[clang] [LifetimeSafety] Document record type origin tracking for lifetimebound calls (PR #189508)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Zhijie Wang (aeft)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/189508.diff


1 Files Affected:

- (modified) clang/docs/LifetimeSafety.rst (+25-2) 


``````````diff
diff --git a/clang/docs/LifetimeSafety.rst b/clang/docs/LifetimeSafety.rst
index ac76231dede67..efebb61699ee7 100644
--- a/clang/docs/LifetimeSafety.rst
+++ b/clang/docs/LifetimeSafety.rst
@@ -145,8 +145,8 @@ LifetimeBound
 
 The ``[[clang::lifetimebound]]`` attribute can be applied to function parameters
 or to the implicit ``this`` parameter of a method (by placing it after the
-method declarator). It indicates that the returned pointer or reference becomes
-invalid when the attributed parameter or ``this`` object is destroyed.
+method declarator). It indicates that the returned value becomes invalid when
+the attributed parameter or ``this`` object is destroyed.
 This is crucial for functions that return views or references to their
 arguments.
 
@@ -172,6 +172,29 @@ Without ``[[clang::lifetimebound]]`` on ``getView()``, the analysis would not
 know that the value returned by ``getView()`` depends on the temporary
 ``MyOwner`` object, and it would not be able to diagnose the dangling ``sv``.
 
+The analysis also tracks record types returned from functions and constructors
+with ``[[clang::lifetimebound]]`` parameters:
+
+.. code-block:: c++
+
+  #include <string>
+
+  struct S {
+    S(const std::string &s [[clang::lifetimebound]]);
+  };
+
+  S getS(const std::string &s [[clang::lifetimebound]]);
+
+  void test() {
+    S a(std::string("temp")); // warning: object whose reference is captured does not live long enough
+                              // note: destroyed here
+    (void)a;                  // note: later used here
+
+    S b = getS(std::string("temp")); // warning: object whose reference is captured does not live long enough
+                                     // note: destroyed here
+    (void)b;                         // note: later used here
+  }
+
 For more details, see `lifetimebound <https://clang.llvm.org/docs/AttributeReference.html#lifetimebound>`_.
 
 NoEscape

``````````

</details>


https://github.com/llvm/llvm-project/pull/189508