Fail the build if xbuild fails (#41)

* Fail the build if xbuild fails

* Debug log now redundant

* Add wasm-opt to release notes

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Version 0.4.0 (2020-02-26)
 
 - Minimize contract wasm binary size:
+  - Run `wasm-opt` on the contract Wasm binary.
   - Uses [`cargo-xbuild`](https://github.com/rust-osdev/cargo-xbuild) to build custom sysroot crates without panic string
 bloat.
   - Automatically removes the `rlib` crate type from `Cargo.toml`, removing redundant metadata.

src/cmd/build.rs

@@ -130,7 +130,9 @@ fn build_cargo_project(crate_metadata: &CrateMetadata, verbosity: Option<Verbosi
         let exit_status = xargo_lib::build(args, "build", Some(config))
             .map_err(|e| anyhow::anyhow!("{}", e))
             .context("Building with xbuild")?;
-        log::debug!("xargo exit status: {:?}", exit_status);
+        if !exit_status.success() {
+            anyhow::bail!("xbuild failed with status {}", exit_status)
+        }
         Ok(())
     };