Show constraint in error message

news/9300.bugfix.rst

@@ -0,0 +1,2 @@
+New resolver: Show relevant entries from user-supplied constraint files in the
+error message to improve debuggability.

src/pip/_internal/resolution/resolvelib/factory.py

@@ -404,8 +404,24 @@ def _report_requires_python_error(
  )
  return UnsupportedPythonVersion(message)
 
- def get_installation_error(self, e):
- # type: (ResolutionImpossible) -> InstallationError
+ def _report_single_requirement_conflict(self, req, parent):
+ # type: (Requirement, Candidate) -> DistributionNotFound
+ if parent is None:
+ req_disp = str(req)
+ else:
+ req_disp = f"{req} (from {parent.name})"
+ logger.critical(
+ "Could not find a version that satisfies the requirement %s",
+ req_disp,
+ )
+ return DistributionNotFound(f"No matching distribution found for {req}")
+
+ def get_installation_error(
+ self,
+ e, # type: ResolutionImpossible
+ constraints, # type: Dict[str, Constraint]
+ ):
+ # type: (...) -> InstallationError
 
  assert e.causes, "Installation error reported with no cause"
 
@@ -425,15 +441,8 @@ def get_installation_error(self, e):
  # satisfied. We just report that case.
  if len(e.causes) == 1:
  req, parent = e.causes[0]
- if parent is None:
- req_disp = str(req)
- else:
- req_disp = f"{req} (from {parent.name})"
- logger.critical(
- "Could not find a version that satisfies the requirement %s",
- req_disp,
- )
- return DistributionNotFound(f"No matching distribution found for {req}")
+ if req.name not in constraints:
+ return self._report_single_requirement_conflict(req, parent)
 
  # OK, we now have a list of requirements that can't all be
  # satisfied at once.
@@ -475,13 +484,20 @@ def describe_trigger(parent):
  )
  logger.critical(msg)
  msg = "\nThe conflict is caused by:"
+
+ relevant_constraints = set()
  for req, parent in e.causes:
+ if req.name in constraints:
+ relevant_constraints.add(req.name)
  msg = msg + "\n "
  if parent:
  msg = msg + "{} {} depends on ".format(parent.name, parent.version)
  else:
  msg = msg + "The user requested "
  msg = msg + req.format_for_error()
+ for key in relevant_constraints:
+ spec = constraints[key].specifier
+ msg += f"\n The user requested (constraint) {key}{spec}"
 
  msg = (
  msg

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -122,7 +122,7 @@ def resolve(self, root_reqs, check_supported_wheels):
  )
 
  except ResolutionImpossible as e:
- error = self.factory.get_installation_error(e)
+ error = self.factory.get_installation_error(e, constraints)
  six.raise_from(error, e)
 
  req_set = RequirementSet(check_supported_wheels=check_supported_wheels)

tests/functional/test_install_reqs.py

@@ -357,7 +357,7 @@ def test_constraints_local_editable_install_causes_error(
  assert 'Could not satisfy constraints' in result.stderr, str(result)
  else:
  # Because singlemodule only has 0.0.1 available.
- assert 'No matching distribution found' in result.stderr, str(result)
+ assert 'Cannot install singlemodule 0.0.1' in result.stderr, str(result)
 
 
 @pytest.mark.network
@@ -386,7 +386,7 @@ def test_constraints_local_install_causes_error(
  assert 'Could not satisfy constraints' in result.stderr, str(result)
  else:
  # Because singlemodule only has 0.0.1 available.
- assert 'No matching distribution found' in result.stderr, str(result)
+ assert 'Cannot install singlemodule 0.0.1' in result.stderr, str(result)
 
 
 def test_constraints_constrain_to_local_editable(

tests/functional/test_new_resolver.py

@@ -687,7 +687,7 @@ def test_new_resolver_constraint_on_dependency(script):
 @pytest.mark.parametrize(
  "constraint_version, expect_error, message",
  [
- ("1.0", True, "ERROR: No matching distribution found for foo 2.0"),
+ ("1.0", True, "Cannot install foo 2.0"),
  ("2.0", False, "Successfully installed foo-2.0"),
  ],
 )

tests/functional/test_new_resolver_errors.py

@@ -24,3 +24,24 @@ def test_new_resolver_conflict_requirements_file(tmpdir, script):
 
  message = "package versions have conflicting dependencies"
  assert message in result.stderr, str(result)
+
+
+def test_new_resolver_conflict_constraints_file(tmpdir, script):
+ create_basic_wheel_for_package(script, "pkg", "1.0")
+
+ constrats_file = tmpdir.joinpath("constraints.txt")
+ constrats_file.write_text("pkg!=1.0")
+
+ result = script.pip(
+ "install",
+ "--no-cache-dir", "--no-index",
+ "--find-links", script.scratch_path,
+ "-c", constrats_file,
+ "pkg==1.0",
+ expect_error=True,
+ )
+
+ assert "ResolutionImpossible" in result.stderr, str(result)
+
+ message = "The user requested (constraint) pkg!=1.0"
+ assert message in result.stdout, str(result)