Remove backtraces on error when running rerun binary (#4746)

### What
* Closes #4738

Starting in [`anyhow
1.0.77`](https://github.com/dtolnay/anyhow/releases/tag/1.0.77), a
backtrace will be printed on error if `RUST_BACKTRACE` is set, and we
set `RUST_BACKTRACE=1` in:


https://github.com/rerun-io/rerun/blob/d204936e4a186b6f264425f7a3d3849f94b7b86f/crates/re_log/src/setup.rs#L32-L35

We do this because we want to print stack traces on panics.

However, for `anyhow::Error` our error messages _should_ be good enough
to not require a stack trace,
so with this PR we now explicitly print out the error instead of relying
in the formatting that happens when returning `anyhow::Result` from
`main`.

### Result
```
❯ cargo run -p rerun-cli --quiet -- .github/workflows/documentation.yaml    
[2024-01-09T10:09:31Z INFO  re_data_source::load_file] Loading ".github/workflows/documentation.yaml"…
Error: ".github/workflows/documentation.yaml" -> No data-loader support for ".github/workflows/documentation.yaml"
```

### 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:
[app.rerun.io](https://app.rerun.io/pr/4746/index.html)
* Using examples from latest `main` build:
[app.rerun.io](https://app.rerun.io/pr/4746/index.html?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[app.rerun.io](https://app.rerun.io/pr/4746/index.html?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

- [PR Build Summary](https://build.rerun.io/pr/4746)
- [Docs
preview](https://rerun.io/preview/dfadee45bb4767f1e81e2459b8e3f93aabcb5c39/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/dfadee45bb4767f1e81e2459b8e3f93aabcb5c39/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

Cargo.toml

@@ -97,7 +97,7 @@ emath = "0.24.1"
 
 # All of our direct external dependencies should be found here:
 ahash = "0.8"
-anyhow = "1.0"
+anyhow = { version = "1.0", default-features = false }
 arboard = { version = "3.2", default-features = false }
 argh = "0.1.12"
 array-init = "2.1"

crates/re_build_tools/Cargo.toml

@@ -17,7 +17,7 @@ all-features = true
 
 
 [dependencies]
-anyhow.workspace = true
+anyhow = { workspace = true, default-features = true }
 cargo_metadata.workspace = true
 glob.workspace = true
 sha2.workspace = true

crates/re_log/src/setup.rs

@@ -29,8 +29,15 @@ pub fn default_log_filter() -> String {
 /// Directs [`log`] calls to stderr.
 #[cfg(not(target_arch = "wasm32"))]
 pub fn setup_native_logging() {
-    if std::env::var("RUST_BACKTRACE").is_err() {
-        // Make sure we always produce backtraces for the (hopefully rare) cases when we crash!
+    if cfg!(debug_assertions) && std::env::var("RUST_BACKTRACE").is_err() {
+        // In debug build, default `RUST_BACKTRACE` to `1` if it is not set.
+        // This ensures sure we produce backtraces if our examples (etc) panics.
+
+        // Our own crash handler (`re_crash_handler`) always prints a backtraces
+        // (currently ignoring `RUST_BACKTRACE`) but we only use that for `rerun-cli`, our main binary.
+
+        // `RUST_BACKTRACE` also turns on printing backtraces for `anyhow::Error`s that
+        // are returned from `main` (i.e. if `main` returns `anyhow::Result`).
         std::env::set_var("RUST_BACKTRACE", "1");
     }
 

crates/rerun-cli/Cargo.toml

@@ -47,6 +47,7 @@ web_viewer = ["rerun/web_viewer", "rerun/sdk"]
 
 [dependencies]
 re_build_info.workspace = true
+re_error.workspace = true
 re_log.workspace = true
 re_memory.workspace = true
 rerun = { workspace = true, features = [

crates/rerun-cli/src/bin/rerun.rs

@@ -17,7 +17,7 @@ static GLOBAL: AccountingAllocator<mimalloc::MiMalloc> =
     AccountingAllocator::new(mimalloc::MiMalloc);
 
 #[tokio::main]
-async fn main() -> anyhow::Result<std::process::ExitCode> {
+async fn main() -> std::process::ExitCode {
     re_log::setup_native_logging();
 
     // Name the rayon threads for the benefit of debuggers and profilers:
@@ -27,7 +27,16 @@ async fn main() -> anyhow::Result<std::process::ExitCode> {
         .unwrap();
 
     let build_info = re_build_info::build_info!();
-    rerun::run(build_info, rerun::CallSource::Cli, std::env::args())
-        .await
-        .map(std::process::ExitCode::from)
+
+    let result = rerun::run(build_info, rerun::CallSource::Cli, std::env::args()).await;
+
+    match result {
+        Ok(exit_code) => std::process::ExitCode::from(exit_code),
+        Err(err) => {
+            // Note: we do not print the backtrace here, because our error messages should be short, readable, and actionable.
+            // If we instead return an `anyhow::Result` from `main`, then the backtrace will be printed if `RUST_BACKTRACE=1`.
+            eprintln!("Error: {}", re_error::format(err));
+            std::process::ExitCode::FAILURE
+        }
+    }
 }