Merge pull request #8033 from pfmoore/messages

Make message more user friendly when unable to resolve

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

@@ -50,6 +50,10 @@ def __init__(self, ireq, factory):
         self._factory = factory
         self.extras = ireq.req.extras
 
+    def __str__(self):
+        # type: () -> str
+        return str(self._ireq.req)
+
     def __repr__(self):
         # type: () -> str
         return "{class_name}({requirement!r})".format(

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

@@ -1,4 +1,5 @@
 import functools
+import logging
 
 from pip._vendor import six
 from pip._vendor.packaging.utils import canonicalize_name
@@ -25,6 +26,9 @@
     from pip._internal.resolution.base import InstallRequirementProvider
 
 
+logger = logging.getLogger(__name__)
+
+
 class Resolver(BaseResolver):
     def __init__(
         self,
@@ -74,9 +78,27 @@ def resolve(self, root_reqs, check_supported_wheels):
 
         try:
             self._result = resolver.resolve(requirements)
+
         except ResolutionImpossible as e:
             error = self.factory.get_installation_error(e)
             if not error:
+                # TODO: This needs fixing, we need to look at the
+                # factory.get_installation_error infrastructure, as that
+                # doesn't really allow for the logger.critical calls I'm
+                # using here.
+                for req, parent in e.causes:
+                    logger.critical(
+                        "Could not find a version that satisfies " +
+                        "the requirement " +
+                        str(req) +
+                        ("" if parent is None else " (from {})".format(
+                            parent.name
+                        ))
+                    )
+                raise InstallationError(
+                    "No matching distribution found for " +
+                    ", ".join([r.name for r, _ in e.causes])
+                )
                 raise
             six.raise_from(error, e)
 

tests/functional/test_new_resolver.py

@@ -156,6 +156,41 @@ def test_new_resolver_installs_extras(script):
     assert_installed(script, base="0.1.0", dep="0.1.0")
 
 
+def test_new_resolver_installed_message(script):
+    create_basic_wheel_for_package(script, "A", "1.0")
+    result = script.pip(
+        "install", "--unstable-feature=resolver",
+        "--no-cache-dir", "--no-index",
+        "--find-links", script.scratch_path,
+        "A",
+        expect_stderr=False,
+    )
+    assert "Successfully installed A-1.0" in result.stdout, str(result)
+
+
+def test_new_resolver_no_dist_message(script):
+    create_basic_wheel_for_package(script, "A", "1.0")
+    result = script.pip(
+        "install", "--unstable-feature=resolver",
+        "--no-cache-dir", "--no-index",
+        "--find-links", script.scratch_path,
+        "B",
+        expect_error=True,
+        expect_stderr=True,
+    )
+
+    # Full messages from old resolver:
+    # ERROR: Could not find a version that satisfies the
+    #        requirement xxx (from versions: none)
+    # ERROR: No matching distribution found for xxx
+
+    assert "Could not find a version that satisfies the requirement B" \
+        in result.stderr, str(result)
+    # TODO: This reports the canonical name of the project. But the current
+    #       resolver reports the originally specified name (i.e. uppercase B)
+    assert "No matching distribution found for b" in result.stderr, str(result)
+
+
 def test_new_resolver_installs_editable(script):
     create_basic_wheel_for_package(
         script,