Retain casing of required package names (#248)

src/pipdeptree/__init__.py

@@ -270,7 +270,19 @@ class PackageDAG(Mapping):
     def from_pkgs(cls, pkgs):
         pkgs = [DistPackage(p) for p in pkgs]
         idx = {p.key: p for p in pkgs}
-        m = {p: [ReqPackage(r, idx.get(r.key)) for r in p.requires()] for p in pkgs}
+        m = {}
+        for p in pkgs:
+            reqs = []
+            for r in p.requires():
+                d = idx.get(r.key)
+                # pip's _vendor.packaging.requirements.Requirement uses the exact casing of a dependency's name found in
+                # a project's build config, which is not ideal when rendering.
+                # See https://github.com/tox-dev/pipdeptree/issues/242
+                r.project_name = d.project_name if d is not None else r.project_name
+                pkg = ReqPackage(r, d)
+                reqs.append(pkg)
+            m[p] = reqs
+
         return cls(m)
 
     def __init__(self, m) -> None:

tests/test_pipdeptree.py

@@ -39,7 +39,7 @@ if TYPE_CHECKING:
 def mock_pkgs(simple_graph):
     for node, children in simple_graph.items():
         nk, nv = node
-        m = mock.Mock(key=nk, project_name=nk, version=nv)
+        m = mock.Mock(key=nk.lower(), project_name=nk, version=nv)
         as_req = mock.Mock(key=nk, project_name=nk, specs=[("==", nv)])
         m.as_requirement = mock.Mock(return_value=as_req)
         reqs = []
@@ -162,6 +162,20 @@ def test_package_dag_reverse():
     assert all(isinstance(v, ReqPackage) for v in chain.from_iterable(t2.values()))
 
 
+def test_package_dag_from_pkgs():
+    # when pip's _vendor.packaging.requirements.Requirement's requires() gives a lowercased package name but the actual
+    # package name in PyPI is mixed case, expect the mixed case version
+    graph = {
+        ("examplePy", "1.2.3"): [("hellopy", [(">=", "2.0.0")])],
+        ("HelloPy", "2.2.0"): [],
+    }
+    t = mock_package_dag(graph)
+    parent_key = "examplepy"
+    c = t.get_children(parent_key)
+    assert len(c) == 1
+    assert c[0].project_name == "HelloPy"
+
+
 # Tests for Package classes
 #
 # Note: For all render methods, we are only testing for frozen=False