Warn when piped data is not used

[Copilot]

When data is piped in alongside target files and no flag (such as --replacement-pipe or --replacement-js) indicates how to use it, the piped data is silently ignored. This change introduces warnings as a third message kind alongside info and errors, alerting users to unused piped input.

Summary of Changes

• Warning Output (src/output.ts):

  • Implemented warn(msg, data) writing to stderr with a 🟡 prefix.
  • Suppressed when --quiet or --quiet-total is set.
  • Does not abort execution, including when --halt or --bail is enabled.

• Unused Pipe Detection (src/engine.ts):

  • Emits 🟡 Data is piped in, but no flag tells what to do with it. It is not used. in handlePipedData() when files are specified and piped data exists.
  • Omits warning when piped data is explicitly handled via --replacement-pipe, referenced via --replacement-js, dismissed via --void-pipe, or consists only of empty content/single line breaks (\n, \r\n).

• Documentation (README.md):

  • Removed Error != warning from the future ideas list.

• Test Suite:

  • Added unit test coverage in test/js/fix/719.test.js covering emission, non-halting behavior, pipe consumption flags, and quiet flag suppression.
  • Added CLI test cases in test/cli/run.sh.

Example

# Before: silently ignores piped input and modifies my.file
cat notes.txt | rexreplace foo bar my.file
my.file

# After: emits warning to stderr without blocking file replacement
cat notes.txt | rexreplace foo bar my.file
 🟡 Data is piped in, but no flag tells what to do with it. It is not used.
my.file

• Fixes Warn when piped data is not used #719

[mathiasrw]

@copilot Are we able to detect this before we start listening to the pipe so we send the warning but simley ignore the content and dont load it into mem?

[mathiasrw]

@copilot

[mathiasrw]

Why this? what is the reasoning?

[Copilot]

@copilot Are we able to detect this before we start listening to the pipe so we send the warning but simley ignore the content and dont load it into mem?

Yes. In src/cli.ts, before attaching listeners to process.stdin, we can check if !process.stdin.isTTY, files are specified (config.includeGlob.length > 0), and no flags will use the pipe (!config.replacementPipe && !config.replacementJs && !config.voidPipe). When met, we can emit the warning and run rexreplace.engine(config) immediately without reading or buffering stdin into memory.

The trade-off is that without reading from the pipe, we cannot inspect the content, so we cannot distinguish between actual data and an empty pipe or single newline (cat /dev/null or printf '\n'); any redirected/piped stdin would trigger the warning. If we still want to ignore empty/newline-only input without loading the entire stream into memory, we would need to read just the first chunk to check it and then discard the rest of the stream.

[Copilot]

@copilot

Regarding lines 165-166 (config.pipedData !== '\n' && config.pipedData !== '\r\n'):

This follows the behavior on the reference v8.0 branch ('' !== pipeData && '\n' !== pipeData), mentioned in the issue description under "To decide: Empty piped data, or only a line break: is that also a warning? On the v8.0 branch it was not."

Commands like echo "" frequently produce a trailing newline (\n or \r\n on Windows) even when no meaningful content was intended to be piped. Treating a lone newline the same as empty input avoids false-positive warnings in those cases.

If you would prefer to warn on single line breaks as well, let me know and I can remove those conditions.

[mathiasrw]

Closing, as this is covered elsewhere now.

• The warning for piped data that is not used came into main with Fix files from absolute path to close #726 and add RR_VOID_PIPE env var. #730.
• The one part that was still missing (no warning when only \r\n is piped in) is in No warning when only a Windows line break is piped in #731.

The idea from the thread about warning before the pipe is read is dropped, to keep the implementation simple. --void-pipe / RR_VOID_PIPE already makes sure the piped data is not loaded.