Crate harn_hostlib 

harn-hostlib: opt-in host builtins for code intelligence (tree-sitter, repo scanning, deterministic indexing) and tool execution (search, file I/O, git, process lifecycle, file watcher).

This crate is the Rust home of two classes of optional host capabilities:

1. Code intelligence — ast/, code_index/, scanner/, fs_watch/.
2. Deterministic tools — tools/ (search, fs, git, process).

These don’t belong inside harn-vm — pulling tree-sitter grammars, ripgrep, and notify into the VM would balloon the footprint of every pipeline that doesn’t index host code. Instead, this crate exposes a single HostlibCapability trait. Embedders such as harn-cli’s ACP server) compose the modules they need via HostlibRegistry and wire the resulting builtins into the VM through harn_vm::Vm::register_builtin / harn_vm::Vm::register_async_builtin.

Status

The AST, scanner, code-index, and deterministic-tool surfaces are implemented. fs_watch/ still registers its public contract with HostlibError::Unimplemented handlers. Module names, method names, and JSON schemas under schemas/ are the source of truth for hostlib request/response compatibility, so they must stay stable while module bodies evolve.

Re-exports

pub use error::HostlibError;

Modules

ast

AST host capability.

code_index

Code index host capability.

error

Error type for hostlib host calls.

fs_watch

File-system watch host capability.

process

Process abstraction used by the deterministic process tools.

scanner

Repo scanner host capability.

schemas

Embedded JSON Schemas for every hostlib host method.

tools

Deterministic tools capability.

Structs

BuiltinRegistry

Mutable collector each capability writes into during register.

HostlibRegistry

Composes capabilities and emits VM registrations.

RegisteredBuiltin

One registered builtin. The name is what Harn scripts call (e.g. hostlib_ast_parse_file); module and method are the canonical schema-directory coordinates (schemas/<module>/<method>.request.json).

Traits

HostlibCapability

One module’s worth of builtins. Kept tiny on purpose: capabilities exist purely so tests can reason about the surface without booting a VM, and so embedders can opt into individual modules.

Functions

install_default

Convenience: build a HostlibRegistry populated with every capability the crate ships, register them on the supplied VM, and return the registry so callers can introspect (e.g. for schema-drift tests).