Improve pyproject.toml validation messages

Based on the following discussions:

- pypa/packaging.python.org#1031 (comment)
- pypa/packaging-problems#604

it seems that people are having a hard time finding information about
validation error due to the long traceback and debug info.

The idea behind this change is to make the most relevant information
to fix the error easier to spot.

setuptools/config/pyprojecttoml.py

@@ -41,10 +41,14 @@ def validate(config: dict, filepath: _Path) -> bool:
     try:
         return validator.validate(config)
     except validator.ValidationError as ex:
-        _logger.error(f"configuration error: {ex.summary}")  # type: ignore
-        _logger.debug(ex.details)  # type: ignore
-        error = ValueError(f"invalid pyproject.toml config: {ex.name}")  # type: ignore
-        raise error from None
+        summary = f"configuration error: {ex.summary}"
+        if ex.name.strip("`") != "project":
+            # Probably it is just a field missing/misnamed, not worthy the verbosity...
+            _logger.debug(summary)
+            _logger.debug(ex.details)
+
+        error = f"invalid pyproject.toml config: {ex.name}."
+        raise ValueError(f"{error}\n{summary}") from None
 
 
 def apply_configuration(

setuptools/tests/config/test_pyprojecttoml.py

@@ -1,4 +1,3 @@
-import logging
 import re
 from configparser import ConfigParser
 from inspect import cleandoc
@@ -307,7 +306,7 @@ def test_ignore_unrelated_config(tmp_path, example):
 
 
 @pytest.mark.parametrize(
-    "example, error_msg, value_shown_in_debug",
+    "example, error_msg",
     [
         (
             """
@@ -316,30 +315,18 @@ def test_ignore_unrelated_config(tmp_path, example):
             version = "1.2"
             requires = ['pywin32; platform_system=="Windows"' ]
             """,
-            "configuration error: `project` must not contain {'requires'} properties",
-            '"requires": ["pywin32; platform_system==\\"Windows\\""]',
+            "configuration error: .project. must not contain ..requires.. properties",
         ),
     ],
 )
-def test_invalid_example(tmp_path, caplog, example, error_msg, value_shown_in_debug):
-    caplog.set_level(logging.DEBUG)
+def test_invalid_example(tmp_path, example, error_msg):
     pyproject = tmp_path / "pyproject.toml"
     pyproject.write_text(cleandoc(example))
 
-    caplog.clear()
-    with pytest.raises(ValueError, match="invalid pyproject.toml"):
+    pattern = re.compile(f"invalid pyproject.toml.*{error_msg}.*", re.M | re.S)
+    with pytest.raises(ValueError, match=pattern):
         read_configuration(pyproject)
 
-    # Make sure the logs give guidance to the user
-    error_log = caplog.record_tuples[0]
-    assert error_log[1] == logging.ERROR
-    assert error_msg in error_log[2]
-
-    debug_log = caplog.record_tuples[1]
-    assert debug_log[1] == logging.DEBUG
-    debug_msg = "".join(line.strip() for line in debug_log[2].splitlines())
-    assert value_shown_in_debug in debug_msg
-
 
 @pytest.mark.parametrize("config", ("", "[tool.something]\nvalue = 42"))
 def test_empty(tmp_path, config):