Add solutions for common errors (#2396)

poetry.lock

@@ -215,7 +215,7 @@ version = "0.4.3"
 [[package]]
 category = "main"
 description = "Updated configparser from Python 3.7 for Python 2.6+."
-marker = "python_version >= \"2.7\" and python_version < \"2.8\" or python_version == \"2.7\" and python_version == \"2.7\" or python_version < \"3\""
+marker = "python_version < \"3\" or python_version >= \"2.7\" and python_version < \"2.8\""
 name = "configparser"
 optional = false
 python-versions = ">=2.6"
@@ -228,7 +228,7 @@ testing = ["pytest (>=3.5,<3.7.3 || >3.7.3)", "pytest-checkdocs (>=1.2)", "pytes
 [[package]]
 category = "main"
 description = "Backports and enhancements for the contextlib module"
-marker = "python_version >= \"2.7\" and python_version < \"2.8\" or python_version < \"3.4\""
+marker = "python_version < \"3.4\" or python_version >= \"2.7\" and python_version < \"2.8\""
 name = "contextlib2"
 optional = false
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
@@ -446,7 +446,7 @@ testing = ["packaging", "importlib-resources"]
 [[package]]
 category = "main"
 description = "Read resources from Python packages"
-marker = "python_version >= \"2.7\" and python_version < \"2.8\" or python_version < \"3.7\""
+marker = "python_version < \"3.7\" or python_version >= \"2.7\" and python_version < \"2.8\""
 name = "importlib-resources"
 optional = false
 python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,>=2.7"
@@ -1512,7 +1512,7 @@ docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
 testing = ["jaraco.itertools", "func-timeout"]
 
 [metadata]
-content-hash = "6e86bcf4be1389d9d1dbd87bd5383089bec887c5a7e9c5e48b09b936699e035d"
+content-hash = "90cb5177483057d7bf7dea367cb6ccf0968861777c801f3bb41b0f745cccdc24"
 python-versions = "~2.7 || ^3.5"
 
 [metadata.files]

poetry/console/config/application_config.py

@@ -29,6 +29,7 @@ from poetry.console.commands.command import Command
 from poetry.console.commands.env_command import EnvCommand
 from poetry.console.logging.io_formatter import IOFormatter
 from poetry.console.logging.io_handler import IOHandler
+from poetry.utils._compat import PY36
 
 
 class ApplicationConfig(BaseApplicationConfig):
@@ -46,6 +47,15 @@ class ApplicationConfig(BaseApplicationConfig):
         self.add_event_listener(PRE_HANDLE, self.register_command_loggers)
         self.add_event_listener(PRE_HANDLE, self.set_env)
 
+        if PY36:
+            from poetry.mixology.solutions.providers import (
+                PythonRequirementSolutionProvider,
+            )
+
+            self._solution_provider_repository.register_solution_providers(
+                [PythonRequirementSolutionProvider]
+            )
+
     def register_command_loggers(
         self, event, event_name, _
     ):  # type: (PreHandleEvent, str, Any) -> None

poetry/mixology/failure.py

@@ -2,6 +2,8 @@ from typing import Dict
 from typing import List
 from typing import Tuple
 
+from poetry.core.semver import parse_constraint
+
 from .incompatibility import Incompatibility
 from .incompatibility_cause import ConflictCause
 from .incompatibility_cause import PythonCause
@@ -44,10 +46,15 @@ class _Writer:
                     )
                     required_python_version_notification = True
 
+                root_constraint = parse_constraint(
+                    incompatibility.cause.root_python_version
+                )
+                constraint = parse_constraint(incompatibility.cause.python_version)
                 buffer.append(
-                    "  - {} requires Python {}".format(
+                    "  - {} requires Python {}, so it will not be satisfied for Python {}".format(
                         incompatibility.terms[0].dependency.name,
                         incompatibility.cause.python_version,
+                        root_constraint.difference(constraint),
                     )
                 )
 

poetry/mixology/solutions/providers/__init__.py

+from .python_requirement_solution_provider import PythonRequirementSolutionProvider

poetry/mixology/solutions/providers/python_requirement_solution_provider.py

+import re
+
+from typing import List
+
+from crashtest.contracts.has_solutions_for_exception import HasSolutionsForException
+from crashtest.contracts.solution import Solution
+
+
+class PythonRequirementSolutionProvider(HasSolutionsForException):
+    def can_solve(self, exception):  # type: (Exception) -> bool
+        from poetry.puzzle.exceptions import SolverProblemError
+
+        if not isinstance(exception, SolverProblemError):
+            return False
+
+        m = re.match(
+            "^The current project's Python requirement (.+) is not compatible "
+            "with some of the required packages Python requirement",
+            str(exception),
+        )
+
+        if not m:
+            return False
+
+        return True
+
+    def get_solutions(self, exception):  # type: (Exception) -> List[Solution]
+        from ..solutions.python_requirement_solution import PythonRequirementSolution
+
+        return [PythonRequirementSolution(exception)]

poetry/mixology/solutions/solutions/__init__.py

+from .python_requirement_solution import PythonRequirementSolution

poetry/mixology/solutions/solutions/python_requirement_solution.py

+from crashtest.contracts.solution import Solution
+
+
+class PythonRequirementSolution(Solution):
+    def __init__(self, exception):
+        from poetry.mixology.incompatibility_cause import PythonCause
+        from poetry.core.semver import parse_constraint
+
+        self._title = "Check your dependencies Python requirement."
+
+        failure = exception.error
+        version_solutions = []
+        for incompatibility in failure._incompatibility.external_incompatibilities:
+            if isinstance(incompatibility.cause, PythonCause):
+                root_constraint = parse_constraint(
+                    incompatibility.cause.root_python_version
+                )
+                constraint = parse_constraint(incompatibility.cause.python_version)
+
+                version_solutions.append(
+                    "For <fg=default;options=bold>{}</>, a possible solution would be "
+                    'to set the `<fg=default;options=bold>python</>` property to <fg=yellow>"{}"</>'.format(
+                        incompatibility.terms[0].dependency.name,
+                        root_constraint.intersect(constraint),
+                    )
+                )
+
+        description = (
+            "The Python requirement can be specified via the `<fg=default;options=bold>python</>` "
+            "or `<fg=default;options=bold>markers</>` properties"
+        )
+        if version_solutions:
+            description += "\n\n" + "\n".join(version_solutions)
+
+        description += "\n"
+
+        self._description = description
+
+    @property
+    def solution_title(self) -> str:
+        return self._title
+
+    @property
+    def solution_description(self):
+        return self._description
+
+    @property
+    def documentation_links(self):
+        return [
+            "https://python-poetry.org/docs/dependency-specification/#python-restricted-dependencies",
+            "https://python-poetry.org/docs/dependency-specification/#using-environment-markers",
+        ]

poetry/mixology/version_solver.py

 # -*- coding: utf-8 -*-
 import time
 
+from typing import TYPE_CHECKING
 from typing import Any
 from typing import Dict
 from typing import List
@@ -11,7 +12,6 @@ from poetry.core.packages import Package
 from poetry.core.packages import ProjectPackage
 from poetry.core.semver import Version
 from poetry.core.semver import VersionRange
-from poetry.puzzle.provider import Provider
 
 from .failure import SolveFailure
 from .incompatibility import Incompatibility
@@ -25,6 +25,10 @@ from .set_relation import SetRelation
 from .term import Term
 
 
+if TYPE_CHECKING:
+    from poetry.puzzle.provider import Provider
+
+
 _conflict = object()
 
 

pyproject.toml

@@ -27,6 +27,7 @@ python = "~2.7 || ^3.5"
 poetry-core = "^1.0.0a6"
 cleo = "^0.8.1"
 clikit = "^0.6.2"
+crashtest = { version = "^0.3.0", python = "^3.6" }
 requests = "^2.18"
 cachy = "^0.3.0"
 requests-toolbelt = "^0.8.0"

tests/mixology/solutions/providers/test_python_requirement_solution_provider.py

+import pytest
+
+from poetry.core.packages.dependency import Dependency
+from poetry.mixology.failure import SolveFailure
+from poetry.mixology.incompatibility import Incompatibility
+from poetry.mixology.incompatibility_cause import NoVersionsCause
+from poetry.mixology.incompatibility_cause import PythonCause
+from poetry.mixology.term import Term
+from poetry.puzzle.exceptions import SolverProblemError
+from poetry.utils._compat import PY36
+
+
+@pytest.mark.skipif(
+    not PY36, reason="Error solutions are only available for Python ^3.6"
+)
+def test_it_can_solve_python_incompatibility_solver_errors():
+    from poetry.mixology.solutions.providers import PythonRequirementSolutionProvider
+    from poetry.mixology.solutions.solutions import PythonRequirementSolution
+
+    incompatibility = Incompatibility(
+        [Term(Dependency("foo", "^1.0"), True)], PythonCause("^3.5", ">=3.6")
+    )
+    exception = SolverProblemError(SolveFailure(incompatibility))
+    provider = PythonRequirementSolutionProvider()
+
+    assert provider.can_solve(exception)
+    assert isinstance(provider.get_solutions(exception)[0], PythonRequirementSolution)
+
+
+@pytest.mark.skipif(
+    not PY36, reason="Error solutions are only available for Python ^3.6"
+)
+def test_it_cannot_solve_other_solver_errors():
+    from poetry.mixology.solutions.providers import PythonRequirementSolutionProvider
+
+    incompatibility = Incompatibility(
+        [Term(Dependency("foo", "^1.0"), True)], NoVersionsCause()
+    )
+    exception = SolverProblemError(SolveFailure(incompatibility))
+    provider = PythonRequirementSolutionProvider()
+
+    assert not provider.can_solve(exception)

tests/mixology/solutions/solutions/test_python_requirement_solution.py

+import pytest
+
+from clikit.io.buffered_io import BufferedIO
+
+from poetry.core.packages.dependency import Dependency
+from poetry.mixology.failure import SolveFailure
+from poetry.mixology.incompatibility import Incompatibility
+from poetry.mixology.incompatibility_cause import PythonCause
+from poetry.mixology.term import Term
+from poetry.puzzle.exceptions import SolverProblemError
+from poetry.utils._compat import PY36
+
+
+@pytest.mark.skipif(
+    not PY36, reason="Error solutions are only available for Python ^3.6"
+)
+def test_it_provides_the_correct_solution():
+    from poetry.mixology.solutions.solutions import PythonRequirementSolution
+
+    incompatibility = Incompatibility(
+        [Term(Dependency("foo", "^1.0"), True)], PythonCause("^3.5", ">=3.6")
+    )
+    exception = SolverProblemError(SolveFailure(incompatibility))
+    solution = PythonRequirementSolution(exception)
+
+    title = "Check your dependencies Python requirement."
+    description = """\
+The Python requirement can be specified via the `python` or `markers` properties
+
+For foo, a possible solution would be to set the `python` property to ">=3.6,<4.0"\
+"""
+    links = [
+        "https://python-poetry.org/docs/dependency-specification/#python-restricted-dependencies",
+        "https://python-poetry.org/docs/dependency-specification/#using-environment-markers",
+    ]
+
+    assert title == solution.solution_title
+    assert (
+        description == BufferedIO().remove_format(solution.solution_description).strip()
+    )
+    assert links == solution.documentation_links

tests/mixology/version_solver/test_python_constraint.py

@@ -10,7 +10,7 @@ def test_dependency_does_not_match_root_python_constraint(root, provider, repo):
 
     error = """The current project's Python requirement (^3.6) \
 is not compatible with some of the required packages Python requirement:
-  - foo requires Python <3.5
+  - foo requires Python <3.5, so it will not be satisfied for Python >=3.6,<4.0
 
 Because no versions of foo match !=1.0.0
  and foo (1.0.0) requires Python <3.5, foo is forbidden.