simplify join_paths error message and add test

crates/cargo-util/src/paths.rs

@@ -19,18 +19,17 @@ use tempfile::Builder as TempFileBuilder;
 /// error message.
 pub fn join_paths<T: AsRef<OsStr>>(paths: &[T], env: &str) -> Result<OsString> {
     env::join_paths(paths.iter()).with_context(|| {
-        let paths = paths.iter()
-            .map(|s| s.as_ref().to_string_lossy())
-            .map(|s| format!("  \"{s}\""))
-            .collect::<Vec<String>>()
-            .join(",\n");
-
-        format!(
-            "failed to join paths from `${env}` together\n\
-                 If you set `${env}` manually, check if it contains an unterminated quote character \
-                 or path separators (usually `:` or `;`). Please avoid using them. \
-                 Otherwise, check if any of paths listed below contain one of those characters:\n{paths}"
-        )
+        let mut message = format!(
+            "failed to join paths from `${env}` together\n\n\
+             Check if any of path segments listed below contain an \
+             unterminated quote character or path separator:"
+        );
+        for path in paths {
+            use std::fmt::Write;
+            write!(&mut message, "\n    {:?}", Path::new(path)).unwrap();
+        }
+
+        message
     })
 }
 
@@ -745,3 +744,44 @@ fn exclude_from_time_machine(path: &Path) {
     // Errors are ignored, since it's an optional feature and failure
     // doesn't prevent Cargo from working
 }
+
+#[cfg(test)]
+mod tests {
+    use super::join_paths;
+
+    #[test]
+    fn join_paths_lists_paths_on_error() {
+        let valid_paths = vec!["/testing/one", "/testing/two"];
+        // does not fail on valid input
+        let _joined = join_paths(&valid_paths, "TESTING1").unwrap();
+
+        #[cfg(unix)]
+        {
+            let invalid_paths = vec!["/testing/one", "/testing/t:wo/three"];
+            let err = join_paths(&invalid_paths, "TESTING2").unwrap_err();
+            assert_eq!(
+                err.to_string(),
+                "failed to join paths from `$TESTING2` together\n\n\
+             Check if any of path segments listed below contain an \
+             unterminated quote character or path separator:\
+             \n    \"/testing/one\"\
+             \n    \"/testing/t:wo/three\"\
+             "
+            );
+        }
+        #[cfg(windows)]
+        {
+            let invalid_paths = vec!["/testing/one", "/testing/t\"wo/three"];
+            let err = join_paths(&invalid_paths, "TESTING2").unwrap_err();
+            assert_eq!(
+                err.to_string(),
+                "failed to join paths from `$TESTING2` together\n\n\
+             Check if any of path segments listed below contain an \
+             unterminated quote character or path separator:\
+             \n    \"/testing/one\"\
+             \n    \"/testing/t\\\"wo/three\"\
+             "
+            );
+        }
+    }
+}