feat: handle invalid WIT-based WASM plugins with helpful error messages

- Add error handling in WasmHost::load_plugin() to detect WIT interface mismatches
- Provide user-friendly error messages with specific solutions:
  - Link to compatible plugin versions for current pluginlab version
  - Suggest updating to latest pluginlab version
- Add comprehensive test case for invalid WIT plugin scenarios
- Include test fixture (valid-plugin-with-invalid-wit.wasm) for testing
- Update README with documentation about WIT compatibility errors and solutions

This improves the user experience when using incompatible plugins by
providing clear guidance on how to resolve version mismatches.

Author: topheman

crates/pluginlab/README.md

@@ -143,3 +143,34 @@ pluginlab\
   --allow-all
     </pre>
 </summary>
+
+<p></p>
+
+If you pass to the `pluginlab` cli a valid plugin but with an incompatible version (cli and plugin not sharing the same `wit` files which defines the interfaces how they interact), you will get an error like the following, which tells you the problem and offers you two solutions:
+
+- use a version of the plugin compatible with the version of the `pluginlab` cli you are using (giving you a link to the releases)
+- use the latest version of the `pluginlab` cli (by running `cargo install pluginlab`)
+
+```
+pluginlab\
+  --repl-logic https://topheman.github.io/webassembly-component-model-experiments/plugins/repl_logic_guest.wasm\
+  --plugins https://topheman.github.io/webassembly-component-model-experiments/plugins/plugin_echo.wasm
+[Host] Starting REPL host...
+[Host] Loading REPL logic from: https://topheman.github.io/webassembly-component-model-experiments/plugins/repl_logic_guest.wasm
+[Host] Loading plugin: https://topheman.github.io/webassembly-component-model-experiments/plugins/plugin_echo.wasm
+[Host]
+[Host] Error: Failed instanciating https://topheman.github.io/webassembly-component-model-experiments/plugins/plugin_echo.wasm
+[Host] You are most likely trying to use a plugin not compatible with pluginlab@0.4.1
+[Host]
+[Host] Try using a compatible version of the plugin by passing the following flag:
+[Host] --plugins https://github.com/topheman/webassembly-component-model-experiments/releases/download/pluginlab@0.4.1/plugin_echo.wasm
+[Host]
+[Host] If it doesn't work, make sure to use the latest version of pluginlab: `cargo install pluginlab`
+[Host]
+[Host] Original error:
+Error: failed to convert function to given type
+
+Caused by:
+    0: type mismatch with results
+    1: expected record of 3 fields, found 4 fields
+```

crates/pluginlab/src/wasm_host.rs

@@ -31,16 +31,36 @@ impl WasmHost {
 
     pub async fn load_plugin(&mut self, engine: &WasmEngine, source: &str) -> Result<()> {
         let component = engine.load_component(source).await?;
-        let plugin = engine
-            .instantiate_plugin(&mut self.store, component)
-            .await?;
-
-        // Get the plugin name from the plugin itself
-        let plugin_name = plugin.repl_api_plugin().call_name(&mut self.store).await?;
-
-        self.plugins.insert(plugin_name, PluginInstance { plugin });
-
-        Ok(())
+        match engine.instantiate_plugin(&mut self.store, component).await {
+            Ok(plugin) => {
+                // Get the plugin name from the plugin itself
+                let plugin_name = plugin.repl_api_plugin().call_name(&mut self.store).await?;
+                self.plugins.insert(plugin_name, PluginInstance { plugin });
+                return Ok(());
+            }
+            Err(e) => {
+                if e.to_string()
+                    .contains("failed to convert function to given type")
+                {
+                    let plugin_filename = source.split("/").last().unwrap();
+                    let crate_version = env!("CARGO_PKG_VERSION");
+                    eprintln!("[Host]");
+                    eprintln!("[Host] Error: Failed instanciating {}", source);
+                    eprintln!(
+                        "[Host] You are most likely trying to use a plugin not compatible with pluginlab@{}",
+                        crate_version
+                    );
+                    eprintln!("[Host]");
+                    eprintln!("[Host] Try using a compatible version of the plugin by passing the following flag:");
+                    eprintln!("[Host] --plugins https://github.com/topheman/webassembly-component-model-experiments/releases/download/pluginlab@{}/{}", crate_version, plugin_filename);
+                    eprintln!("[Host]");
+                    eprintln!("[Host] If it doesn't work, make sure to use the latest version of pluginlab: `cargo install pluginlab`");
+                    eprintln!("[Host]");
+                    eprintln!("[Host] Original error:");
+                }
+                return Err(e);
+            }
+        }
     }
 
     pub async fn load_repl_logic(&mut self, engine: &WasmEngine, source: &str) -> Result<()> {

crates/pluginlab/tests/e2e_cli_host.rs

@@ -88,4 +88,42 @@ mod e2e_cli_host {
             .exp_string("ls: : Operation not permitted")
             .expect("Didn't get expected error output");
     }
+
+    #[test]
+    fn test_with_wrong_version_of_plugin() {
+        let crate_version = env!("CARGO_PKG_VERSION");
+        let project_root = find_project_root();
+        println!("Setting current directory to: {:?}", project_root);
+        std::env::set_current_dir(&project_root).unwrap();
+        let mut session = spawn(
+            &build_command(
+                &["fixtures/valid-plugin-with-invalid-wit.wasm"],
+                "repl_logic_guest.wasm",
+            ),
+            Some(TEST_TIMEOUT),
+        )
+        .expect("Can't launch pluginlab with plugin greet");
+
+        session
+            .exp_string("[Host] Starting REPL host...")
+            .expect("Didn't see startup message");
+        session
+            .exp_string("[Host] Loading plugin:")
+            .expect("Didn't see plugin loading message");
+        session
+            .exp_string(format!(
+"[Host] Error: Failed instanciating fixtures/valid-plugin-with-invalid-wit.wasm\r
+[Host] You are most likely trying to use a plugin not compatible with pluginlab@{}\r
+[Host]\r
+[Host] Try using a compatible version of the plugin by passing the following flag:\r
+[Host] --plugins https://github.com/topheman/webassembly-component-model-experiments/releases/download/pluginlab@{}/valid-plugin-with-invalid-wit.wasm\r
+[Host]\r
+[Host] If it doesn't work, make sure to use the latest version of pluginlab: `cargo install pluginlab`\r
+[Host]\r
+[Host] Original error:",
+                crate_version,
+                crate_version,
+            ).as_str())
+            .expect("Didn't see error output");
+    }
 }