From 27abb49113734d681c73ec948539f186c37f725a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Eustace?= <sebastien@eustace.io>
Date: Fri, 6 Dec 2019 15:13:57 +0100
Subject: [PATCH] Improve the error message displayed on Python requirements
 conflict (#1681)

---
 poetry/mixology/failure.py                    | 25 +++++++++++++------
 .../version_solver/test_python_constraint.py  |  4 ++-
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/poetry/mixology/failure.py b/poetry/mixology/failure.py
index 1a5bbfc8832..e6854335af3 100644
--- a/poetry/mixology/failure.py
+++ b/poetry/mixology/failure.py
@@ -31,18 +31,27 @@ def __init__(self, root):  # type: (Incompatibility) -> None
     def write(self):
         buffer = []
 
-        required_python_version = None
+        required_python_version_notification = False
         for incompatibility in self._root.external_incompatibilities:
             if isinstance(incompatibility.cause, PythonCause):
-                required_python_version = incompatibility.cause.root_python_version
-                break
+                if not required_python_version_notification:
+                    buffer.append(
+                        "The current project's Python requirement ({}) "
+                        "is not compatible with some of the required "
+                        "packages Python requirement:".format(
+                            incompatibility.cause.root_python_version
+                        )
+                    )
+                    required_python_version_notification = True
 
-        if required_python_version is not None:
-            buffer.append(
-                "The current project must support the following Python versions: {}".format(
-                    required_python_version
+                buffer.append(
+                    "  - {} requires Python {}".format(
+                        incompatibility.terms[0].dependency.name,
+                        incompatibility.cause.python_version,
+                    )
                 )
-            )
+
+        if required_python_version_notification:
             buffer.append("")
 
         if isinstance(self._root.cause, ConflictCause):
diff --git a/tests/mixology/version_solver/test_python_constraint.py b/tests/mixology/version_solver/test_python_constraint.py
index 3e7b16bae01..910d51be784 100644
--- a/tests/mixology/version_solver/test_python_constraint.py
+++ b/tests/mixology/version_solver/test_python_constraint.py
@@ -8,7 +8,9 @@ def test_dependency_does_not_match_root_python_constraint(root, provider, repo):
 
     add_to_repo(repo, "foo", "1.0.0", python="<3.5")
 
-    error = """The current project must support the following Python versions: ^3.6
+    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
 
 Because no versions of foo match !=1.0.0
  and foo (1.0.0) requires Python <3.5, foo is forbidden.