hive-forge: attach-issue/attach-comment fail on a missing download URL

print_url only printed when browser_download_url was Some, so a 2xx
upload response with no URL printed nothing and still exited 0 — a
caller doing url=$(hive-forge attach-issue …) got an empty string with
no signal anything went wrong.

require_url now errors, naming the attachment's id/name, when the
forge returns no download URL.

hive-forge/src/verbs/attach.rs

@@ -51,7 +51,7 @@ pub fn run_issue(client: &Client, args: IssueArgs) -> Result<()> {
         .api()
         .issue_create_issue_attachment(owner, name, index(args.number)?, &bytes, query)
         .send()?;
-    print_url(&resp);
+    println!("{}", require_url(&resp)?);
     Ok(())
 }
 
@@ -78,7 +78,7 @@ pub fn run_comment(client: &Client, args: CommentArgs) -> Result<()> {
         .api()
         .issue_create_issue_comment_attachment(owner, name, index(args.id)?, &bytes, query)
         .send()?;
-    print_url(&resp);
+    println!("{}", require_url(&resp)?);
     Ok(())
 }
 
@@ -93,8 +93,68 @@ fn file_name(path: &Path) -> Option<String> {
     path.file_name().map(|n| n.to_string_lossy().into_owned())
 }
 
-fn print_url(v: &Attachment) {
+/// The uploaded attachment's browser download URL, hard-erroring if the
-    if let Some(url) = &v.browser_download_url {
+/// forge answered 2xx with none. A caller piping the printed URL (e.g.
-        println!("{url}");
+/// `url=$(hive-forge attach-issue …)`) used to get an empty string and no
+/// signal when this was `None` — the upload had happened, but nothing said
+/// so, and nothing said it hadn't.
+fn require_url(v: &Attachment) -> Result<url::Url> {
+    v.browser_download_url.clone().ok_or_else(|| {
+        anyhow::anyhow!(
+            "hive-forge attach: upload succeeded but the forge returned no download URL \
+             (attachment {})",
+            attachment_ident(v)
+        )
+    })
+}
+
+/// Best-effort identifier for an attachment error message — id if present,
+/// else name, else a placeholder so the message never comes out empty.
+fn attachment_ident(v: &Attachment) -> String {
+    match (v.id, v.name.as_deref()) {
+        (Some(id), Some(n)) => format!("id={id} name={n}"),
+        (Some(id), None) => format!("id={id}"),
+        (None, Some(n)) => format!("name={n}"),
+        (None, None) => "<unknown>".to_owned(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::require_url;
+    use forgejo_api::structs::Attachment;
+
+    fn attachment(url: Option<&str>) -> Attachment {
+        Attachment {
+            browser_download_url: url.map(|u| u.parse().unwrap()),
+            created_at: None,
+            download_count: None,
+            id: Some(7),
+            name: Some("out.log".to_owned()),
+            size: None,
+            r#type: None,
+            uuid: None,
+        }
+    }
+
+    #[test]
+    fn control_present_url_is_returned() {
+        let a = attachment(Some("https://forge.example/a/1"));
+        assert_eq!(
+            require_url(&a).unwrap().as_str(),
+            "https://forge.example/a/1"
+        );
+    }
+
+    #[test]
+    fn missing_url_errors_naming_the_attachment() {
+        // A 2xx response with no browser_download_url used to print nothing
+        // and exit 0 — a caller doing `url=$(hive-forge attach-issue …)`
+        // got an empty string with no signal anything went wrong.
+        let a = attachment(None);
+        let err = require_url(&a).unwrap_err();
+        let msg = err.to_string();
+        assert!(msg.contains("id=7"), "missing attachment id: {msg}");
+        assert!(msg.contains("out.log"), "missing attachment name: {msg}");
     }
 }