Abort build if binary artifact ambiguous

proceeding leads to indeterminte result
where trunk picks up an arbitrary binary for the target.
See trunk-rs#475

CHANGELOG.md

@@ -24,6 +24,7 @@ Subheadings to categorize changes are `added, changed, deprecated, removed, fixe
 - Nested WS proxies - if `backend=ws://localhost:8000/ws` is set, queries for `ws://localhost:8080/ws/entityX` will be linked with `ws://localhost:8000/ws/entityX`
 - Updated all dependencies in both Trunk and its examples, to fix currently open security advisories for old dependencies.
 - Fix [trunk/issues/330](https://github.com/thedodd/trunk/issues/330), to properly handle proxy endpoint with and without a slash at the end.
+- Fix [trunk/issues/475](https://github.com/thedodd/trunk/issues/475) indeterminate trunk behaviour when the project defines several binary crates and index.html has no `<link rel="rust" data-bin=...>`
 
 ## 0.16.0
 ### added

src/pipelines/rust.rs

@@ -312,6 +312,17 @@ impl RustApp {
                     _ => None,
                 })
                 .collect::<Result<_>>()?;
+
+        // If there is already a `link data-trunk rel=rust` in index.html
+        // then the --bin flag was passed to the cargo command
+        // and it has built just a single binary
+        if artifacts.len() > 1 {
+            bail!(
+                "found more than one binary crate: {bin_names:?}, \
+                consider adding `<link data-trunk rel=\"rust\" data-bin={{bin}} />` to the index.html",
+                bin_names = artifacts.iter().map(|a| &a.target.name).collect::<Vec<_>>()
+            )
+        }
         let Some(artifact) = artifacts.pop() else {
             bail!("cargo artifacts not found for target crate")
         };