fix(cli): disable ANSI colors for redirected output by default

README.md

@@ -27,8 +27,6 @@ python3 -m pip install .
 python3 scripts/demo.py
 ```
 
-Install from this checkout to use the reviewed source version. The installed tool has no third-party runtime dependencies; cloning and installation can require network access.
-
 ## Features
 
 ### Choose your diff

src/diffnote/cli.py

@@ -30,8 +30,12 @@ def build_parser():
                      help="Print a GitHub PR-body markdown.")
     fmt.add_argument("--json", action="store_true",
                      help="Print machine-readable JSON.")
-    fmt.add_argument("--no-color", action="store_true",
-                     help="Disable ANSI colors.")
+    color = fmt.add_mutually_exclusive_group()
+    color.add_argument("--color", action="store_true", dest="use_color",
+                       help="Force ANSI colors, even when output is redirected.")
+    color.add_argument("--no-color", action="store_false", dest="use_color",
+                       help="Disable ANSI colors.")
+    p.set_defaults(use_color=None)
     fmt.add_argument("--llm", action="store_true",
                      help="Enhance with a local Ollama model (needs Ollama running).")
     return p
@@ -87,7 +91,7 @@ def main(argv=None):
     elif args.markdown:
         print(render.render_markdown(summary, llm_prose))
     else:
-        print(render.render_terminal(summary, use_color=not args.no_color, llm_prose=llm_prose))
+        print(render.render_terminal(summary, use_color=args.use_color, llm_prose=llm_prose))
     return 0
 
 

src/diffnote/render.py

@@ -1,6 +1,7 @@
 """Output renderers: terminal (ANSI), markdown (PR body), json."""
 
 import json as _json
+import sys
 
 RESET = "\033[0m"
 BOLD = "\033[1m"
@@ -16,7 +17,9 @@ def _c(text, code, use_color):
     return f"{code}{text}{RESET}" if use_color else text
 
 
-def render_terminal(summary, use_color=True, llm_prose=None):
+def render_terminal(summary, use_color=None, llm_prose=None):
+    if use_color is None:
+        use_color = sys.stdout.isatty()
     out = []
     bar = "─" * 42
     out.append(_c("diffnote", BOLD + CYAN, use_color) +

tests/test_cli.py

@@ -3,6 +3,8 @@
 import subprocess
 import tempfile
 
+import pytest
+
 from diffnote import cli
 
 
@@ -58,6 +60,25 @@ def test_json_output(capsys):
     assert "title" in data
 
 
+@pytest.mark.parametrize("is_tty,args,has_color", [
+    (True, [], True),
+    (False, [], False),
+    (True, ["--color"], True),
+    (False, ["--color"], True),
+    (True, ["--no-color"], False),
+    (False, ["--no-color"], False),
+])
+def test_terminal_color_selection(capsys, monkeypatch, is_tty, args, has_color):
+    monkeypatch.chdir(_make_dirty_repo())
+    monkeypatch.setattr(cli.sys.stdout, "isatty", lambda: is_tty)
+
+    assert cli.main(args) == 0
+
+    out = capsys.readouterr().out
+    assert "files changed" in out
+    assert ("\033[" in out) is has_color
+
+
 def test_markdown_output(capsys):
     import os
     d = _make_dirty_repo()