From 3642589903743be36449f4e6f8d9a8c091e5c594 Mon Sep 17 00:00:00 2001
From: Paul Moore <p.f.moore@gmail.com>
Date: Mon, 13 Apr 2020 11:16:30 +0100
Subject: [PATCH 1/2] Make message more user friendly when unable to resolve

---
 .../resolution/resolvelib/requirements.py     |  4 +++
 .../resolution/resolvelib/resolver.py         | 28 ++++++++++++++--
 tests/functional/test_new_resolver.py         | 33 +++++++++++++++++++
 3 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/src/pip/_internal/resolution/resolvelib/requirements.py b/src/pip/_internal/resolution/resolvelib/requirements.py
index 027e36aa61e..952973ae7cc 100644
--- a/src/pip/_internal/resolution/resolvelib/requirements.py
+++ b/src/pip/_internal/resolution/resolvelib/requirements.py
@@ -79,6 +79,10 @@ 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(
diff --git a/src/pip/_internal/resolution/resolvelib/resolver.py b/src/pip/_internal/resolution/resolvelib/resolver.py
index 5e6408573c6..d2e571f17bf 100644
--- a/src/pip/_internal/resolution/resolvelib/resolver.py
+++ b/src/pip/_internal/resolution/resolvelib/resolver.py
@@ -1,9 +1,11 @@
 import functools
+import logging
 
 from pip._vendor.packaging.utils import canonicalize_name
-from pip._vendor.resolvelib import BaseReporter
+from pip._vendor.resolvelib import BaseReporter, ResolutionImpossible
 from pip._vendor.resolvelib import Resolver as RLResolver
 
+from pip._internal.exceptions import InstallationError
 from pip._internal.req.req_set import RequirementSet
 from pip._internal.resolution.base import BaseResolver
 from pip._internal.resolution.resolvelib.provider import PipProvider
@@ -23,6 +25,9 @@
     from pip._internal.resolution.base import InstallRequirementProvider
 
 
+logger = logging.getLogger(__name__)
+
+
 class Resolver(BaseResolver):
     def __init__(
         self,
@@ -64,7 +69,26 @@ def resolve(self, root_reqs, check_supported_wheels):
             self.factory.make_requirement_from_install_req(r)
             for r in root_reqs
         ]
-        self._result = resolver.resolve(requirements)
+
+        try:
+            self._result = resolver.resolve(requirements)
+        except ResolutionImpossible as exc:
+            # TODO: This is just an initial version. May need more work.
+            # Also could do with rewriting to fit better into 80-char
+            # lines :-(
+            for req, parent in exc.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 exc.causes])
+            )
 
         req_set = RequirementSet(check_supported_wheels=check_supported_wheels)
         for candidate in self._result.mapping.values():
diff --git a/tests/functional/test_new_resolver.py b/tests/functional/test_new_resolver.py
index 25c726f2574..5d119865e7f 100644
--- a/tests/functional/test_new_resolver.py
+++ b/tests/functional/test_new_resolver.py
@@ -155,6 +155,39 @@ 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)
+    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,

From 8c118c8f3a6fd850e49256c51440142526a3d7c6 Mon Sep 17 00:00:00 2001
From: Paul Moore <p.f.moore@gmail.com>
Date: Tue, 14 Apr 2020 15:18:24 +0100
Subject: [PATCH 2/2] Fix the test to check for canonical name

---
 tests/functional/test_new_resolver.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tests/functional/test_new_resolver.py b/tests/functional/test_new_resolver.py
index 73ceff9aaea..cb384d7a0ac 100644
--- a/tests/functional/test_new_resolver.py
+++ b/tests/functional/test_new_resolver.py
@@ -186,7 +186,9 @@ def test_new_resolver_no_dist_message(script):
 
     assert "Could not find a version that satisfies the requirement B" \
         in result.stderr, str(result)
-    assert "No matching distribution found for 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):