Incorrect output on pip-compile upgrade with --dry-run and --quiet flags

[atugushev]

Environment Versions

1. OS Type: any
2. Python version: any
3. pip version: any
4. pip-tools version: 3.8.0

Steps to replicate

1. echo "six" > requirements.in
2. pip-compile
3. pip-compile --upgrade --dry-run --quiet

Expected result

• --dry-run should print changes to stdout/stderr
• --quiet should suppress "Dry-run, so nothing updated." message

#
# This file is autogenerated by pip-compile
# To update, run:
#
#    pip-compile
#
six==1.12.0

Actual result

But currently it behaves the opposite way:

Dry-run, so nothing updated.

---

Refs:

• pip-compile --quiet --upgrade --dry-run --output-file - should produce output #843
• pip-tools --upgrade --dry-run --output-file requirements.pc should not erase requirements.pc when --dry-run is specified #841 (comment)

[AndydeCleyre]

I think the state now is that the dry run message is indeed suppressed by the quiet flag, but so is the output.

Do we want the dry run flag to effectively bypass the log level for the stderr copy of output? Something like

--- a/piptools/writer.py
+++ b/piptools/writer.py
@@ -245,10 +245,12 @@ class OutputWriter:
     ) -> None:

         for line in self._iter_lines(results, unsafe_requirements, markers, hashes):
-            log.info(line)
             if not self.dry_run:
+                log.info(line)
                 self.dst_file.write(unstyle(line).encode())
                 self.dst_file.write(os.linesep.encode())
+            else:
+                log.log(line)

[AndydeCleyre]

The above change would break two current tests:

• test_quiet_option
• test_dry_run_quiet_option

This is because the command

pip-compile --quiet --dry-run

would produce the header comment in stderr, instead of an empty stderr.

That doesn't violate what the tests intend to check for exactly, IMO.