Off by one error in str::index_mut (specifically) for RangeToInclusive (specifically)

Caught while fleshing out a much beefier test suite for SliceIndex, which I plan to submit as a PR. (this Issue is here just in case that PR never happens).

rust/src/libcore/str/mod.rs

Lines 2107 to 2115 in 1ef1563

    
           fn index_mut(self, slice: &mut str) -> &mut Self::Output { 
        
               assert!(self.end != usize::max_value(), 
        
                   "attempted to index str up to maximum usize"); 
        
               if slice.is_char_boundary(self.end) { 
        
                   unsafe { self.get_unchecked_mut(slice) } 
        
               } else { 
        
                   super::slice_error_fail(slice, 0, self.end + 1) 
        
               } 
        
           }

The unicode character boundary check here should be looking at self.end + 1. Better yet, the method could just delegate to RangeTo instead. (note: it can't delegate to get_mut here without NLL, which seems to be a leading factor as to how this function ended up this way)

Not technically a regression but tagging it as such to ensure that we don't forget about it.

Auto merge of #50039 - ExpHP:quick-50002, r=alexcrichton

@alexcrichton

@alexcrichton my commit message accidentally closed this, which might defeat the purpose of the tag you added

(note: I myself can't reopen it because Github attributed the message to Bors)

Oh that's ok, the tags on the PR take over now for backporting and that's how we'll track this.

smaller PR just to fix rust-lang#50002

(ahhhh, now I see. The tag is used in automation for a Github Project to track regressions. That's actually pretty cool!)

(...don't mind me, just talking to myself)

Rollup merge of rust-lang#50010 - ExpHP:slice-bounds, r=alexcrichton

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Off by one error in str::index_mut (specifically) for RangeToInclusive (specifically) #50002

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	fn index_mut(self, slice: &mut str) -> &mut Self::Output {
	assert!(self.end != usize::max_value(),
	"attempted to index str up to maximum usize");
	if slice.is_char_boundary(self.end) {
	unsafe { self.get_unchecked_mut(slice) }
	} else {
	super::slice_error_fail(slice, 0, self.end + 1)
	}
	}

Off by one error in str::index_mut (specifically) for RangeToInclusive (specifically) #50002

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alexcrichton commented on Apr 21, 2018

ExpHP commented on Apr 21, 2018

alexcrichton commented on Apr 21, 2018

ExpHP commented on May 10, 2018

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