Improve output of re_build_web_viewer (rerun-io#5913)

### What
…and catch failure to run wasm-opt

Review ignoring whitespace changes

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using newly built examples:
[rerun.io/viewer](https://rerun.io/viewer/pr/5913)
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/5913?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/5913?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

- [PR Build Summary](https://build.rerun.io/pr/5913)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

crates/re_build_web_viewer/src/lib.rs

@@ -2,6 +2,8 @@
 
 //! Build the Rerun web-viewer .wasm and generate the .js bindings for it.
 
+use std::time::Instant;
+
 use anyhow::Context as _;
 use cargo_metadata::camino::{Utf8Path, Utf8PathBuf};
 
@@ -61,7 +63,7 @@ pub fn build(
 ) -> anyhow::Result<()> {
     std::env::set_current_dir(workspace_root())?;
 
-    eprintln!("Building web viewer wasm…");
+    eprintln!("Building web viewer…\n");
 
     let crate_name = "re_viewer";
 
@@ -89,88 +91,102 @@ pub fn build(
     std::fs::remove_file(wasm_path.clone()).ok();
     std::fs::remove_file(js_path).ok();
 
-    // --------------------------------------------------------------------------------
-    eprintln!("Compiling rust to wasm in {target_wasm_dir}…");
-
-    let mut cmd = std::process::Command::new("cargo");
-    cmd.args([
-        "build",
-        "--quiet",
-        "--package",
-        crate_name,
-        "--lib",
-        "--target",
-        "wasm32-unknown-unknown",
-        "--target-dir",
-        target_wasm_dir.as_str(),
-        "--no-default-features",
-        "--features=analytics",
-    ]);
-    if profile == Profile::Release {
-        cmd.arg("--release");
-    }
+    {
+        eprintln!("Compiling Rust to wasm in {target_wasm_dir}…");
+        let start_time = Instant::now();
+
+        let mut cmd = std::process::Command::new("cargo");
+        cmd.args([
+            "build",
+            "--quiet",
+            "--package",
+            crate_name,
+            "--lib",
+            "--target",
+            "wasm32-unknown-unknown",
+            "--target-dir",
+            target_wasm_dir.as_str(),
+            "--no-default-features",
+            "--features=analytics",
+        ]);
+        if profile == Profile::Release {
+            cmd.arg("--release");
+        }
 
-    // This is required to enable the web_sys clipboard API which egui_web uses
-    // https://rustwasm.github.io/wasm-bindgen/api/web_sys/struct.Clipboard.html
-    // https://rustwasm.github.io/docs/wasm-bindgen/web-sys/unstable-apis.html
-    // Furthermore, it's necessary for unstable WebGPU apis to work.
-    cmd.env("RUSTFLAGS", "--cfg=web_sys_unstable_apis");
-
-    // When executing this script from a Rust build script, do _not_, under any circumstances,
-    // allow pre-encoded `RUSTFLAGS` to leak into the current environment.
-    // These pre-encoded flags are generally generated by Cargo itself when loading its
-    // configuration from e.g. `$CARGO_HOME/config.toml`; which means they will contain
-    // values that only make sense for the native target host, not for a wasm build.
-    cmd.env("CARGO_ENCODED_RUSTFLAGS", "--cfg=web_sys_unstable_apis");
-
-    eprintln!("{root_dir}> {cmd:?}");
-    let status = cmd
-        .current_dir(root_dir)
-        .status()
-        .context("Failed to build Wasm")?;
-    assert!(status.success(), "Failed to build Wasm");
+        // This is required to enable the web_sys clipboard API which egui_web uses
+        // https://rustwasm.github.io/wasm-bindgen/api/web_sys/struct.Clipboard.html
+        // https://rustwasm.github.io/docs/wasm-bindgen/web-sys/unstable-apis.html
+        // Furthermore, it's necessary for unstable WebGPU apis to work.
+        cmd.env("RUSTFLAGS", "--cfg=web_sys_unstable_apis");
 
-    // --------------------------------------------------------------------------------
-    eprintln!("Generating JS bindings for wasm…");
-
-    let build = profile.as_str();
-
-    let target_wasm_path = target_wasm_dir
-        .join("wasm32-unknown-unknown")
-        .join(build)
-        .join(format!("{crate_name}.wasm"));
-
-    let mut bindgen_cmd = wasm_bindgen_cli_support::Bindgen::new();
-    bindgen_cmd
-        .input_path(target_wasm_path.as_str())
-        .out_name(crate_name);
-    match target {
-        Target::Browser => bindgen_cmd.no_modules(true)?.typescript(false),
-        Target::Module => bindgen_cmd.no_modules(false)?.typescript(true),
-    };
-    if let Err(err) = bindgen_cmd.generate(build_dir.as_str()) {
-        if err
-            .to_string()
-            .starts_with("cannot import from modules (`env`")
-        {
-            // Very common error: "cannot import from modules (`env`) with `--no-modules`"
-            anyhow::bail!(
+        // When executing this script from a Rust build script, do _not_, under any circumstances,
+        // allow pre-encoded `RUSTFLAGS` to leak into the current environment.
+        // These pre-encoded flags are generally generated by Cargo itself when loading its
+        // configuration from e.g. `$CARGO_HOME/config.toml`; which means they will contain
+        // values that only make sense for the native target host, not for a wasm build.
+        cmd.env("CARGO_ENCODED_RUSTFLAGS", "--cfg=web_sys_unstable_apis");
+
+        eprintln!("{root_dir}> {cmd:?}");
+        let status = cmd
+            .current_dir(root_dir)
+            .status()
+            .context("Failed to build Wasm")?;
+
+        anyhow::ensure!(status.success(), "Failed to build Wasm");
+
+        eprintln!(
+            "Web viewer .wasm built in {:.1}s\n",
+            start_time.elapsed().as_secs_f32()
+        );
+    }
+
+    {
+        eprintln!("Generating JS bindings for wasm…");
+        let start_time = Instant::now();
+
+        let build = profile.as_str();
+
+        let target_wasm_path = target_wasm_dir
+            .join("wasm32-unknown-unknown")
+            .join(build)
+            .join(format!("{crate_name}.wasm"));
+
+        let mut bindgen_cmd = wasm_bindgen_cli_support::Bindgen::new();
+        bindgen_cmd
+            .input_path(target_wasm_path.as_str())
+            .out_name(crate_name);
+        match target {
+            Target::Browser => bindgen_cmd.no_modules(true)?.typescript(false),
+            Target::Module => bindgen_cmd.no_modules(false)?.typescript(true),
+        };
+        if let Err(err) = bindgen_cmd.generate(build_dir.as_str()) {
+            if err
+                .to_string()
+                .starts_with("cannot import from modules (`env`")
+            {
+                // Very common error: "cannot import from modules (`env`) with `--no-modules`"
+                anyhow::bail!(
                 "Failed to run wasm-bindgen: {err}. This is often because some dependency is calling `std::time::Instant::now()` or similar. You can try diagnosing this with:\n\
                 wasm2wat {target_wasm_path} | rg '\"env\"'\n\
                 wasm2wat {target_wasm_path} | rg 'call .now\\b' -B 20\n\
                 \n\
                 You can also try https://rustwasm.github.io/twiggy/usage/command-line-interface/paths.html#twiggy-paths
                 "
             );
-        } else {
-            return Err(err.context("Failed to run wasm-bindgen"));
+            } else {
+                return Err(err.context("Failed to run wasm-bindgen"));
+            }
         }
-    }
 
-    // --------------------------------------------------------------------------------
+        eprintln!(
+            "Generated JS bindings in {:.1}s\n",
+            start_time.elapsed().as_secs_f32()
+        );
+    }
 
     if profile == Profile::Release {
         eprintln!("Optimizing wasm with wasm-opt…");
+        let start_time = Instant::now();
 
         // to get wasm-opt:  apt/brew/dnf install binaryen
         let mut cmd = std::process::Command::new("wasm-opt");
@@ -186,12 +202,17 @@ pub fn build(
             .current_dir(root_dir)
             .output()
             .context("Failed to run wasm-opt, it may not be installed")?;
-        if !output.status.success() {
-            eprintln!(
-                "Failed to run wasm-opt:\n{}",
-                String::from_utf8_lossy(&output.stderr)
-            );
-        }
+
+        anyhow::ensure!(
+            output.status.success(),
+            "Failed to run wasm-opt:\n{}",
+            String::from_utf8_lossy(&output.stderr),
+        );
+
+        eprintln!(
+            "Optimized wasm in {:.1}s\n",
+            start_time.elapsed().as_secs_f32()
+        );
     }
 
     // --------------------------------------------------------------------------------