feature cfg away singlepass and llvm backends in cli

Cargo.toml

@@ -38,13 +38,14 @@ members = ["lib/clif-backend", "lib/singlepass-backend", "lib/runtime", "lib/run
 [build-dependencies]
 wabt = "0.7.2"
 glob = "0.2.11"
+rustc_version = "0.2.3"
 
 [features]
-default = ["fast-tests", "wasi", "singlepass", "llvm"]
+default = ["fast-tests", "wasi"]
 debug = ["wasmer-clif-backend/debug", "wasmer-runtime-core/debug"]
 # This feature will allow cargo test to run much faster
 fast-tests = []
-llvm = ["wasmer-llvm-backend"]
-singlepass = ["wasmer-singlepass-backend"]
+"backend:llvm" = ["wasmer-llvm-backend"]
+"backend:singlepass" = ["wasmer-singlepass-backend"]
 wasi = ["wasmer-wasi"]
 vfs = ["wasmer-runtime-abi"]

src/bin/wasmer.rs

@@ -14,12 +14,14 @@ use structopt::StructOpt;
 use wasmer::webassembly::InstanceABI;
 use wasmer::*;
 use wasmer_clif_backend::CraneliftCompiler;
+#[cfg(feature = "backend:llvm")]
 use wasmer_llvm_backend::LLVMCompiler;
 use wasmer_runtime::cache::{Cache as BaseCache, FileSystemCache, WasmHash, WASMER_VERSION_HASH};
 use wasmer_runtime_core::{
     self,
     backend::{Compiler, CompilerConfig},
 };
+#[cfg(feature = "backend:singlepass")]
 use wasmer_singlepass_backend::SinglePassCompiler;
 #[cfg(feature = "wasi")]
 use wasmer_wasi;
@@ -223,9 +225,15 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
     }
 
     let compiler: Box<dyn Compiler> = match options.backend {
+        #[cfg(feature = "backend:singlepass")]
         Backend::Singlepass => Box::new(SinglePassCompiler::new()),
+        #[cfg(not(feature = "backend:singlepass"))]
+        Backend::Singlepass => return Err("The singlepass backend is not enabled".to_string()),
         Backend::Cranelift => Box::new(CraneliftCompiler::new()),
+        #[cfg(feature = "backend:llvm")]
         Backend::LLVM => Box::new(LLVMCompiler::new()),
+        #[cfg(not(feature = "backend:llvm"))]
+        Backend::LLVM => return Err("the llvm backend is not enabled".to_string()),
     };
 
     let module = if !disable_cache {

src/webassembly.rs

@@ -5,7 +5,6 @@ use wasmer_runtime::{
     error::{CallResult, Result},
     ImportObject, Instance, Module,
 };
-use wasmer_runtime_core::backend::CompilerConfig;
 use wasmer_runtime_core::types::Value;
 
 use wasmer_emscripten::run_emscripten_instance;