#! (shebang) stripping doesn't account for spaces.

[eddyb]

A file containing only this correctly errors:

#![bad_attribute]

But this doesn't error, as it's stripped the same way #!/usr/bin/env ... (i.e. "shebang") would be:

#! [bad_attribute]

In this third example, it also strips just the #!, breaking the attribute:

#!
[bad_attribute]

The code responsible is this:

rust/src/librustc_lexer/src/lib.rs

Lines 156 to 160 in 8045865

	/// Line won't be skipped if it represents a valid Rust syntax
	/// (e.g. "#![deny(missing_docs)]").
	pub fn strip_shebang(input: &str) -> Option<usize> {
	debug_assert!(!input.is_empty());
	if !input.starts_with("#!") || input.starts_with("#![") {

It doesn't seem to account for any whitespace between the ! and [.
I believe that we should allow any characters c where c != '\n' && is_whitespace(c) after the #!, and determine whether this is a shebang, by the next character on the same line:

• if there are no non-whitespace characters, it's not a valid shebang
• if the next character is [, this is the start of an inner comment
• otherwise, it's probably a shebang

I have no idea what to do for Rust comment syntax (#!//... and #!/*...), however.

And, of course, at the end of the day, this might be a backwards-incompatible change to make.

cc @matklad @petrochenkov

This issue has been assigned to @rcoh via this comment.

[ayushmishra2005]

@eddyb

As I understood from the description, you are saying that

1. This errors should also come for #! [bad_attribute].

2. #! /usr/bin/end should also be considered as valid shebang and Rust compiler will skip this line.

3. no changes for the third scenario:
   #!
   [bad_attribute]

Please confirm if we are on same page.

[eddyb]

@ayushmishra2005 All of those sound correct, yeah

[ayushmishra2005]

Thanks @eddyb . I would like to pick this issue.

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[JohnTitor]

Fixed by #71372.

[eddyb]

There are issues with the fix (and it didn't go through Crater), so I'm preparing a revert.

[rcoh]

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