Crash when first line is empty and -L is specified with a one character separator.

[ghuls]

Crash when first line is empty and -L is specified with a one character separator.

# File with empty first line.
$ printf '\n1\t2\t3\n4\t5\t6\n'

1       2       3
4       5       6

# Get first 2 columns with regex "\t".
$ printf '\n1\t2\t3\n4\t5\t6\n' | hck -d '\t' -f 1,2 -

1       2
4       5

# Get first 2 columns with regex code using a real TAB character (created by bash).
$ printf '\n1\t2\t3\n4\t5\t6\n' | hck -d $'\t' -f 1,2 -

1       2
4       5


# Get first 2 columns with literal separator option using a real TAB character (created by bash).
$ printf '\n1\t2\t3\n4\t5\t6\n' | hck -L -d $'\t' -f 1,2 -
thread 'main' panicked at 'attempted to index slice up to maximum usize', /software/hck/src/lib/core.rs:528:59
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

# Will print all columns as "\t" is not treated as a regex.
$ printf '\n1\t2\t3\n4\t5\t6\n' | hck -L -d '\t' -f 1,2 -

1       2       3
4       5       6

# With one space as delimiter, we get a crash too when using the literal separator option.
$ printf '\n1\t2\t3\n4\t5\t6\n' | hck -L -d ' ' -f 1,2 -
thread 'main' panicked at 'attempted to index slice up to maximum usize', /software/hck/src/lib/core.rs:528:59
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

# With two spaces as delimiter, it works.
$ printf '\n1\t2\t3\n4\t5\t6\n' | hck -L -d '  ' -f 1,2 -

1       2       3
4       5       6

[ghuls]

Something like this probably will fix it.

diff --git a/src/lib/core.rs b/src/lib/core.rs
index dc45f43..476dfdc 100644
--- a/src/lib/core.rs
+++ b/src/lib/core.rs
@@ -520,7 +520,11 @@ where
                     line.push((start, index - 1));
                     start = index + 1;
                 } else if bytes[index] == newline {
-                    line.push((start, index - 1));
+                    if (index != 0) {
+                        line.push((start, index - 1));
+                    } else {
+                        line.push((0, 0));
+                    }
                     let items = self.fields.iter().flat_map(|f| {
                         let slice = line
                             .get(f.low..=min(f.high, line.len().saturating_sub(1)))

Although for performance reasons it might be better to check before the for index in iter loop if the first byte is a newline character, so this condition does not have to be checked in each iteration.

[sstadick]

I closed it too soon. v0.6.5-alpha is adding an extra line when there is a blank line at the start.

[sstadick]

Okay, see v0.6.5 release which should be building now.

[sstadick]

@ghuls also, again, thanks for taking the time to make a detailed issue! You make these really easy to fix 👍

[ghuls]

Thanks for the fast fix.