Make it clear when using default input

src/validate_pyproject/cli.py

@@ -58,6 +58,8 @@ def critical_logging():
         raise
 
 
+_STDIN = argparse.FileType("r")("-")
+
 META: Dict[str, dict] = {
     "version": dict(
         flags=("-V", "--version"),
@@ -67,7 +69,7 @@ def critical_logging():
     "input_file": dict(
         dest="input_file",
         nargs="*",
-        default=[argparse.FileType("r")("-")],
+        # default=[_STDIN],  # postponed to facilitate testing
         type=argparse.FileType("r"),
         help="TOML file to be verified (`stdin` by default)",
     ),
@@ -120,6 +122,7 @@ def __meta__(plugins: Sequence[PluginWrapper]) -> Dict[str, dict]:
     """'Hyper parameters' to instruct :mod:`argparse` how to create the CLI"""
     meta = {k: v.copy() for k, v in META.items()}
     meta["enable"]["choices"] = set([p.tool for p in plugins])
+    meta["input_file"]["default"] = [_STDIN]  # lazily defined to facilitate testing
     return meta
 
 
@@ -216,12 +219,7 @@ def run(args: Sequence[str] = ()):
     exceptions = _ExceptionGroup()
     for file in params.input_file:
         try:
-            toml_equivalent = loads(file.read())
-            validator(toml_equivalent)
-            if params.dump_json:
-                print(json.dumps(toml_equivalent, indent=2))
-            else:
-                print(f"Valid {_format_file(file)}")
+            _run_on_file(validator, params, file)
         except _REGULAR_EXCEPTIONS as ex:
             exceptions.add(f"Invalid {_format_file(file)}", ex)
 
@@ -230,6 +228,18 @@ def run(args: Sequence[str] = ()):
     return 0
 
 
+def _run_on_file(validator: Validator, params: CliParams, file: io.TextIOBase):
+    if file in (sys.stdin, _STDIN):
+        print("Expecting input via `stdin`...", file=sys.stderr, flush=True)
+
+    toml_equivalent = loads(file.read())
+    validator(toml_equivalent)
+    if params.dump_json:
+        print(json.dumps(toml_equivalent, indent=2))
+    else:
+        print(f"Valid {_format_file(file)}")
+
+
 main = exceptions2exit()(run)
 
 

tests/test_cli.py

@@ -1,7 +1,9 @@
 import inspect
+import io
 import logging
 import sys
 from pathlib import Path
+from unittest.mock import Mock
 from uuid import uuid4
 
 import pytest
@@ -120,6 +122,19 @@ def test_invalid_disabled(self, invalid_example):
         assert cli.main([str(invalid_example), "-D", "setuptools"]) == 0
 
 
+class TestInput:
+    def test_inform_user_about_stdin(self, monkeypatch):
+        print_mock = Mock()
+        fake_stdin = io.StringIO('[project]\nname="test"\nversion="0.42"\n')
+        with monkeypatch.context() as ctx:
+            ctx.setattr("validate_pyproject.cli._STDIN", fake_stdin)
+            ctx.setattr("sys.argv", ["validate-pyproject"])
+            ctx.setattr("builtins.print", print_mock)
+            cli.run()
+        calls = print_mock.call_args_list
+        assert any("input via `stdin`" in x.args[0] for x in calls)
+
+
 class TestOutput:
     def test_valid(self, capsys, valid_example):
         cli.main([str(valid_example)])