Merge pull request #4 from ok2/fix/web-error-messages

fix(web): surface Forth messages from host-word throws

CHANGELOG.md

@@ -5,6 +5,22 @@ All notable changes to WAFER are documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.4] - 2026-08-06
+
+### Fixed
+
+- **Errors from host words in the browser build read like Forth errors
+  again.** A host word signals failure by throwing across the JS
+  boundary, and the browser runtime reported the exception with its
+  `Debug` form, so an empty-stack `RESIZE` came back as
+  `call_func(134) failed: JsValue(Error: Stack underflow ...)` trailed by
+  an engine stack trace. The thrown message is the Forth message, so it
+  is now surfaced verbatim — `Stack underflow`, exactly what the native
+  CLI prints. Exceptions that carry no message keep the call context,
+  since those are genuine runtime faults rather than Forth throws.
+  `CATCH` was never affected: it reads the throw code from its own
+  channel, not from the message.
+
 ## [0.2.3] - 2026-08-06
 
 ### Fixed

Cargo.lock

@@ -1589,7 +1589,7 @@ checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
 [[package]]
 name = "wafer"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "anyhow",
  "clap",
@@ -1600,7 +1600,7 @@ dependencies = [
 
 [[package]]
 name = "wafer-core"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "anyhow",
  "insta",
@@ -1615,7 +1615,7 @@ dependencies = [
 
 [[package]]
 name = "wafer-web"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "anyhow",
  "js-sys",

Cargo.toml

@@ -3,7 +3,7 @@ members = ["crates/*"]
 resolver = "2"
 
 [workspace.package]
-version = "0.2.3"
+version = "0.2.4"
 edition = "2024"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/ok2/wafer"

crates/cli/Cargo.toml

@@ -9,7 +9,7 @@ license.workspace = true
 workspace = true
 
 [dependencies]
-wafer-core = { path = "../core", version = "0.2.3" }
+wafer-core = { path = "../core", version = "0.2.4" }
 wasmtime = { workspace = true }
 anyhow = { workspace = true }
 clap = { version = "4", features = ["derive"] }

crates/web/Cargo.toml

@@ -12,7 +12,7 @@ workspace = true
 crate-type = ["cdylib", "rlib"]
 
 [dependencies]
-wafer-core = { path = "../core", version = "0.2.3", default-features = false, features = ["crypto"] }
+wafer-core = { path = "../core", version = "0.2.4", default-features = false, features = ["crypto"] }
 wasm-bindgen = "0.2"
 js-sys = "0.3"
 send_wrapper = { workspace = true }

crates/web/src/runtime_web.rs

@@ -38,6 +38,23 @@ impl WebHostAccess {
     }
 }
 
+/// An exception on its way back out of compiled code. Host words rethrow the
+/// Forth message (`Stack underflow`, an `ABORT"` text, a `THROW` description),
+/// so surface exactly that and nothing else — the JS `Error` carries the whole
+/// engine stack in its message, which is noise to a Forth programmer. Anything
+/// without a message is a genuine runtime fault and keeps the call context.
+fn call_error(fn_index: u32, e: &JsValue) -> anyhow::Error {
+    match Reflect::get(e, &"message".into())
+        .ok()
+        .and_then(|m| m.as_string())
+        .and_then(|m| m.lines().next().map(str::trim).map(str::to_string))
+        .filter(|m| !m.is_empty())
+    {
+        Some(msg) => anyhow::anyhow!("{msg}"),
+        None => anyhow::anyhow!("call_func({fn_index}) failed: {e:?}"),
+    }
+}
+
 impl HostAccess for WebHostAccess {
     fn mem_read_i32(&mut self, addr: u32) -> i32 {
         let view = js_sys::Int32Array::new(&self.buffer());
@@ -134,7 +151,7 @@ impl HostAccess for WebHostAccess {
             .dyn_into()
             .map_err(|_| anyhow::anyhow!("table entry {fn_index} is not a function"))?;
         func.call0(&JsValue::NULL)
-            .map_err(|e| anyhow::anyhow!("call_func({fn_index}) failed: {e:?}"))?;
+            .map_err(|e| call_error(fn_index, &e))?;
         Ok(())
     }
 }
@@ -406,7 +423,7 @@ impl Runtime for WebRuntime {
             .dyn_into()
             .map_err(|_| anyhow::anyhow!("table entry {fn_index} is not callable"))?;
         func.call0(&JsValue::NULL)
-            .map_err(|e| anyhow::anyhow!("call_func({fn_index}) failed: {e:?}"))?;
+            .map_err(|e| call_error(fn_index, &e))?;
         Ok(())
     }