Write warnings to stderr during resolution

- Fixes #3273

Signed-off-by: Dan Ryan <[email protected]>

news/3273.bugfix.rst

@@ -0,0 +1 @@
+Pipenv will ensure that warnings do not interfere with the resolution process by suppressing warnings' usage of standard output and writing to standard error instead.

pipenv/utils.py

@@ -448,6 +448,12 @@ def _should_include_hash(ireq):
             return self.hashes
 
 
+def _show_warning(message, category, filename, lineno, line):
+    warnings.showwarning(message=message, category=category, filename=filename,
+                         lineno=lineno, file=sys.stderr, line=line)
+    sys.stderr.flush()
+
+
 def actually_resolve_deps(
     deps,
     index_lookup,
@@ -462,13 +468,19 @@ def actually_resolve_deps(
 
     if not req_dir:
         req_dir = create_tracked_tempdir(suffix="-requirements", prefix="pipenv-")
+    warning_list = []
+
+    with warnings.catch_warnings(record=True) as warning_list:
     constraints = get_resolver_metadata(
         deps, index_lookup, markers_lookup, project, sources,
     )
     resolver = Resolver(constraints, req_dir, project, sources, clear=clear, pre=pre)
     resolved_tree = resolver.resolve()
     hashes = resolver.resolve_hashes()
 
+    for warning in warning_list:
+        _show_warning(warning.message, warning.category, warning.filename, warning.lineno,
+                      warning.line)
     return (resolved_tree, hashes, markers_lookup, resolver)
 
 
@@ -844,7 +856,6 @@ def mkdir_p(newdir):
                     raise
 
 
-
 def is_required_version(version, specified_version):
     """Check to see if there's a hard requirement for version
     number provided in the Pipfile.

tests/integration/test_lock.py

@@ -503,3 +503,13 @@ def test_lock_with_incomplete_source(PipenvInstance, pypi):
         c = p.pipenv('install')
         assert c.return_code == 0
         assert p.lockfile['_meta']['sources']
+
+
+@pytest.mark.lock
+@pytest.mark.install
+def test_lock_no_warnings(PipenvInstance, pypi):
+    with PipenvInstance(pypi=pypi, chdir=True) as p:
+        os.environ["PYTHONWARNINGS"] = str("once")
+        c = p.pipenv("install six")
+        assert c.return_code == 0
+        assert "Warning" in c.err