Autodetect default backend, add features for architecture type

Cargo.toml

@@ -36,6 +36,7 @@ wasmer-kernel-loader = { path = "lib/kernel-loader", optional = true }
 wasmer-dev-utils = { path = "lib/dev-utils", optional = true }
 wasmer-wasi-tests = { path = "lib/wasi-tests", optional = true }
 wasmer-middleware-common-tests = { path = "lib/middleware-common-tests", optional = true }
+wasmer-runtime-core-tests = { path = "lib/runtime-core-tests", optional = true }
 wasmer-emscripten-tests = { path = "lib/emscripten-tests", optional = true }
 
 [workspace]
@@ -73,8 +74,10 @@ serde = { version = "1", features = ["derive"] } # used by the plugin example
 typetag = "0.1" # used by the plugin example
 
 [features]
-default = ["fast-tests", "wasi", "backend-cranelift"]
+default = ["fast-tests", "wasi", "x86_64"]
 "loader-kernel" = ["wasmer-kernel-loader"]
+aarch64 = ["backend-singlepass"]
+x86_64 = ["backend-cranelift"]
 debug = ["wasmer-runtime-core/debug"]
 trace = ["wasmer-runtime-core/trace"]
 extra-debug = ["wasmer-clif-backend/debug", "wasmer-runtime-core/debug"]
@@ -84,20 +87,23 @@ backend-cranelift = [
     "wasmer-runtime-core/backend-cranelift",
     "wasmer-runtime/cranelift",
     "wasmer-middleware-common-tests/clif",
+    "wasmer-runtime-core-tests/backend-cranelift",
     "wasmer-wasi-tests/clif"
 ]
 backend-llvm = [
     "wasmer-llvm-backend",
     "wasmer-runtime-core/backend-llvm",
     "wasmer-runtime/llvm",
     "wasmer-middleware-common-tests/llvm",
+    "wasmer-runtime-core-tests/backend-llvm",
     "wasmer-wasi-tests/llvm"
 ]
 backend-singlepass = [
     "wasmer-singlepass-backend",
     "wasmer-runtime-core/backend-singlepass",
     "wasmer-runtime/singlepass",
     "wasmer-middleware-common-tests/singlepass",
+    "wasmer-runtime-core-tests/backend-singlepass",
     "wasmer-wasi-tests/singlepass"
 ]
 wasi = ["wasmer-wasi"]

lib/middleware-common-tests/Cargo.toml

@@ -10,12 +10,13 @@ publish = false
 [dependencies]
 wasmer-runtime-core = { path = "../runtime-core", version = "0.10.2" }
 wasmer-middleware-common = { path = "../middleware-common", version = "0.10.2" }
-wasmer-clif-backend = { path = "../clif-backend", version = "0.10.2" }
+wasmer-clif-backend = { path = "../clif-backend", version = "0.10.2", optional = true }
 wasmer-llvm-backend = { path = "../llvm-backend", version = "0.10.2", optional = true }
 wasmer-singlepass-backend = { path = "../singlepass-backend", version = "0.10.2", optional = true }
 
 [features]
-clif = []
+default = ["clif"]
+clif = ["wasmer-clif-backend"]
 llvm = ["wasmer-llvm-backend"]
 singlepass = ["wasmer-singlepass-backend"]
 

lib/runtime-core-tests/Cargo.toml

@@ -15,7 +15,7 @@ wasmer-singlepass-backend = { path = "../singlepass-backend", version = "0.10.2"
 wasmer-llvm-backend = { path = "../llvm-backend", version = "0.10.2", optional = true }
 
 [features]
-default = ["backend-cranelift"]
+default = []
 backend-cranelift = ["wasmer-clif-backend"]
 backend-singlepass = ["wasmer-singlepass-backend"]
 backend-llvm = ["wasmer-llvm-backend"]

lib/runtime/Cargo.toml

@@ -34,7 +34,7 @@ path = "../llvm-backend"
 optional = true
 
 [features]
-default = ["cranelift", "default-backend-cranelift"]
+default = ["cranelift"]
 cranelift = ["wasmer-clif-backend"]
 cache = ["cranelift"]
 debug = ["wasmer-clif-backend/debug", "wasmer-runtime-core/debug"]

lib/runtime/build.rs

@@ -0,0 +1,38 @@
+//! This build script sets the default compiler using special output.
+//!
+//! See https://doc.rust-lang.org/cargo/reference/build-scripts.html
+//! for details.
+
+/// This function tells Cargo which default backend to use
+fn set_default_backend() {
+    // we must use this rather than `cfg` because the build.rs executes on the
+    // compiling system.  This method works with cross compilation too.
+    match std::env::var("CARGO_CFG_TARGET_ARCH")
+        .expect("compilation target env var")
+        .as_ref()
+    {
+        "x86_64" => {
+            println!("cargo:rustc-cfg=feature=\"default-backend-cranelift\"");
+        }
+        "aarch64" => {
+            println!("cargo:rustc-cfg=feature=\"default-backend-singlepass\"");
+        }
+        other => {
+            println!("cargo:warning=compiling for untested architecture: \"{}\"!  Attempting to use LLVM", other);
+            println!("cargo:rustc-cfg=feature=\"default-backend-llvm\"");
+        }
+    }
+}
+
+/// This function checks if the user specified a default backend
+fn has_default_backend() -> bool {
+    std::env::var("CARGO_FEATURE_DEFAULT_BACKEND_SINGLEPASS").is_ok()
+        || std::env::var("CARGO_FEATURE_DEFAULT_BACKEND_CRANELIFT").is_ok()
+        || std::env::var("CARGO_FEATURE_DEFAULT_BACKEND_LLVM").is_ok()
+}
+
+fn main() {
+    if !has_default_backend() {
+        set_default_backend();
+    }
+}