[clang-tidy][doc] add more information in twine-local's document

[HerrCai0907]

explain more about use-after-free in llvm-twine-local
add note about manually adjusting code after applying fix-it.
fixed: #154810

[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: Congcong Cai (HerrCai0907)

Changes

explain more about use-after-free in llvm-twine-local
add note about manually adjusting code after applying fix-it.
fixed: #154810

---

Full diff: https://github.com/llvm/llvm-project/pull/166266.diff

1 Files Affected:

• (modified) clang-tools-extra/docs/clang-tidy/checks/llvm/twine-local.rst (+18)

diff --git a/clang-tools-extra/docs/clang-tidy/checks/llvm/twine-local.rst b/clang-tools-extra/docs/clang-tidy/checks/llvm/twine-local.rst
index ec9ef1c60913c..019fa973331dc 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/llvm/twine-local.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/llvm/twine-local.rst
@@ -14,3 +14,21 @@ should be generally avoided.
   // becomes
 
   static std::string Moo = (Twine("bark") + "bah").str();
+
+The ``llvm::Twine`` does not own the memory of its contents, so it is not
+recommended to use ``Twine`` created from temporary strings or string literals.
+
+.. code-block:: c++
+
+  static Twine getModuleIdentifier(StringRef moduleName) {
+    return moduleName + "_module";
+  }
+  void foo() {
+    Twine result = getModuleIdentifier(std::string{"abc"} + "def");
+    // temporary std::string is destroyed here, result is dangling
+  }
+
+After applying this fix-it hints, the code will use ``std::string`` instead of
+``Twine`` for local variables. However, ``llvm::Twine`` has lots of methods that
+are incompatible with ``std::string``, so the user may need to adjust the code
+manually after applying the fix-it hints.

[vbvictor]

LGTM

[vbvictor]

nit: I'm little confused why we sometimes use Twine and sometimes llvm::Twine. Could we always use one variant (like Twine)