Add color output

README.md

@@ -306,6 +306,16 @@ This will output a JSON file with the following information:
 Larger files naturally take longer to check, but files that take way too long should be
 looked into, as an issue might only manifest themselves when a file reaches a certain size.
 
+## Disable Color
+
+Color output is enabled by default in Refurb. To disable it, do one of the following:
+
+* Set the `NO_COLOR` env var.
+
+* Use the `--no-color` flag.
+
+* Set `color = false` in the config file.
+
 ## Developing / Contributing
 
 ### Setup

refurb/main.py

@@ -1,7 +1,7 @@
 import json
 import re
 import time
-from collections.abc import Sequence
+from collections.abc import Callable, Sequence
 from contextlib import suppress
 from functools import cache, partial
 from importlib import metadata
@@ -257,10 +257,53 @@ def format_as_github_annotation(error: Error | str) -> str:
     )
 
 
-def format_errors(errors: Sequence[Error | str], settings: Settings) -> str:
-    formatter = format_as_github_annotation if settings.format == "github" else str
+ERROR_DIFF_PATTERN = re.compile(r"`([^`]*)`([^`]*)`([^`]*)`")
+
+
+def format_with_color(error: Error | str) -> str:
+    if isinstance(error, str):
+        return error
+
+    blue = "\x1b[94m"
+    yellow = "\x1b[33m"
+    gray = "\x1b[90m"
+    green = "\x1b[92m"
+    red = "\x1b[91m"
+    reset = "\x1b[0m"
+
+    # Add red/green color for diffs, assuming the 2 pairs of backticks are in the form:
+    # Replace `old` with `new`
+    if error.msg.count("`") == 4:
+        parts = [
+            f"{gray}`{red}\\1{gray}`{reset}",
+            "\\2",
+            f"{gray}`{green}\\3{gray}`{reset}",
+        ]
 
-    done = "\n".join(formatter(error) for error in errors)  # type: ignore
+        error.msg = ERROR_DIFF_PATTERN.sub("".join(parts), error.msg)
+
+    parts = [
+        f"{blue}{error.filename}{reset}",
+        f"{gray}:{error.line}:{error.column + 1}{reset}",
+        " ",
+        f"{yellow}[{error.prefix}{error.code}]{reset}",
+        f"{gray}:{reset}",
+        " ",
+        error.msg,
+    ]
+
+    return "".join(parts)
+
+
+def format_errors(errors: Sequence[Error | str], settings: Settings) -> str:
+    if settings.format == "github":
+        formatter: Callable[[Error | str], str] = format_as_github_annotation
+    elif settings.color:
+        formatter = format_with_color
+    else:
+        formatter = str
+
+    done = "\n".join(formatter(error) for error in errors)
 
     if not settings.quiet and any(isinstance(err, Error) for err in errors):
         done += "\n\nRun `refurb --explain ERR` to further explain an error. Use `--quiet` to silence this message"

refurb/settings.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import os
 import re
 import sys
 from dataclasses import dataclass, field, replace
@@ -43,13 +44,17 @@ class Settings:
     sort_by: Literal["filename", "error"] | None = None
     verbose: bool = False
     timing_stats: Path | None = None
+    color: bool = True
 
     def __post_init__(self) -> None:
         if self.enable_all and self.disable_all:
             raise ValueError(
                 'refurb: "enable all" and "disable all" can\'t be used at the same time'  # noqa: E501
             )
 
+        if os.getenv("NO_COLOR"):
+            self.color = False
+
     @staticmethod
     def merge(old: Settings, new: Settings) -> Settings:
         if not old.disable_all and new.disable_all:
@@ -85,6 +90,7 @@ def merge(old: Settings, new: Settings) -> Settings:
             sort_by=new.sort_by or old.sort_by,
             verbose=old.verbose or new.verbose,
             timing_stats=old.timing_stats or new.timing_stats,
+            color=old.color and new.color,
         )
 
     def get_python_version(self) -> tuple[int, int]:
@@ -155,8 +161,8 @@ def parse_amendment(amendment: dict[str, Any]) -> set[ErrorClassifier]:  # type:
 
 
 def pop_type(ty: type[T], type_name: str = "") -> Callable[..., T]:  # type: ignore[misc]
-    def inner(config: dict[str, Any], name: str) -> T:  # type: ignore[misc]
-        x = config.pop(name, ty())
+    def inner(config: dict[str, Any], name: str, *, default: T | None = None) -> T:  # type: ignore[misc]
+        x = config.pop(name, default or ty())
 
         if isinstance(x, ty):
             return x
@@ -188,6 +194,7 @@ def parse_config_file(contents: str) -> Settings:
     settings.quiet = pop_bool(config, "quiet")
     settings.disable_all = pop_bool(config, "disable_all")
     settings.enable_all = pop_bool(config, "enable_all")
+    settings.color = pop_bool(config, "color", default=True)
 
     enable = pop_list(config, "enable")
     disable = pop_list(config, "disable")
@@ -313,6 +320,9 @@ def get_next_arg(arg: str, args: Iterator[str]) -> str:
         elif arg == "--timing-stats":
             settings.timing_stats = Path(get_next_arg(arg, iargs))
 
+        elif arg == "--no-color":
+            settings.color = False
+
         elif arg == "--":
             settings.mypy_args = list(iargs)
 

test/test_arg_parsing.py

@@ -1,4 +1,6 @@
+import os
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
 
@@ -125,6 +127,7 @@ def test_parse_config_file() -> None:
 enable = ["FURB111", "FURB222"]
 format = "github"
 sort_by = "error"
+color = false
 """
 
     config = parse_config_file(contents)
@@ -135,6 +138,7 @@ def test_parse_config_file() -> None:
         enable={ErrorCode(111), ErrorCode(222)},
         format="github",
         sort_by="error",
+        color=False,
     )
 
 
@@ -666,3 +670,14 @@ def test_parse_timing_stats_flag() -> None:
 def test_parse_timing_stats_flag_without_arg_is_an_error() -> None:
     with pytest.raises(ValueError, match='refurb: missing argument after "--timing-stats"'):
         parse_args(["--timing-stats"])
+
+
+def test_parse_no_color_flag() -> None:
+    assert parse_args(["--no-color"]) == Settings(color=False)
+
+
+def test_no_color_env_var_disables_color() -> None:
+    with patch.dict(os.environ, {"NO_COLOR": "1"}):
+        settings = Settings()
+
+        assert not settings.color

test/test_main.py

@@ -299,3 +299,27 @@ def test_timing_stats_outputs_stats_file() -> None:
                 return
 
         pytest.fail("Data is not in proper format")
+
+
+def test_color_is_enabled_by_default():
+    with patch("builtins.print") as p:
+        main(["test/data/err_123.py"])
+
+        p.assert_called_once()
+        assert "\x1b" in p.call_args[0][0]
+
+
+def test_no_color_printed_when_disabled():
+    with patch("builtins.print") as p:
+        main(["test/data/err_123.py", "--no-color"])
+
+        p.assert_called_once()
+        assert "\x1b" not in p.call_args[0][0]
+
+
+def test_error_github_actions_formatting():
+    with patch("builtins.print") as p:
+        main(["test/data/err_123.py", "--format", "github"])
+
+        p.assert_called_once()
+        assert "::error" in p.call_args[0][0]