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repl: fix history truncation of long lines #15258

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13 changes: 12 additions & 1 deletion src/libcmd/repl-interacter.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,8 @@ extern "C" {
}
#endif

#include <fstream>

#include "nix/util/signals.hh"
#include "nix/util/finally.hh"
#include "nix/cmd/repl-interacter.hh"
Expand Down Expand Up @@ -119,8 +121,17 @@ ReadlineLikeInteracter::Guard ReadlineLikeInteracter::init(detail::ReplCompleter
}
#if !USE_READLINE
el_hist_size = 1000;
#endif
// editline's read_history uses a fixed 256-byte buffer (SCREEN_INC),
// which silently splits lines longer than 255 characters into separate
// history entries. Use std::getline instead, which has no length limit.
if (std::ifstream ifs(historyFile); ifs.good()) {
std::string line;
while (std::getline(ifs, line))
add_history(line.c_str());
}
#else
read_history(historyFile.c_str());
#endif
auto oldRepl = curRepl;
curRepl = repl;
Guard restoreRepl([oldRepl] { curRepl = oldRepl; });
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25 changes: 24 additions & 1 deletion tests/repl-completion.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,9 @@ runCommand "repl-completion"
}
exit 0
'';
passAsFile = [ "expectScript" ];
passAsFile = [
"expectScript"
];
}
''
export NIX_STORE=$TMPDIR/store
Expand All @@ -41,5 +43,26 @@ runCommand "repl-completion"

nix-store --init
expect $expectScriptPath

# Write a 300-char line to the history file, then run a REPL session
# that reads it back (read_history) and writes it out (write_history).
histFile=$HOME/.local/share/nix/repl-history
mkdir -p "$(dirname "$histFile")"
printf '%0300d\n' 0 | tr '0' 'a' > "$histFile"
echo "short" >> "$histFile"

# unbuffer allocates a pty so nix repl runs the interactive
# ReadlineLikeInteracter path (read_history on init, write_history
# on exit). Plain piped input skips history entirely.
echo ":q" | unbuffer -p nix repl --offline --extra-experimental-features nix-command 2>/dev/null || true

# Verify the long line survived the read/write cycle.
maxLen=$(awk '{ print length }' "$histFile" | sort -rn | head -1)
if [ "$maxLen" -lt 300 ]; then
echo "FAIL: long history line was truncated (max length: $maxLen)"
exit 1
fi
echo "Long history line preserved (length: $maxLen)."

touch $out
''
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