Why does the importC example not compile?

[kdevel]

https://dlang.org/spec/importc.html

`square.c`
```
int square(int i)
{
    return i * i;
}
```

`demo.d`
```
import std.stdio;
import square;
void main()
{
     int i = 7;
     writefln("The square of %s is %s", i, square(i));
}
```

```
$ dmd --version
DMD64 D Compiler v2.101.1
Copyright (C) 1999-2022 by The D Language Foundation, All Rights 
Reserved written by Walter Bright
$ dmd demo.d square.c
demo.d(6): Error: function expected before `()`, not `module 
square` of type `void`
```

I would have expected that each and every piece of code in the 
documentation is automatically compiled with any new compiler 
release.