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Enable pretty by default #19510

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f94fc8f
feat: Enable --pretty by default.
null-dreams Jul 24, 2025
54a0196
fix(tests): Adapt TypeCheckSuite to default to non-pretty output
null-dreams Jul 24, 2025
e0d968e
fix(tests): Adapt CmdlineSuite to default to non-pretty output
null-dreams Jul 24, 2025
201f436
fix(tests): Adapt pythoneval suite to default to non-pretty output
null-dreams Jul 24, 2025
9d498a8
fix(tests): Adapt errorstream suite to default to non-pretty output
null-dreams Jul 24, 2025
0a9e326
fix(tests): Adapt DaemonSuite to handle new pretty default
null-dreams Jul 24, 2025
f07217d
fix(tests): Adapt PEP561Suite to default to non-pretty output
null-dreams Jul 24, 2025
d4de5a7
fix(tests): Update Stubtest unit tests to expect pretty output
null-dreams Jul 24, 2025
ce8cc29
docs: Update docs for pretty-by-default behavior
null-dreams Jul 24, 2025
7b79b5a
style: Fix ruff linting error in testdaemon.py
null-dreams Jul 25, 2025
d67c367
chore: Re-trigger CI
null-dreams Jul 25, 2025
afc6585
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jul 26, 2025
23e5980
fix: Remove redundant `flag_list` in `parse_options`
null-dreams Jul 31, 2025
66121c9
refactor(cli): Simplify flag implementation using inverted `add_inver…
null-dreams Jul 31, 2025
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6 changes: 3 additions & 3 deletions docs/source/command_line.rst
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Expand Up @@ -910,10 +910,10 @@ in error messages.

See :ref:`error-codes` for more information.

.. option:: --pretty
.. option:: --no-pretty

Use visually nicer output in error messages: use soft word wrap,
show source code snippets, and show error location markers.
Disable pretty error messages and use the old, plain output format.
Pretty-printing is enable by default.

.. option:: --no-color-output

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3 changes: 2 additions & 1 deletion docs/source/config_file.rst
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Expand Up @@ -896,10 +896,11 @@ These options may only be set in the global section (``[mypy]``).
.. confval:: pretty

:type: boolean
:default: False
:default: True

Use visually nicer output in error messages: use soft word wrap,
show source code snippets, and show error location markers.
Pretty printing is enabled by default, but can be disabled.

.. confval:: color_output

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15 changes: 7 additions & 8 deletions mypy/main.py
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Expand Up @@ -991,21 +991,20 @@ def add_invertible_flag(
help="Show links to error code documentation",
group=error_group,
)
add_invertible_flag(
"--pretty",
default=False,
help="Use visually nicer output in error messages:"
" Use soft word wrap, show source code snippets,"
" and show error location markers",
group=error_group,
)
add_invertible_flag(
"--no-color-output",
dest="color_output",
default=True,
help="Do not colorize error messages",
group=error_group,
)
add_invertible_flag(
"--no-pretty",
default=True,
dest="pretty",
help="Disable pretty error message",
group=error_group,
)
add_invertible_flag(
"--no-error-summary",
dest="error_summary",
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2 changes: 1 addition & 1 deletion mypy/options.py
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Expand Up @@ -357,7 +357,7 @@ def __init__(self) -> None:
self.hide_error_codes = False
self.show_error_code_links = False
# Use soft word wrap and show trimmed source snippets with error location markers.
self.pretty = False
self.pretty = True
self.dump_graph = False
self.dump_deps = False
self.logical_deps = False
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5 changes: 4 additions & 1 deletion mypy/test/helpers.py
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Expand Up @@ -342,6 +342,8 @@ def parse_options(

if flags:
flag_list = flags.group(1).split()
if "--pretty" not in flag_list:
flag_list.append("--no-pretty")
flag_list.append("--no-site-packages") # the tests shouldn't need an installed Python
targets, options = process_options(flag_list, require_targets=False)
if targets:
Expand All @@ -350,11 +352,12 @@ def parse_options(
if "--show-error-codes" not in flag_list:
options.hide_error_codes = True
else:
flag_list = []
options = Options()
options.pretty = False
options.error_summary = False
options.hide_error_codes = True
options.force_union_syntax = True
flag_list = []

# Allow custom python version to override testfile_pyversion.
if all(flag.split("=")[0] != "--python-version" for flag in flag_list):
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9 changes: 7 additions & 2 deletions mypy/test/testcmdline.py
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Expand Up @@ -131,8 +131,13 @@ def parse_args(line: str) -> list[str]:
"""
m = re.match("# cmd: mypy (.*)$", line)
if not m:
return [] # No args; mypy will spit out an error.
return m.group(1).split()
return ["--no-pretty"] # No args; mypy will spit out an error.
args = m.group(1).split()

if "--pretty" not in args:
args.append("--no-pretty")

return args


def parse_cwd(line: str) -> str | None:
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12 changes: 12 additions & 0 deletions mypy/test/testdaemon.py
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Expand Up @@ -79,6 +79,18 @@ def parse_script(input: list[str]) -> list[list[str]]:
def run_cmd(input: str) -> tuple[int, str]:
if input[1:].startswith("mypy run --") and "--show-error-codes" not in input:
input += " --hide-error-codes"
is_pretty_test = "# NO-MODIFY" in input
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Okay, I must be missing something - why won't just checking for --pretty flag do? Yes, it will deviate from normal behavior, but be consistent with all other tests - essentially sticking to old default unless requested otherwise.

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Hello @sterliakov , this is still my main approach and it is also partly working in the this test-runner to maintain the consistent behavior with all other test-runners.However, I discovered a critical technical constraint: the dmypy client itself does not accept the --pretty or --no-pretty flags.

The formatting flags must be directly passed to the server, which only worked in these two ways for me:
- During startup: $ dmypy start -- --no-pretty
- During one-shot run: $ dmypy run -- --no-pretty

Because the testcases contains a mix of commands where the flag will and won't work, I had to make #NO-MODIFY as the magic comment to recognize where to not modify the command.

For demonstration:

[case testDaemonRecheck]
$ dmypy start -- --follow-imports=error --no-error-summary
Daemon started
$ dmypy check foo.py bar.py
$ dmypy recheck
$ dmypy recheck --update foo.py --remove bar.py sir_not_appearing_in_this_film.py
foo.py:1: error: Import of "bar" ignored  [misc]
foo.py:1: note: (Using --follow-imports=error, module not passed on command line)
== Return code: 1
$ dmypy recheck --update bar.py
$ dmypy recheck --update sir_not_appearing_in_this_film.py
$ dmypy recheck --update --remove
$ dmypy stop
Daemon stopped
[file foo.py]

In this case, my first approach was to insert the --pretty flag in all of them. But dmypy recheck threw an unrecognized argument error. So I realized I cannot insert any flag in the commands following dmypy start...
Therefore, I preferred to adding --pretty flag during startup. But then the test-runner logic detecting so such --pretty flag in the other commands automatically injects the --no-pretty flag which also throws an unrecognized argument error. This led to the realization, that I also need to mark these commands someway, that the test-runner doesn't inject --no-pretty in them. The best I could think of was a magic comment #NO-MODIFY which I can use to detect these lines where the test-runner shouldn't be interfering.

I understand that this is a very bare-bones workaround, and I am open to any suggestions to make it cleaner.

modified_input = input.replace("# NO-MODIFY", "").strip()
cond1 = "--pretty" not in modified_input
cond2 = modified_input.startswith(("dmypy run", "dmypy check"))
cond3 = not is_pretty_test
if cond1 and cond2 and cond3:
parts = modified_input.split(" ", 2)
command, subcommand = parts[0], parts[1]
args = parts[2] if len(parts) > 2 else ""
input = f"{command} {subcommand} {args} --no-pretty".strip()
else:
input = modified_input
if input.startswith("dmypy "):
input = sys.executable + " -m mypy." + input
if input.startswith("mypy "):
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1 change: 1 addition & 0 deletions mypy/test/testerrorstream.py
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Expand Up @@ -25,6 +25,7 @@ def test_error_stream(testcase: DataDrivenTestCase) -> None:
The argument contains the description of the test case.
"""
options = Options()
options.pretty = False
options.show_traceback = True
options.hide_error_codes = True

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7 changes: 5 additions & 2 deletions mypy/test/testpep561.py
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Expand Up @@ -174,5 +174,8 @@ def parse_pkgs(comment: str) -> tuple[list[str], list[str]]:
def parse_mypy_args(line: str) -> list[str]:
m = re.match("# flags: (.*)$", line)
if not m:
return [] # No args; mypy will spit out an error.
return m.group(1).split()
return ["--no-pretty"] # No args; mypy will spit out an error.
args = m.group(1).split()
args.append("--no-pretty")

return args
6 changes: 6 additions & 0 deletions mypy/test/testpythoneval.py
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Expand Up @@ -54,6 +54,9 @@ def test_python_evaluation(testcase: DataDrivenTestCase, cache_dir: str) -> None
"--allow-empty-bodies",
"--test-env", # Speeds up some checks
]

mypy_cmdline.append("--no-pretty")

interpreter = python3_path
mypy_cmdline.append(f"--python-version={'.'.join(map(str, PYTHON3_VERSION))}")

Expand All @@ -69,6 +72,9 @@ def test_python_evaluation(testcase: DataDrivenTestCase, cache_dir: str) -> None
sys.version_info.minor,
):
return
if "--pretty" in additional_flags:
mypy_cmdline.remove("--no-pretty")

mypy_cmdline.extend(additional_flags)

# Write the program to a file.
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10 changes: 8 additions & 2 deletions mypy/test/teststubtest.py
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Expand Up @@ -2581,13 +2581,17 @@ def test_mypy_build(self) -> None:
output = run_stubtest(stub="+", runtime="", options=[])
assert output == (
"error: not checking stubs due to failed mypy compile:\n{}.pyi:1: "
"error: Invalid syntax [syntax]\n".format(TEST_MODULE_NAME)
"error: Invalid syntax [syntax]\n"
" +\n"
" ^\n".format(TEST_MODULE_NAME)
)

output = run_stubtest(stub="def f(): ...\ndef f(): ...", runtime="", options=[])
assert output == (
"error: not checking stubs due to mypy build errors:\n{}.pyi:2: "
'error: Name "f" already defined on line 1 [no-redef]\n'.format(TEST_MODULE_NAME)
'error: Name "f" already defined on line 1 [no-redef]\n'
" def f(): ...\n"
" ^~~~~~~~~~~~\n".format(TEST_MODULE_NAME)
)

def test_missing_stubs(self) -> None:
Expand Down Expand Up @@ -2665,6 +2669,8 @@ def test_config_file_error_codes(self) -> None:
assert output == (
"error: not checking stubs due to mypy build errors:\n"
'test_module.pyi:1: error: Name "SOME_GLOBAL_CONST" is not defined [name-defined]\n'
" temp = SOME_GLOBAL_CONST\n"
" ^~~~~~~~~~~~~~~~~\n"
)

config_file = "[mypy]\ndisable_error_code = name-defined\n"
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