays/maps, obj.member, obj[key], optional chaining (?. and ?.[key]), slice syntax ([a:b], [:b], [a:]), map key literals including null.
  • Host/runtime calls:
    • builtins via namespaces: io::..., re::..., json::..., jit::..., math::...
    • host namespaces via use <namespace>;, use <namespace> as <alias>;, or use <namespace>::{name as local};
  • RustScript rewrites:
    • Option::None -> null
    • Option::Some(expr) -> (expr)
    • print("...", ...) and println("...", ...) support Rust-style std::fmt formatting
  • RustScript compile-time type rules:
    • unresolved unknown states are compile errors on the RustScript path
    • + is inferred as string concatenation when either side is known string
    • known mixed numeric arithmetic widens to float
    • incompatible known if/else expression results and branch-local merges are compile errors

Source Plugin Contract

A source plugin supplies three things:

  1. parse_source(...) -> FrontendIr
  2. parse_imports(...) -> Vec<ModuleImport>
  3. strip_imports(...) -> String

Register the plugin on compile options:

use pd_vm::{compile_source_file_with_options, CompileSourceFileOptions};

let options = CompileSourceFileOptions::new()
    .with_source_plugin(pd_vm_compat_frontends::plugin());
let compiled = compile_source_file_with_options("examples/example.js", options)?;

compile_source_file() without options only handles built-in .rss files. .js and .lua paths need a plugin registered for their SourceFlavor.

Frontend-wide Policy Notes

  • All accepted sources lower into FrontendIr, then use the same linker, type metadata pass, bytecode backend, debugger metadata, and VM runtime.
  • Plugin frontends can reuse the shared expression parser through parse_source_with_dialect(...), or build FrontendIr directly.
  • Plugins own compatibility-language import parsing and import stripping so core module loading does not encode language-specific import syntax.