scanner: disallow shebang outside of *.vsh files

[ttytm]

No description provided.

[spytheman]

why?

[ttytm]

Good question. Could be better to keep it valid it for .v files and treat it as a shebang is in script files. Recognized as shebang when it's at the beginning of the file.

Currently this compiles. Which got me into this PR.

module main

type Bar = string

fn main() {
	#!/usr/bin/env -S v
	dump('abc')
}

[ttytm]

In case #! shouldn't be a valid way for regular comments.

[spytheman]

I think it should be valid, only on the first line, no matter the extension.

[spytheman]

Note that you can:

#!/usr/bin/env -S v -raw-vsh-tmp-prefix tmp run
dump('abc')

Save this file as just abc (without any extension), then do chmod 755 abc, and then do: ./abc

[spytheman]

You can also skip the run in the first line, in which case, v will generate a tmp.abc executable just once, and doing ./abc after that, will just start ./tmp.abc directly, without having to compile it again, which will be much faster.
That is a documented feature, see https://github.com/vlang/v/blob/master/doc/docs.md#vsh-scripts-with-no-extension, and making the scanner depend on the extension will break it.

#0 10:40:00 ᛋ master /v/oo❱touch abc
#0 10:40:04 ᛋ master /v/oo❱xtime ./abc
[./abc:2] 'abc': abc
CPU: 0.33s      Real: 0.31s     Elapsed: 0:00.31        RAM: 58268KB    ./abc
#0 10:40:05 ᛋ master /v/oo❱xtime ./abc
[./abc:2] 'abc': abc
CPU: 0.00s      Real: 0.00s     Elapsed: 0:00.00        RAM: 5064KB     ./abc
#0 10:40:06 ᛋ master /v/oo❱xtime ./abc
[./abc:2] 'abc': abc
CPU: 0.00s      Real: 0.00s     Elapsed: 0:00.00        RAM: 5064KB     ./abc
#0 10:40:07 ᛋ master /v/oo❱

[ttytm]

With the new changes a shebang that's not on the first line is disallowed.

Shebangs are not recognized when it has empty lines beforehand.

script.sh: won't use cat if there's an empty line beforehand:

#!/bin/cat

echo 'hello'

script.vsh: with an empty line

#!/usr/bin/env -S v

println('hello world')

Currently results in:

./test.vsh: line 4: syntax error near unexpected token `'hello world''
./test.vsh: line 4: `println('hello world')'

With the changes it would be:

bugs/shebang.v:3:1: error: a shebang is only valid at the top of the file
    1 | 
    2 | 
    3 | #!/usr/bin/env -S v
      | ^
    4 | 
    5 | println('hello')

The new error will stop v fmt to remove the empty lines beforehand

[spytheman]

Excellent work.