Fix wasm-opt regression (use-ink#187)

* Use `--zero-filled-memory` for `wasm-opt`

* Assert that compiled contract template is below 3k

* Apply cargo fmt

* Remove superfluous comment

* Improve error message on `wasm-opt` error

* Specify minimum binaryen version

README.md

@@ -13,8 +13,8 @@ A CLI tool for helping setting up and managing WebAssembly smart contracts writt
 We optimize the resulting contract Wasm using `binaryen`. You have two options for installing it:
 
   - _The preferred way:_  
-    Install [`binaryen`](https://github.com/WebAssembly/binaryen#tools). Many package managers
-    have it available nowadays ‒ e.g. it's a package for [Debian/Ubuntu](https://tracker.debian.org/pkg/binaryen),
+    Install [`binaryen`](https://github.com/WebAssembly/binaryen#tools) with a version >= 99.
+    Many package managers have it available nowadays ‒ e.g. it's a package for [Debian/Ubuntu](https://tracker.debian.org/pkg/binaryen),
     [Homebrew](https://formulae.brew.sh/formula/binaryen) and [Arch Linux](https://archlinux.org/packages/community/x86_64/binaryen/).
     After you've installed the package execute `cargo install --force cargo-contract`.
 

src/cmd/build.rs

@@ -23,7 +23,7 @@ use std::{
 };
 
 #[cfg(not(feature = "binaryen-as-dependency"))]
-use std::process::Command;
+use std::{process::Command, str};
 
 use crate::{
     crate_metadata::CrateMetadata,
@@ -352,11 +352,22 @@ fn do_optimization(
         .arg(format!("-O{}", optimization_level))
         .arg("-o")
         .arg(dest_optimized)
+        // the memory in our module is imported, `wasm-opt` needs to be told that
+        // the memory is initialized to zeros, otherwise it won't run the
+        // memory-packing pre-pass.
+        .arg("--zero-filled-memory")
         .output()?;
 
     if !output.status.success() {
-        // Dump the output streams produced by `wasm-opt` into the stdout/stderr.
-        anyhow::bail!("wasm-opt optimization failed");
+        let err = str::from_utf8(&output.stderr)
+            .expect("cannot convert stderr output of wasm-opt to string")
+            .trim();
+        anyhow::bail!(
+            "The wasm-opt optimization failed.\n\
+            A possible source of error could be that you have an outdated binaryen package installed.\n\n\
+            The error which wasm-opt returned was: \n{}",
+            err
+        );
     }
     Ok(())
 }
@@ -469,6 +480,10 @@ mod tests_ci_only {
             // would fail for that.
             assert!(res.target_directory.ends_with("target/ink"));
             assert!(res.optimization_result.unwrap().optimized_size > 0.0);
+
+            // our optimized contract template should always be below 3k.
+            assert!(res.optimization_result.unwrap().optimized_size < 3.0);
+
             Ok(())
         })
     }