feat(wasmtime): add error hint for missing WASI imports

This commit adds some code to print an error hint when a failed
`wasmtime run` command could have been called with arguments (in
particular `-S <capability>`) that would have enabled the command to succeed.

Signed-off-by: Victor Adossi <[email protected]>

crates/cli-flags/src/lib.rs

@@ -457,6 +457,18 @@ wasmtime_option_group! {
     }
 }
 
+impl WasiOptions {
+    /// Get the name of a relevant WASI option for a given import
+    pub fn option_for_import(import_name: &str) -> Option<&str> {
+        // TODO: do we have common import parsing machinery?
+        if import_name.contains("wasi:http") {
+            return Some("http");
+        }
+        // TODO: fill out
+        return None;
+    }
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub struct WasiNnGraph {
     pub format: String,

src/commands/run.rs

@@ -15,6 +15,7 @@ use std::sync::{Arc, Mutex};
 use std::thread;
 use wasi_common::sync::{ambient_authority, Dir, TcpListener, WasiCtxBuilder};
 use wasmtime::{Engine, Func, Module, Store, StoreLimits, Val, ValType};
+use wasmtime_cli_flags::WasiOptions;
 use wasmtime_wasi::{IoView, WasiView};
 
 #[cfg(feature = "wasi-nn")]
@@ -472,12 +473,20 @@ impl RunCommand {
 
                 let component = module.unwrap_component();
 
-                let command = wasmtime_wasi::bindings::Command::instantiate_async(
+                let command = match wasmtime_wasi::bindings::Command::instantiate_async(
                     &mut *store,
                     component,
                     linker,
                 )
-                .await?;
+                .await
+                {
+                    Ok(c) => c,
+                    Err(e) => {
+                        print_wasi_import_option_hint(&e.to_string(), component, store);
+                        bail!(e);
+                    }
+                };
+
                 let result = command
                     .wasi_cli_run()
                     .call_run(&mut *store)
@@ -1026,3 +1035,28 @@ fn write_core_dump(
         .with_context(|| format!("failed to write core dump file at `{path}`"))?;
     Ok(())
 }
+
+/// Print a hint about wasi import options for a given error
+/// message, only if it contains an error that is likely to refer
+/// to a missing option (i.e. -S <wasi import>)
+#[cfg(feature = "component-model")]
+fn print_wasi_import_option_hint(
+    err_string: &str,
+    component: &wasmtime::component::Component,
+    store: &mut Store<Host>,
+) {
+    if err_string.contains("matching implementation was not found in the linker") {
+        // Check if we're missing some imports that could have been provided by
+        for (name, _) in component.component_type().imports(store.engine()) {
+            if err_string.contains(&name) {
+                if let Some(option) = WasiOptions::option_for_import(&name) {
+                    eprintln!(
+                        "warning: missing import [{name}] has a WASI import option [{option}]  \
+                         that has not been enabled -- consider re-running with '-S {option}'.\n\
+                         Run `wasmtime -S help` for a full list of WASI import options.\n",
+                    );
+                }
+            }
+        }
+    }
+}