Fix dependency resolution for conditional development dependencies (#1482)

poetry/puzzle/provider.py

@@ -534,8 +534,8 @@ class Provider:
     ):  # type: (DependencyPackage) -> DependencyPackage
         if package.is_root():
             package = package.clone()
-
-        if not package.is_root() and package.source_type not in {
+            requires = package.all_requires
+        elif not package.is_root() and package.source_type not in {
             "directory",
             "file",
             "url",
@@ -550,10 +550,13 @@ class Provider:
                     repository=package.dependency.source_name,
                 ),
             )
+            requires = package.requires
+        else:
+            requires = package.requires
 
         dependencies = [
             r
-            for r in package.requires
+            for r in requires
             if self._package.python_constraint.allows_any(r.python_constraint)
         ]
 
@@ -582,6 +585,8 @@ class Provider:
 
             duplicates[dep.name].append(dep)
 
+        print(package)
+        print(duplicates)
         dependencies = []
         for dep_name, deps in duplicates.items():
             if len(deps) == 1:

tests/puzzle/test_solver.py

@@ -1811,3 +1811,27 @@ def test_solver_discards_packages_with_empty_markers(
             {"job": "install", "package": package_a},
         ],
     )
+
+
+def test_solver_does_not_raise_conflict_for_conditional_dev_dependencies(
+    solver, repo, package
+):
+    package.python_versions = "~2.7 || ^3.5"
+    package.add_dependency("A", {"version": "^1.0", "python": "~2.7"}, category="dev")
+    package.add_dependency("A", {"version": "^2.0", "python": "^3.5"}, category="dev")
+
+    package_a100 = get_package("A", "1.0.0")
+    package_a200 = get_package("A", "2.0.0")
+
+    repo.add_package(package_a100)
+    repo.add_package(package_a200)
+
+    ops = solver.solve()
+
+    check_solver_result(
+        ops,
+        [
+            {"job": "install", "package": package_a100},
+            {"job": "install", "package": package_a200},
+        ],
+    )