<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/130652>130652</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang: "function definition is not allowed here" when compiling GNU C with nested functions
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          carnivorecookies
      </td>
    </tr>
</table>

<pre>
    The following code fails to compile on clang 20.1.0 (and earlier versions), but successfully compiles on GCC:
```c
#include <stdio.h>

int main() {
        int foo() {
                return 1;
        }
        printf("%d\n", foo());
}
```
with the following error:
```
<source>:4:12: error: function definition is not allowed here
    4 |         int foo() {
      | ^
<source>:7:17: error: call to undeclared function 'foo'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    7 |         printf("%d\n", foo());
      |                        ^
2 errors generated.
```
even when using any of the GNU C standards (using any of the following compiler flags: `-std=gnu89`, `-std=gnu99`, `-std=gnu11`, `-std=gnu17`, and `-std=gnu23`)
according to the GNU website, nested functions are supported in GNU C:
<https://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html>
> A nested function is a function defined inside another function. **Nested functions are supported as an extension in GNU C, but are not supported by GNU C++.**

(emphasis added by me)
</pre>
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