[clang-tools-extra] [clang-tidy] Portability Avoid Unprototyped Functions Check (PR #161023)

[via cfe-commits]

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+.. title:: clang-tidy - portability-avoid-unprototyped-functions
+
+portability-avoid-unprototyped-functions
+========================================
+
+Checks if unprototyped function types are used in the source code.
+
+For example:
+
+.. code-block:: c
+
+  void foo();         // Bad: unprototyped function declaration
+  void foo(void);     // Good: a function declaration that takes no parameters
+
+  void (*ptr)();      // Bad: pointer to an unprototyped function
+  void (*ptr)(void);  // Good: pointer to a function that takes no parameters
+
+Before C23 ``void foo()`` means a function that takes any number of parameters, so the following snippet is valid.
+
+.. code-block:: c
+
+  // -std=c17
+  void foo();
+
+  int main() {
+    foo(1, 2, 3);
+
+    return 0;
+  }
+
+Starting from C23 however, ``void foo()`` means a function that takes no parameters, so the same snippet is invalid.
+
+.. code-block:: c
+
+  // -std=c23
+  void foo();
+
+  int main() {
+    foo(1, 2, 3);
+  //    ^ error: too many arguments to function call, expected 0, have 3
+
+    return 0;
+  }
+
+Similarly a pointer to an unprototyped function binds to any function before C23, so the following snippet is considered valid.
+
+.. code-block:: c
+
+  // -std=c17
+  void foo(int x, int y);
+
+  int main() {
+    void (*ptr)() = &foo;
+
+    return 0;
+  }
+
+From C23 however, the smae pointer will only bind to functions that take no parameters.
----------------
EugeneZelenko wrote:

```suggestion
From C23 however, the same pointer will only bind to functions that take no parameters.
```

https://github.com/llvm/llvm-project/pull/161023