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

@matklad

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.

@eddyb

@eddyb

As I understood from the description, you are saying that

This errors should also come for #! [bad_attribute].
#! /usr/bin/end should also be considered as valid shebang and Rust compiler will skip this line.
no changes for the third scenario:
#!
[bad_attribute]

Please confirm if we are on same page.

@ayushmishra2005

@ayushmishra2005 All of those sound correct, yeah

@eddyb

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

@rustbot claim

Fix #! (shebang) stripping account space issue rust-lang#70528

Refactoring and added test-cases rust-lang#70528

Rollup merge of rust-lang#71372 - ayushmishra2005:shebang_stripping, …

Fixed by #71372.

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

@rustbot

@rustbot claim

Fix bug in shebang handling

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#! (shebang) stripping doesn't account for spaces. #70528

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	/// 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("#![") {

#! (shebang) stripping doesn't account for spaces. #70528

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ayushmishra2005 commented on Apr 18, 2020

eddyb commented on Apr 18, 2020

ayushmishra2005 commented on Apr 19, 2020

JohnTitor commented on Apr 22, 2020

eddyb commented on Apr 28, 2020

rcoh commented on May 9, 2020

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