Respect wasm file placed in a temp path by rustdoc (#2881)

* Respect wasm file placed in a temp path by rustdoc

* fmt

crates/cli/src/bin/wasm-bindgen-test-runner/main.rs

@@ -47,14 +47,25 @@ fn main() -> anyhow::Result<()> {
         None => bail!("must have a file to test as first argument"),
     };
 
-    // Assume a cargo-like directory layout and generate output at
-    // `target/wasm32-unknown-unknown/wbg-tmp/...`
-    let tmpdir = wasm_file_to_test
-        .parent() // chop off file name
-        .and_then(|p| p.parent()) // chop off `deps`
-        .and_then(|p| p.parent()) // chop off `debug`
-        .map(|p| p.join("wbg-tmp"))
-        .ok_or_else(|| anyhow!("file to test doesn't follow the expected Cargo conventions"))?;
+    // wasm_file_to_test may be
+    // - a cargo-like directory layout and generate output at
+    //      `target/wasm32-unknown-unknown/...`
+    // - a tmp directory, generated by rustdoc
+    // we would like a directory we have write access to. if we assume cargo-like directories,
+    // we end up with the path `/wbg-out`
+    let tmpdir = if wasm_file_to_test
+        .to_string_lossy()
+        .starts_with("/tmp/rustdoc")
+    {
+        wasm_file_to_test.parent() // chop off the file name and give us the /tmp/rustdoc<hash> directory
+    } else {
+        wasm_file_to_test
+            .parent() // chop off file name
+            .and_then(|p| dbg!(p.parent())) // chop off `deps`
+            .and_then(|p| dbg!(p.parent())) // chop off `debug`
+    }
+    .map(|p| p.join("wbg-tmp"))
+    .ok_or_else(|| anyhow!("file to test doesn't follow the expected Cargo conventions"))?;
 
     // Make sure there's no stale state from before
     drop(fs::remove_dir_all(&tmpdir));