messages: replace tabs with spaces in open_stream() (#151)

The tabs complicate the internal book-keeping because "\t12" has 3
characters but is printed to the terminal with a varying number of
spaces (depending on the user's tabwidth). For the pipe reader used
in open_stream(), this issue manifested as a bug where lines containing
tabs would result in multiple lines being printed (instead of just the
last one), which breaks the "ephemeral" aspect of the stream.

Note that this discovery implies that we should probably revisit this
tab issue in more places; in particular, the Printer does multiple
comparisons between the len() of the text and the terminal width, so
if the text has tabs that comparison will be incorrect. However, this
commit aims only to fix the (unreleased) behavior of showing subprocess
output as ephemeral messages inside open_stream().

craft_cli/messages.py

@@ -221,6 +221,9 @@ def _write(self, data: bytes) -> None:
 
             # write the useful line to intended outputs
             unicode_line = useful_line.decode("utf8")
+            # replace tabs with a set number of spaces so that the printer
+            # can correctly count the characters.
+            unicode_line = unicode_line.replace("\t", "  ")
             text = f":: {unicode_line}"
             self.printer.show(self.stream, text, **self.printer_flags)
 

examples.py

@@ -382,11 +382,26 @@ def example_26():
     emit.message("Application End.")
 
 
-def example_27(mode_name, total_messages=10):
+def _run_noisy_subprocess(mode_name, total_messages, subprocess_code):
     """Capture the output of a noisy subprocess in different modes."""
     mode = EmitterMode[mode_name.upper()]
     emit.set_mode(mode)
 
+    temp_fh, temp_name = tempfile.mkstemp()
+    with open(temp_fh, "wt", encoding="utf8") as fh:
+        fh.write(subprocess_code)
+
+    emit.progress("About to run a noisy subprocess")
+    time.sleep(1)
+    with emit.open_stream("Running custom Python app in unbuffered mode") as stream:
+        cmd = [sys.executable, "-u", temp_name, str(total_messages)]
+        subprocess.check_call(cmd, stdout=stream, stderr=stream)
+    os.unlink(temp_name)
+    emit.message("All done!")
+
+
+def example_27(mode_name, total_messages=10):
+    """Capture the output of a noisy subprocess in different modes."""
     example_test_sub_app = textwrap.dedent(
         """
         import sys
@@ -406,17 +421,34 @@ def example_27(mode_name, total_messages=10):
                 time.sleep(5)
     """
     )
-    temp_fh, temp_name = tempfile.mkstemp()
-    with open(temp_fh, "wt", encoding="utf8") as fh:
-        fh.write(example_test_sub_app)
+    _run_noisy_subprocess(mode_name, total_messages, example_test_sub_app)
 
-    emit.progress("About to run a noisy subprocess")
-    time.sleep(1)
-    with emit.open_stream("Running custom Python app in unbuffered mode") as stream:
-        cmd = [sys.executable, "-u", temp_name, str(total_messages)]
-        subprocess.run(cmd, stdout=stream, stderr=stream)
-    os.unlink(temp_name)
-    emit.message("All done!")
+
+def example_28(mode_name, total_messages=10):
+    """Capture the multi-line, tab-containing output of a noisy subprocess."""
+    example_test_sub_app = textwrap.dedent(
+        """
+        import sys
+        import time
+        import textwrap
+
+        total = int(sys.argv[1])
+        for idx in range(total):
+            #short = random() > .2
+            delay = 1
+            delay_for_spinner = False # random() > .9
+            message = textwrap.dedent(f'''
+            This first message should never appear.
+            \tThis second message shouldn't appear either.
+            \tThis line should appear, preceded "::   " ({idx} / {total}).
+            ''').strip()
+            print(message,flush=True)
+            time.sleep(delay)
+            if delay_for_spinner:
+                time.sleep(5)
+    """
+    )
+    _run_noisy_subprocess(mode_name, total_messages, example_test_sub_app)
 
 
 # -- end of test cases

tests/unit/test_messages_stream_cm.py

@@ -244,6 +244,19 @@ def test_pipereader_ephemeral(recording_printer, stream):
     assert msg.bar_total is None
 
 
+@pytest.mark.parametrize("stream", [sys.stdout, sys.stderr])
+def test_pipereader_tabs(recording_printer, stream):
+    """Check that tabs are converted to spaces."""
+    flags = {"use_timestamp": False, "ephemeral": False, "end_line": True}
+    prt = _PipeReaderThread(recording_printer, stream, flags)
+    prt.start()
+    os.write(prt.write_pipe, b"\t123\t456\n")
+    prt.stop()
+
+    (msg,) = recording_printer.written_terminal_lines  # pylint: disable=unbalanced-tuple-unpacking
+    assert msg.text == "::   123  456"  # tabs expanded into 2 spaces
+
+
 def test_pipereader_chunk_assembler(recording_printer, monkeypatch):
     """Converts ok arbitrary chunks to lines."""
     monkeypatch.setattr(messages, "_PIPE_READER_CHUNK_SIZE", 5)