Fix package name not being canonicalize in commands/show

Add test to check if a capitalized name is being shown properly
Add new stub package to support the test

src/pip/_internal/commands/show.py

@@ -138,9 +138,10 @@ def print_results(distributions, list_files=False, verbose=False):
             write_output("---")
 
         name = dist.get('name', '')
+        canonical_name = canonicalize_name(dist.get('name', ''))
         required_by = [
             pkg.project_name for pkg in pkg_resources.working_set
-            if name in [required.name for required in pkg.requires()]
+            if canonical_name in [required.name for required in pkg.requires()]
         ]
 
         write_output("Name: %s", name)

tests/data/src/requires_capitalized/requires_capitalized/__init__.py

@@ -0,0 +1 @@
+#

tests/data/src/requires_capitalized/setup.py

@@ -0,0 +1,6 @@
+from setuptools import find_packages, setup
+
+setup(name='Requires_Capitalized',
+      version='0.1',
+      install_requires=['simple==1.0']
+      )

tests/functional/test_show.py

@@ -205,7 +205,7 @@ def test_package_name_is_canonicalized(script, data):
     assert underscore_upper_show_result.stdout == dash_show_result.stdout
 
 
-def test_show_required_by_packages(script, data):
+def test_show_required_by_packages_simple(script, data):
     """
     Test that installed packages that depend on this package are shown
     """
@@ -219,3 +219,20 @@ def test_show_required_by_packages(script, data):
 
     assert 'Name: simple' in lines
     assert 'Required-by: requires-simple' in lines
+
+
+def test_show_required_by_packages_capitalized(script, data):
+    """
+    Test that installed packages that depend on this package are shown where the package has a capital letter
+    """
+    editable_path = os.path.join(data.src, 'requires_capitalized')
+    script.pip(
+        'install', '--no-index', '-f', data.find_links, editable_path
+    )
+
+    result = script.pip('show', 'simple')
+    lines = result.stdout.splitlines()
+    print(lines)
+
+    assert 'Name: simple' in lines
+    assert 'Required-by: Requires-Capitalized' in lines