Mercurial collapses lines into single line when piping output

Question

I'd like to sort based on the output of a mercurial (hg) command. The output from hg log is collapsed into 1 line when piping to another command but I want to keep separate lines.

Here's a minimum reproducible case:

# Initial setup
mkdir /tmp/hgbug; cd /tmp/hgbug; hg init; 
touch README.md; hg add README.md
h commit -m "initial commit"

# Bug - the echo command replaces a complex find command
echo '1a\n2b\n3c\n' | xargs -I % hg log --template '%' | sort

# Actual Output
# 1a2b3c

# Expected Output
# 1a
# 2b
# 3c

The interesting part is that mercurial doesn't collapse the lines when the output isn't piped or redirected.

echo '1a\n2b\n3c\n' | xargs -I % hg log --template '%'
# Actual Output
# 1a
# 2b
# 3c

How do I prevent mercurial from collapsing lines when redirecting output?

To clarify, here's a more complete example comparing the output of hg with echo using both xargs and a while loop.

#!/bin/bash
cd /tmp/hgbug

echo '# hg log - xargs'
echo $'1a\n2b\n3c' | xargs -I {} hg log --template "hg-{}" | sort

echo
echo '# plain echo - xargs'
echo $'1a\n2b\n3c' | xargs -I {} echo "echo-{}" | sort

echo
echo '# hg log - while read'
echo $'1a\n2b\n3c' | while read -r file; do hg log --template "hg-$file"; done | sort

echo
echo '# plain echo - while read'
echo $'1a\n2b\n3c' | while read -r file; do echo "echo-$file"; done | sort

That script outputs the following:

# hg log - xargs
hg-1ahg-2bhg-3c

# plain echo - xargs
echo-1a
echo-2b
echo-3c

# hg log - while read
hg-1ahg-2bhg-3c

# plain echo - while read
echo-1a
echo-2b
echo-3c

Answer 1

hg log doesn't add a trailing newline to output when the --template flag is set and the shell command is redirected or piped to another command.

To make it work, you need to add the newline to the template string like so:

echo '1a\n2b\n3c\n' | xargs -I % hg log --template '%\n' | sort
# Output
1a
2b
3c