Add support for automatically executing `wasm-opt`

This commit adds support for automatically executing the `wasm-opt`
binary from the [Binaryen project][binaryen]. By default `wasm-pack`
will now, in release and profiling modes, execute `wasm-opt -O` over the
final binary. The goal here is to enable optimizations that further
reduce binary size or improve runtime. In the long run it's expected
that `wasm-opt`'s optimizations may mostly make their way into LLVM, but
it's empirically true today that `wasm-opt` plus LLVM is the best
combination for size and speed today.

A configuration section for `wasm-opt` has been added as [previously
proposed][fitzgen], namely:

```toml
[package.metadata.wasm-pack.profile.release]
wasm-opt = ['-Os']
```

The `wasm-opt` binary is downloaded from Binaryen's [own
releases](https://github.com/webassembly/binaryen/releases). They're
available for the same platforms that we download predownloaded binaries
for `wasm-bindgen` on. We'll also opportunistically use `wasm-opt` in
`PATH` if it's available. If we're untable to run `wasm-opt`, though, a
warning diagnostic is printed informing such.

Closes #159

[binaryen]: https://github.com/webassembly/binaryen
[fitzgen]: https://github.com/rustwasm/wasm-pack/issues/159#issuecomment-454888890

docs/src/cargo-toml-configuration.md

@@ -9,6 +9,17 @@ the `--dev`, `--profiling`, and `--release` flags passed to `wasm-pack build`.
 The available configuration options and their default values are shown below:
 
 ```toml
+[package.metadata.wasm-pack.profile.dev]
+# Should `wasm-opt` be used to further optimize the wasm binary generated after
+# the Rust compiler has finished? Using `wasm-opt` can often further decrease
+# binary size or do clever tricks that haven't made their way into LLVM yet.
+#
+# Configuration can be set to `false` if you want to disable it (as is the
+# default for the dev profile), or it can be an array of strings which are
+# explicit arguments to pass to `wasm-opt`. For example `['-Os']` would optimize
+# for size while `['-O4']` would execute very expensive optimizations passes
+wasm-opt = false
+
 [package.metadata.wasm-pack.profile.dev.wasm-bindgen]
 # Should we enable wasm-bindgen's debug assertions in its generated JS glue?
 debug-js-glue = true
@@ -17,11 +28,17 @@ demangle-name-section = true
 # Should we emit the DWARF debug info custom sections?
 dwarf-debug-info = false
 
+[package.metadata.wasm-pack.profile.profiling]
+wasm-opt = ['-O']
+
 [package.metadata.wasm-pack.profile.profiling.wasm-bindgen]
 debug-js-glue = false
 demangle-name-section = true
 dwarf-debug-info = false
 
+[package.metadata.wasm-pack.profile.release]
+wasm-opt = ['-O']
+
 [package.metadata.wasm-pack.profile.release.wasm-bindgen]
 debug-js-glue = false
 demangle-name-section = true

src/child.rs

@@ -33,9 +33,10 @@ pub fn run(mut command: Command, command_name: &str) -> Result<(), Error> {
         Ok(())
     } else {
         bail!(
-            "failed to execute `{}`: exited with {}",
+            "failed to execute `{}`: exited with {}\n  full command: {:?}",
             command_name,
-            status
+            status,
+            command,
         )
     }
 }
@@ -53,9 +54,10 @@ pub fn run_capture_stdout(mut command: Command, command_name: &str) -> Result<St
         Ok(String::from_utf8_lossy(&output.stdout).into_owned())
     } else {
         bail!(
-            "failed to execute `{}`: exited with {}",
+            "failed to execute `{}`: exited with {}\n  full command: {:?}",
             command_name,
-            output.status
+            output.status,
+            command,
         )
     }
 }

src/command/build.rs

@@ -1,5 +1,6 @@
 //! Implementation of the `wasm-pack build` command.
 
+use crate::wasm_opt;
 use binary_install::{Cache, Download};
 use bindgen;
 use build;
@@ -47,6 +48,16 @@ pub enum BuildMode {
     Force,
 }
 
+impl BuildMode {
+    fn install_permitted(&self) -> bool {
+        match self {
+            BuildMode::Normal => true,
+            BuildMode::Force => true,
+            BuildMode::Noinstall => false,
+        }
+    }
+}
+
 impl Default for BuildMode {
     fn default() -> BuildMode {
         BuildMode::Normal
@@ -284,6 +295,7 @@ impl Build {
             step_copy_license,
             step_install_wasm_bindgen,
             step_run_wasm_bindgen,
+            step_run_wasm_opt,
             step_create_json,
         ]);
         steps
@@ -366,13 +378,11 @@ impl Build {
         let lockfile = Lockfile::new(&self.crate_data)?;
         let bindgen_version = lockfile.require_wasm_bindgen()?;
         info!("Installing wasm-bindgen-cli...");
-        let install_permitted = match self.mode {
-            BuildMode::Normal => true,
-            BuildMode::Force => true,
-            BuildMode::Noinstall => false,
-        };
-        let bindgen =
-            bindgen::install_wasm_bindgen(&self.cache, &bindgen_version, install_permitted)?;
+        let bindgen = bindgen::install_wasm_bindgen(
+            &self.cache,
+            &bindgen_version,
+            self.mode.install_permitted(),
+        )?;
         self.bindgen = Some(bindgen);
         info!("Installing wasm-bindgen-cli was successful.");
         Ok(())
@@ -392,4 +402,23 @@ impl Build {
         info!("wasm bindings were built at {:#?}.", &self.out_dir);
         Ok(())
     }
+
+    fn step_run_wasm_opt(&mut self) -> Result<(), Error> {
+        let args = match self
+            .crate_data
+            .configured_profile(self.profile)
+            .wasm_opt_args()
+        {
+            Some(args) => args,
+            None => return Ok(()),
+        };
+        info!("executing wasm-opt with {:?}", args);
+        wasm_opt::run(
+            &self.cache,
+            &self.out_dir,
+            &args,
+            self.mode.install_permitted(),
+        )?;
+        Ok(())
+    }
 }

src/lib.rs

@@ -39,6 +39,7 @@ pub mod progressbar;
 pub mod readme;
 pub mod target;
 pub mod test;
+pub mod wasm_opt;
 
 use progressbar::ProgressOutput;
 

src/manifest/mod.rs

@@ -104,6 +104,8 @@ impl Default for CargoWasmPackProfiles {
 pub struct CargoWasmPackProfile {
     #[serde(default, rename = "wasm-bindgen")]
     wasm_bindgen: CargoWasmPackProfileWasmBindgen,
+    #[serde(default, rename = "wasm-opt")]
+    wasm_opt: Option<CargoWasmPackProfileWasmOpt>,
 }
 
 #[derive(Default, Deserialize)]
@@ -233,6 +235,19 @@ impl Crate {
     }
 }
 
+#[derive(Clone, Deserialize)]
+#[serde(untagged)]
+enum CargoWasmPackProfileWasmOpt {
+    Enabled(bool),
+    ExplicitArgs(Vec<String>),
+}
+
+impl Default for CargoWasmPackProfileWasmOpt {
+    fn default() -> Self {
+        CargoWasmPackProfileWasmOpt::Enabled(false)
+    }
+}
+
 impl CargoWasmPackProfile {
     fn default_dev() -> Self {
         CargoWasmPackProfile {
@@ -241,6 +256,7 @@ impl CargoWasmPackProfile {
                 demangle_name_section: Some(true),
                 dwarf_debug_info: Some(false),
             },
+            wasm_opt: None,
         }
     }
 
@@ -251,6 +267,7 @@ impl CargoWasmPackProfile {
                 demangle_name_section: Some(true),
                 dwarf_debug_info: Some(false),
             },
+            wasm_opt: Some(CargoWasmPackProfileWasmOpt::Enabled(true)),
         }
     }
 
@@ -261,6 +278,7 @@ impl CargoWasmPackProfile {
                 demangle_name_section: Some(true),
                 dwarf_debug_info: Some(false),
             },
+            wasm_opt: Some(CargoWasmPackProfileWasmOpt::Enabled(true)),
         }
     }
 
@@ -300,6 +318,10 @@ impl CargoWasmPackProfile {
         d!(wasm_bindgen.debug_js_glue);
         d!(wasm_bindgen.demangle_name_section);
         d!(wasm_bindgen.dwarf_debug_info);
+
+        if self.wasm_opt.is_none() {
+            self.wasm_opt = defaults.wasm_opt.clone();
+        }
     }
 
     /// Get this profile's configured `[wasm-bindgen.debug-js-glue]` value.
@@ -316,6 +338,15 @@ impl CargoWasmPackProfile {
     pub fn wasm_bindgen_dwarf_debug_info(&self) -> bool {
         self.wasm_bindgen.dwarf_debug_info.unwrap()
     }
+
+    /// Get this profile's configured arguments for `wasm-opt`, if enabled.
+    pub fn wasm_opt_args(&self) -> Option<Vec<String>> {
+        match self.wasm_opt.as_ref()? {
+            CargoWasmPackProfileWasmOpt::Enabled(false) => None,
+            CargoWasmPackProfileWasmOpt::Enabled(true) => Some(vec!["-O".to_string()]),
+            CargoWasmPackProfileWasmOpt::ExplicitArgs(s) => Some(s.clone()),
+        }
+    }
 }
 
 struct NpmData {

src/wasm_opt.rs

@@ -0,0 +1,108 @@
+//! Support for downloading and executing `wasm-opt`
+
+use crate::child;
+use crate::emoji;
+use crate::target;
+use crate::PBAR;
+use binary_install::Cache;
+use log::debug;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+/// Execute `wasm-opt` over wasm binaries found in `out_dir`, downloading if
+/// necessary into `cache`. Passes `args` to each invocation of `wasm-opt`.
+pub fn run(
+    cache: &Cache,
+    out_dir: &Path,
+    args: &[String],
+    install_permitted: bool,
+) -> Result<(), failure::Error> {
+    let wasm_opt = match find_wasm_opt(cache, install_permitted)? {
+        WasmOpt::Found(path) => path,
+        WasmOpt::CannotInstall => {
+            PBAR.info("Skipping wasm-opt as no downloading was requested");
+            return Ok(());
+        }
+        WasmOpt::PlatformNotSupported => {
+            PBAR.info("Skipping wasm-opt because it is not supported on this platform");
+            return Ok(());
+        }
+    };
+
+    PBAR.info("Optimizing wasm binaries with `wasm-opt`...");
+
+    for file in out_dir.read_dir()? {
+        let file = file?;
+        let path = file.path();
+        if path.extension().and_then(|s| s.to_str()) != Some("wasm") {
+            continue;
+        }
+
+        let tmp = path.with_extension("wasm-opt.wasm");
+        let mut cmd = Command::new(&wasm_opt);
+        cmd.arg(&path).arg("-o").arg(&tmp).args(args);
+        child::run(cmd, "wasm-opt")?;
+        std::fs::rename(&tmp, &path)?;
+    }
+
+    Ok(())
+}
+
+/// Possible results of `find_wasm_opt`
+pub enum WasmOpt {
+    /// Couldn't install wasm-opt because downloads are forbidden
+    CannotInstall,
+    /// The current platform doesn't support precompiled binaries
+    PlatformNotSupported,
+    /// We found `wasm-opt` at the specified path
+    Found(PathBuf),
+}
+
+/// Attempts to find `wasm-opt` in `PATH` locally, or failing that downloads a
+/// precompiled binary.
+///
+/// Returns `Some` if a binary was found or it was successfully downloaded.
+/// Returns `None` if a binary wasn't found in `PATH` and this platform doesn't
+/// have precompiled binaries. Returns an error if we failed to download the
+/// binary.
+pub fn find_wasm_opt(cache: &Cache, install_permitted: bool) -> Result<WasmOpt, failure::Error> {
+    // First attempt to look up in PATH. If found assume it works.
+    if let Ok(path) = which::which("wasm-opt") {
+        debug!("found wasm-opt at {:?}", path);
+        return Ok(WasmOpt::Found(path));
+    }
+
+    // ... and if that fails download a precompiled version.
+    let target = if target::LINUX && target::x86_64 {
+        "x86_64-linux"
+    } else if target::MACOS && target::x86_64 {
+        "x86_64-apple-darwin"
+    } else if target::WINDOWS && target::x86_64 {
+        "x86_64-windows"
+    } else {
+        return Ok(WasmOpt::PlatformNotSupported);
+    };
+    let url = format!(
+        "https://github.com/WebAssembly/binaryen/releases/download/{vers}/binaryen-{vers}-{target}.tar.gz",
+        vers = "version_78",
+        target = target,
+    );
+
+    let download = |permit_install| cache.download(permit_install, "wasm-opt", &["wasm-opt"], &url);
+
+    let dl = match download(false)? {
+        Some(dl) => dl,
+        None if !install_permitted => return Ok(WasmOpt::CannotInstall),
+        None => {
+            let msg = format!("{}Installing wasm-opt...", emoji::DOWN_ARROW);
+            PBAR.info(&msg);
+
+            match download(install_permitted)? {
+                Some(dl) => dl,
+                None => return Ok(WasmOpt::CannotInstall),
+            }
+        }
+    };
+
+    Ok(WasmOpt::Found(dl.binary("wasm-opt")?))
+}

tests/all/main.rs

@@ -19,4 +19,5 @@ mod manifest;
 mod readme;
 mod test;
 mod utils;
+mod wasm_opt;
 mod webdriver;

tests/all/utils/fixture.rs

@@ -214,6 +214,10 @@ impl Fixture {
     /// Takes care not to re-install for every fixture, but only the one time
     /// for the whole test suite.
     pub fn install_local_wasm_bindgen(&self) -> PathBuf {
+        // If wasm-bindgen is being used then it's very likely wasm-opt is going
+        // to be used as well.
+        self.install_wasm_opt();
+
         static INSTALL_WASM_BINDGEN: Once = ONCE_INIT;
         let cache = self.cache();
         let version = "0.2.37";
@@ -236,6 +240,15 @@ impl Fixture {
         download().unwrap().binary("wasm-bindgen").unwrap()
     }
 
+    pub fn install_wasm_opt(&self) {
+        static INSTALL_WASM_OPT: Once = ONCE_INIT;
+        let cache = self.cache();
+
+        INSTALL_WASM_OPT.call_once(|| {
+            wasm_pack::wasm_opt::find_wasm_opt(&cache, true).unwrap();
+        });
+    }
+
     /// Download `geckodriver` and return its path.
     ///
     /// Takes care to ensure that only one `geckodriver` is downloaded for the whole

tests/all/wasm_opt.rs

@@ -0,0 +1,189 @@
+use assert_cmd::prelude::*;
+use predicates::prelude::*;
+use utils;
+
+#[test]
+fn off_in_dev() {
+    let fixture = utils::fixture::Fixture::new();
+    fixture.readme().cargo_toml("foo").file("src/lib.rs", "");
+    fixture.install_local_wasm_bindgen();
+    fixture.install_wasm_opt();
+
+    fixture
+        .wasm_pack()
+        .arg("build")
+        .arg("--dev")
+        .assert()
+        .stderr(predicates::str::contains("wasm-opt").not())
+        .success();
+}
+
+#[test]
+fn on_in_release() {
+    let fixture = utils::fixture::Fixture::new();
+    fixture.readme().cargo_toml("foo").file("src/lib.rs", "");
+    fixture.install_local_wasm_bindgen();
+    fixture.install_wasm_opt();
+
+    fixture
+        .wasm_pack()
+        .arg("build")
+        .assert()
+        .stderr(predicates::str::contains("wasm-opt"))
+        .success();
+}
+
+#[test]
+fn disable_in_release() {
+    let fixture = utils::fixture::Fixture::new();
+    fixture
+        .readme()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                authors = []
+                description = ""
+                license = "MIT"
+                name = "foo"
+                repository = ""
+                version = "0.1.0"
+
+                [lib]
+                crate-type = ["cdylib"]
+
+                [dependencies]
+                wasm-bindgen = "0.2"
+
+                [package.metadata.wasm-pack.profile.release]
+                wasm-opt = false
+            "#,
+        )
+        .file("src/lib.rs", "");
+    fixture.install_local_wasm_bindgen();
+    fixture.install_wasm_opt();
+
+    fixture
+        .wasm_pack()
+        .arg("build")
+        .assert()
+        .stderr(predicates::str::contains("wasm-opt").not())
+        .success();
+}
+
+#[test]
+fn enable_in_dev() {
+    let fixture = utils::fixture::Fixture::new();
+    fixture
+        .readme()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                authors = []
+                description = ""
+                license = "MIT"
+                name = "foo"
+                repository = ""
+                version = "0.1.0"
+
+                [lib]
+                crate-type = ["cdylib"]
+
+                [dependencies]
+                wasm-bindgen = "0.2"
+
+                [package.metadata.wasm-pack.profile.dev]
+                wasm-opt = true
+            "#,
+        )
+        .file("src/lib.rs", "");
+    fixture.install_local_wasm_bindgen();
+    fixture.install_wasm_opt();
+
+    fixture
+        .wasm_pack()
+        .arg("build")
+        .arg("--dev")
+        .assert()
+        .stderr(predicates::str::contains(
+            "Optimizing wasm binaries with `wasm-opt`",
+        ))
+        .success();
+}
+
+#[test]
+fn custom_args() {
+    let fixture = utils::fixture::Fixture::new();
+    fixture
+        .readme()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                authors = []
+                description = ""
+                license = "MIT"
+                name = "foo"
+                repository = ""
+                version = "0.1.0"
+
+                [lib]
+                crate-type = ["cdylib"]
+
+                [dependencies]
+                wasm-bindgen = "0.2"
+
+                [package.metadata.wasm-pack.profile.release]
+                wasm-opt = ['--not-accepted-argument']
+            "#,
+        )
+        .file("src/lib.rs", "");
+    fixture.install_local_wasm_bindgen();
+    fixture.install_wasm_opt();
+
+    fixture
+        .wasm_pack()
+        .arg("build")
+        .assert()
+        .stderr(predicates::str::contains("--not-accepted-argument"))
+        .failure();
+}
+
+#[test]
+fn misconfigured() {
+    let fixture = utils::fixture::Fixture::new();
+    fixture
+        .readme()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                authors = []
+                description = ""
+                license = "MIT"
+                name = "foo"
+                repository = ""
+                version = "0.1.0"
+
+                [lib]
+                crate-type = ["cdylib"]
+
+                [dependencies]
+                wasm-bindgen = "0.2"
+
+                [package.metadata.wasm-pack.profile.release]
+                wasm-opt = 32
+            "#,
+        )
+        .file("src/lib.rs", "");
+    fixture.install_local_wasm_bindgen();
+    fixture.install_wasm_opt();
+
+    fixture
+        .wasm_pack()
+        .arg("build")
+        .assert()
+        .stderr(predicates::str::contains("failed to parse manifest"))
+        .failure();
+}