Fix examples manifest version detection (#3859)

### What

Closes #3842

- CI `main` and non-CI -> `version/nightly`
- CI `release-x.y.z-alpha.N` -> `version/{root_crate_version}`
- CI any other branch -> `commit/{sha}`

### 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 [demo.rerun.io](https://demo.rerun.io/pr/3859) (if
applicable)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG

- [PR Build Summary](https://build.rerun.io/pr/3859)
- [Docs
preview](https://rerun.io/preview/9e7cfa2eae2460e38983ffcfeb1bd46b07a4f715/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/9e7cfa2eae2460e38983ffcfeb1bd46b07a4f715/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://ref.rerun.io/dev/bench/)
- [Wasm size tracking](https://ref.rerun.io/dev/sizes/)

crates/re_build_tools/src/git.rs

@@ -43,15 +43,22 @@ pub fn rebuild_if_branch_or_commit_changes() {
     }
 }
 
-pub fn commit_hash() -> anyhow::Result<String> {
+/// Get the full commit hash
+pub fn git_commit_hash() -> anyhow::Result<String> {
     let git_hash = run_command("git", &["rev-parse", "HEAD"])?;
     if git_hash.is_empty() {
         anyhow::bail!("empty commit hash");
     }
     Ok(git_hash)
 }
 
-pub fn branch() -> anyhow::Result<String> {
+/// Get the first 7 characters of the commit hash
+pub fn git_commit_short_hash() -> anyhow::Result<String> {
+    Ok(git_commit_hash()?[0..7].to_string())
+}
+
+/// Get the current git branch name
+pub fn git_branch() -> anyhow::Result<String> {
     run_command("git", &["symbolic-ref", "--short", "HEAD"])
 }
 

crates/re_build_tools/src/lib.rs

@@ -14,6 +14,7 @@ mod rebuild_detector;
 
 pub(crate) use self::rebuild_detector::Packages;
 
+pub use self::git::{git_branch, git_commit_hash, git_commit_short_hash};
 pub use self::hashing::{
     compute_crate_hash, compute_dir_filtered_hash, compute_dir_hash, compute_file_hash,
     compute_strings_hash, iter_dir, read_versioning_hash, write_versioning_hash,
@@ -142,8 +143,14 @@ pub fn export_build_info_vars_for_crate(crate_name: &str) {
     }
 
     if export_git_info {
-        set_env("RE_BUILD_GIT_HASH", &git::commit_hash().unwrap_or_default());
-        set_env("RE_BUILD_GIT_BRANCH", &git::branch().unwrap_or_default());
+        set_env(
+            "RE_BUILD_GIT_HASH",
+            &git::git_commit_hash().unwrap_or_default(),
+        );
+        set_env(
+            "RE_BUILD_GIT_BRANCH",
+            &git::git_branch().unwrap_or_default(),
+        );
 
         // Make sure the above are up-to-date
         git::rebuild_if_branch_or_commit_changes();
@@ -249,3 +256,8 @@ fn rust_llvm_versions() -> anyhow::Result<(String, String)> {
         llvm_version.unwrap_or_else(|| "unknown".to_owned()),
     ))
 }
+
+/// Returns info parsed from an invocation of the `cargo metadata` command
+pub fn cargo_metadata() -> anyhow::Result<cargo_metadata::Metadata> {
+    Ok(cargo_metadata::MetadataCommand::new().exec()?)
+}

crates/re_viewer/Cargo.toml

@@ -104,10 +104,10 @@ wasm-bindgen-futures.workspace = true
 web-sys = { workspace = true, features = ["Window"] }
 
 [build-dependencies]
+anyhow.workspace = true
 re_build_tools.workspace = true
 
 # External
 serde = { workspace = true, features = ["derive"] }
 serde_json.workspace = true
 serde_yaml.workspace = true
-xshell.workspace = true

crates/re_viewer/build.rs

@@ -15,44 +15,6 @@
 
 use std::path::Path;
 
-use xshell::cmd;
-use xshell::Shell;
-
-type AnyError = Box<dyn std::error::Error + Send + Sync + 'static>;
-type Result<T, E = AnyError> = std::result::Result<T, E>;
-
-#[derive(Debug)]
-struct Error(String);
-
-impl std::fmt::Display for Error {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.write_str(&self.0)
-    }
-}
-
-impl std::error::Error for Error {}
-
-macro_rules! error {
-    ($lit:literal) => (Error($lit.to_owned()));
-    ($($tt:tt)*) => (Error(format!($($tt)*)));
-}
-
-macro_rules! bail {
-    ($lit:literal) => (return Err(error!($lit)));
-    ($($tt:tt)*) => (return Err(error!($($tt)*).into()));
-}
-
-fn git_branch_name(sh: &Shell) -> Result<String> {
-    Ok(String::from_utf8(
-        cmd!(sh, "git rev-parse --abbrev-ref HEAD").output()?.stdout,
-    )?)
-}
-
-fn git_short_hash(sh: &Shell) -> Result<String> {
-    let full_hash = String::from_utf8(cmd!(sh, "git rev-parse HEAD").output()?.stdout)?;
-    Ok(full_hash.trim()[0..7].to_string())
-}
-
 fn parse_release_version(branch: &str) -> Option<&str> {
     // release-\d+.\d+.\d+(-alpha.\d+)?
 
@@ -136,7 +98,7 @@ struct Example {
     readme: Frontmatter,
 }
 
-fn examples() -> Result<Vec<Example>> {
+fn examples() -> anyhow::Result<Vec<Example>> {
     let mut examples = vec![];
     let dir = "../../examples/python";
     assert!(std::path::Path::new(dir).exists(), "Failed to find {dir}");
@@ -168,7 +130,7 @@ fn examples() -> Result<Vec<Example>> {
     Ok(examples)
 }
 
-fn parse_frontmatter<P: AsRef<Path>>(path: P) -> Result<Option<Frontmatter>> {
+fn parse_frontmatter<P: AsRef<Path>>(path: P) -> anyhow::Result<Option<Frontmatter>> {
     let path = path.as_ref();
     let content = std::fs::read_to_string(path)?;
     let content = content.replace('\r', ""); // Windows, god damn you
@@ -177,44 +139,55 @@ fn parse_frontmatter<P: AsRef<Path>>(path: P) -> Result<Option<Frontmatter>> {
         return Ok(None);
     };
     let Some(end) = content.find("---") else {
-        bail!("{:?} has invalid frontmatter", path);
+        anyhow::bail!("{:?} has invalid frontmatter", path);
     };
     Ok(Some(serde_yaml::from_str(&content[..end]).map_err(
         |e| {
-            error!(
+            anyhow::anyhow!(
                 "failed to read {:?}: {e}",
                 path.parent().unwrap().file_name().unwrap()
             )
         },
     )?))
 }
 
-fn get_base_url() -> Result<String> {
-    let mut base_url = re_build_tools::get_and_track_env_var("EXAMPLES_MANIFEST_BASE_URL")
-        .unwrap_or_else(|_e| "https://demo.rerun.io/version/nightly".into());
-
-    if re_build_tools::is_on_ci() {
-        let sh = Shell::new()?;
-        let branch = git_branch_name(&sh)?;
-        // If we are on `main`, leave the base url at `version/nightly`
-        if branch != "main" {
-            if let Some(version) = parse_release_version(&branch) {
-                // In builds on `release-x.y.z` branches, use `version/{x.y.z}`.
-                base_url = format!("https://demo.rerun.io/version/{version}");
-            } else {
-                // On any other branch, use `commit/{short_sha}`.
-                let sha = git_short_hash(&sh)?;
-                base_url = format!("https://demo.rerun.io/commit/{sha}");
-            }
-        }
+fn get_base_url() -> anyhow::Result<String> {
+    if let Ok(base_url) = re_build_tools::get_and_track_env_var("EXAMPLES_MANIFEST_BASE_URL") {
+        // override via env var
+        return Ok(base_url);
+    }
+
+    let branch = re_build_tools::git_branch()?;
+    if branch == "main" || !re_build_tools::is_on_ci() {
+        // on `main` and local builds, use `version/nightly`
+        // this will point to data uploaded by `.github/workflows/reusable_upload_web_demo.yml`
+        // on every commit to the `main` branch
+        return Ok("https://demo.rerun.io/version/nightly".into());
+    }
+
+    if parse_release_version(&branch).is_some() {
+        let metadata = re_build_tools::cargo_metadata()?;
+        let workspace_root = metadata
+            .root_package()
+            .ok_or_else(|| anyhow::anyhow!("failed to find workspace root"))?;
+
+        // on `release-x.y.z` builds, use `version/{crate_version}`
+        // this will point to data uploaded by `.github/workflows/reusable_build_and_publish_web.yml`
+        return Ok(format!(
+            "https://demo.rerun.io/version/{}",
+            workspace_root.version
+        ));
     }
 
-    Ok(base_url)
+    // any other branch that is not `main`, use `commit/{sha}`
+    // this will point to data uploaded by `.github/workflows/reusable_upload_web_demo.yml`
+    let sha = re_build_tools::git_commit_short_hash()?;
+    Ok(format!("https://demo.rerun.io/commit/{sha}"))
 }
 
 const MANIFEST_PATH: &str = concat!(env!("CARGO_MANIFEST_DIR"), "/data/examples_manifest.json");
 
-fn write_examples_manifest() -> Result<()> {
+fn write_examples_manifest() -> anyhow::Result<()> {
     let base_url = get_base_url()?;
 
     let mut manifest = vec![];