[clang] [NFC][analyzer] Document optin.portability.UnixAPI (PR #150005)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Donát Nagy (NagyDonat)

<details>
<summary>Changes</summary>

This commit provides a brief documentation for the checker optin.portability.UnixAPI.

Unfortunately the name of this checker is meaninglessly vague and its functionality is very closely related to unix.Malloc, so it should be eventually "rebranded" to a more user-friendly presentation.

---
Full diff: https://github.com/llvm/llvm-project/pull/150005.diff


2 Files Affected:

- (modified) clang/docs/analyzer/checkers.rst (+10-1) 
- (modified) clang/include/clang/StaticAnalyzer/Checkers/Checkers.td (+2-2) 


``````````diff
diff --git a/clang/docs/analyzer/checkers.rst b/clang/docs/analyzer/checkers.rst
index 26c5028e04955..4e8b31869bb56 100644
--- a/clang/docs/analyzer/checkers.rst
+++ b/clang/docs/analyzer/checkers.rst
@@ -1103,7 +1103,16 @@ To override this threshold to e.g. 4 bytes, use the
 
 optin.portability.UnixAPI
 """""""""""""""""""""""""
-Finds implementation-defined behavior in UNIX/Posix functions.
+Reports situations where 0 is passed as the "size" argument of various
+allocation functions ( ``calloc``, ``malloc``, ``realloc``, ``reallocf``,
+``alloca``, ``__builtin_alloca``, ``__builtin_alloca_with_align``, ``valloc``).
+
+Note that similar functionality is also supported by :ref:`unix-Malloc` which
+reports code that *uses* memory allocated with size zero.
+
+(The name of this checker is motivated by the fact that it was originally
+introduced with the vague goal that it "Finds implementation-defined behavior
+in UNIX/Posix functions.")
 
 
 optin.taint
diff --git a/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td b/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
index 2234143004b6f..38584c98fcc91 100644
--- a/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
+++ b/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
@@ -1656,8 +1656,8 @@ def CloneChecker : Checker<"CloneChecker">,
 let ParentPackage = PortabilityOptIn in {
 
 def UnixAPIPortabilityChecker : Checker<"UnixAPI">,
-  HelpText<"Finds implementation-defined behavior in UNIX/Posix functions">,
-  Documentation<NotDocumented>;
+  HelpText<"Finds dynamic memory allocation with size zero">,
+  Documentation<HasDocumentation>;
 
 } // end optin.portability
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/150005