Share the stderr with the user, when non-zero exit code (#927)

* Share the stderr with the user, when failing a require_command() due to non-zero exit code.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Too long line.

* Just log at the place where the call is made.

* Undo added empty lines.

* Test for log-output in case of non-zero return code from a command.

---------

Co-authored-by: Arvid Müllern-Aspegren <x@rvid.se>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/setuptools_scm/_run_cmd.py

@@ -175,6 +175,9 @@ def has_command(
 ) -> bool:
     try:
         p = run([name, *args], cwd=".", timeout=5)
+        if p.returncode != 0:
+            log.error(f"Command '{name}' returned non-zero. This is stderr:")
+            log.error(p.stderr)
     except OSError as e:
         log.warning("command %s missing: %s", name, e)
         res = False

testing/test_functions.py

@@ -153,6 +153,20 @@ def test_has_command() -> None:
         assert not has_command("yadayada_setuptools_aint_ne")
 
 
+def test_has_command_logs_stderr(caplog: pytest.LogCaptureFixture) -> None:
+    """
+    If the name provided to has_command() exists as a command, but gives a non-zero
+    return code, there should be a log message generated.
+    """
+    with pytest.warns(RuntimeWarning, match="ls"):
+        has_command("ls", ["--a-flag-that-doesnt-exist-should-give-output-on-stderr"])
+    found_it = False
+    for record in caplog.records:
+        if "returned non-zero. This is stderr" in record.message:
+            found_it = True
+    assert found_it, "Did not find expected log record for "
+
+
 @pytest.mark.parametrize(
     "tag, expected_version",
     [