[PR] fix(services/upyun): do not panic when creating the service root [opendal]

["PDGGK (via GitHub)" <gi...@apache.org>]

PDGGK opened a new pull request, #8050:
URL: https://github.com/apache/opendal/pull/8050

   ## Which issue does this PR close?
   
   None filed — reporting and fixing together.
   
   ## Rationale of this change
   
   `UpyunCore::create_dir` dropped the trailing slash by slicing off the last byte:
   
   ```rust
   let path = build_abs_path(&self.root, path);
   let path = path[..path.len() - 1].to_string();
   ```
   
   `build_abs_path` returns an **empty string** when the root is `/` and the path is `/`:
   
   ```rust
   pub fn build_abs_path(root: &str, path: &str) -> String {
       let p = root[1..].to_string();   // "/" -> ""
       if path == "/" { p } else { ... }
   }
   ```
   
   so `path.len() - 1` underflows and the call panics with `attempt to subtract with overflow` instead of returning a `Result`.
   
   **The root is reachable from the public API.** `Operator::create_dir` only rejects a path that does not end with `/`:
   
   ```rust
   if !validate_path(&path, EntryMode::DIR) { return Err(...) }
   ```
   
   and `"/"` does end with `/`, so `op.create_dir("/").await` on a default-rooted upyun operator panics inside the library rather than returning an error.
   
   This was the **only** remaining `len() - 1]` slice under `core/services`. The sibling services already use `trim_end_matches('/')` for exactly this (`azdls/src/core.rs` uses it in five places), which is total and produces an identical result for a normalized path, since `normalize_path` leaves exactly one trailing slash.
   
   ## Are there any user-facing changes?
   
   A panic becomes ordinary behaviour: the request is built against the bucket root and the service's own response decides the outcome. No change for any non-root path.
   
   ## Tests
   
   Two unit tests on the extracted `folder_path` helper. The root case panics against the previous expression:
   
   ```
   thread 'core::tests::folder_path_handles_the_service_root' panicked at
     services/upyun/src/core.rs:79:12: attempt to subtract with overflow
   test result: FAILED. 3 passed; 1 failed
   ```
   
   The trailing-slash case passes **both** before and after, so it serves as the control showing the first is not trivially red.
   
   With the fix: 4/4 pass. `cargo fmt --check` exits 0, `cargo clippy --all-targets` is clean.
   


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Re: [PR] fix(services/upyun): do not panic when creating the service root [opendal]

["erickguan (via GitHub)" <gi...@apache.org>]

erickguan merged PR #8050:
URL: https://github.com/apache/opendal/pull/8050


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