Merge #1033

1033: Improve default compiler story for wasmer cli r=MarkMcCaskey a=MarkMcCaskey

This PR needs the following to be ready to ship:

- [x] Verified make commands are still fine
- [x] Verified this doesn't do anything bad in CI

This PR adds:
- compile_error if no backend is specified in wasmer.rs
- readds clif as the default
- improves the error message saying "specified backend not found" to include the name of the backend that it couldn't find

Co-authored-by: Mark McCaskey <mark@wasmer.io>
Co-authored-by: Mark McCaskey <5770194+markmccaskey@users.noreply.github.com>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## **[Unreleased]**
 
+- [#1033](https://github.com/wasmerio/wasmer/pull/1033) Set cranelift backend as default compiler backend again, require at least one backend to be enabled for Wasmer CLI
 - [#1030](https://github.com/wasmerio/wasmer/pull/1030) Ability to generate `ImportObject` for a specific version WASI version with the C API.
 - [#1028](https://github.com/wasmerio/wasmer/pull/1028) Introduce strict/non-strict modes for `get_wasi_version`
 - [#1029](https://github.com/wasmerio/wasmer/pull/1029) Add the “floating” `WasiVersion::Latest` version.

Cargo.toml

@@ -74,7 +74,7 @@ serde = { version = "1", features = ["derive"] } # used by the plugin example
 typetag = "0.1" # used by the plugin example
 
 [features]
-default = ["fast-tests", "wasi"]
+default = ["fast-tests", "wasi", "backend-cranelift"]
 "loader-kernel" = ["wasmer-kernel-loader"]
 debug = ["wasmer-runtime-core/debug"]
 trace = ["wasmer-runtime-core/trace"]

src/bin/wasmer.rs

@@ -47,6 +47,13 @@ use std::{cell::RefCell, io::Write, rc::Rc};
 #[cfg(feature = "backend-llvm")]
 use wasmer_runtime_core::backend::BackendCompilerConfig;
 
+#[cfg(not(any(
+    feature = "backend-cranelift",
+    feature = "backend-llvm",
+    feature = "backend-singlepass"
+)))]
+compile_error!("Please enable one or more of the compiler backends");
+
 #[derive(Debug, StructOpt)]
 #[structopt(name = "wasmer", about = "Wasm execution runtime.", author)]
 /// The options for the wasmer Command Line Interface
@@ -619,7 +626,12 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
     }
 
     let compiler: Box<dyn Compiler> = get_compiler_by_backend(options.backend, options)
-        .ok_or_else(|| "the requested backend is not enabled")?;
+        .ok_or_else(|| {
+            format!(
+                "the requested backend, \"{}\", is not enabled",
+                options.backend.to_string()
+            )
+        })?;
 
     #[allow(unused_mut)]
     let mut backend_specific_config = None;