harn_hostlib/
error.rs

1//! Error type for hostlib host calls.
2//!
3//! Builtins translate this into VM-level errors via [`Into<harn_vm::VmError>`]
4//! so that Harn scripts see structured exceptions rather than panics.
5
6use std::collections::BTreeMap;
7use std::rc::Rc;
8
9use harn_vm::{VmError, VmValue};
10
11/// All errors a hostlib builtin can surface.
12///
13/// Variants intentionally describe the *kind* of failure rather than the
14/// specific module — every module routes its missing-implementation errors
15/// through [`HostlibError::Unimplemented`] so embedders and tests can
16/// distinguish intentionally scaffolded contracts from runtime failures.
17#[derive(Debug, thiserror::Error)]
18pub enum HostlibError {
19    /// The method exists in the registration table but has no implementation
20    /// yet. This is the canonical scaffold-stage error: it tells callers
21    /// "the contract is stable, but this module has not been implemented."
22    #[error(
23        "hostlib: {builtin} is not implemented yet (scaffolded contract without an implementation)"
24    )]
25    Unimplemented {
26        /// Fully-qualified builtin name, e.g. `"hostlib_ast_parse_file"`.
27        builtin: &'static str,
28    },
29
30    /// A required parameter was missing from the call payload.
31    #[error("hostlib: {builtin}: missing required parameter '{param}'")]
32    MissingParameter {
33        /// Fully-qualified builtin name.
34        builtin: &'static str,
35        /// Name of the missing parameter.
36        param: &'static str,
37    },
38
39    /// A parameter was present but had the wrong shape (wrong type, malformed).
40    #[error("hostlib: {builtin}: invalid parameter '{param}': {message}")]
41    InvalidParameter {
42        /// Fully-qualified builtin name.
43        builtin: &'static str,
44        /// Name of the invalid parameter.
45        param: &'static str,
46        /// Human-readable description of the violation.
47        message: String,
48    },
49
50    /// Catch-all wrapper for I/O, parsing, or other backend failures.
51    #[error("hostlib: {builtin}: {message}")]
52    Backend {
53        /// Fully-qualified builtin name.
54        builtin: &'static str,
55        /// Human-readable failure description.
56        message: String,
57    },
58}
59
60impl HostlibError {
61    /// The fully-qualified builtin name this error came from. Useful for
62    /// embedder logging and for the routing tests in `tests/`.
63    pub fn builtin(&self) -> &'static str {
64        match self {
65            HostlibError::Unimplemented { builtin }
66            | HostlibError::MissingParameter { builtin, .. }
67            | HostlibError::InvalidParameter { builtin, .. }
68            | HostlibError::Backend { builtin, .. } => builtin,
69        }
70    }
71}
72
73impl From<HostlibError> for VmError {
74    fn from(err: HostlibError) -> VmError {
75        // Surface as a `Thrown` dict so Harn `try`/`catch` can pattern-match
76        // on `kind`, `builtin`, and `message`. This matches how the existing
77        // `host_call` error path shapes its exceptions.
78        let kind = match err {
79            HostlibError::Unimplemented { .. } => "unimplemented",
80            HostlibError::MissingParameter { .. } => "missing_parameter",
81            HostlibError::InvalidParameter { .. } => "invalid_parameter",
82            HostlibError::Backend { .. } => "backend_error",
83        };
84        let builtin = err.builtin();
85        let message = err.to_string();
86
87        let mut dict: BTreeMap<String, VmValue> = BTreeMap::new();
88        dict.insert("kind".to_string(), VmValue::String(Rc::from(kind)));
89        dict.insert("builtin".to_string(), VmValue::String(Rc::from(builtin)));
90        dict.insert("message".to_string(), VmValue::String(Rc::from(message)));
91        VmError::Thrown(VmValue::Dict(Rc::new(dict)))
92    }
93}
harn_hostlib/error.rs

harn_hostlib/
error.rs
